In the past week there have been eight new reports of late blight in NY and the New England States, several in counties where late blight had not yet been reported this season. A common theme in these reports is that plants looked fine one day and were heavily infected 2-3 days later. This could mean that the early stages of infection were missed, or that there were a large number of spores in the air that were deposited on leaves while they were wet from rain or dew.
Late blight is a plant disease that mainly attacks potatoes and tomatoes, although it can sometimes be found on other crops. It is caused by an oomycete pathogen that survives from one season to the next in infected tubers and when in the presence of wet weather conditions the organism produces spores that infect plants. The disease can be introduced early in the season by infected seed potatoes, plants that grew from diseased potatoes and were not harvest last season, compost piles, or infected tomato transplants. The spores can be carried through air and in rainy, wet conditions can penetrate the soil.
For farmers, NOFA recommends that they “scout tomatoes and potatoes regularly and thoroughly, focusing on parts of the field that are shaded or poorly drained.” It has been found that the most effective form of prevention for farmers adhering to certified organic production is the use of copper fungicides.
NOFA has multiple resources for growers that offer information on preventive measures that impede the late blight pathogen from over wintering on the farm. There are also additional materials available that outline prevention techniques and identifiable symptoms of late blight from other organizations such as the Cornell Cooperative Extension.
If you are shopping at your local farmers market or receive a weekly CSA share there are some simple things to take note of:
-Unaffected parts of blighted tomatoes and potatoes are safe to eat. The pathogen does not produce a toxin that can make people sick.
-Deterioration of produce can occur quickly after infection; therefore, affected tomatoes and potatoes should be consumed right away. This also implies that shelf life of these crops may be shortened.
-Consumers and growers alike, are instructed to put affected produce into the trash rather than the compost to prevent the spread of the pathogen.
To learn more about late blight you can find resources from your local agricultural association or extension agent, or next time you’re at your neighborhood farmers market ask your farmer.
Infographic source: Visual.ly
Late Blight resource from The University of Vermont