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LifestyleColumnistsJessica Damiano

Late blight discovered near Riverhead

These brown stem lesions are typical symptoms of

These brown stem lesions are typical symptoms of late blight disease. Credit: Cornell University

Here we go again. Meg McGrath, my plant pathologist friend with Cornell University in Riverhead dealt me some bad news today: Late blight is back. Again.

"Unfortunately, so early in the season, late blight has been found in a potato crop in the Riverhead area. Based on the appearance of the symptoms, it did not start in this field. I am trying to find the source. There also could be other sources not found yet. This first find reveals that conditions have been favorable for late blight."

If you've been following along the past few years, you know the drill: It's imperative you start inspecting potato and tomato plants now. "This is something that needs to be done every week," McGrath instructs. " Keeping an eye out for symptoms, reporting, and managing late blight are the responsibility of anyone growing these crops."

This year, I'm growing potatoes for the first time. So far, my tomatoes have been spared this blight, but now I'll have two crops to scrutinize.

Late blight, the disease responsible for the great Irish Potato Famine in the 1840s, reared its ugly head on Long Island in 2009, and has been back every year since. Last year, McGrath told me she was very concerned that late blight is going to continue to devastate crops and gardens every year, "especially if we don't all work together on managing it." 

The disease is caused by a pathogen that can release millions of spores per plant per day, especially during wet weather. Those spores are carried by wind "typically within 30 miles but potentially long distances until air currents or rain bring them back down," McGrath said. Theoretically, spores from one infected plant in Nassau County could destroy an entire crop on a farm in Riverhead, she said, which is why it's so important not to poo-poo this.

The disease causes elongated brown lesions on stems and and large grayish-green to brown spots on leaves that cause the plant to blacken, wilt and die.  White mold full of spores encircles spots visible on the undersides of leaves. Home gardeners should inspect tomato and potato plants for symptoms. If late blight is detected, plants should immediately be bagged tightly in plastic and set in the sun for a few days until they die, then disposed of only in the trash. Never composted or left on the ground in piles, as spores will continue to form until the plant dries up..

McGrath has launched a new informational brochure on her website at Click the link in the upper right corner.

If you suspect your plants are affected, bring them to one of the two Suffolk CCE clinics for diagnosis — 423 Griffing Ave., Riverhead, or the CCE office at Bayard Cutting Arboretum, 440 Montauk Hwy., Great River. It will help you because if your plant does not have late blight, you'll know you won't have to yank them out. And it will help us all to help the CCE track where the blight is surfacing.


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