JAMESTOWN, N.Y. — Cornell Cooperative Extension Vegetable Program warns “Late Blight is present in Chautauqua County and is expected it to be found fairly soon in Cattaraugus County and Pennsylvania.” Given the current weather patterns, there is real risk that late blight has already travelled on the storm fronts to new places. Now is the time to be very on top of your tomato and potato crop health – scout your fields twice weekly and start spraying!
Disease spots are often dark gray to brown in color and may or may not have a ring of pale green tissue around them. They are often irregular in shape and size, and often become as large as a quarter. Leaf spots will often have small fuzzy white spores on the underside of the leaf in wet and humid conditions. Symptoms progress quickly and are often first found in areas where airflow is poor, such as near weedy patches, hedgerows, in low-spots, or where the canopy is dense. Late blight will put dark brown to black smears on plant stems. Tomato fruit may also develop large, greasy-looking, brown, gray, or black smears on the upper part of the fruit. Late blight does not resemble yellowing leaves with lots of small black specks that are worse lower in the canopy.
Potatoes will exhibit similar foliar and stem lesions. In potatoes the disease can have a darker presentation and more quickly kill foliage. Late blight can and will infect potato tubers. Infected volunteer potato tubers carry the disease over from one year to the next. Because of this, any potatoes which are close to maturity should now be mown off and the vines thoroughly killed to prevent late blight infection. Tubers should be left in the ground for 3 weeks. Tubers cannot be infected if there are no vines above ground, and the waiting period allows infected tubers to start showing disease symptoms.
Late blight is much more easily prevented by regular (weekly) applications of chlorothalonil, which goes by product names like Bravo, Echo, and other generics. Chlorothalonil must be applied before disease presence, and will slow the on-set of symptom development. Unfortunately, it is likely that many farms in the area have already been exposed. Therefore, growers should have at least 1 effective treatment material on-hand.
Late blight is difficult to stop once it establishes in a canopy, and is best treated quickly. Examples of effective chemistries include Ridomil, Gavel, Ranman, Orondis, Revus, Zing, and Zampro. Materials can be used inside high tunnels so long as there is not a greenhouse use prohibition statement on the label. Other options are listed in the Cornell Vegetable Recommendations.
If you suspect that you have late blight, please give us a call immediately. We need to track the disease to help protect other farms by knowing where it has moved to and helping you to get your outbreak to stop sporulating. Emily Reynolds, CCE Chautauqua Executive Director 716-664-9502, Ext. 201 please leave a message including your name, farm location and species affected.
More details, photos and a Reference chart of fungicides used for late blight control, are available on the CCE Website http://chautauqua.cce.cornell.edu/agriculture
The Cornell Vegetable Program is one of many programs offered by Cornell Cooperative Extension of Chautauqua County (CCE-Chautauqua). CCE-Chautauqua is a subordinate governmental agency with an educational mission that operates under a form of organization and administration approved by Cornell University as agent for the State of New York. It is tax-exempt under section 501(c)(3) of the Internal Revenue Code. The association is part of the national cooperative extension system, an educational partnership between County, State, and Federal governments. As New York’s land grant university Cornell administers the system in this state. Each Cornell Cooperative Extension association is an independent employer that is governed by an elected Board of Directors with general oversight from Cornell. All associations work to meet the needs of the counties in which they are located as well as state and national goals. For more information, call 716-664-9502 or visit our website at www.cce.cornell.edu/chautauqua. Cornell University Cooperative Extension provides equal program and employment opportunities.
Cornell Cooperative Extension
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