TREES AND SHRUBS - ORNAMENTAL


Common abiotic problems on Montana trees

Aspen diseases
Anthracnose on ash and maples
Bacterial blight of trees and shrubs
Cytospora canker - Deciduous trees
Cytospora canker - Spruce trees
Rhizosphaeria needle cast of spruce
Disease in trees:  How much can trees tolerate?
Dutch elm disease
Firewood from diseased elm trees
Iron chlorosis
Juniper dieback and juniper twig blight
Juniper-hawthorn rust (cedar-apple rust)
Mysteries of cedar-apple rust
Leaf scorch (Environmental)
Powdery mildew
Powdery mildew of lilac
Pruning diseased wood from trees and ornamentals
Slime fluxing
Spruce dieback
Sunscald on trees
 


COMMON ABIOTIC PROBLEMS ON MONTANA TREES

Planting/cultural problems
High temperature/drought
Winter-related
Nutrient/chemical



Common abiotic problems:  Planting/cultural problems
Transplant shock
Nurserymen often prune the roots of trees to be used as bare root transplants or containerized trees. These trees must reestablish an adequate root system in the new location before the entire plant can begin normal growth During this period of system shock, stress symptoms are normal. Symptoms include: overall stunting of leaves and annual shoot growth, wilt, scorch, and abnormally high amount of winter-killed twigs and/or buds. As a rule of thumb, the transplant shock period lasts one year for each one inch of stem caliper.

To minimize transplant shock problems, use correct planting techniques, give trees adequate water for three years after planting, and use no fertilizer for the first two years.

Deep planting
Tree death often arises from planting trees too deeply. If the root collar area of newly-planted trees is several inches below the landscape grade, the tree has been planted too deeply! This is more of a problem when trees are planted in clay soils, and/or compacted soils, but surface mulches, exposed sites, or turf established to the stem of the tree can aggravate the problem.

Deep planting results in reduced oxygen and water to the fine root systems. This in turn causes poor root regeneration of transplanted trees, gradual death of existing roots, lower tree vitality, and increased vulnerability to biotic problems and environmental extremes. Sometimes deep planting causes a slow and progressive decline in vitality that may progress for 5 to 10 years.

Soil penetration problems
Trees planted in small planting holes, especially in soils that are severely compacted, exhibit transplant shock symptoms for unusually long periods. Symptoms include annual scorching and wilting, nutrient deficiency symptoms, tip dieback, slower healing of pruning wounds, and general decline.

Sometimes trees never recover completely and languish their entire lives. Roots can eventually penetrate the interface of the planting hole (where the existing soil meets the prepared planting hole soil). However, when the existing soil is a very compact clay, it may take several years for the new roots to penetrate extensively enough to support "normal" stem and canopy growth.

Girdling roots
Girdling roots grow in a circular pattern around the trunk resulting in root death and loss of the anchorage system. Not all girdling roots are problematic. Only those that occur at the root collar area or above are considered chronically dangerous. Girdling roots that occur below the root collar area are not normally a threat to tree health or stability. It is nearly impossible to look at a developing girdling root and predict that it will cause problems for the tree. Problems are more likely in this situation though.

Genetically induced girdling roots: Certain tree species are prone to problematic girdling roots. The maples, especially Norway maple, are at the top of this list. Other species include poplars, the littleleaf linden cultivar "Greenspire", and the American beech. Culturally induced girdling roots: All trees develop root systems that could eventually result in girdling root problems, depending on how they were grown and/or planted. Pot-bound plants often develop girdling roots if the roots are not pruned at planting time. Girdling roots can develop from poor planting techniques, such as "twirling" a bare-root system into a planting hole that is too small for the roots, planting too deep, or planting in small soil volumes.

Symptoms include: leaning, early seasonal senescence, excessive twig dieback, thin appearance to crown, and little or no stem taper at ground level. Dig a few inches into the soil near the trunk and look for roots growing right next to the trunk in a circular pattern. . Generally, you can find girdling roots in this way without hurting the tree.

Root disturbance
One of the most common and yet least recognized causes of tree problems is root disturbance, often associated with some sort of construction activity such as laying of pipe or cable, street widening, placing a new building in an older site or turning residential areas into parking lots or patios. Even shallow cultivation in the root zone of trees can damage important roots growing close to the surface. Transplanting established trees with wide, spreading root systems can also result in decline through loss of a substantial part of the root system.

Piling only a few inches soil under the dripline of established trees can suffocate the roots resulting in tree death. This commonly occurs as a result of building construction or establishment of landscaping berms.

Excessive mulch
Mulches have many very beneficial uses which include water retention, winter protection, weed control, and lawnmower protection. However, damage from incorrect mulch applications around trees and shrubs is becoming more common as homeowners and professionals recognize these benefits. Problems may arise under certain circumstances: excessively deep applications of fine-textured organic mulches; mulches piled up against the trunk of young and/or thin-barked trees and shrubs; and plastic ground covers applied before the top-dressed mulch, especially when the plastic is in contact with heavy, clay soils.

Excessive mulching results in deterioration of fine roots, low oxygen levels to roots, formation of adventitious roots from stems covered by mulches, and mulch girdling. With mulch girdling, the trunk grows normally above the mulch line, but puts on little trunk growth below the mulch line. Symptoms of excessive mulching include: blackened roots, scorch, wilt, nutrient deficiency, early senescence, stunting, poorly anchored trees and shrubs, and excessive adventitious rooting off the trunk below the mulch line.



Common abiotic problems:  High temperature/drought

Drought
Individual trees vary widely in their resistance to drought.However, in years of low rainfall, many tree species can be substantially weakened or killed by drought. Deciduous trees appear to die from the top down, have small, off-colored leaves, and narrow growth rings. Conifers generally die from the bottom up when subjected to drought. Drought and any factor that weakens a tree may allow invasion by many secondary fungi and insects.

Leaf scorch
When adequate temperature and moisture suddenly turns hot and dry, leaf scorch may occur. Affected trees generally have yellow or brown leaf edges. The affected leaves may remain on the tree or the leaves may drop early. Watering during hot, dry weather may prevent or alleviate this problem.



Common abiotic problems:  Winter-related

Fall freeze damage
Plants still growing actively in the fall may be damaged by unseasonably cold periods. This damage occurs before the plant has moved into its winter rest as indicated by development of fall color and normal leaf drop. Frozen leaves often hang on the tree until spring. Damage may range from no twig damage to death of the entire tree.

Planting trees and shrubs adapted to the climate is very important. Also, allowing trees to grow at a slower rate by not pushing them with fertilizer and excessive watering can minimize winter freeze damage.

Winter freeze damage
By January 1, most Montana trees have experienced enough cold units to meet dormancy requirements. After this, trees can begin to grow again when conditions are appropriate. Chinooks may cause winter thaw periods wherein daytime temperatures exceed 60 F for several days at a time. Non-adapted trees may begin growing again as though it was spring, only to succumb to winter injury when temperatures drop again. In such cases, only the main trunk and scaffold branches may be viable in the spring.

Planting species adapted to changing Montana conditions can lessen chances of winter freeze damage. Planting marginally-hardy species in protected locations also is important. Examples of protected locations include the north side of a house or the interior of an effective shelterbelt.

Winter desiccation
Winter desiccation is a condition that is most common with evergreens. Winter sun and wind cause water loss from the needles, while roots are in frozen soil and unable to replace this water. The usual symptom is purpling or death of needles on the windward side or on the side facing the afternoon sun. Such symptoms may be more severe in newly transplanted plants that have not yet established a good root system. Late fall and winter watering can minimize winter desiccation.

Sunscald
Bark on the southwest side of tree trunks may be killed by sunscald. Sunscald occurs when bark warms and thaws in the afternoon sun, then refreezes when nighttime temperatures drop rapidly.

Damage is most common on the darker-colored, smooth-barked trees such as mountainash, apple, and maple. Tree wraps can help prevent sunscald. Planting in a site that is shaded in the winter is recommended for susceptible trees.

Frost cracking
Frost cracking is caused by extremely rapid temperature changes in bark and wood. As with sunscald, the bark and wood on the sunny side of the tree warms during the day. If a cold front moves in with a dramatic drop in temperature (i.e., from 30 F to -20F in a very short period of time), uneven contraction of the wood causes a crack to form suddenly. Sometimes the crack sounds like a gun shot.

Damage is most common in hardwood plants such as green ash. Frost cracking is not common and trees usually heal the cracks with few reprecussions.



