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Sep
10
Posted by:
WCM Staff
9/10/2009 11:50 AM
Tomato late blight has now been confirmed in 19 WI counties. Reports have come from home gardens, small farms, and larger farms (both organic and conventional). Tomato Late Blight in Wisconsin
A.J. Gevens, Department of Plant Pathology, UW-Madison
Dr. Amanda Gevens, Extension Potato and Vegetable Plant Pathologist, UW-Madison Department of Plant Pathology, visits a tomato field to give a visual report on the disease, its symptoms and its management. You can watch the new 11 minute video here.
Tomato late blight has now been confirmed in 19 WI counties. Reports have come from home gardens, small farms, and larger farms (both organic and conventional). In all cases, symptoms have included large water-soaked, dark brown lesions with sporulation on foliage. Lesions quickly expanded to blight entire leaflets, stems, and fruits. Late blight inoculum has been widely dispersed aerially in WI. To date, we have four confirmed reports of late blight on potatoes (Dane, Columbia, Portage, and Marathon). Growers must continue to be on high alert with inoculum available in the heart of commercial potato production. This late blight strain has been identified as US#14 which is an A2 mating type, resistant to metalaxyl, and can be highly virulent on potato. Please contact your county agent, the plant disease diagnostic clinic, or myself with concerns or suspicious samples.
Will the late blight pathogen overwinter? Phytophthora infestans US#14 is an A2 mating type. Currently, WI does not have the mating pair (A1) that is needed in order for persistent, cold-tolerant, overwintering spores, or oospores to be formed. In this scenario, the late blight pathogen needs to have living plant material available to it to remain viable. This is what we call an obligate parasite - the late blight pathogen is obligated to have living tomato (or potato) plant parts in order to survive. By destroying infected plants, we are eliminating the pathogen. The hearty winter frost will also serve to kill infected plants and late blight. So, based on our current WI disease scenario, it is unlikely that late blight will overwinter in our soil.
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