Tomato growers may need to change their usual way of controlling diseases. That is because the most common tomato disease – early blight – has become resistant to an important group of fungicides.
This group, called the Qoi’s, includes Quadris, Cabrio, and Tanos – mainstays of many tomato spray programs. Many populations of the early blight fungus in Tennessee and other states are totally resistant to this group of fungicides. If your tomato crops have shown unusual blight severity the last few years despite regular (weekly) fungicide sprays, resistance is probably the reason. That is assuming, of course, that a Qoi was used frequently, about every other fungicide application.
What changes should you make in your spray program? Since early blight is the driving force for the tomato spray program, a product having at least moderate activity against early blight should be used in each spray.
Research in Tennessee has shown that Fontelis and Inspire Super provide outstanding control of early blight. Both products can be used in a program because they are in different mode of action groups. Because of limitations on the number of times that these products can be used, both will need to be included.
A third product such as mancozeb or chlorothalonil will need to be used in alternate weeks. This is to fill in all the available slots over the course of a long tomato spray program. Example spray programs here.
Early blight takes a heavy toll on tomato production because of its frequent occurrence. Although spray programs must be designed to control early blight, other diseases also have to be considered. Fontelis and Inspire Super are effective against other fungal diseases. However, they have no late blight or bacterial disease activity. Appropriate products will need to be added if those diseases are a factor in your field.
A word of caution: Fontelis and Inspire Super are not immune from the threat of the resistance that happened to the Qoi’s. Start using them preventively, early in the program, and do not use them on severely diseased crops.
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