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Alerts
Volume 54 Number 18 Date 08/28/2009 LATE BLIGHT - Late blight, caused by Phytophthora infestans, has to date been confirmed on TOMATO in 13 counties (Columbia, Dane, Green, Iowa, Jefferson, Lafayette, Portage, Racine, Rock, Sauk, Waukesha, Waupaca and Walworth), and on POTATO in 3 counties. The infections on potato were in a research plot in Columbia County, a commercial production field in Portage County, and the most recent detection, a home garden in Dane County. On tomato, the UW-Extension recommends protecting uninfected plants with fungicide, although pre-harvest interval requirements limit the selection of compounds available to copper formulations. Once plants become infected, further efforts at control are usually fruitless (pun intended). Fruit from infected plants can be harvested for ripening indoors, but tomatoes from infected plants may not store well. Sound fruit from infected plants poses no threat to human health. On potato, the recommendations are for a strict 5-day fungicide spray interval. Vine-killing (or mowing for organic growers) as soon as tubers have reached suitable size will also reduce the threat to the crop. Digging should be delayed 10-14 days after vine-killing. Proper disposal of infected plant material is important for limiting spread of the disease. The pathogen will not overwinter in Wisconsin outside of intact host tissue, so the key is destruction of infected plant material. The best method available to most growers is chopping and tilling in where host material will freeze and decompose. Urban growers may have access to municipal composting facilities that are large and managed to achieve adequate heating. On a small scale, gardeners may dispose of infected plants with their garbage. Some rural growers have been burning infected plants, but this may be more than is necessary. Infected plant material should not be home-composted, as most home compost piles do not heat sufficiently to kill the pathogen. -- Adrian Barta, DATCP Plant Pathologist 
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