Late Blight on Tomatoes and Potatoes
    Home gardeners need to be on the lookout for Late Blight – a very destructive and very infectious disease that’s killing tomato and potato plants in gardens and on commercial farms in the eastern U.S.  Late blight is the same disease that caused the Irish Potato Famine in the 1840s. It has never occurred this early and this widespread in the U.S. One of the most visible early symptoms of the disease is brown spots (lesions) on stems. They begin small and firm, and then quickly enlarge, with white fungal growth developing under moist conditions that leads to a soft rot collapsing the stem. Online images at www.tinyurl.com/lateblightontomato.

You need to act quickly to protect your garden-grown tomato and potato plants and to make sure that your plants don’t become a source of spores that could infect commercial farms, as late blight spores are easily dispersed by wind.

Here are the steps you should take:

1.    Examine your tomato and potato plants thoroughly at least once a week for signs of late blight.

2.    Spray fungicides preventively and regularly and/or

3.    Be prepared to destroy your plants when late blight starts to become severe. Seal them in a plastic bag. Do not put them in the compost pile. Leave the bag ‘cooking’ in sunlight for several hours to kill plant and pathogen, and then put in the trash.

If you want to try to control late blight with fungicides, you need to begin spraying fungicide now – even before you see symptoms – and you need to continue spraying regularly. Use a product that contains chlorothalonil. Copper is not very effective on late blight.  Petunias, which are closely related to tomatoes and potatoes, can also be infected by late blight and show similar symptoms.

If you suspect your tomatoes or potatoes have late blight feel free to bring them in to the Piscataquis County Extension Office, 156 East Main St., Dover-Foxcroft for confirmation.  You can also send samples to the UMaine Extension Pest Management Office at 491 College Ave., University of Maine, Orono, ME  04473. 

Source: Cornell’s Blog by Meg Mcgrath http://blogs.cornell.edu/hort/2009/06/ accessed July, 2009

Back to Newsletter Index Page