Julie Rubaud, owner of Red Wagon Plants in Hinesburg, said home gardeners and farmers all share a responsibility in keeping late blight, a damaging fungal disease, at bay. She is urging local growers to destroy any infected plants by cutting down the foliage and burning it or disposing of it in sealed garbage bags at the dump.
“UVM extension does a great job of educating both the general public and professional growers,” Rubaud said. “We are always happy to help pass on information we learn in our professional circles so that home gardeners have access to relevant information.”
This year’s first case of late blight was identified July 7 at Full Moon Farm, an organic farm in Hinesburg. It was verified by Ann Hazelrigg, the Extension Plant Pathologist who directs the UVM Plant Diagnostic Clinic. It’s generally found on tomatoes and potatoes and needs to be destroyed upon detection to prohibit spores from reaching, and destroying, nearby crops, she said.
“Late blight spores are easily carried long distances on the wind, so anyone growing tomatoes or potatoes should inspect their plants daily for signs of the disease,” Hazelrigg said. “The pathogen needs living plant tissue to survive, so once infected plants are destroyed, the spores will die and not spread the disease.
Hazelrigg also identified late blight at Pete’s Greens in Craftsbury. Both farms have taken proper measures to destroy the diseased plants, she said.
Rachel Nevitt of Full Moon Farm said she spotted a large dead area, about 100 square feet, in her potato field. It was the white sporulation pattern on the underside of the leaves that led her to believe it was late blight. She and her husband, David Zuckerman, mowed the field from the outside in, and then flame weeded the entire area.
Plants need to be destroyed as soon as the late blight is detected, Nevitt said. “This goes for home gardeners, too. This is a community problem. Spores spread 50 miles on a breeze.”
Although the disease can infect tomatillos, eggplants, peppers, petunias and other members of the potato family, in Vermont it has only been found on tomatoes and potatoes in recent years. Damage from phytophthora infestans, the pathogen causing late blight in these crops, was especially widespread in 2009 when it was transported here on tomato transplants shipped from southern states, Hazelrigg said.
Recent storms have most likely blown the spores in from western New York or New Jersey, Hazelrigg said. Vigilance and quick action on the part of home gardeners and growers will help control its spread and protect commercial farmers’ tomato and potato crops.
Late blight starts as nickel-sized, water-soaked spots on tomato and potato leaves. Unlike other fungal blights, the spots typically don’t start at the bottom of the plant but are seen first on the upper leaves, Hazelrigg said. “Stems and fruit also can be infected with the disease,” she said. “Infected tomato fruit develops large brown areas. If plants are infected, the unaffected fruit on plants can be safely eaten but should not be canned.”
If potato vines become infected, cut the top vines before the stems become heavily infected. In small plantings, bagging and putting vines in the landfill will reduce the chance of spread to other plantings.
“Hot, dry weather can slow the spread of the disease,” Hazelrigg said. “But with rainy weather or heavy dews, use fungicides for protection. These products will only be effective if used before the disease appears. Reapply every five to seven days if wet weather persists.”
For home gardens, apply a garden fungicide labeled for tomato or potato use that contains the active ingredient chlorothalonil. Organic growers should use a copper fungicide labeled for these crops, she said.
Fungicides will only protect healthy tissue, so infected leaves cannot be saved. Good coverage of all foliage is critical, Hazelrigg said. Repeat applications are needed to protect new growth from infection. Be sure to always follow instructions on the pesticide label carefully.
To submit samples to confirm late blight in your garden, go to the UVM Extension Master Gardener web site at www.uvm.edu/mastergardener.
Contact Lynn Monty at 985-3091 or Lynn@WindRidgePublishing.com. Follow her on Twitter at www.twitter.com/VermontSongbird.