Common Diseases in the Garden

Common Diseases in the Garden

Diseases can cause serious vegetable losses in home gardens. For disease to occur, plant pathogens must come in contact with a susceptible host plant. Pathogens can be carried to the plants by various means, including transplants, soil, humans, animals, insects, infested seed, and wind or water, alone or in combination. Favorable environmental conditions must be present for the plant pathogen to infect and thrive on the plants.

Many plant disorders can be caused by temperature and moisture stresses, nutrient deficiencies or excesses, or herbicide injuries.

Insects often transmit diseases by carrying viruses, such as bacterial wilt of cucumbers and squash. Weeds in and around the garden also can harbor disease organisms.

Prevention is the best approach to managing plant diseases in the home garden, but sometimes diseases occur despite the best efforts at prevention. Disease-resistant plant varieties are available to prevent some common diseases.

Chemicals are seldom needed and often are not economical for use in the home garden. If you decide to use chemicals. Read and follow the directions on the product label.

Plants from the same family often are susceptible to the same diseases. Therefore, one could expect a disease that attacks many members of the same family to spread through the garden if plants from the same family are planted close to each other and no steps are taken to prevent the disease or to manage it once it appears. Examples of plants by family are as follows:

Disease and symtoms Resistant varieties Chemical options Controls before planting Controls during season
Rust (fungus) -- elongated orange-red, reddish-brown or black pustules on leaves and stems. Rust fungus over winters on leaves and stems X Do not crowd plants. Sanitation1 Remove ferns in the fall. Limit overhead watering. mancozeb wettable sulfur applied after harvest
Seed decay and damping off (fungi) -- Preemergence and postemergence damping off, root rots and stem rots.   Use treated seed. Plant in warm soil.    
Downy mildew (fungus) -- spots begin as light areas in leaf margins. Whitish mold develops on undersides of leaves. Plants become dwarfed and yellowish.   Plant healthy sets. Use a 3-year rotation.   maneb
Blossom-end rot (physiological problem) -- fruit becomes water-soaked near blossom end. Tissues collapse and dry out rapidly, leaving whitish papery area. Secondary fungi may invade, turning this area black.   Maintain proper balance of calcium in soil. Water evenly.  
Blossom-end rot (physiological disorder) -- water-soaked spots on blossom end of green or ripening fruit (may not be noticed until fruit is ripe). Spots enlarge and become slightly depressed. Spots turn black and rot due to secondary fungi.   Maintain adequate calcium level by liming if soil test indicates low calcium. Maintain an even soil-moisture level. Use mulches to retain moisture. Do not oversupply nitrogen.  

1 Sanitation includes removing plant debris from the garden, whether it originates in the current growing season or the previous year. Remove affected plants from the garden and destroy them so that they do not act as a source of disease-causing microorganisms. Discard any plant, transplant, or seed piece that does not look healthy. Diseased plants should not be added to home compost piles; the temperature reached in most home compost piles is not high enough to kill plant pathogens.

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