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June 28, 2005 Key Time for Wheat Fungicide Spraying in North Dakota North Dakota State University Integrated Pest Management field scouts and some independent crop consultants are reporting that leaf rust is common in many wheat fields all the way from the South Dakota border to northern counties. “Generally, severities range in the trace to 5 percent range, but dew periods have been favorable for continued development,” according to Marcia McMullen, NDSU Extension Service plant pathologist. Much of the spring wheat fields in the southern to central counties are near or in the flowering stages, while most winter wheat has finished flowering in the southern counties. Leaf rust thresholds, established in many winter wheat states, are averages of one to three pustules on the flag leaf and five to10 on the leaf right below the flag leaf. These are thresholds for susceptible cultivars. If much higher levels are seen on the flag leaf, it may be too late to spray. “Keep in mind that some rust being observed may be on more resistant varieties that are having MR (moderate resistance) reactions, with yellow halos around small rust pustules,” McMullen says. “On the other hand, susceptible varieties, such as Oxen, are showing reactions with no yellow halos and abundant sporulation. The variety Alsen predominately has an MR reaction, but a few plants in an Alsen population also have a susceptible reaction.” Based on weather conditions, the NDSU small grain disease forecasting Web site indicates that some areas of the state are at high risk for scab infection. Shaukat Ali, NDSU Plant Pathology research specialist, is conducting spore trapping for fusarium head blight spores and found low to moderate spore numbers in his Fargo spore trap. He only has a spore trap in Fargo. Jeff Stein and Marty Draper, South Dakota State University plant pathologists, have reported some noticeable scab infections in winter wheat in South Dakota. So what do farmers do if the wheat crop is in the late boot to early heading stage and they want to spray for rust and scab?
“If a variety is susceptible or moderately susceptible to leaf rust and scab,” McMullen says. “that past experience tells us that producers should wait to spray until early flowering. In NDSU trials at various locations across the state, we have had excellent success at controlling leaf rust and scab by waiting until the early flowering application. At this growth stage, growers should be suing a triazole fungicide. “The triazoles Folicur and Tilt have some short-term curative activity and are better products for controlling scab and do well on leaf rust,” McMullen says. “Both products should be applied at 4 fluid ounces per acre, not at a reduced rate. Why risk reduced disease control with reduced rates?” The difficulty this year, McMullen says, may be in getting the aerial applicator or the ground sprayer in the field at the appropriate time. For more information on fusarium head blight and leaf rust, go to www.ext.nodak.edu/extpubs/. For more information on small grain disease forecasting, go to www.ag.ndsu.nodak.edu/cropdisease/ ### Source:
Marcia McMullen, (701) 231-7627, mmcmulle@ndsuext.nodak.edu |
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North Dakota State University |
