The upper stems of tomato plants infected with late blight develop dark lesions. Infected plants in home gardens should be removed immediately and either burned or put in a plastic bag for disposal.
WEST LAFAYETTE, Ind. — Late blight was confirmed recently on
several tomato samples from Tippecanoe County in west-central Indiana, leading
the Purdue University Plant and Pest Diagnostic Laboratory to urge growers to
inspect their plants for the destructive disease.
Symptoms of late blight, caused by the fungal-like organism
Phytophthora infestans, include olive green to brown spots on leaves with
slightly fuzzy-white fungal growth on the underside when conditions have been
humid, such as in the early morning or after rain.
The lesion border sometimes is yellow or has a water-soaked
appearance. Brown to blackish lesions also develop on upper stems, and brown
spots develop on tomato fruit.
The disease can spread quickly in tomato and potato
plantings in cool and wet conditions. Its spread is slowed by hot, sunny
“All growers should assume their crops may eventually be
affected and thus should be on a weekly schedule to both thoroughly inspect
their potato and tomato plantings and apply fungicides if the weather remains
cool and cloudy,” Tom Creswell, PPDL director, and senior plant disease
diagnostician Gail Ruhl advised on the PPDL’s website.
They said infected plants in home gardens should be removed
immediately and either burned or put in a plastic bag for disposal.
“Do not compost affected plants, as spores will spread from
this infected debris to other healthy tomato plants,” they said.
Because there are many similar diseases on tomato leaves,
identification of late blight requires examination by microscope. Samples can be
submitted for analysis to Plant and Pest Diagnostic Laboratory, LSPS-Room 101,
Purdue University, 915 W. State St., West Lafayette, IN 47907-2054.