Common abiotic problems:  Nutrient/chemical

Iron deficiency
Iron deficiency occurs commonly in certain Montana trees and shrubs such as maple, rose, and raspberry. Symptoms include yellowed leaves surrounding leaf veins that remain green. Although iron levels are sufficient in many soils, this iron may not be released to the plant in high pH soils.

Spraying a solution iron chelate on the leaves in the early season often provides a rapid improvement in the plant color. However, this foliar iron often must be reapplied again even within the same growing season. Iron can also be injected into the tree trunk for a longer-lasting effect. Soil applications of iron generally are not effective since the higher pH quickly renders this iron unavailable to the plant.

Herbicide damage
Tree damage from herbicide sprays or granules applied to turf or surrounding cropland is very common in Montana. Affected leaves become distorted, twisted, curled, or cupped, and margins may turn brown. Trees may be killed by this treatment, but more often are stunted for a year.

Salt toxicity
Salt applied to streets, driveways, or sidewalks in winter is absorbed by tree roots during the growing season. This results in varying degrees of browning of the leaf edges, especially during drought periods. Gradual dieback may occur in some salt damaged trees; some trees may be killed.


Aspen diseases

A grove of aspens with leaves quaking in the wind or in glowing yellow fall color is an arresting site. Quaking aspens (Populus tremuloides) have one of the largest natural ranges of any tree. They grow natively across Canada and as far south as Pennsylvania, Missouri, and the western mountains reaching into Mexico. Pockets of western Montana are home to many native quaking aspens. Aspens are most common at higher elevations and in riparian areas at lower elevations. However, they also grow in some rather dry sites near ponderosa pine and Douglas-fir.

Aspens grow rapidly to reach maximum heights of 50 to 60 feet. They are considered a short-lived species since they rarely live to 150 years old. As ornamentals, individual aspens commonly live for only 20 - 40 years reaching a height of 30 - 40 feet. Although their lifespan is short, aspens produce new shoots from their roots. In wet sites, aspens can produce 100 suckers per square meter. These new shoots grow into mature trees that are genetically-identical to the mother tree. This clonal reproduction results in the solid stands of aspens found in nature. Their dense, shallow root system allows them to survive in boggy areas.

Aspens need full sun since they are extremely intolerant of shade. They can grow in most soil types and pH may range from 5.0 to 8.0. However, they prefer well-drained soils. Higher elevation locations such as Bozeman and Butte are good for ornamental planting. Aspens are a "pioneer" tree species that can survive in many locations, but hot, dry sites are least favorable to growth.

Aspens are very popular among Montana homeowners. However, they are susceptible to numerous problems that can detract from their beauty in the home lawn. The natural suckering can be a problem for homeowners that want to keep aspens "within bounds." The short lifespan can be problematic and aspens become susceptible to more problems as they age. They are prone to more diseases and insects than most other trees grown in Montana.

There are several diseases that can cause black spots on leaves or twig dieback, or both, on aspen. These include shoot and leaf blight, bacterial blight, and Cytospora and Hypoxylon canker.

BACTERIAL BLIGHT causes young leaves and the attached twigs to turn black quickly. Cankers (oval, sunken areas), also can develop on the south side of trunks and branches in trees with this disease. The disease is not usually fatal to trees, especially mature ones, but can cause stunting.

To manage bacterial blight, prune infected tree branches, making the cuts about 8 inches below the damaged area. Sterilize pruning tools after each cut in a solution of 1 part household bleach to 9 parts water. Burn or dispose of the pruned material. Rake and dispose of leaves and debris in the fall. If bacterial blight is a chronic problem in your aspen trees, begin treatment in spring when leaves start to emerge. Spray the tree 3 or 4 times, once every ten days, with Bordeaux mix or other product labeled for bacterial blight.

VENTURIA LEAF AND SHOOT BLIGHT is also a fungal disease that causes black or brown lesions that kill the leaf and shoots on aspen. Within a few days, the blackened leaf tissue turns olive green as the fungus continues to grow. In wet years, all terminal shoots may be killed, but damage does not spread to the rest of the tree. Young saplings are more prone to damage than older trees. Prune infected shoots, disinfecting pruners between cuts. Rake and remove fallen leaves to help prevent reinfection next spring.

SEPTORIA LEAF SPOT is another fungal disease in aspen. Symptoms are the brown or black mostly circular spots on the leaves. Damage does not usually extend into the stem. The fungus overwinters in dead leaves and twigs. Severe infections can result in partial defoliation of the tree, but is usually not fatal to the tree, which will generate new leaves. However, cankers can be produced that can girdle and kill stems or branches, or serve as infection courts for other diseases.

To control Septoria leaf spot, remove and dispose of fallen leaves and stems. In spring, spray trees 2 or 3 times with a Bordeaux mix or other fungicide labeled for septoria leaf spot to prevent infection. If you purchase aspen trees, ask for disease-resistant clones. Plant trees with plenty of room to allow for good air circulation, and prune with the same goal in mind.

A fourth cause of black spots on aspen leaves is WINTER DAMAGE. Environmental factors, such as cold, drought, or wind can cause damage in the winter months that does not become evident until leaves begin to form. To check for winter damage, cut a twig from the branch, and split it lengthwise. Winter damage causes the inside of the twig to be brown or black.

To minimize winter problems, do not fertilize aspens! High nitrogen fertilizers encourages rapid growth, and the new shoots often are not able to harden off before fall freezes occur. It is better to let trees grow at a slower rate than to push them to grow faster and die faster. Deep-kwater all trees (both evergreens and deciduous) in the fall after leaves of deciduous trees have turned fall color, but before the ground freezes. Water the extended root area 2-3 times farther than the branches extend, to a depth of two feet.

Cytospora and Hypoxylon cankers are common fungal diseases of fast-growing trees such as aspen. These fungi infect the branches and trunk resulting in sunker cankers and tree dieback. The pathogen mainly infects trees already stressed by drought, insects, winter injury, pruning, and similar factors. To avoid Cytospora, plant in a favorable site in a location that mimics the native range of the species. Prune only in late winter when trees are dormant. Water trees judiciously and control other pest problems.

Written by Sherry Lajeunesse and Martha Mikkelson, Extension Urban Pest Management Specialist and Plant Disease Diagnostician, Montana State University. Jan. 1998.
 


ANTHRACNOSE ON ASH AND MAPLE

Favorable conditions and symptoms
Cool, wet spring weather in spring can create ideal conditions for ANTHRACNOSE diseases on ash and maple. On ash, look for irregular, rapidly expanding, water-soaked spots on new leaves. Young lesions are greenish-brown to dark brown. Severe infections may lead to girdling and wilting of young shoot bases. Leaf drop and twig blight can occur also. Symptoms of maple anthracnose include brown to black areas that run along the leaf veins. There may be crinkling and distortion of severely infected leaves. Leaf drop and twig cankers may occur. Frost injury and leaf scorch can cause similar sysmptoms.

Look-alike symptoms
Leaf scorch looks similar to anthracnose.  This drought-related problem also is more common than anthracnose in Montana.

Damage
Anthracnose rarely kills trees. However, severe disease levels can predispose them to other disease, insect, and environmental problems.

Controls
Dry weather is the best control for this disease. Raking and destroying fallen leaves and pruning severely infected branches may help somewhat. Fungicides rarely are needed for anthracnose in Montana. However, if the disease does become a chronic problem, fungicides such as chlorothalonil and mancozeb are most effective if sprayed in early spring at bud break, followed by regular intervals during wet weather. By the time symptoms become widespread on the leaves, it is usually too late for good control.

References:
Pests of Landscape Trees and Shrubs; An Integrated Pest Management Guide. 1994. University of California. Oakland,
    CA  94608-1239. Pub. #3359. 327 pp.
Pirone, P., J. Hartman, M. Sall, and T. Pirone. 1988. Tree Maintenance. Sixth Edition. Oxford Univ. Press, New York, NY   10016. 514 pp.
Plant Health Guide. 1995. Meister Pub. Co. Willoughby, OH 44094-5992. 178 pp.
Sinclair, W., et al. 1987. Diseases of Trees and Shrubs. Cornell Univ. Press, Ithaca, N.Y. 576 pp.

Written by Sherry Lajeunesse and Martha Mikkelson, Extension Urban Pest Management Specialist and Plant Disease Diagnostician, Montana State University. Jan. 1998.
 


Bacterial blight of trees and shrubs
 Bacterial blight causes brown leaf spots (often surrounded by yellow areas) and rapid browning of young shoots. Young plant parts are more severely infected. The bacterium attacks lilacs, pear, cherry, maple, and other ornamentals.

