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8.15.14 Late Blight Update

This week has been very active for late blight reports, with new reports coming in from multiple counties in New York, as well as reports from Massachusetts, Pennsylvania, New Jersey, Maryland, Maine, and Ontario, Canada.  If you haven’t already, please sign up for alerts on, where you can also see a map of where late blight has been found this season.  Most, but not all, isolates identified in the Northeast this season continue to be US-23, which is sensitive to mefenoxam, the active ingredient in Ridomil.  Conventional growers, it’s worth getting an isolate ID, as one of the two other isolates identified is intermediate in its sensitivity to mefenoxam, and the other is unknown sensitivity.  Instructions for submitting a sample for isolate identification can be found at

Given the number of reports and the recent favorable weather, everyone should be on the lookout for late blight on their farms or in their gardens.  For help with scouting and identification, see the late blight scouting and late blight imitators videos, or take a sample to your local Cooperative Extension office.  If you identify late blight, please don’t ignore it and allow infected plants to produce spores that can infect nearby farms and gardens.  Either treat with a fungicide or destroy infected plants as soon as you can.


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