Update: Late Blight

The latest update on Late Blight from the UNH Cooperative Extension:

Date: Wed, Jun 29, 2011 at 1:13 PM

Late blight has been diagnosed on Long Island on potato and tomato crops. The farms produced their own transplants, so it’s not a case of infected transplants arriving from one Typhoid Mary site. Please consider using protectant fungicides on your crops. Consult the vegetable management guide or contact me directly for options.

—Amy Ouellette, Agriculture Educator
UNH Cooperative Extension – Merrimack County

For more information: www.extension.unh.edu

Addendum, from Becky Sideman, UNH Cooperative Extension:

Late blight has been found on a few tomato and potato fields in Long Island. While not that close yet, until quite recently the weather has been conducive to late blight development. Growers should be vigilant in scouting carefully for the disease.

Late blight is often confused with other common tomato diseases. These include gray mold (botrytis), drought stress, early blight, and septoria leaf spot. All of these are already in the area! To refresh your memory on the symptoms of late blight and help determine whether what you are seeing is actually one of these other diseases, see the following:



Growers should keep an eye on the weather. Especially if a cloudy or rainy period is predicted, consider preventative fungicide applications. For organic growers, this means copper (the current OMRI list includes Champ WG and NuCop 50WP, among others). Conventional growers have other options including chlorothalonil and mancozeb.

For conventional growers, if late blight is found in the area, we will recommend fungicides that are more effective on late blight; check out the following table for details:


If you think you have late blight, please contact your county educator or Cheryl Smith at the Plant Diagnostic Lab at 603-862-3200 or cheryl.smith@unh.edu. Instructions for submitting samples can be found at http://extension.unh.edu/Agric/AGPDTS/PlantH.htm. Digital images are also often helpful in making a preliminary diagnosis.

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