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Update: Late blight now confirmed on tomato and potato in Mifflin Co., PA

Posted: June 8, 2012

This past week late blight was confirmed on potato and/or tomato in Blair, Franklin and now Mifflin Co., PA.
Symptoms of late blight on tomato include gray-brown lesions on the upper leaf surface and elongated chocolate lesions on the stems. Photo: Beth K. Gugino

Symptoms of late blight on tomato include gray-brown lesions on the upper leaf surface and elongated chocolate lesions on the stems. Photo: Beth K. Gugino

Yesterday late blight was confirmed in two commercial potato fields on nearby farms as well as in one tomato field on one of the same farms in Mifflin Co., PA. We are still working on identifying the source and characterizing the genotype (strain).

Although the weather appears to be trending towards warmer and drier conditions, it is still important to be scouting your crops regularly and using a protectant fungicide. Spore production by the pathogen and spread are most favored by temperatures between 65 and 70F and high relative humidity or leaf wetness. Scout your field regularly especially areas where foliage tends to remain wet the longest…lower lying shadier areas.

Now is the time to also be checking cull piles for volunteer potatoes as well as scouting previous potato fields for volunteers and destroying them. With the warmer than usual winter, many potato tubers survived that would have died when exposed to more prolonged freezing temperatures. If you suspect late blight on any volunteers or elsewhere on your farm, please contact your local county Penn State Extension office or let me know via email at bkgugino@psu.edu or by phone at 814-865-7328.

Additional images of late blight on tomatoes and potatoes can be found at the Penn State Extension Vegetable and Small Fruit website under the Vegetable Disease Images link on the homepage at http://extension.psu.edu/vegetable-fruit.