It has been in the US for over a century, but it has become more of a concern in the Northeast in recent years. Late blight is the same disease that caused the Irish Potato Famine in the 1840s. All tomato and potato plants grown in home gardens and in commercial fields are susceptible to late blight! Given the right conditions, the spores are easily carried for miles in wind currents to infect susceptible plants in even the most remote parts in our region. Because the disease can move very easily from one garden or field to others, it is critical that both home gardeners and farmers know how the disease works, what to look for, and how to manage it. Remember, the label is the law.Home gardeners should be aware of Late Blight caused by Phytophthora infestans – a very destructive and very infectious disease that kills tomato and potato plants in gardens and on commercial farms across the U.S. And observe the number of days between pesticide application and when you can harvest your crop. Be sure that the plant you wish to treat is listed on the label of the pesticide you intend to use. Always follow the pesticide label directions attached to the pesticide container you are using. Rotate fungicide groups and/or tank mix fungicides to avoid producing fungicide-resistant isolates.ĬAUTION: Mention of a pesticide or use of a pesticide label is for educational purposes only. For a current list of fungicides for late blight management visit the Midwest Vegetable Production Guide.Fungicides specific to water molds must be used and applications repeated according to label instructions. Phytophthora infestans is a water mold and not a true fungus.Fungicide applications should be made prior to infection when environmental conditions favor disease to be the most effective. Products are available for management of late blight on tomatoes and potatoes.Under ideal conditions, such as a greenhouse, petunia also may become infected. The host range is typically limited to potato and tomato, but hairy nightshade ( Solanum physalifolium) is a closely related weed that can readily become infected and may contribute to disease spread.Many clonal lineages affect both tomato and potato, but some lineages are specific to one host or the other. These are called clonal lineages and designated by a number code (i.e. There are many different strains of P.These sporangia easily become air-borne, resulting in prolific spread of the pathogen. infestans can infect and produce thousands of sporangia per lesion in less than five days. Overwintering in a tomato production system is unlikely but infected tomato fruits may give rise to infected volunteer seedlings the following season. infestans can overwinter in Minnesota if protected in potato cull piles. The most common routes of introduction each season are infected potato seed tubers, infected tomato transplants shipped in from other regions, or windblown sporangia (asexual spores) from the south that then infect fields and circulate locally.Late blight doesn’t appear in Minnesota every year.Prolonged hot dry days can halt pathogen spread. Late blight favors cool (60☏ to 70☏), damp conditions.Late blight ( Phytophthora infestans) is a water mold.Infected potato tubers become discolored (anywhere from brown to red to purple), and infected by secondary soft rot bacteria.In high humidity, thin powdery white fungal growth appears on infected leaves, tomato fruit and stems.Spots may become mushy as secondary bacteria invade. In tomatoes, firm, dark brown, circular spots grow to cover large parts of fruits.In cool, wet weather, entire fields turn brown and wilted as if hit by frost.Stem infections are firm and dark brown with a rounded edge.Infections progress through leaflets and petioles, resulting in large sections of dry brown foliage.Leaves have large, dark brown blotches with a green gray edge not confined by major leaf veins.Late blight infects leaves, stems and fruit
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