Late blight is striking tomatoes and potatos

Q&A

A reader asks:

We are a local grower in Mansfield and were told that there is some type of disease being carried via the rain from the Southern States. We heard that the tomato plants need to be sprayed with a fungicide. We wanted to know if you have heard anything about this and if so, can you recommend a good fungicide spray. We appreciate your help with this matter.

Carol responds:

If you want to try to protect your plants with fungicides, begin spraying now before you see symptoms. Use a product that contains chlorothalonil, such as Daconil, every week if it stays rainy. and don't water tomato plants with an overhead sprinkler, as damp leaves invite fungus.

The fungus that caused the Great Irish Potato Famine in the 1840's has been spread across the northeast this summer in large part by big box store delivery trucks. Infected tomato plants grown by the giant Bonnie Plants company of Alabama have been removed from Lowe's, Wal-Mart, Home Depot and Kmart stores in all six New England states.

Thomas A. Zitter, a plant pathology at Cornell University, wrote in a June 27 report. "We have spread the word of this impending disaster, and within a day the original supplier, working with U.S. Department of Agriculture in the affected states, has removed most of the initial source plants."

Phytophthora infestans attacks only members of the nightshade or potato family, including tomatoes and petunias. Brown spots, or lesions, appear on the stems and leaves of infected plants and spread quickly, producing a white fungal growth in moist weather. The fungus is not toxic to humans, but quickly rots tomatoes and potatoes. Most other vegetables such as lettuce, peppers, squash, carrots, green beans and broccoli are not affected.

Late blight first appeared throughout the northeast in early June of this year, according to Scott Soares, State Commissioner of Agriculture. He is asking home gardeners to check their tomato plants daily for the highly contagious wind borne fungal spores that can spread to commercial crops.

"If you bought your tomato plants from local growers or grew your own from seed, your plants are less likely to be infected."
Fungus thrived in June's cool wet weather and if July turns sunny, problems will abate, Soares said. Meantime, gardeners should dispose of all parts of diseased plants in sealed plastic bags put in the garbage.

For more information and photographs about late blight, visit:

http://www.umassvegetable.org/LateBlightAlertforTomatoandPotato.html

http://vegetablemdonline.ppath.cornell.edu/factsheets/Potato_LateBlt.htm

http://www.hort.cornell.edu/department/Facilities/lihrec/vegpath/photos/lateblight_tomato.htm

If you think you have seen late blight of potato and tomato, you can report it online to http://massnrc.org/pests/, or call the MDAR Plant Pest Hotline at 617-626-1779 of the state Department of Agriculture at 617-626-1700.