Control Late Blight on Tomatoes and Potatoes in North Carolina

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10/25/2022 – Originally published 8/9/2009 – Updated on 12/9/2020 -I’ve been getting lots of questions on late blight, especially in the western part of the state. So I’m sharing some information I distributed to extension agents in WNC.

There’s been a lot of concern about late blight, especially among the organic tomato growers. At the time I wrote this article in August 2009 there were cases confirmed on tomatoes and potatoes in Buncombe, Henderson, Jackson, Tyrrell, Camden, Pasquotank, and Hoke counties. I’m sure there were many more cases out there, these are just the ones reported through the North Carolina State University Plant Disease and Insect Clinic or confirmed by the pathologist at the Research and Extension Center in Mills River.

Farmers using conventional agricultural chemicals have a pretty good arsenal of products to protect their plants with. Here is a link to the NC Extension Plant Pathology leaflet on the topic: LINK.

Organic growers, late blight is more of a challenge for you, especially if the tomatoes are out in the open and not protected by a high-tunnel. There is a great article on organic management of late blight on tomato and potato on eOrganic. It was written by an former extension specialist in Oregon, and I think you will find very informative. Copper products (check OMRI list for specific ones), Serenade, Regalia, and Sporatec are some of the products that may give you some control. The key to using these products successfully is they must be applied BEFORE you have an infection. So if you are going to spray, now is the time to start. Also, you need to get excellent coverage of the foliage. A powered mist blower works great. Also, spray frequently. If you spray and it rains an hour later and washes it all off, spray again. We are on a five day spray schedule with our organic tomato research plots right now. And alternate products. We are using copper every other spray right now. Please remember to read the labels for any product you spray, and pay attention to any REIs (restricted entry intervals) and PHIs (preharvest intervals). For example, following copper sprays, you are not to re-enter the field for 24 hours unless wearing the specified PPEs (personal protective equipment). Also remember not to work your plants when they are wet, clean your tools and picking buckets. Do everything you can not to spread disease from plant to plant. If you already have some infection, remove affected leaves and keep spraying. As always, check with your certifier about any restrictions on product use and timing!

One other note, this is the year to keep close records on the varieties you grow. You will probably notice a big difference in diseases among varieties, especially with heirloom tomatoes. This will help in your variety selections for next year.

Hope this helps!