 As with most bacterial diseases, mild, moist weather favor bacterial blight. Factors that weaken or injure plants make infection more likely.  These include wounds, frost damage, improper nutrition, or other diseases or insects. The bacteria spread via wind, rain, insects, tools, and infected nursery stock.

Adequate plant spacing and pruning to allow good air circulation can minimize this disease.  If infection occurs, prune out and burn all affected tissues as soon as you see them. After each cut, sterilize pruning sheers in rubbing alcohol or diluted bleach (1 part bleach to 9 parts water).  When spring weather is favorable for infection, Bordeaux mixture or copper fungicides can be used as protectant fungicides in the spring just before bud break. When using pesticides, always follow instructions on the product label.


Cytospora Canker - Deciduous trees

Trees affected
Dead, sunken areas on tree trunks and branches sometimes are caused by Cytospora canker. Many deciduous trees (trees that lose their leaves in the fall) are susceptible. Common hosts are fruit trees, poplars, aspens, cottonwoods, willows, and spruce. Cankers often are associated with pruning wounds.

Symptoms
Long, sunken areas form on the trunk or branches. The cankered bark often is cracked or discolored with a ridge around the margin. Small, black "pimples" may be on twigs and branches or within the canker. Small branches and twigs are girdled rapidly, while larger branches and the trunk may take several years to become girdled and die.

On spruce, the lowest branches die, then branch death progresses up the tree. Dying branches first turn yellow-green, then purple, followed by needle drop. Profuse resin flows from infected branches, coats the entire surface of the bark around the cankers, and drips onto lower branches. See "Cytospora canker on spruce."

Disease spread
Cytospora overwinters on the bark and in the cankers. During wet weather in spring, spores form and wash to other branches by rain. These spores also can be transported by insects, pruning tools, and clothing. If the spores land on a wound, they can cause an infection. A canker will eventually develop as the fungus invades healthy bark.

Control
To control Cytospora canker, remove and burn all cankered limbs and sprouts preferably in late winter. Avoid wounds such as lawnmower or vehicle damage. Maintain plant vigor through proper watering and fertilizing. Keep in mind that fertilizer actually can encourage Cytospora indirectly by promoting winter injury of new tissues whose growth was encouraged by the fertilizer.

Water trees deeply over the entire extended root zone area. For deciduous trees this area is 2-3 times farther than the branches extend. For conifers, water 1½ times farther than the branches. Allow the water to soak to a depth of about 3 feet. Deep water all trees in late fall, after leaves of deciduous trees have turned autumn color but before the ground freezes. Water again in spring as soon as the ground thaws. For more information on good watering practices, see the topic sheet in this series "Watering Trees and Lawns: The Pest Connection".

In most of Montana, tree fertilizers are not needed. Avoid unnecessary fertilization since it can lead to other pest problems, winter damage, contamination of groundwater, overly rapid growth, and unnecessary expenses. To determine if your trees need fertilizing, have the soil tested or look for symptoms of nutrient deficiency such as yellowing, stunted growth, or twisted, deformed foliage. For additional information, see the topic sheet in this series, "Fertilizing Trees & Shrubs: Good Practices Can Help Prevent Pest Problems".

References:
Harris, R.W. 1992. Arboriculture; Integrated Management of Landscape Trees, Shrubs, and Vines. Prentice- Hall, Inc., Englewood Cliffs, NJ. 674 pp.
Pests of Landscape Trees and Shrubs; An Integrated Pest Management Guide. 1994.
University of California. Oakland, CA 94608-1239. Pub. #3359. 327 pp.
Pirone, P., J. Hartman, M. Sall, and T. Pirone. 1988. Tree Maintenance. Sixth Edition. Oxford Univ. Press, New York, NY 10016. 514 pp.
Shigo, A.L. 1986. A New Tree Biology. Shigo and Associates, Durham, NH 03824. 595 pp.

Written by Sherry Lajeunesse and Martha Mikkelson, Extension Urban Pest Management Specialist and Plant Disease Diagnostician. January, 1998.


Cytospora Canker of spruce
The fungal disease Cytospora canker is most damaging on Colorado and Norway spruces.  Engleman and white spruces (including Black Hills spruce) also can be infected. Diseased trees rarely are killed outright; however, they often become misshapen with bare, distorted branches.
 
The first indication of Cytospora canker is dying lower branches.  In following years, other branches die, leaving scattered dead branches throughout the tree.  Infected branches commonly have patches of young amber that age to form blue-white resin on the upper sides of the branches, usually close to the main stem.  In contrast to healthy tissue, the inner bark and cambium tissue inside the cankers is reddish-brown while the sapwood beneath remains light-colored. Removal of thin bark slivers just beyond the resin should expose black structures that range from the size of a pinhead to that of a small nailhead. These are the spore-producing bodies of the fungus.

The fungus invades trees through wounds. The disease spores spread to new branches or trees by rainsplash, wind, insects, birds, and man.  Older trees weakened from drought and hail injury are most susceptible.  Other environmental stresses such as insect or mechanical injury also favor Cytospora.

Since stressed trees are more susceptible, the best way to prevent Cytospora canker is to maintain healthy, vigorous trees.  Especially important are a planting site that mimics the species' natural habitat and proper watering.  Avoid planting spruces where they will have little room to grow. Occasional fertilizer in poor soils can help minimize Cytospora.
Remove and destroy infected branches.  The best time to prune is in late winter before spores are released in the spring; however, it is acceptable to prune dead branches during dry weather at any time of year. Prune 4 to 6 inches ahead of the canker, cutting back to the nearest living lateral branch or to the trunk.  Disinfect tools with a 10% bleach solution or 70% alcohol between cuts to avoid spreading the disease.  Fungicides are not effective against Cytospora.


Rhizosphaera Needle Cast of Spruce
Rhizosphaera needle cast is most severe on Colorado spruce and Englemann spruce. This fungal disease is very common in the Midwest and Great Lakes states, but is less of a problem in Montana.  Rhizosphaera is most common in nurseries, windbreaks, and Christmas tree plantations since the fungi can spread from tree to tree easily. Ornamental spruces sometimes are infected, too.

Rhizosphaera causes second year needles to turn yellow and then purplish brown before dropping from the tree. Infected needles usually shed from the tree a year after infection, leaving branches with current year needles only. Pinprick-sized black dots produced in rows on discolored needles indicate that Rhizosphaera is involved. These spore-producing bodies are visible through a magnifying lens.

Prolonged periods of spring rain are necessary for infection.  Most Rhizosphaeria spores survive on dead needles on the ground.  Rain falling on the ground splashes spores onto lower branches where infection begins. Subsequent rains move the spores to progressively higher branches.  Even though infection usually occurs in the spring, symptoms of Rhizosphaeria are not visible until late fall or the following summer.  Then needles turn yellow and purplish-brown.

In locations where conditions commonly are favorable for disease, control nearby weeds and debris and prune lower branches to increase air circulation. Remove infected needles from under the tree and destroy them to minimize disease spread.
Two applications of fungicides such as chlorothalonil or Bordeaux mixutre provide good disease control.  The first application should occur when new needles are about half expanded (3/4-1") and a second application 2 to 3 weeks later.  For moderate infections, two years of fungicide treatments are recommended.


Diseases in Trees: How Much Can Trees Tolerate?

As summer wears on, we see more and more damage from diseases accumulating on landscape trees. How much is too much? It depends on the tree, the disease present, and the time of season. Although we do not have frequent disease problems in trees in Montana, there are many diseases that can attack trees, and they can be difficult to diagnose.

Some common symptoms that usually are less severe are powdery mildew, rusts, and sooty molds. Powdery mildew causes powdery, white accumulations on foliage. Rust fungi cause small, round spots of orange powder on deciduous tree leaves or orange galls on conifer branches. Sooty mold, a black fungus that forms on leaves and twigs in association with aphids, usually is not a serious problem either.

Most pathogens that cause brown or black spots on tree leaves are not serious, although they can cause twig dieback. In those instances, prune and dispose of the heavily-infected branches. Generally by September, leaf diseases are not very important since the tree has already stored enough nutrients and carbohydrates for winter, and the leaves are not as crucial as they were earlier in the season.

Symptoms that may indicate a serious problem are sunken, discolored areas in the bark of trunks or branches. These are called cankers. Cankers can girdle trunks and branches, causing tissue death beyond the cankered area. Wilting leaves, splitting bark, decaying wood, or deformed, streaked, or mottled foliage are other symptoms that may indicate more serious problems. If you see any of these symptoms, try to get the problem identified, and implement the appropriate control measures.

