BY VALERIE SUDOL
There's bad news for backyard tomato-growers. A widespread outbreak of the same contagious blight that caused the 19th century Irish potato famine is threatening this year's home harvest.
Rutgers and Cornell universities have just issued a joint bulletin about the infection, caused by the pathogen Phytophthora infestans (italic) and also known as late blight. Of special concern are tomato plants purchased at "big box" retail outlets from Ohio to Maine.
Vegetable pathologists from Departments of Agriculture in affected states have been working in recent days to remove diseased plants from store shelves. Wholesale growers that supplied the plants have not been publicly identified, but are cooperating in the sweep, according to university authorities. Officials believe that infected plants were widely purchased and planted throughout the Northeast."Never before has such an extensive distribution of infected plants occurred," the bulletin read in part. "Since our summer thus far has been cool with frequent rains, weather conditions have been very conducive for late blight development."
Commercial farmers in New Jersey are familiar with the disease and are expected to act quickly to prevent its spread, which otherwise would mean the "certain death" of their entire crop. Officials are more concerned about backyard growers who may not recognize late blight and who may fail to take prompt action to remove infected plants.
With disease spores easily carried long distances by the wind, late blight could spread from home vegetable patches to other gardens in the neighborhood and to nearby farm fields. Pathologists believe that the contagious spores spread quickly on store shelves from infected plants to disease-free seedlings, expanding the number of affected specimens.
Homeowners are being urged to inspect tomato plants daily for signs of the disease. Rutgers' specialists advise homeowners to remove infected plants and put them in tightly closed plastic bags for disposal in the garbage - not the compost heap. Fungicides can be effective against the disease, but only if applied before symptoms appear. Symptomatic plants are, for all intents and purposes, doomed.
The chief symptom of late blight is development of watery lesions on leaves, stems and fruit. These soon become covered in fuzzy, white fungal growth that contains the infectious spores. Symptoms can develop within a few days on fruit that appears unblemished when harvested.
Seed-grown plants raised at home are not implicated in the outbreak, but are susceptible to infection. The late blight infestation comes in a season when more homeowners than ever have taken up vegetable gardening as a hedge against rising food costs. And cool, rainy weather has created perfect conditions for the disease.
Rain fell in some region of New Jersey every day of last month expect June 1, according to state climatologist David Robinson. With statewide rainfall recorded at 6.61 inches vs. the long-term average of 3.79 inches, it was the sixth wettest June on record. Cloud cover kept temperatures down to an average of 67.7 degrees, making it the 24th coolest June on record.
Tomatoes are at special risk as the most popular backyard crop, but homeowners growing potatoes also should also be alert to signs of late blight. The disease can infect potato tubers and be spread by the spores they harbor.
Late blight can mimic other leaf and fruit diseases affecting tomatoes and potatoes. Homeowners who want a definitive diagnosis before destroying their plants can submit samples to the Rutgers Plant Diagnostic Lab following instructions on the web site. Results often can be e-mailed or faxed within 24 hours.
Vegetable specialists from Rutgers and Cornell will host a web seminar on late blight and other important tomato diseases from 7:30 to 9:30 p.m. July 2. Click on this link to join the session. Interested gardeners can make the connection up to 30 minutes before the program begins.