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Late blight takes its toll on tomatoes

Photo credit: M Grabowski, U of M Extension

The last two weeks the Extension Office and local greenhouses have been awash with one question: "What's wrong with my tomatoes??" If you are one of these folks the chances are good that you have been hit with Late Blight.

Late blight is a disease of tomato and potato that infects leaves, stems, and fruits of tomato plants. Late blight is caused by the oomycete Phytophthora infestans. Oomycetes are fungus-like organisms also called water molds. The disease spreads quickly in fields and home gardens. Late blight is the culprit responsible for the Irish Potato famine of the 1840s. Here in EOT County, our recent cool and wet weather is likely the cause of the blight.

What are the symptoms?

• Leaves have large, dark brown blotches with a green gray edge

• Infections progress results in large sections of dry brown foliage

• Stem infections are firm and dark brown with a rounded edge

• Firm, dark brown, circular spots grow to cover large parts of fruits. Spots may become mushy as secondary bacteria invade

• In cool, wet weather, entire fields turn brown and wilted as if hit by frost

What can a gardener do?

Unfortunately, like hail or frost, late blight is just one of those curve balls mother nature can throw at us. If your tomatoes are looking tough, don't take it personally. Though we can't control the weather, there are a few things you can do this season to set yourself up for next spring.

• Destroy the affected plants by bagging them up and throwing them out or burying them very deeply.

• Do not put them in your compost pile as the spores can overwinter

• Pull up the plants on a very sunny day if you can, as the UV light will help kill spores set loose during the pulling process.

• Plant tomato varieties resistant to blight: Mountain Magic, Plum Regal, Defiant, and Iron Lady are just a few.

Can I still eat the tomatoes?

Yes. Tomatoes affected by blight aren't always appealing to the eye, but you should be able to safely eat the undamaged parts of the fruit. It is not recommended to use these tomatoes for canning. Green tomatoes can be picked from dead vines and kept indoors to ripen.

More information on late blight and resistant tomato varieties can be found on the University of Minnesota Extension website.

www.extension.umn.edu/garden/fruit-vegetable/plant-diseases/late-blight-...

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