GENERAL PLANT DISEASE TOPICS
How to discourage plant diseases in your garden and yard
Sanitation - Proactive plant disease management
Symptoms of common plant diseasese
 


How to discourage plant diseases in your garden and yard

1) Select a suitable location for planting. Some plants like sunny locations; others prefer more shade. Plants also differ in their tolerance to soil types, pH, moisture, wind, and other factors. Avoid extremely wet soils because they may favor many root disorders.

2) Practice rotation in your garden plot. If possible, change the location of the entire garden occasionally, to help prevent the buildup of disease-causing organisms. Even when a garden is maintained in the same location, it is important to rotate specific crops to a different area of the garden each year. An example of a poor rotation is tomato followed by eggplant followed by potato since all are susceptible to similar pathogens. A better rotation is tomato, followed by corn, beans, or lettuce.

3) Select disease-resistant varieties where they are available and adapted to your growing conditions. Lists of resistant plants can be found in many texts and seed catalogues.

Plant resistant cultivars when 1) minimum maintenance is desired (home grounds, rights of way, low-budget operations); 2) inoculum is always present; 3) environmental conditions usually favor disease at some time; or 4) adequate chemical controls are not available.

Using susceptible cultivars is acceptable when 1) inoculum is rarely present, 2) environmental conditions rarely favor disease development, 3) or intensive management practices are being used. Non-host species should be used when the pathogen has a very wide host range and cannot be eliminated from a site and when no resistant cultivars of the disease-prone plant are available .

4)  Use only disease-free seed and transplants. Buy seeds and plants from a reputable source. Many disease-causing organisms are carried to your garden on seeds and transplants.

5)  Maintain soil fertility through careful use of fertilizers, soil amendments, costs, etc. Plants that are too weak or too vigorous as a result of improper fertilization will be more subject to diseases.

6)  Do not overcrowd your plants. The high humidity that results beneath the plant canopy may favor certain fungal diseases. Thin your plants to permit free air movement.

7)  Water properly. Try to maintain an even water supply and avoid dry-wet fluctuations. Drip systems and soaker hoses are better than overhead sprinklers.

8)  Control insect pests. Some insects spread diseases to other plants if they remain in the garden.

9)  Destroy and remove diseased plants as soon as you observe them. They may serve as a source of spread to others plants if they remain in the garden. Do not compost diseased plant parts.

10)  Spade under or compost crop refuse as soon as possible after harvesting the garden. This not only recycles some good organic matter to the soil, but also removes the possibility of disease-causing organisms remaining overwinter in the garden.

11)  Be alert to leaf diseases that occur annually on certain plants and take care of them early, before the damage becomes so severe that the plant is lost.
 

Sanitation - Proactive Plant Disease Management
 
 

Many plant diseases spend the winter in foliage and plant material left from the summer. A good way to reduce winter survival of the disease organisms is to remove old plant material and compost it or dispose of it. Composting healthy plant material can recycle the nutrients and organic matter it contains, feeding your soil.
 
Debris should be burned, buried, or hot-composted if it comes from areas where disease was a problem last season, such as debris from rose bushes infected with blackspot, or vegetable beds where powdery mildew caused problems. High temperatures are essential to kill the disease organisms, so make sure your compost pile reaches internal temperatures of 140- 160F to kill the disease organisms if you choose to compost materials that come from problem areas. Do not compost plant material infected with viral diseases; place these materials in sealed containers and dispose of them in your trash. After working with diseased plant material, sterilize tools in solution of one part household bleach mixed with nine parts of water to avoid transporting the pathogens to another part of your yard.
 
Removal of old raspberry canes is also a good idea because they can serve as a harborage for diseases such as anthracnose. These sanitation measures can help keep your yard and garden disease-free.
 
References:
 Pirone, P., J. Hartman, M. Sall, and T. Pirone. 1988. Tree Maintenance. Sixth Edition. Oxford Univ. Press, New York, NY 10016. 514 pp.

Controlling Vegetable Pests; Environmentally Friendly Gardening. 1991. C. Putnam, Project Ed. Ortho Books, Chevron Chem. Co., San Ramon, CA 94583. 160 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
 


Symptoms of Common Plant Diseases
 
 Symptoms of our more common yard and garden plant diseases in Montana fall into eight broad catagories: 1) blights, 2) cankers, 3) galls, 4) leaf blisters or curls, 5) mildews, 6) rots, 7) rusts, and 8) wilts.
 
BLIGHTS: Symptoms include sudden withering and death of leaves and branches, or in the case of blossoms, wilting and discoloration. Conspicuous spots or irregular dead areas on leaves and twigs which cause foliage to distort and drop prematurely could be a blight. Damage from blights can be minor, as in the case of some anthracnose blights, to serious, as in the case of fireblight.
 
CANKER: symptoms usually form on woody stems and may be sunken areas, cracks, or raised areas of dead or abnormal tissue. Sometimes the cankers ooze conspicuously, or in the case of evergreens, drip sap onto the branches beneath. Cankers can sometimes be one of the symptoms manifested by another disease.
 
GALLS: are swollen masses of abnormal tissue that range in size from small to quite large. Certain insects can also cause galls. Cut a gall open and search for signs of an insect inside- if you find none, the gall is probably caused by a disease.
 
LEAF BLISTERS are yellow bumps on the upper surfaces of the leaves with gray depressions on the lower surfaces. LEAF CURL DISEASES cause new leaves to be pale or reddish with the midrib deformed. The leaves pucker and curl as they expand. Certain insects cause similar symptoms, but on closer inspection, if insects are the cause the insects themselves or other signs of their presence can be seen.
 
MILDEWS are usually one of two types. Downy mildew is usually a white to purple, fuzzy growth, usually on the undersides of leaves and along stems. It turns black with age. Powdery mildew is a white to grayish powdery growth on the upper surfaces of leaves.
 
ROT DISEASES cause decay of roots, stems, wood, flowers, and fruit. They can be soft and squishy or hard and dry, and color can be either light or dark.
 
RUST DISEASES typically produce symptoms that include a powdery tan to rust-colored coating or soft tentacles.
 
WILT DISEASES cause permanent wilting, often followed by death of part or all of the plant.
 
Most symptoms you find in your yard or garden will be caused by insects or environmental problems such as water stress or nutrient deficiencies, so try to rule out these possibilities first. If you have yard and garden reference books, you can often identify the disease based on the categories of symptoms listed above. The species of plant on which the symptoms occur will also help identify the problem as most diseases are quite specific in the kinds of plants they will attack. If you need additional assistance with identification, your county Extension agent can help.
 
References:
 Agrios, G.N. 1988. Plant Pathology. Third edition. Academic Press, San Diego, CA. 803 pp.

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

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

Turfgrass Compendium. The American Phytopathological Society Disease Compendia Series, St. Paul, Minnesota. 126 pp.
 
    Written by Sherry Lajeunesse, Extension Urban Pest Management Specialist. Sept., 1997