Late blight in Delaware tomatoes confirmed

Late blight, a disease caused by the fungus-like organism Phytophthora infestans, has been confirmed in New Castle County, Del., this week on tomato fruit.

This occurrence probably resulted from infected crop residue in the soil, or sporangia of the pathogen being blown in during rain storms, according to Nancy Gregory, plant diagnostician in the Department of Plant and Soil Sciences in the University of Delaware's College of Agriculture and Natural Resources.

The wet weather has favored a number of leaf-spotting fungi and bacteria that are commonly found on tomato in the Delaware area. Therefore, there are many spots on tomato leaves and fruit that are not late blight. 

Potato is susceptible, but most potatoes in the area have been dug. Surrounding states have also had reports on tomato, and growers and homeowners should inspect tomato plants.

Any large, dark, olive green to brown water-soaked areas may be late blight. Samples may be sent to county Cooperative Extension offices or to the UD Plant Diagnostic Clinic with appropriate forms.

Confirmed late blight infected plants should be removed from gardens or fields and destroyed, so as not to spread the disease. Late blight is favored by cool, wet conditions. The late blight pathogen or infected plants will not cause any harm to humans.