by Cheryl Smith, UNH Plant Diagnostic Lab and Becky Sideman, Vegetable & Berry Specialist.
As of July 31, 2017, Angie Madieras from the UMass Diagnostic Lab just diagnosed late blight on cherry tomatoes (‘5-star grape’ and ‘purple bumble bee’) in Hampshire County, MA.
We encourage any growers with tomato and potato in Southern NH (esp. Rockingham, Hillsborough, and Cheshire counties) that plan to protect their plants to apply protectant fungicides now, and consider having late-blight specific fungicides on hand prior to the next spell of cloudy/humid weather.
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.
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 specialist, Cheryl 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:
- Remove plants.
- Place in a plastic bag.
- 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.
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. This page showing other diseases that are often confused with late blight may be particularly helpful. If you have any questions, please get in touch.