References:
North Dakota Tree Handbook. 1995. Agriculture and Natural Resources, North Dakota State Universit, Fargo, ND. 228 pp.
Pirone, P., J. Hartman, M. Sall, and T. Pirone. 1988. Tree Maintenance. Sixth Edition. Oxford Univ. Press, New York, NY 10016. 514 pp.
Sinclair, W., et al. 1987. Diseases of Trees and Shrubs. Cornell Univ. Press, Ithaca, N.Y. 576 pp.

Written by Sherry Lajeunesse and Martha Mikkelson, Extension Urban Pest Management Specialist and Plant Disease Diagnostician. January 1998.
 


Dutch Elm Disease

History of disease
Dutch elm disease (DED) is the most destructive shade tree disease in the United States today.  The disease first entered the United States when elm logs carrying the disease were imported from Europe before 1930.  Since then, countless numbers of beautiful, old American elm trees have been killed throughout North America.  In Montana, many of these popular shade trees have been killed in our larger urban areas, and the disease continues to move into smaller communities and rural areas.

Affected species
American elms are very susceptible.  Siberian and Chinese elms are not immune, but they rarely are infected.

Symptoms
Protecting American elms from DED is expensive and difficult and it is crucial to detect  DED in its early stages!  The earliest symptoms are yellowing and/or wilting of the leaves on a single branch, usually a branch in the upper crown.  Peel the bark back to reveal the sapwood of thumb-sized branches showing symptoms. DED causes brown streaks in the sapwood.  If these streaks are present, contact your county extension agent to have these branches tested for DED.
 
ONCE SYMPTOMS ARE VISIBLE ON 5% OF THE TREE, THE TREE WILL DIE. When a diseased tree is found, you must cut and burn or debark the tree before the following spring to prevent spread to other trees in the area.  There is no cure, and pruning is not effective. Once leaves reach full size, the symptoms spread very rapidly to progressively larger branches and eventually to the entire tree. Often an entire tree dies in one summer.

Disease spread
The disease is a vascular wilt, which means that it blocks the flow of water and minerals within the sapwood of the tree.  The causal agent, a fungus, spreads in two distinct ways: from tree to tree by root grafts, and over longer distances by means of elm bark beetles.  Because adjacent elms (within 10 m of each other) often fuse their root systems together, the DED fungus passes directly from an infected tree to an adjacent healthy tree through their joined sapwood. The disease can spread quickly through rows or groups of elms as a result of root-graft transmission.

The rapid spread of DED is due to a destructive pathogen that is spread through a very efficient insect vector.  Two species of elm bark beetles (not the same as elm leaf beetles) spread the disease.  These tiny (less than 1/4" long) insects lay their eggs below the bark of dead and dying elm trees.  The larvae pupate to adults. While chewing their way out of the bark, their bodies become covered in sticky spores of the DED fungus.  They fly to healthy trees (which are often under some stress) where they feed on tender sapwood of young twig crotches. This directed movement from dying to healthy elms makes the life cycle of these bark beetles extremely efficient vectors of DED!

Control overview
Control of DED is based largely on eliminating breeding sites for the beetle vectors.  Monitoring elms for DED symptoms, and prompt destruction of infected trees, protectant fungicides and insecticides, and planting of resistant varieties are recommended.

Prevention of disease
Pruning of healthy elms should be done in late fall to early winter to prevent attraction of elm bark beetles to the pruning wounds.  Limbs which have been pruned from the tree should be burned or buried to eliminate breeding sites, or covered with tightly sealed clear plastic to keep beetles out.

Spring applications of the insecticide methoxychlor and malathion to prevent beetle infestation are sometimes used to prevent bark beetles from feeding on healthy elms, especially in areas where planted elms grow near wild groves of American elms.  These insecticides provide two weeks of control.  Therefore in some cities, elm bark beetle eggs in dead elm logs are caged so that spray programs can correspond to time of beetle emergence from the dead trees.

If an American elm becomes diseased and other elms are within 60 feet of that elm, it is very important to destroy root grafts between these trees before removing the infected tree. This is because removing a DED-killed elm actually increases transmission of DED to adjacent trees whose roots are grafted to the DED tree.  Destroying the root grafts can be done by  mechanical or chemical  methods.  The mechanical method involves digging trenches at least two feet deep between adjacent trees to try to halt spread through roots.  The chemical method involves pouring a solution of Vapam into drill holes located between the trees.  This method often is used if there are underground lines in the areas that prohibit the digging of trenches. Use a dilute solution of Vapam (1 part Vapam to 3 parts water) and make the drill holes according to the following dimensions:  0.75 - 1 inch diameter, 15 inches deep, and 6 to 9 inches apart. Do not overflow holes and cover holes immediately after filling.  Do not apply within 10 ft of a healthy tree.

Fungicides
Preventative fungicides such as Alamo and Arbortect that can be injected into trees are especially valuable. The procedure is relatively expensive and should be done only by professionals who have received sufficient training in the technique.  Small holes are drilled in the tree for insertion of the implants.  Incorrect drilling can damage the tree.  When done correctly, implants are safe and fairly effective in preventing Dutch elm disease. However, injections are expensive and the wounds that result also can harm the tree. Therefore, there is a limit to the number of times a tree can be injected.

Avoid companies that inject fungicides by pounding pipes into trees and pouring materials into the pipes.  The procedure is completely ineffective and causes irreparable damage. For more information on the use of the method, see the fact sheet in this series, "Tree Injections and Implants".

Wood from diseasesd trees
Wood from diseased trees should not be saved for firewood because the beetle larvae will continue to mature and emerge from the cut wood.  If the bark is completely removed, the elm wood can be used as firewood.  Insecticides applied to the infested cut wood are not effective.  Nor is it safe to burn wood treated with insecticides indoors.

Resistant varieties
Resistant varieties are very promising. Several American elm varieties have been selected for resistance to DED.  The most DED-resistant elms are hybrids of European and Asian elms.  American Liberty Elm is a true Amercian elm that was selected from 6 individual trees found between the 1930's and the 1950's that successfully resisted DED.  Of 250,000 trees planted in 650 communities, only 30 trees have been lost to DED. ‘Liberty' is not available through commercial nurseries.  However, you can purchase elms directly from the Elm Research Institute or from local Boy Scout troops and civic organizations that are maintaining a Johnny Elmseed nursery.  Call the Elm Research Institute at 1-603-358-6199 to the Elm Research Institute at Elm Street, Westmoreland, NH 03467 for more information.

Valley Forge and New Harmony are DED-resistant American elms that recently have become commercially available.  However, they are hardy only in USDA Hardiness zones 5 to 7.  Therefore, they are unlikely to survive well in Montana which consists mostly of zones 3 and  4.

References:
Cranshaw, W.  1995.  Management Recommendations for Insect Pests of Trees and Shrubs.  Colorado State  Univ, Ft. Collins, CO.   Extension publication XCM-38.  78 pp.
Elm Research Institute Homepage. http://www.forelms.org/erihome.htm
Gleason, M.  1997.  Department of Plant Pathology, Iowa State University.  http://www.ipm.iastate.edu/ipm/hortnews/1992/7-15-1992/delm.html
Harris, R.W. 1992.  Arboriculture; Integrated Management of Landscape Trees, Shrubs, and Vines.  Prentice-Hall, Inc., Englewood Cliffs, NJ.  674 pp.
Pscheidt, J.W. 1996. Pacific Northwest Plant Disease Control Handbook. Oregon State University.
Pirone, P., J. Hartman, M. Sall, and T. Pirone. 1988.  Tree Maintenance.  Sixth Edition.  Oxford Univ. Press,  New York, NY  10016.  514 pp.
Plant Health Guide.  1995.  Meister Pub. Co.  Willoughby, OH  44094-5992.  178 pp.
Sinclair, W., et al.  1987.  Diseases of Trees and Shrubs.  Cornell Univ. Press, Ithaca, N.Y.  576 pp.
Stipes, R.J. and Campana, R.J.  1981. Compendium of Elm Diseases. American Phytopathological Society, St. Paul, MN.

Written by Sherry Lajeunesse and Martha Mikkelson, Extension Urban Pest Management Specialist and Plant Disease Diagnostician.  January 1998.


Firewood from Dutch Elm-Diseased Trees

See "Identifying Elm Firewood" publication - this factoid needs work
Wood from trees infected with Dutch-elm disease should be debarked before storage or buried or burned immediately after tree cutting to prevent spread of this fatal disease to healthy trees. This is because infected trees which are cut down can contain beetles carry the disease to healthy trees. The beetles fly around and feed from about April 1 to September 15, so it is especially important to get rid of all elm firewood during that period or completely debark the logs. Since burning elm firewood kills the beetle grubs and eliminates beetle breeding sites, it is the most effective method of disposal.

