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Alternaria Leaf Blight (Early Blight on
tomato) - Alternaria spp. (Alternaria solani on tomato)   Clemson
University, USDA Cooperative Extension Slide Series, www.ipmimages.org
  Clemson University, USDA Cooperative Extension Slide Series, www.ipmimages.org  HOSTS: Cucurbits (cucumber, squash), Solanaceous crops (eggplant, pepper, potato, tomato) and other vegetables
such as peas, onion and cabbage. DESCRIPTION:
Alternaria
is a fungus which causes leaf spotting. Leaf spots progress from older
leaves to newer. Spots are circular, target-shaped, and often
surrounded by a slight yellow area. Entire leaves may die and
drop from the plant. They may also be found around stem ends on fruits
and on stem. LIFE
CYCLE: Alternaria
survives in plant debris and may be spread by insects or
wind, and by rain/irrigation. Spores germinate in several hours during
high humidity conditions. Infection occurs through natural plant
openings if water remains on plant tissue for more than a couple of
hours. After 2-3 days, first symptoms appear. Optimum temperatures for
infection are 60-75° F, high humidity, and low fertility.CONTROLS:Cultural: This disease is spread by splashing water and by walking through plants when wet. Keep water off leaves. Water with soaker hoses or drip irrigation. Use 3 – 4 year rotations between susceptible crops. Maintain adequate nitrogen levels. Remove and destroy infected leaves. Chemical: Sulfur and copper can be sprayed when temperatures are between 55 and 85° F and weather is wet, to protect leaves from infection. These "least toxic" options are less effective when overhead irrigation is applied. |
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