Be Prepared for Late Blight (and other Leaf Disease!)

Our Fruit and Vegetable Coordinator, Maryellen Sheehan, shares very timely information about late blight, a serious disease affecting tomatoes and potatoes.  Gardeners and farmers alike should be careful to scout for and properly dispose of the infected plants.

These past few cool, wet weeks were unfortunately quite conducive to a host of foliar diseases. Keep an extra eye on your tomatoes and potatoes for signs of late blight in particular, which has been confirmed in parts of western, central and eastern NY, Long Island, and central PA.  A national map of confirmed late blight cases (and sample submission protocol) can be found at:

Late blight spores are airborne and move quickly. We generally see lesions on middle and upper level leaves, but key signs are when the moist looking, gray-brown lesions form on the plant stems and leaflets. On potatoes, the lesions can almost look greasy. Identification and scouting help can be found in E-Organic’s scouting video: and NYSIPM’s video to help separate late blight from all of its imitators (this is also a bad year for early blight and other leaf funk):

Images courtesy of Meg McGrath and the Long Island Horticultural Information & Research Center

Images courtesy of Meg McGrath and the Long Island Horticultural Information & Research Center

If you find suspected late blight on your farm, please report it immediately to your Cornell Cooperative Extension Vegetable specialist (or through and find out how to send in a sample (it’s important to have these samples to see which race of blight is spreading this year).

The late blight pathogen comes on so fast, by the time it is found in a planting, it is often too late to save the crop. Preventative management, including pruning, wide plant spacing, trellising, and preventative sprays, is key to blight management. If you scout daily, catch an infection early, and have a lightly affected planting with good airflow and trellising, it might be possible to try and save the plants by starting off just removing any affected tissue and beginning a fungicide program immediately (remember to check with your organic certifier before using any products!). However, a widespread infection on heavy, lush plant growth will likely not be controllable. Late blight spores spread disease rapidly, so removing infected plants quickly helps prevent infection spread to neighboring plants (and your farming neighbors).

Additional late blight management articles can be found at:


One thought on “Be Prepared for Late Blight (and other Leaf Disease!)

  1. Pingback: Be Prepared for Late Blight (and other Leaf Disease!) « The Virtual Grange

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