Debarking the wood is a good way to rid the wood of elm bark beetles, thereby limiting spread of the disease. There have been no DED problems associated with using debarked wood for firewood

Insecticides do not effectively kill beetles in the wood . Since the beetles tunnel beneath the bark, it is difficult to obtain the complete insecticide coverage of the wood that is necessary for good beetle control. In addition, burning insecticide-treated wood in an indoor fireplace is not recommended.

References:
Harris, R.W. 1992. Arboriculture; Integrated Management of Landscape Trees, Shrubs, and Vines. Prentice- Hall, Inc., Englewood Cliffs, NJ. 674 pp.
Johnson, W., and H. Lyon. 1991. Insects That Feed On Trees and Shrubs. Cornell Univ. Press, Ithaca, N.Y. 560 pp.
Sinclair, W., et al. 1987. Diseases of Trees and Shrubs. Cornell Univ. Press, Ithaca, N.Y. 576 pp.

Written by Sherry Lajeunesse, Extension Urban Pest Management Specialist. Sept., 1997
 


Iron Chlorosis

Symptoms
Iron chlorosis causes leaves to turn yellow while the leaf midrib remains green. Advanced symptoms include very pale leaves that turn brown at the tips.

Cause of problem
Iron chlorosis is a common problem, especially for plants more suited to acidic soils, which have a low pH. If the pH of the soil is too high, which is often the case with our alkaline western soils, iron chlorosis can result. Usually adequate iron is present in the soil. However, high pH results in conversion of the iron to a form that the roots cannot absorb. Have the soil pH tested so you will know your "starting point."

Iron chlorosis is an iron deficiency that can be caused by several other things too, such as roots that are damaged by tilling, dry soil, and sandy soil with insufficient organic matter. Tilling damage and dry soil make the roots less able to take in nutrients.

 Control
You can try to gradually lower the soil pH although this may take a long time. Try adding 1-2 inches of compost to the soil every few years, or add sulphur or peat moss. Plants also can be mulched with conifer needles which will leach some acids into the soil.

Short-term solutions include foliar application of iron chelate which is available from most garden supply stores. Try spraying 1 tbsp. iron chelate/gallon water on the tree leaves in early summer. You should see improvement in leaf color within 2 weeks. However, you will have to reapply the iron chelate as symptoms reappear.

Select trees and shrubs adapted to the soil type, climate, and other conditions in your yard to save problems in the long term. If soil is "improved" so certain plants can be grown, you must maintain the improvements each year. Plants growing under "foreign" conditions are under continual stress, resulting in more pest and environmental problems.

References:
Evans, G., and A. Epps. 1994. Choosing Trees and Shrubs for Montana Landscapes. Extension Publication EB 123, Montana State Univ.- Bozeman. Bozeman, MT 59717. 61 pp.
Pests of Landscape Trees and Shrubs; An Integrated Pest Management Guide. 1994. University of California. Oakland, CA 94608-1239. Pub. #3359. 327 pp.
Pirone, P., J. Hartman, M. Sall, and T. Pirone. 1988. Tree Maintenance. Sixth Edition. Oxford Univ. Press, New York, NY 10016. 514 pp.
Sinclair, W., et al. 1987. Diseases of Trees and Shrubs. Cornell Univ. Press, Ithaca, N.Y. 576 pp.

Written by Sherry Lajeunesse, Extension Urban Pest Management Specialist. Sept., 1997
 


Juniper Dieback & Juniper Twig Blight
 
Causes of dieback
 Dieback of ornamental junipers is noticeable nearly every year across Montana. Both wet and dry condition can be the culprits. In general, junipers are adapted to dry, barren, rocky or sandy soils (which provide excellent drainage and aeration) and full sun. They do not fare well when planted in heavy clay, waterlogged soils, or are heavily mulched with bark and/or black plastic.

Some Montana conditions exceed junipers' tolerance for drought, however. For example, they continuously lose water through transpiration during winter months and cannot replace lost moisture in frozen ground. Therefore, they can suffer drought stress even in winter. Junipers planted near building foundations receive less moisture than shrubs out in the open. It is important to monitor soil moisture in such areas by using a Paul Brown probe or similar means. Deep water these junipers when the soil becomes too dry.

Water junipers so the moisture soaks at least one foot deep several times a year, especially in late fall just before the ground freezes. Water again in the spring as soon as the ground thaws. Avoid watering in late summer until time for the final watering in fall to give the shrubs time to "harden off" for winter.
 
JUNIPER TWIG BLIGHT is a second cause of juniper dieback. This disease usually is a problem of seedlings and nursery stock. Shrubs and trees older than five years rarely are seriously affected.

Symptoms
1.   Dieback occurs on tips of branches that are the diameter of a pencil or smaller. Infected foliage becomes pale, then reddish brown, then turns brown or ash-gray after death.
2.   Scrape away the bark until you reach living wood. A sharp line between discolored dead wood and healthy wood is a strong sign that Phomopsis is the problem.
3.   Look at the base of the ash-gray scale needles for small, black fruiting bodies. The fruiting bodies form the spores that cause new infections. In wet weather, spores ooze from the fruiting bodies and splash onto new foliage. The spores are produced year round and infect yellowish-green juvenile foliage. The darker green mature foliage is resistant to infection.
 
Look-alike symptoms
Two other fungi can cause twig blight in juniper: Kabatina juniperi and Cercospora sequoiae var. juniperi. The distribution and severity of the two diseases is not yet known. The symptoms are identical for the Phomopsis and Kabatina twig blights, but the Cercospora twig blight is different.
 
Favorable conditions
Most severely-diseased plantings result from overly-wet conditions. Junipers have two flushes of growth under natural conditions, one in spring and another in summer. Pruning also stimulates new growth. When this growth coincides with wet, warm weather or frequent overhead sprinkler irrigation, severe twig blight can occur. Junipers growing in poorly drained, shaded and overwatered sites are most susceptible. Under such conditions, the entire shrub may die.
 
Control
1.   Do not buy plants that have dead or dying twigs.
2.   Plant junipers where air circulation will allow the foliage to dry quickly after dews, rain, or sprinkler irrigation.
3.   Do not crowd plants. Avoid sprinkler irrigation if possible.
4.   Plant resistant varieties.
5.   Prune out infected branches during dry weather.
6.   Apply fungicides such as Clearys 3336, Fore, or Kocide whenever new growth begins and conditions are wet.
7.   Where twig blight has been a problem, protect spring and fall growth with a fungicide. Fungicides are not needed during dry weather.
 
Resistant Varieties
There are varieties of juniper which are resistant to juniper twig blight, and the whole issue can be avoided by planting these varieties. Ask your Extension agent or nurseryman if these varieties are fully hardy in yard area.
Chinese juniper (Juniperus chinensi)
'Fimina',' Iowa', 'Keteleeri', 'Pfitzeriana Aurea', 'Robusta', 'var.sargentii, var. sargentii glauca, 'Shoosmith'
Common juniper (J. communis )
'Aureo-spica', 'Depressa', 'Hispanica', 'Hulkjaerhus', 'Prostrata aurea', 'Repanda', 'Saxatilis', 'Suecica'
Creeping juniper ( J. horizontalis )
'Plumosa', 'Plumosa aurea', 'Procumbens'
Savin juniper ( J. sabina )
'Broadmoor', 'Knap Hill', 'Skandia'
Western red cedar (J. squamata )
campbellii, fargesii, prostrata, pumila
Rocky Mountain Juniper ( J. scopulorum)
'Silver King'
Eastern Redcedar ( J. virginiana)
'Tripartita'
 
References:
Evans, G., and A. Epps. 1994. Choosing Trees and Shrubs for Montana Landscapes. Extension Publication EB 123, Montana State Univ.- Bozeman. Bozeman, MT 59717. 61 pp.
Michigan Horticultural Extension. Twig blight of juniper. http://www.dlcwest.com/~createdforyou/juniper2.html
Moorman, G.W. 1997. Juniper twig blight. Plant Disease Facts. Pennsylvania State University. http://www.cas.psu.edu/docs/CASDEPT/PLANT/ext/jtwigblt.html
Pirone, P., J. Hartman, M. Sall, and T. Pirone. 1988. Tree Maintenance. Sixth Edition. Oxford Univ. Press, New York, NY    10016. 514 pp.
Sinclair, W., et al. 1987. Diseases of Trees and Shrubs. Cornell Univ. Press, Ithaca, N.Y. 576 pp.
 
