Summer 1995
Consider Foliar Fungicide in Case of Scab
by Tracy Sayler, Communications Specialist; Minnesota Wheat Council
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Prairie Grains is the
official publication of
the Minnesota
Association of
Wheat Growers,
North Dakota Grain
Growers Association,
South Dakota Wheat,
Inc., and the
Minnesota Barley
Growers Association.
With wet conditions impairing tillage last fall and again this past spring, the reservoir of scab inoculum available to infect crops this season remains high, according to Roger Jones, University of Minnesota extension plant pathologist.
But that does not mean the Red River Valley is going to have a three-peat scab epidemic. Dry weather at grain flowering may keep the disease in check. "We just have to see how things unfold," says Jones.
Just in case the unthinkable does occur, however, growers may want to be prepared for a foliar fungicide application at grain heading.
Officially available to apply this growing season is benomyl (Benlate, marketed by Dupont) which has received a label modification adding scab to the list of diseases for which Benlate may be applied on wheat.
The application rate is 1/2 pound per acre. Do not apply within 21 days of harvest. The optimum time to apply benomyl is when 15% to 25% of a wheat crop is flowering (not heading). Note that benomyl cannot be applied to barley.
"Understand that benomyl offers suppression of scab, not control. Effects will be less exposure to DON (vomitoxin) and improved yield and test weight," says Jones. "In an epidemic, farmers will still have scab in fields sprayed with benomyl, but there will be less scab than if they had not sprayed."
Leave an unsprayed test strip of wheat to compare with sprayed wheat in a field, Jones advises.
For added leaf spot control, mancozeb may be tank-mixed with benomyl. Apply mancozeb at one lb. per acre and benomyl at 1/2 lb. per acre. There is a 28-day waiting period before harvest for a mancozeb-benomyl application.
The cost of benomyl is about $7.50 per acre, and mancozeb, about $2.50 per acre. The application cost is about $3.50 per acre.
Jones says spring wheat varieties that are moderately susceptible to scab- Grandin, Sharp and 2375 -- will respond most to a fungicide application. It would not be effective on Marshall.
"Fungicide treatments will not overcome the severity of scab that can occur in highly susceptible varieties such as Norm, Vance, Gus, and Bergen," says Jones. "Hopefully, very few acres of these varieties are planted this year."
REQUEST FOR TILT SUBMITTED
A request has been submitted to federal regulators to modify the application timing of Tilt on wheat and barley. "We are asking that application timing be changed from flag leaf emergence to heading, which would allow the option of using Tilt to suppress scab in wheat and barley," says Jones.
The status of this request, called a section 18 request under a federal law which governs pesticide use, should be known by the end of June.
REGIONAL FUNGICIDE TESTING UNDERWAY
Crop researchers in Minnesota, North Dakota, and South Dakota have a cooperative foliar fungicide testing program underway this summer.
The program, funded in part by checkoff dollars administered by the Minnesota Wheat Research and Promotion Council, involves three phases.
Phase one includes field testing of foliar fungicides in the marketplace, since current data on their use for scab suppression is limited.
The second phase will include replicated trials of foliar fungicides not yet in the marketplace which may have activity against scab. Phase three will involve trials of experimental fungicides that are further away from commercialization than compounds in phase two.
Jones, NDSU Extension Plant Pathologist Marcia McMullen, and SDSU Extension Plant Pathologist Dale Gallenberg are heading the regional fungicide evaluation project. Evaluations will take place on spring wheat, durum, and barley.
While fungicides aren't going to be the answer in controlling scab, they may play a role as a scab management tool, says Jones.