Late blight UPDATE

Current situation (8/12/14):

Late blight has now been found across Southern NH. We encourage any growers that plan to protect their plants in southern and central NH to use late-blight specific fungicides. If you believe you have late blight on either tomato or potato, you may send photos (details below) OR submit a sample free of charge. Write “late blight confirmation” on the top of the UNH-PDL submittal form.

Late Blight Timeline:

  • 7/30/14: late blight on tomato and potato confirmed in Cheshire county NH.
  • 7/23/14: late blight confirmed on potato in Franklin county MA, on tomato in Hampshire county MA.
  • 7/11/14: late blight confirmed on potato in Cumberland county ME.

Original update (7/10/14):

With storms traveling northeast across the region, the disease may spread. We suggest that growers with tomato and potato in Southern NH (esp. Rockingham, Hillsborough, and Cheshire counties) should use protectant fungicides in advance of the storm. For a current list of fungicide recommendations, please see the New England Vegetable Guide.

Please scout for symptoms. If you suspect late blight in your tomatoes and/or potato crops, please have it checked out. One way to do this quickly is to send digital images to either your county field specialistCheryl Smith, or Becky Sideman You can also send or bring samples to the Plant Diagnostic Lab in Durham.

For home gardeners: At this point in the season, if symptoms begin appearing on tomato or potato plants and you are sure that it is late blight, follow these steps:

  1. Remove plants.
  2. Place in a plastic bag.
  3. Seal bag and discard in trash OR completely bury plants deep enough underground so plants will decompose and will not re-sprout. DO NOT put the plants in a compost pile, as spores will still spread from this debris.

If you are not sure whether it is late blight, e-mail photos to the UNH Cooperative Extension Education Center, Cheryl Smith, or Becky Sideman.

Fungicides must be applied BEFORE symptoms appear. Fungicides containing chlorothalonil, or copper formulations are relatively effective for late blight prevention. For organic production, copper-based formulations are effective.

For more details, images, and management options, watch this video or visit Cornell’s Long Island Horticultural Research & Extension Center.  If you have any questions, please get in touch.


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