Blight fungus affects several plants in the vegetable garden, but none so devastatingly as the potato and tomato. Blight disease causes severe damage to the plant and fruit, sometimes ruining entire crops and making the soil undesirable for further planting.
Symptoms of blight begins on the foliage of the plant as pale green spots. The spots look like water spots. Circular or irregular shaped lesions then appear and merge with healthy tissue. Cottony-white mold appears after moist or humid periods. Dry rot will appear along the stems of potato plants. Blight eventually destroys the fruit of the tomato plant, and the potato, turning it black.
Spread of the fungus occurs under the soil and through the release of spores. Spores travel along the wind once released from the plants' foliage, making infection of nearby plants likely. Spread through the soil makes the area dangerous to replant. Moist conditions and poorly draining soil exasperates the condition, making spores reproduce quickly.
Planting certified seed that is approved as disease-free will prevent the introduction of blight into a garden. Plants should be planted in disease-free soil where blight has never appeared to prevent infection. Infected plants should be removed and destroyed by fire to prevent the spread of spores. Soil with infected plants should be left to stand for several years before replanting, or you can rotate in plants resistant to the disease.
No cultivars are 100 percent resistant to blight, and many plants are susceptible to late blight even when cultivated as a resistant variety. Plants with partial resistance to early blight should be planted if blight has been an issue in the past.
Late Blight and Early Blight
Early and late blight are different diseases, not stages of the same disease. Both late and early blight produce spotting of the leaves, but only late blight turns the fruit a black color. Early blight will affect tomato size and yield.
In soil near an infected area, pesticide application helps reduce the incidence of infection. Application directly to the soil before planting kills fungus and prevents spread. Regular application throughout the season, every seven to 10 days, protects the plants from infection by airborne spore.