April's Ag Advice by April Borders Right now our concerns turn to our winter wheat crop. Dr. Marty Draper, SDSU Extension Plant Pathologist, said that tan spot is beginning to show up in South Dakota winter wheat. He has received several samples of very early tan spot and he suggests that producers scout their fields.
Several varieties of wheat are affected and the disease has not been severe on any of the samples he has seen. Draper said, "However, we are right at the time when we may apply a fungicide with post emergence weed control. If you wait to evaluate after the herbicide has been applied the economics are not there for another pass across the field to apply the fungicide separately. So, be sure to look at the tan spot situation before that herbicide pass."
Producers have several options for early season, reduced rate applications at quite affordable costs:
mancozeb (Dithane, Manzate, Penncozeb, and others) at 1 pound per acre (costs about $3.50/acre)
propiconazole (Tilt, PropiMax, or Bumper) at 2 fluid ounces per acre (costs about $5/acre)
pyraclostrobin (Headline) at 3 fluid ounces per acre (costs about $4.50/acre)
trifloxystrobin + propiconazole (Stratego) at 5 fluid ounces per acre (costs about $5.50/acre).
Draper added that interpretation of the label could also allow the use of azoxystrobin + propiconazole (Quilt) at 7 fluid ounces per acre (costs about $6/acre).
Studies at SDSU have shown the disease control provided by these products to be similar. The more immediate benefit is to slow the disease progress down and if weather turns drier, no disease loss may result. This treatment will not preclude the need for a later application if disease pressure is heavy. Draper said, "If your crop is not a second (or more) consecutive wheat crop, there is no need for a fungicide treatment early in the season."
Another disease that we need to be on the lookout for is rust in our cereal crops. In a recent update that I received from Dr. Draper, it looks as though the rust situation is developing in the south. Oklahoma and Texas have reported stripe rust but is not very severe. It is below levels noted in 2003. There is apparently not much inoculum blowing our way but we are still three weeks before the first South Dakota sighting of stripe rust in 2003.
Leaf rust is also building in Oklahoma. They are seeing intermediate levels of leaf rust in the upper canopy in central Oklahoma. Disease has been quiet severe on susceptible varieties at some sites. They are expecting the disease to continue to build, given their weather forecasts. Leaf rust was observed on April 23 in Kansas. So the bottom line is � it's coming! We will have inoculum blowing north, so don't forget to scout. Be sure to monitor the crop as it approaches the flag leaf emerging.
BYDV (barley yellow dwarf virus) is also quite severe in Oklahoma. So depending on the winds, if aphids reach South Dakota early in crop development we could see some yellow dwarf. There is no recommended treatment for yellow dwarf. Losses will be greater in winter wheat if infection was in the fall. We would hope the spring grains would reach the boot stage before they are exposed to minimize losses. Even so, 5 percent incidence of BYDV looks like a lot in a field, but the potential disease loss due to BYDV is fairly low. Actual losses depend on the stage at which infection occurred and disease incidence.
If you have questions or concerns about any of these diseases in your wheat crops or if you have plants that look suspicious, contact the Clay County Extension Office at 677-7111 for more information.