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If applying fungicides, beware of pre-harvest intervalsKansas Rainfall that has blanketed the Kansas wheat crop in the last few weeks have many farmers considering the application of a foliar fungicide, to fight diseases such as leaf rust, stripe rust, leaf spot and powdery mildew. In mid-April, the threshold of these diseases was low, according to Erick De Wolf, plant pathologist with K-State Research and Extension. However, the cool, damp environment is favorable for further development of fungal diseases. DeWolf recommends vigilant scouting of the wheat crop to stay abreast of fungal disease developments. The disease resistance package varies among wheat varieties. Farmers can check the publication, "Wheat Variety Disease and Insect Ratings," available at your Extension office or online at www.plantpath.ksu.edu to see how their chosen wheat varieties fares against these common foliar diseases. Kansas Wheat reminds farmers that the labels of many popular fungicides require a "pre-harvest interval," or a required period of time that must transpire between fungicide application, and harvest. In 2008, wheat harvest in some Kansas fields was halted due to failure of following the pre-harvest interval. "As producers of the world's most commonly consumed grain, Kansas farmers must remain good stewards of the crop protection products we have at our disposal," says Dusti Fritz, chief executive officer of Kansas Wheat. "For that reason, we want to remind farmers that it is critical to follow the labeled requirements for pre-harvest intervals when using fungicide products." There are two basic categories of foliar fungicides: --Strobilurins prevent diseases only and must be applied before symptoms appear. They have somewhat longer residual activity than triazoles. --Triazoles are a better choice when diseases are already present. They can stop a disease from reproducing and have limited kickback curative ability. --Combination products contain both triazole and strobilurin modes of action. Most pre-harvest intervals range between 30 and 45 days; farmers must stay in contact with commercial applicators to learn when the product was applied. De Wolf says that most fungicide applications should be made between full flag leaf extension and full head emergence. For head scab suppression, apply the appropriate fungicide to the head between the start of flowering and 50 percent flowering.
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