Written by Sherry Lajeunesse and Martha Mikkelson, Extension Urban Pest Management Specialist and Plant Disease Diagnostician. February, 1998.
 


Juniper-Hawthorn Rust
 

Host plants
Juniper-hawthorn rust is a fungal disease that requires two different host species to complete its life cycle; a conifer and a deciduous host. Both must be growing close to each other for the disease to develop. In Montana, juniper is the most common conifer host. Hawthorn and serviceberry (also called juneberry and saskatoon) are common deciduous hosts. Apple is sometimes infected, but rarely.

A closely related, but LESS common species of rust in Montana is CEDER-APPLE RUST. Many of our ornamental evergreens are mistakenly called "cedars", but these actually are junipers. Symptoms and management for both rust species are similar.

Disease spread and symptoms
The fungus overwinters in reddish-brown galls up to two inches in diameter on the branches of the juniper host. In spring, the galls swell, and become covered with spikes. Later they form gelatinous, yellow-orange "sporehorns" that discharge disease spores. The spores blow in the wind to infect the secondary hosts such as hawthorn, serviceberry, or mountainash. On the broadleaf trees, pale yellow-orange spots form on leaves and fruit, and may develop numerous tentacle-like projections about 1/4 inch long.

Controls
Generally, the galls do little permanent harm to juniper trees or alternate hosts. Prune the galls from the infected trees to manage the disease in juniper. When the disease occurs chronically, preventative applications of fungicides can protect valuable alternate hosts growing near infected junipers.

References:
Pacific Northwest Plant Disease Control Handbooks. 1997. Extension Services of Oregon State University. Corvallis, OR 97331-0817.
Pirone, P., J. Hartman, M. Sall, and T. Pirone. 1988. Tree Maintenance. Sixth Edition. Oxford Univ. Press, New York, NY 10016. 514 pp.
Sinclair, W., et al. 1987. Diseases of Trees and Shrubs. Cornell Univ. Press, Ithaca, N.Y. 576 pp.

Written by Sherry Lajeunesse and Martha Mikkelson, Extension Urban Pest Management Specialist and Plant Disease Diagnostician, Montana State University, Jan. 1998.
 


MYSTERIES OF CEDAR-APPLE RUST
Many people think fungi are either boring or annoying, but any long, coffee-ladden discussion about the life style of cedar-apple rust should prove these ridiculous perceptions wrong.  Just think these facts over: 1) Gymnosporangium rusts reduce tree vigor, but do not kill trees outright. 2) Rusts are considered to be some of the most complex and advanced members of the fungal world. 3) Species of the fungus Gymnosporangium must reproduce via a sequence of five different spore types on two very unrelated host plants in order to survive. If you're thinking "Yeah, so what?", read on.

Some diseases, such as damping-off caused by the fungus Rhizoctonia, kill seedlings outright. Others such as Gymnosporangium rusts are common and very visible on certain trees, but they only reduce tree vigor by diverting carbohydrates. As true parasites, they do not kill trees. Now, which do you think is the "smarter" fungus: the pathogen that kills its source of food or the parasite that feeds off the host without causing much growth reduction? The old addage "don't cut off the hand that feeds you" becomes pertinent here. Maybe annual herbaceous plants will be quickly replaced. However, when the target is a relatively slow-growing, long-lived species such as a cedar, it may be best to keep the food source alive, especially when life depends on cedar soup.

Plants had been battling fungal diseases for eons before fungicides were invented to help them. As you can imagine, they have developed all kinds of strategies to keep from being devastated by these killer fungi. And just like the evolution from the bow and arrow to the nuclear bomb, the fungi developed new weapons of attack as the plants got more defensive. Rusts are considered to be at the top of the fungal totem pole in terms of being evolutionarily-advanced. One reason for this lies in their ability to secretly enter plants without tripping burgular alarms (Trojan horse theory). Once inside the plant cells, complex adaptations allow them to "tread and feed lightly" so they do not kill their host. More "primitive" pathogens do not have the ability to do this. Whether this less destructive approach of the rust parasites has slowed the natural development of host resistance is very debatable. Development of resistant plant varieties remains the most important means of controlling rust diseases as a whole. However, rusts often overcome the resistance that plant varieties have attained, attesting to the fact that the coevolution between rust fungi and their hosts is still very dynamic. So, the rusts give us an opportunity to see evolution in progress!

Rusts belong to a group of fungi that have developed very specific host relationships involving both a conifer and a rosaceous host. In other words, when you see Gymnosporangium rust on cedar or juniper, you can expect the same fungus to show up later on roseacous hosts that include either apple, crabapple, saskatoon, pear, hawthorn, or mountain ash. (The exact tree species that are infected depends on which fungal species are involved.) A cedar tree is not at all related to an apple tree, but the same rust species infects both in the course of its life cycle.

Additionally, it is important to remember that the symptoms on the two hosts look entirely different. This is because Gymnosporangium rusts produce five very different spore types, each of which grows on a different area of one of the two hosts. The structures these spore types form include large orange horn-like structures on conifer hosts in spring followed by a spore type well adapted for air-current travel to the roseaceous host. Two rusty-colored spore stages form sequentially on the upper and lower leaf surfaces respectively. The latter spore type also infects the fruit. Another "travelling" spore type is then produced. After these spores move back to the conifer host, they infect this tree again causing hard galls to form on the twigs. The rust spends the winter in the protective gall and begins this complicated cycle all over again in the spring.

The development of parasitism involves very specialized evolution in order to divert food from the host without greatly harming it. Forming a parasitic relationship with two hosts seems doubly difficult. So why would a fungus evolve such an odd dependancy on these two hosts? And what is the advantage of producing five different kinds of spores on these two hosts when other fungi seem to cause disease with just one spore type on one host? I don't claim to know all the answers. My theory is there are advantages to infecting cedars earlier in the spring and moving to apple leaves and fruit as they develop later. Since each spore type develops in a different location, this allows specialization in many niches or "spaces". Crowding is less likely to inhibit colonization of the host and differences in food sources can allow for more fungal diversity. Maybe the sporadic nature of the fungus on each host also allows less chance for host resistance development.

Gymnosporangium rusts do have a very colorful life cycle that is worthy of any philosopher's pondering. I'll admit that I am an oddball plant pathologist, but certainly in this case the question of "why does cedar-apple rust behave so strangely?" is much more intriquing than "how do I get rid of it?"
 
Written by Martha Mikkelson, Plant disease diagnostician, Montana State University.


Leaf Scorch (Environmental)
 
Symptoms
Symptoms of leaf scorch due to environmental causes include browning of the leaf margins and\or yellowing or darkening of tissues between the main leaf veins. As the condition progresses, entire leaves may dry up, turn brown and become brittle. Leaves sometimes wilt rapidly and may remain pale green in color, even when dried out. Damage usually is more noticeable on the windward or southern side of trees. Plants may lose many leaves prematurely during late summer and have some twig dieback.
 
Causes
Leaf scorch can be caused by adverse environmental conditions, such as soil compaction, transplant shock, nutrient deficiency, drought, salt toxicity, and weed killer injury. Leaf scorch is common in Montana due to cold soils and slow root growth. The loss of leaves is seldom fatal, but favorable conditions should be corrected if possible to prevent decline or death of the tree. Stressed plants are susceptible to secondary problems such as attack by insects or diseases.
 
Controls
Prune sprouts and diseased branches to prevent leaf scorch. Maintain plant vigor through proper watering and fertilizing. Water deeply to encourage deep root systems that enable trees to withstand environmental stress such as drought and winter desiccation.
 
Check soil moisture at least 12 inches down. If the soil is rather dry, water trees slowly and deeply, allowing water to penetrate at least two feet. Deep-water the entire area under the canopy, one and one-half to three times farther than the branches. Because 95% of the roots of most trees are found in the top 18 inches of soil in this extended area. Sufficient moisture will help keep the trees vigorous enough to withstand pest attacks, as well as help prevent winter injury. It is very important to deep-water trees and shrubs at least twice a year, especially in areas where the water table is far below the soil surface or on sites exposed to wind; water every fall, after leaves turn autumn color, but before the ground freezes (perhaps at the same time fall fertilizers are applied if needed), and again in spring, as soon as the ground thaws to replenish dehydrated roots.
 
