Late blight spotted nearby; report it if you see it on your tomatoes

symptoms of late blight on tomatoes
Here are symptoms of late blight on tomatoes. If you think you have this disease on your tomatoes, please contact the Cornell Cooperative Extension Office in your county so they can take action. Photo courtesy Cornell Vegetable Program

Late blight, a devastating disease of tomatoes and potatoes, has been detected in northern Pennsylvania (Erie County, Pennsylvania). If you see it on your plants, please contact the Cornell Cooperative Extension in your county.

Late blight is best known for causing the Irish Potato Famine and can kill plants in just one week, according to Cornell Cooperative Extension in Chautauqua County.

It is caused by a fungus-like organism that spreads dozens of miles on storm fronts, so it could come to your garden.

Identifying late blight

Disease spots are often dark gray to brown in color and may or may not have a ring of pale green tissue around them. They are often irregular in shape and size, and often become as large as a quarter. Leaf spots will often have small fuzzy white spores on the underside of the leaf in wet and humid conditions. 

Late blight will put dark brown to black smears on plant stems, as if someone took a small, muddy paint brush to the plants. 

Tomato fruit may also develop large, greasy-looking, brown, gray or black smears on the upper part of the fruit. 

Don’t confuse late blight with the normal yellowing of leaves. The normal yellow leaves will have lots of small black specks, and the affected leaves will be mostly at the bottom of the plant. 

Dealing with late blight

See a factsheet here. It has information on what to do if your plants are affected by late blight. Here are fungicide recommendations for late blight.

If you think you have late blight, please make sure you contact the Cornell Cooperative Extension in your county so they can take action. What is just a disappointment to a home gardener can be devastating to area farmers.

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