Tomato Blight Information

Even a ripe red tomato can get ruined by late blight

By: Sandy Feather ©2009
Penn State Extension

Q. All of my tomatoes died from the late blight that was so prevalent this year. I have removed the plants and cleaned up as well as possible, but should I spray a fungicide on the soil to kill any remaining spores so this doesn’t happen again next year?

A. 2009 will long be remembered as the summer without tomatoes (or potatoes) for many growers, backyard and commercial alike. Late blight showed up early and remains active to date. Apparently infected transplants were unknowingly sold by a mega-grower in the South to big box stores throughout the Northeast. These transplants were sold and planted in home gardens everywhere, and favorable weather conditions made the disease run rampant.

Commercial growers who tend to make preventative fungicide applications when conditions favor late blight development may have been caught off guard since it arrived so early.


The fungus that causes late blight, Phytophthora infestans, requires live tissue to overwinter in our climate. The only way it survives winter in western Pennsylvania is on infected potato tubers that have been overlooked at harvest or in commercial potato cull piles. The fungus does survive the winter in the southern United States and gets blown to the north on summer winds. Spores can easily move 40 miles in a day.

blighted tomato foliage
Blighted tomato leaves



Spraying the soil with a fungicide now will not have any impact on next year’s late blight potential. The fungicides available to home gardeners are best used to spray tomatoes preventatively, before symptoms of the disease develop. You may be able to turn things around if you catch late blight in the very earliest stage of development and begin spraying, but you cannot “cure” a plant that is even moderately infected. A thorough clean up of the infected plant material and ruthlessly pulling any volunteer tomato or potato plants that show up in the garden next spring should minimize any localized infections. You can make preventative fungicide applications to next year’s plants when cloudy, wet, and moderately warm weather conditions favor disease development. Conventional gardeners can use Bonide Fung-onil, Ortho Garden Disease Control, and other chlorothalonil products labeled to control late blight on tomatoes and potatoes. Organic gardeners can use fixed copper fungicides, but they are not as effective against late blight as chlorothalonil.

blighted tomatoes
Tomatoes ruined by late blight


Our office has received many questions about the safety of eating or caning fruits from late blight-infected plants. According to Penn State’s food safety faculty, it is safe to eat and can unblemished fruits. Discard any that show spots of disease.


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