Avoid frequent, light waterings, and watering only at the base of the tree trunk. Trees suffering from drought can be selectively pruned to reduce transpiration, which is the loss of water due to evaporation through the leaves. Drought occurs when transpiration exceeds the plant's ability to supply water through the roots. Prior to planting, reduce foliage of transplants by pruning to minimize early injury due to water stress.
 
To determine if trees need fertilizing, have the soil tested and supply any missing nutrients. Avoid overfertilization, which can also harm trees and ornamentals. In most of Montana, additional tree fertilizers are not needed, especially when planted in turf areas that receive fertilizers. Unless trees are showing symptoms of nutrient deficience, such as chlorosis, stunted growth, or deformed foliage, refrain from fertilizing them unless soil tests indicate otherwise.
 
Compacted soil can be loosened over time by the annual use of core aerators, which remove a plug of soil up to four inches long, and then adding an inch or so of finished compost. The compost will soon work its way down into the soil, loosening it over time. Using dark-colored permanent mulches under the entire canopy area can help prevent compaction once soil is loosened.
 
When using herbicides near trees, do not allow mist to settle onto trees, and avoid spraying under the dripline since roots can take up many herbicides. Apply pesticides only on windless days to avoid problems with drift.
 
References:
 Harris, R.W. 1992. Arboriculture; Integrated Management of Landscape Trees, Shrubs, and Vines. Prentice- Hall, Inc., Englewood Cliffs, NJ. 674 pp.

North Dakota Tree Handbook. 1995. Agriculture and Natural Resources, North Dakota State University, Fargo, ND. 228 pp.

Pirone, P., J. Hartman, M. Sall, and T. Pirone. 1988. Tree Maintenance. Sixth Edition. Oxford Univ. Press, New York, NY 10016. 514 pp.
 
Written by Sherry Lajeunesse and Martha Mikkelson, Extension Urban Pest Management Specialist and Plant Disease Diagnositician. February, 1998.
 


Powdery Mildew
 
Symptoms
Patches of white or grayish powder on garden plants, lawns, shade trees, or shrubs are probably powdery mildew. Powdery mildew is a fungal disease found throughout North America. It can cause severe problems in irrigated areas. Powdery mildew can attack a wide variety of turf plants, garden vegetables, and landscape trees and shrubs. The degree of damage varies with the plant and environmental conditions. In some cases, yield is lost or plants might die. In other species of plant, yield is not affected and damage is negligible.
 
Susceptible plants
In gardens and orchards, powdery mildew is common on peas, cucumbers, squash, strawberries, raspberries, apples, and cherries. On garden plants, look for patches of grayish-white powder on either the upper or lower surfaces of leaves or on various parts of the plants.

Controls
As soon as diseased garden plants are discovered, prune out and destroy the infected parts. Disinfect pruning tools in a bleach solution of one part household bleach to four parts water after each cut. If the infestations are severe, remove and destroy entire plants that are infected.
 
In addition to pruning, fungicidal soap, which is manufactured by several companies, can help to control the disease. Fungicidal soaps are safe for both humans and the environment and are made from highly refined fatty acids, a form of soap. Another option is to spray once a week with a solution of one teaspoon baking soda dissolved in one quart of water. Antitranspirants, such as Wilt-pruf or VaporGard, have also been shown to prevent powdery mildew when applied every two or three weeks. Sulfur-based fungicides applied every 7-10 days will also help prevent spread of powdery mildew to healthy plants. Be sure to spray the undersides of leaves as well as the upper surfaces when using any of these sprays.
 
To manage powdery mildew in fruit trees, follow the same methods just discussed. In areas where powdery mildew is a chronic and severe problem in fruit trees, a preventative spraying program should begin in spring, with weekly applications of a fungicide such as lime sulphur to prevent establishment of the disease.
 
Shade trees and ornamentals are usually not severely damaged by powdery mildew. Many times all that is needed for trees and ornamentals is pruning and cleanup of fallen leaves and debris in the fall, unless the infestation is serious.
 
Powdery mildew in lawns is seldom serious enough to warrant chemical control. In shady areas that might be more prone to infection, shade tolerant grasses such as creeping red fescue can be planted. Raise the mowing height for grasses in shady areas that are prone to powdery mildew infection, and avoid over- or under-application of nitrogen. Organic fertilizers or slow-release formulations of lawn fertilizers are good choices. Watering lawns in the morning gives the plants the rest of the day to dry off, discouraging establishment of diseases, including powdery mildew. The longer plants remain wet, the more susceptible they are to infection by diseases. Do not work around plants when they are wet, as the disease spores can easily be transported to other plants on your clothes, hands, and tools under these conditions. Thin plants to allow air circulation and penetration of sunlight.
 
References:
 Agrios, G.N. 1988. Plant Pathology. Third edition. Academic Press, San Diego, CA. 803 pp.

Flint, M.L. 1990. Pests of the Garden and Small Farm. Univ. of California. Oakland, CA 94608-1239. Pub. #3332. 276 pp.

Howard, R., J. Garland, and W. Seaman. 1994. Diseases and Pests of Vegetable Crops in Canada, An llustrated Compendium. Canadian Phytopathological Society  & Entomological Society of Canada, Ottawa, Ont. K2A 1Y8. 554 pp.

Pacific Northwest Plant Disease Control Handbooks. 1997. Extension Services of OSU. Corvallis, OR 97331-0817.
 

Written by Sherry Lajeunesse, Extension Urban Pest Management Specialist. Sept., 1997.
 


Powdery mildew of lilac
 Powdery mildew forms a grayish-white powdery mat on the leaves. Infected leaves may turn yellow and fall off.  New growth often is stunted.  Hot, humid weather favors this disease. Generally, mildew occurs in late summer and does little harm.  Most French hybrids are very susceptible, but Manchurian lilacs (‘Miss Kim'), Meyer lilacs, and Japanese tree lilacs are quite resistant to mildew.

 To prevent mildew, do not plant lilacs in the shade!  Space and prune shrubs properly to allow good air circulation. High nitrogen fertilizer favor mildew so minimize their use.  Fungicides usually are not needed for mildew control. However, if it becomes an yearly problem, contact your county extension agent about fungicide use.


Pruning Diseased Wood from Trees and Ornamentals
 
When, why and what to prune
Late winter or early spring is a good time to inspect trees and ornamentals for symptoms of disease and to prune out any diseased plant material you find. Pruning is one of the best ways to keep the disease from spreading to other parts of the tree or to healthy trees. It is usually best to prune when woody plants are still in dormant stages to reduce problems from diseases and insects. Also, before leaves are formed it is easier to see symptoms of diseased wood.
 
Some of the more common problems you might find are black knot in plum and chokecherry; blight (including fire blight) which can occur in apple, crabapple, saskatoon berry, mountain ash, and raspberry; canker, which can be found in most trees and shrubs; and rusts, which can be found in apple, crabapple, juniper, cedar, and saskatoon berry.
 
Symptoms
The symptoms associated with these diseases include:
- swellings and knots that are black and hard (black knot);
- twigs that appear blackened as though scorched by fire, sometimes curled into a 'shepherd's crook' on the tip (blight or fire blight);
- purplish to chocolate brown spots or bands;
- tissues which crack open and expose the wood underneath, or sunken, elongated areas which are often cracked or discolored (canker).
 
In the case of conifers, needles can turn yellow-green then purple, then drop. Heavy resin can flow from infected conifer branches, coating the surface of the bark around cankers and dripping onto lower branches. Galls that are brown, warty or decayed can also indicate diseases, as can pronounced swellings, or large numbers of smaller branches called witches' brooms.
 
Control
To prune the diseased material, cut off the infected area along with at least eight inches of healthy tissue. Sterilize your pruning tools between each cut by dipping them in a solution of household bleach diluted one part bleach to nine parts water, leaving the tool in the solution for 15 seconds. When you are finished pruning, disinfect the tools a final time, then coat the metal parts with a light oil. Be aware that your hands, gloves, clothing, and gardening tools can also spread the pathogens, especially when foliage is wet. Burn or bury the diseased plant material to destroy the pathogens as soon as possible and do your pruning in dry weather to minimize the spread of the diseases. Not all symptoms you find will be caused by pathogens; some can be caused by environmental or physical damage, such as sunscorch, winter injury, or dog urine. If you are not sure, or need help with the pruning process, contact your county Extension agent.
 
References:
Agrios, G.N. 1988. Plant Pathology. Third edition. Academic Press, San Diego, CA. 803 pp.

Harris, R.W. 1992. Arboriculture; Integrated Management of Landscape Trees, Shrubs, and Vines. Prentice- Hall, Inc., Englewood Cliffs, NJ. 674 pp.

