Blight is a general name given to a number of fungi- and bacterium-caused diseases that thrive in cool to warm, damp weather. They usually begin as small, dark lesions on stems, leaves and/or fruit. The spots enlarge under moist conditions and may begin to exhibit white mold. Browning and shriveling of the foliage will follow over the next few weeks. Blight is an aggressive disease, and its spores can travel for miles in the wind.
Types of Blight
Three Blights are most troublesome for gardeners. They are most common on tomatoes and potatoes.
- Early Blight produces dark brown to black spots that gradually form concentric rings. It usually starts on lower leaves and moves up through the plant. Entire leaves turn yellow and drop. Lesions may also appear on stems.
- Late Blight forms dark, water-soaked looking spots that start along the edge of the leaf. White, downy fungus may also appear on the leaf undersides. Water-soaked spots also form on the fruit and gradually turn dark brown.
- Septoria Leaf Spot appears on lower leaves around the time of first fruit set on tomatoes. Spots are small with dark brown edges and gray to tan in the middle. Leaves turn yellow and wither.
A fourth blight, Southern Blight or Crown Rot, attacks the crown of ornamental plants, causing them to wilt and often die.
- Begin with disease-free transplants, and when available, use resistant varieties (contact your local cooperative extension).
- Rotate plants so they are not planted in the same spot year after year.
- Remove infected leaves as soon as you see them.
- Avoid getting foliage wet, especially late in the day. Do not water from above.
- Space plants properly for good air circulation.
- Clean up fallen plant debris and work the soil in fall.
- Destroy infected plants and control weeds (some may spread disease).
- Mulch to reduce splashing water.