On leaflets, late blight symptoms begin as small, water-soaked lesions that quickly expand to form large gray, pale green or dark brown blotches on leaves, petioles and stems ( Figure 1). The combination of several factors, including susceptible hosts (plants that can become infected with the late blight pathogen), new strains of the pathogen, inoculum buildup from recent epidemics and ideal weather suitable for disease development provide conditions for a “perfect storm” of annual late blight epidemics.Īll above-ground plant parts of tomatoes and potatoes are susceptible to late blight. Wind can carry the pathogen long distances. Temperatures between about 59 and 80 F allow the disease to progress rapidly, but the pathogen is active at a wide range of temperatures.
EARLY BLIGHT ON TOMATOES IN NEW AREA FREE
The late blight pathogen requires cool to moderate temperatures and free moisture from dew, rain or overhead sprinklers. Weather conditions that promote late blight development Many gardeners and small producers were unprepared for the recent epidemics and did not recognize the disease until too late. Widespread cool, wet weather during the 20 growing seasons was particularly conducive to disease development, and the disease progressed rapidly. Evidence suggests that the source of some of the new strains was infected tomato seedlings from production facilities in the South that were distributed to big-box retail stores across North America. New strains of the pathogen that are able to infect both potatoes and tomatoes have been identified during the recent epidemics. Several strains of the pathogen occur, and in the past, most strains in the central North American region infected only tomatoes or potatoes. and parts of Canada, devastating tomatoes and potatoes in gardens and commercial settings. In 20, the disease was found at epidemic levels in the north-central U.S. This disease has occurred sporadically in North America for decades. It is the same disease that destroyed potato crops in Ireland, leading to the Irish potato famine in the 1840s. Late blight is caused by Phytophthora infestans, a pathogen in the “water molds” group of organisms. Gardeners and growers alike have a responsibility to do their parts to control it. As a result, late blight is a community problem that affects everyone. The pathogen that causes late blight is windborne and can devastate yields quickly in the garden and commercial fields if left unchecked. This plant menace can show up any time during the growing season on a susceptible plant when the right weather conditions and the pathogen are present. Other related plants such as petunia and hairy nightshade also are affected. Late blight is a potentially devastating plant disease that affects potatoes and tomatoes. Late Blight: A Plant Disease That Impacts the Community University of Wisconsin Extension Late Blight Bulletin Links with additional information on late blight:
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