Ellis, B.W. and F. Marshall. 1991. The Organic Gardner's Handbook of Natural Insect and Disease Control: A Complete Problem-Solving Guide to Keeping Your Garden and Yard Healthy Without Chemicals. Rodale Press, Emmaus, Pennsylvania. 418 pp.
 
Written by Sherry Lajeunesse, Extension Urban Pest Management Specialist. Sept., 1997
 


 Slime Fluxing
 
 Foul-smelling, slimy, weeping wounds on trees could be a conditions known as slime flux. The condition is caused when bacteria grow in fluids seeping from cracks or wounds in trees, or from crotch areas where fluids can accumulate. It is associated with a condition called wetwood that affects inner portions of the tree. Many species of tree can be affected, but slime flux and wetwood are most commonly found in elms and poplars, including the cottonwoods. It can also affect aspen, fir, maples (including box elder), white pine, mountain ash, paper birch, and others.
 
Usually, slime flux and wetwood in landscape trees is unimportant except for the undesirable appearance of the dark fluids seeping down the trunk of the tree. Severe infestations can sometimes cause foliage on upper branches to wilt and branches to die back. It does not result in tree mortality, however.
 
It is fortunate the damage is not severe, because there are no known cures. Drain tubes can be installed by tree care professionals for cosmetic purposes, allowing the fluids to drop to the ground rather than running down the side of the tree. Note: drilling holes in trees with this condition can spread the condition to other portions of the tree. For the most part, there is little you can do, or should do.
 
References:
 Harris, R.W. 1992. Arboriculture; Integrated Management of Landscape Trees, Shrubs, and Vines. Prentice- Hall, Inc., Englewood Cliffs, NJ. 674 pp.

Pirone, P., J. et al. 1988. Tree Maintenance. 6th Edition. Oxford Univ. Press, New York, NY 10016. 514 pp.

Sinclair, W., et al. 1987. Diseases of Trees and Shrubs. Cornell Univ. Press, Ithaca, N.Y. 576 pp.
 

Written by Sherry Lajeunesse, Extension Urban Pest Management Specialist. Sept., 1997
 


Spruce Dieback
 
 The vast majority of damage we see on spruce trees in Montana is not caused by diseases, but rather by environmental causes such as drought and freeze damage. The damage may not become apparent for many months or even years, which often results in misdiagnosis. Symptoms are usually dieback that begins from the needle tips and moves back toward the branch, in a rather uniform pattern. Sometime whole branches or portions of the tree may be killed. Color varies from brown to yellow to reddish-brown.
 
Heavy fall moisture can result in flushes of growth susceptible to winter damage. In addition, warm periods during winter, including chinooks, can cause spruce needles to loose moisture through transpiration and because the ground is frozen, roots can not absorb more moisture from the soil. Drying out (desiccation) of tissues can result.
 
Trees that go into winter under dry conditions also account for much of the damage we see every year. Most tree roots, of even the tallest trees, are in the upper 18 inches of soil, meaning that trees can become drought-stressed much more quickly in both winter and summer than we would suppose. Without a deep watering that soaks into the ground at least two feet in late fall, just before the ground freezes, the tree is very susceptible to drying out, resulting in dead needles and branches the following spring or summer. Windy, sub-zero temperatures increase moisture lost through transpiration, making the problem even worse.
 
To help prevent dieback, stop watering all your trees, including spruce trees, after early August. Then give them all one final deep watering after deciduous trees have changed to autumn color, but before the ground freezes. Water the entire area under and around the tree half again beyond the dripline of the evergreen trees. For example, if the branches extend six feet from the tree trunk, water at least nine feet around the trunk. (Roots of deciduous trees extend 2-3 times farther than the branches, so water that extended area for those trees.) Allow the water to soak down a minimum of two feet. A good, deep watering again in spring, as soon as the ground thaws can provide the tree with important moisture it may have lost during winter. In years when fertilizer is needed by the tree, you may wish to apply a appropriate granular product, then follow with this deep fall watering.
 
 Fertilizing trees can also result in similar problems, especially to the flush of new growth that results. In most parts of Montana, trees need no fertilizing. This is particularly true in turf areas that receive occasional applications of fertilizer. In areas where soil tests show nutrients ARE lacking, fertilizing only once every 3-4 years is usually sufficient. If you do not conduct a soil test, do not apply fertilizers unless trees are showing symptoms of nutrient deficiency. Avoid annual applications of tree fertilizer. When fertilizers are necessary, apply them in fall, before the leaves of deciduous tree turn autumn color, but before the ground freezes, then apply your deep fall watering to help carry the fertilizers into the root zone. Research has shown that in spring trees use nutrients they stored the autumn before; spring-applied fertilizers will not be absorbed until early summer, about the time deciduous trees are fully leafed. If you wish to make tree fertilizer applications in spring, wait until this time.
 
In areas with heavy clay soil or very shallow water tables, another cause of dieback can be soils saturated with water, leading to oxygen starvation of the roots. If needles three or more years old are dying, the problem is not too serious. If new growth is affected, chances of recovery are not as good. Deep sampling of soils with a soil probe in these areas can help determine if drainage improvement is needed.
 
To prevent dieback in areas where heavy soils are not a problem, stop watering spruce trees after midsummer, until one final deep watering after deciduous trees have changed to autumn color, but before the ground freezes. Water the entire area under and around the tree half again beyond the dripline of the evergreen trees. For example, if the branches extend six feet from the tree trunk, water at least nine feet around the trunk. Allow the water to soak down a minimum of two feet. A good, deep watering again in spring, as soon as the ground thaws can provide the tree with important moisture it may have lost during winter. In years when fertilizer is needed by the tree, you may wish to apply a appropriate granular product, then follow with this deep fall watering.
 
References:
 Harris, R.W. 1992. Arboriculture; Integrated Management of Landscape Trees, Shrubs, and Vines. Prentice- Hall, Inc., Englewood Cliffs, NJ. 674 pp.

Lajeunesse, S., G. Johnson, and J. Jacobsen. 1997. Proactive Pest Management; Using landscape design and plant vigor to manage weeds, insects, and diseases. Montana State Univ., Extension Service, Video No. 38. Bozeman, Montana. 23 min.

North Dakota Tree Handbook. 1995. Agriculture and Natural Resources, North Dakota State University, Fargo, ND. 228 pp.

Shigo, A.L. 1986. A New Tree Biology. Shigo and Associates, Durham, NH 03824. 595 pp.

Sinclair, W., et al. 1987. Diseases of Trees and Shrubs. Cornell Univ. Press, Ithaca, N.Y. 576 pp.
 

Written by Sherry Lajeunesse, Extension Urban Pest Management Specialist. Sept., 1997
 


Sunscald on Trees
 
Cause and symptoms
Sunscald may sound like something that happens in hot weather, but on trees and ornamentals it is a cold-weather problem, occurring in winter and early spring. Tender bark on a southern surface warms much more from winter sun than the bark on the northern surface. The temperature of dark-colored bark in particular is raised considerably by the sun's rays. If a chilling breeze comes along or a cloud suddenly covers the sun, the mercury falls rapidly. The sudden drop in temperature can make the plant cells rupture, causing damage to the bark. Damage that occurred in winter might not be apparent until spring. Sunscald is particularly noticeable on young trees planted where daytime heat is high, such as beside a wall that reflects the sun's heat, or on the south side of the trunk. In warm weather, light-colored mulches can also reflect heat onto tree trunks. As a result parts of a tree, or even the entire tree, can be damaged. This is especially true for young trees. Bacteria or insects may enter the damaged bark and cause further problems.

Controls
Sunscald on trees can be prevented by wrapping the trunks with a commercially available tree wrap or with burlap or agricultural fleece. You can also guard against sunscald by painting the bark of young trees with white interior latex paint mixed with water 1:1, in the fall. The light color reflects the sun's rays and prevents sudden temperature changes. Using dark-colored mulching material that will absorb the sun's heat, rather than reflecting it onto the tree's trunk.
 
 References:
 North Dakota Tree Handbook. 1995. Agriculture and Natural Resources, North Dakota State Univ., Fargo, ND. 228 pp.

Pests of Landscape Trees and Shrubs; An Integrated Pest Management Guide. 1994. University of California. Oakland, CA 94608-1239. Pub. #3359. 327 pp.

Pirone, P., J. Hartman, M. Sall, and T. Pirone. 1988. Tree Maintenance. Sixth Edition. Oxford Univ. Press, New York, NY 10016. 514 pp.
 
Written by Sherry Lajeunesse, Extension Urban Pest Management Specialist. Sept., 1997