The Carlisle Mosquito Online

Friday, July 31, 2009

Blight hits Carlisle

A pathogen which strikes tomatoes and potatoes called “late blight” is spreading rapidly through New England due to the cool wet weather and has appeared in gardens in Carlisle. According to information from the University of Massachusetts, Phytophthora infestans kills plants rapidly and is difficult to eradicate. Gardeners at the Foss Farm community gardens have recently discovered late blight on their crops. “We’ve lost 90% of our tomatoes at Foss Farm. It’s disastrous,” said Carol Foster.

The late blight has occurred within the U.S. for at least a century, but this is reportedly the most widespread outbreak to occur in New England. It is the same organism that caused the Irish potato blight in the 1840s.

Late blight appears as olive or brown patches on stems and leaves and can kill plants within a few days. In moist conditions, fuzzy white areas may also appear on the undersides of leaves. Pictures of the blight are available at www.umassvegetable.org/LateBlightAlertforTomatoandPotato.html.

Spores are spread by the wind. According to a fact sheet from Cornell University [www.hort.cornell.edu/department/Facilities/lihrec/vegpath/lbfaq.pdf], the recommended method of controlling late blight is non-organic: apply fungicide before symptoms are observed and reapply weekly. No reliable organic treatment is known. Gardeners are advised to pull out diseased plants, seal them in plastic bags and dispose of them in the trash. Do not compost the plants, as the disease may be spread.

“I think if you want to be organic and commercial, your goose is pretty much cooked if you get the blight,”says Conservationist of the Year John Lee, who runs Allendale Farm in Brookline. Lee has used organic farming practices for several years and admits he will face tough decisions if his tomato crop is hit. On a brighter note, he said, “I’ve pretty much harvested my potatoes for the season and they were clean as a whistle.” He has not heard of anyone whose potatoes have been affected yet.

According to the Cornell information, while the blight also infects perennial weeds such as bittersweet nightshade and hairy nightshade, “in the Northeast, potato tuber is the only plant tissue it is able to survive in” over the winter.

Arborist and gardener John Bakewell notes that it is very easy for potato growers to miss a few of the underground tubers when harvesting. For this reason, he believes the blight may reappear next year. Bakewell suggests crop-rotation is an organic way to minimize many kinds of garden pests. He recommends back-yard gardeners specialize in one or a few crops each year and vary them each year.

For any gardener who suspects late blight on a plant, Bakewell says, “My personal recommendation is ‘search and destroy.’ Take no prisoners. Put them in a bag and ask questions later.” ∆


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