13 February 2011

Blight Disease

Late blight is a fungus of which mainly tomatoes and potatoes are susceptible. It can also affect other vegetation within the same family (Solanaceae). Late blight was a factor in the Irish Potato famine of the 1850’s. Late blight is produced from a pathogen that is known to survive from one season to the next in infected potato tubers. This pathogen produces such a great number of spores that they can then be carried via the wind to both neighboring gardens and farms and also many miles away.

Late blight can only survive on live tissue, therefore it is important to be careful that you plant only healthy transplants or certified potato seed to lessen the chance of infection. If you have a small amount of plants and they become infected, it is necessary to destroy the plants by cutting them off and immediately bagging and disposing of them. If you have a large amount of infected plants, then either thoroughly till them under or cut them off and bury them to avoid having them produce large numbers of spores that could potentially infect neighboring gardens and farms.

The Northeast had such a tremendous problem with late blight two years ago because of all the wet weather we had. Try not to overwater your plants; let them dry in between waterings, do not water over the tops of the leaves but rather water at the base of the plants and water in the morning rather than at night. Most diseases thrive under wet, humid conditions. By watering in the morning, you can take advantage of the sun and air currents to dry off the plants and keep disease at bay.

There are preventative fungicides you can spray; be sure to read the label carefully and make sure what you choose is labeled for blight. Alternatively, you can try spraying a one percent solution of hydrogen peroxide to the plants once a week as a preventative measure; every three days if you start to see lesions.

For fact sheets and pictures of late blight, visit Cornell’s website at:


You can also contact your local County Extension agent and can find them at the above website address.

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