Late blight of tomato
causes large, brown, wet-looking lesions on tomato
leaves, dark lesions on tomato stems and leaf petioles and causes
fruit to turn brown and rot. The same fungal-like organism that causes
late blight of tomato also causes late blight of potato, the disease
was responsible for the Irish potato famine in the mid 1840’s.
summer and fall of 2009, late blight of tomato was reported in Indiana
the first time in many years. Tomatoes grown by homeowners and commercial
growers were affected by the disease. In all, late blight was confirmed
over 30 counties in Indiana. It is likely that late blight arrived
Indiana in 2009 on tomato transplants. Late blight has not been observed
the past to live through Indiana winters.
Late blight, caused by the fungus-like organism,
occurs in moist weather with cool nights and moderately warm days.
Dark-green to nearly black wet-looking spots begin spreading in
leaf edge. In wet weather, the spots may have a downy, white growth
lower leaf surface near the outer portion of the spot. Spots also
the fruits. At first, the spots are gray-green and water-soaked,
soon enlarge and turn dark brown and firm, with a rough surface.
conditions are favorable, the disease may progress very rapidly.
2010 States with Confirmed Reports of Late
Indiana - June 30
- Dearborn Co (6/30)
- Wayne Co (7/16)
Ohio - June 23
Michigan - June 21
blight edges toward Southern Indiana - Indy Star, June 9,
Tomato disease reaches Indiana's southern border - Purdue
University News Service, June 8,
growers: Be on the lookout for late blight this year - AgAnswers,
June 1, 2010
blight surrounds Ohio; growers, gardeners should prepare -
June 1, 2010
blight confirmed in Indiana in 2009 - AgAnswers, August 7,
Click image to enlarge
The large brown area of this tomato leaf is affected
by late blight. The edge of the lesion has a white coloration which
is the fungal-like organism which causes