While grain prices are dismal and our wheat crop has considerable variation in its’ stage of development throughout the county and state. With the above average precipitation and cooler weather some wheat fields are looking good.
Weather conditions have been very favorable for continued development of stripe rust and leaf rust over the past 2 weeks. There are now reports of stripe rust moving to the upper canopy in South Central Kansas. This is significant because these leaves contribute much of the resources used to develop grain. The risk of severe yield loss increases when the disease becomes established on these leaves prior to flowering, reports Erick DeWolf, Extension Plant Pathologist.
“There are also multiple reports now of stripe rust occurring on the upper leaves of wheat varieties that were previously considered resistant to the disease. The infection types appear susceptible to moderately susceptible and are supporting ample spore production”, reports DeWolf.
Varieties previously thought resistant now showing stripe rust include: Larry, SY Monument, LCS Chrome, AG Icon. WB Grainfield is also showing signs of more disease than normal. “The stripe rust reaction for WB Grainfield has been down graded to intermediate in recent years, but now appears to be moderately susceptible to susceptible”, says DeWolf.
All these varieties have the resistance gene Yr17 but are also believed to have additional resistance genes that help hold the stripe rust in check. Some rust resistance genes become more active as the plants mature and temperatures increase. At this point, it is not clear if the resistance will become more active or not. With the disease already becoming established on the upper leaves, it seems unwise to count on this type of resistance to prevent damage.
Some growers in this area are taking action to suppress the disease with fungicides, but this activity is being slowed by rainy weather”, DeWolf said.
On Monday in the Cottonwood District – Barton County Wheat demonstration plot I was able to find very low levels of stripe rust in the lower canopy on 4 different varieties, 2 of which have had resistance to stripe rust in the past. In the Cottonwood District – Ellis County Wheat demonstration plot I was not able to find any leaf or stripe rust on Monday, but I suspect by late this week or next week that may change.
On Thursday morning I went South of Hays and randomly looked at some fields and was only able to find a few leaf rust pustules in the lower canopy in a few fields. I have received a picture of a leaf from a field in southern Ellis County that had stripe rust on it as well.
Now is the time to be out scouting your wheat fields for foliar rust diseases. Those fields that have good yield potential may be top priorities for consideration of a fungicide application, if any rust diseases are found. Remember that the flag leaf can account for as much as 40 to 50% percent of the yield due to its’ function of carbohydrate production—for grain fill, so protecting it from rust diseases is important.
Research conducted by K-State indicates that a single fungicide application made to susceptible wheat varieties when the risk of disease is high will often result in a 4 to 13 percent yield increase, with an average increase of approximately 10 percent relative to untreated wheat. Important considerations when making fungicide application decisions include application timing, timely disease scouting, and knowledge of a variety’s genetic resistance to disease.
In general, growers have access to many products that can provide very good to excellent control of stripe rust, leaf rust, and other common leaf diseases. There are also significant differences in product price. With low wheat prices, it could be important for growers to do their homework before pulling the trigger on any possible fungicide application this year. Historically, the cost of fungicide products range from about $2 to $15 per acre, with generic tebuconazole, and propiconazole products being the lowest-cost options.
I realize that with the current price of wheat it may be hard to justify another expense. This information is intended to keep farmers informed which can assist them to make the best decision possible for their operation.
Stacy Campbell is Agriculture & Natural Resources Extension Agent for the Cottonwood Extension District
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