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Wheat rust update
By Assefa Gebre-Amlak CSU Pest Management Specialist, northern region We have had reports from the southeastern part of the state that both leaf rust and stripe rust are becoming very evident. One report indicated moderate to severe rust on TAM110, but no rust on Jagalene or TAM 111. It may be getting late to apply fungicides in the southern part of the state. Dr. Ned Tisserat CSU Plant Pathologist warns that applications cannot be made after the beginning of flowering. We found no evidence of rust in the Akron area (Washington County), so apparently it has not made its way up to the northern part of the state yet. Many of the fields in this area were just beginning to head. Dr. Tisserat's suggestion in the northern part of the state is to wait as long as possible before making the decision to apply a fungicide. You may not recover the cost of application if rust is a no-show or develops late. If you don't see any rust in the field just before flowering then don't spray. If you start to see light to moderate rust in the fields in the next couple of days and you have high yield potential, then consider an application. Description of fungicide applications according to Dr. Eric DeWolf at Kansas State University are as follows. The strobiluron fungicides are really good preventive fungicides, but don't work as well as a curative. So if the flag leaf is relatively clean, then one of the stobilurons would be a good choice. But if you have a lot of rust already, you probably should include a product or combination product that contains a triazole. Fungicides for wheat disease control (Dr. DeWolf at KSU) Fungicides will be appropriate in many (Kansas) fields this year. A field would be a candidate for a fungicide application if it is at the flag leaf emergence through heading stages for growth, and leaf rust can be found at low levels on F-1 and Flag leaves. For most foliar diseases, we expect a foliar fungicide to help maintain an average of at least 10 to 15 percent of the yield potential when disease is severe on the last two leaves. For leaf rust, the potential yield loss is much greater. If leaf rust becomes established on the flag leaf prior to heading, yield losses may exceed 30 percent in susceptible varieties. It is too late to apply a fungicide if leaf rust has already exceeded 5 to 15 percent severity on the flag leaves at heading (more than 40 pustules in a 2-inch area). In this situation the next generation of lesions is already developing within the plants, and considerable damage to the leaf tissue has already occurred. The economic return for investing in a fungicide when leaf rust has advanced to this level becomes uncertain, and it may be best to forgo the application. The choice of fungicide is also an important factor. There are three types of fungicides: --Strobilurins (Headline, Quadris). --Triazoles (Tilt, PropiMax) --Combination products, strobilurin + triazole (Quilt, Stratego) All of these fungicides provide very good control of leaf rust and powdery mildew if applied prior to infection. However, the efficacy of the strobilurins can decrease significantly if the disease is already established in a leaf. This class of fungicides has very little curative activity and will not stop the fungi once infection has taken place. The triazoles fungicides have a stronger curative activity than the strobilurins, and would be the best choice if rust has been observed in your fields, or is known to be active in your area. The combination products would be another option if disease is already active. These products combine the triazole and strobilurin chemistries and pick-up the curative activity from the triazole. Quilt has a higher level of the triazole than Stratego and would provide curative activity similar to a solo triazole if disease is established in the crop. All the fungicides are labeled for application through the heading stages of growth. These products are locally systemic which means they will be rain fast as soon as they dry on the leaves but will not move into parts of the plant that are not covered by the fungicide. The products will provide 14 to 21 days of protection depending on the level of disease pressure. Date: 5/30/07
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