Managing Late Blight in Tomato and Potato - An Essential Part of Gardening

by Meg McGrath, Department of Plant Pathology and Plant-Microbe Biology, Cornell University

Late blight is a unique disease.  It is arguably the most destructive plant disease.  Due to the quantity of spores easily dispersed by wind, a planting with late blight that is not managed, even a small garden, can have devastating impact on other plantings.  This was well documented in 2009.  Therefore, unlike other diseases, late blight needs to be treated as a "Community Disease".  Anyone growing susceptible plants needs to take responsibility and implement a good management program to ensure they don't become a 'typhoid Mary'.

In 2010 late blight could again appear early in the growing season wherever infected potatoes from 2009 in the ground or compost pile are left to sprout and grow thereby providing the over-wintered pathogen new foliage for producing its wind-dispersed spores.  Thus it will be critical for managing late blight successfully this year to destroy left-over potatoes and any volunteer potato plants as soon as they emerge. 

Other management practices include:

• Using disease-free tomato transplants and seed potatoes,
• Selecting resistant varieties,
• Regularly checking the web for reports of late blight,
• Controlling solanaceous weeds (in particular hairy nightshade and bittersweet nightshade),
• Applying fungicides preventively,
• Using practices that minimize humidity and leaf wetness,
• A least weekly inspecting plants for symptoms,
• Informing extension staff plus neighbors when late blight develops,
• Removing affected foliage, and
• Promptly destroying plants when management is not successful.
• Additionally, share information about late blight with other gardeners.

For more information on late blight, including symptoms, management, and occurrence in 2010: http://www.hort.cornell.edu/lateblight