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Extension > Local Extension Offices > Stearns > County Horticulture Educator > Articles > Late Blight on has Arrived!

Late Blight on has Arrived!

University of Minnesota Extension, Stearns County News
September 13, 2017        
           

Source:  Brenda Postels, Extension Educator-Horticulture
University of Minnesota Extension
Stearns & Benton Counties


Late Blight on has Arrived!
By Brenda Postels, University of Minnesota Extension

ST. CLOUD, Minn. (09/06/2017) — The University of Minnesota Extension offices often get asked, “What is wrong with my tomatoes?”  The last two weeks in particular have seen a strong uptick in this particular question.   If you are one of those people, chances are good that you are experiencing 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 fungus-like organisms also called water molds. Late blight is the culprit responsible for the Irish Potato famine of the 1840s.  Cool and damp weather is likely responsible for our recent and sudden surge.  Once a plant is infected, the disease spreads quickly in fields and home gardens.

How can you identify late blight?  First of all, inspect the leaves. The infection starts by showing dark brown blotches with a gray-green edge.  As the disease progresses it results in large sections of dry brown foliage.  The tomato fruits start out showing dark brown circular spots which can grow large enough to cover the fruit.  Spots can then become mushy. It appears that the fruit is rotting on the stem as secondary bacteria invade.  The blight can spread from plant-to-plant quickly especially in cool weather and entire rows and fields can look like they were hit with a hard frost.

Now that you have identified the problem, what can you do about it? First of all, don’t take it personally!  Even the most experienced gardeners and professions are experiencing late blights as spores from can travel on the wind from 3 to 5 miles!  The best you can do this year is to quickly salvage what you can and dispose of the rest promptly.  Try to pull up the plants on calm, sunny day.  The UV light from the sun will help kill any spores that might drop off during the pulling process. Dispose of the plants by bagging them up and throwing in the trash or by burying deeply. Clean your hands and tools before moving on to healthy areas of your garden.

Of course you will wonder if it is safe to 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 but freezing is acceptable.  Green tomatoes can be picked from dead vines and kept indoors to ripen.

Though no tomato varieties are completely immune to late blight, there are varieties that are resistant to infection by the late blight fungus. So, next year, when it's time to decide which varieties to plant, keep an eye out for these.  You might also want to plant some varieties that mature early so if late blight does strike, you may still get a harvest.  For more information on late blight, go to: http://www.extension.umn.edu/garden/fruit-vegetable/plant-diseases/late-blight-tomato

Contacts

Beth Berlin
Extension Educator, Horticulture
(320) 255-6169
adam0062@umn.edu
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