Q&A on current wheat disease and fungicide use issues
I have received several questions over the past few days on wheat diseases and potential fungicide application issues this year.
Q: Is stripe rust a potential concern in Kansas this spring?
A: Yes, it’s certainly possible. But it’s still too early to know for sure whether it will occur. There is a fair amount of stripe rust being reported now on wheat in Texas and Oklahoma. Recent conditions have been cool and wet in many areas of those states. Where conditions are wet in Kansas, stripe rust could soon be found on wheat. The recent rains may have moved stripe rust into Kansas but it will take time for the disease to become established. The first generation of stripe rust infections does not cause as much damage as the second or third generations after an infection takes hold, so if the weather warms up soon that will help minimize the long-term risk of yield loss from stripe rust even if an initial infection were to occur soon. Stripe rust thrives best when nighttime temperatures are in the 40’s or low 50’s. If nighttime lows are in the 60’s, stripe rust activity will slow down considerably. Wheat in far south central Kansas has headed in many cases as of April 17, but wheat in the northern half of Kansas is just now around the flag leaf stage – give or take several days. In general, wheat is about two weeks ahead of normal in most areas of the state. Given that, it seems likely that the biggest threat of stripe rust epidemics causing a significant yield loss might be in the northern half of Kansas, north of McPherson where wheat is currently at an earlier stage of growth. But if stripe rust moves up quickly into Kansas and conditions are cool and wet, wheat in the southern half of Kansas could also be at risk. By the time wheat is past the soft dough stage of grain fill, a stripe rust infection will result in less yield loss. Wheat producers in all of Kansas should be scouting their fields regularly, starting now.
Q: What about leaf rust?
A: Yes, leaf rust is also a concern for Kansas producers this year. Leaf rust is also active now in many areas of Texas and Oklahoma, and spores could blow into Kansas this spring. We are at a time of year now when temperatures will start to warm into the range in which leaf rust thrives – with nighttime lows in the 60’s. As with stripe rust, scouting for leaf rust will be important.
Q: Which fungicides can be applied latest in the season on wheat?
A: Always consult the label on this since any label violations could have unwelcome consequences. In general, the triazole fungicides can be applied the latest. Tebuconazole products (Folicur and generic products), Caramba, and Prosaro can be applied through the flowering stage. But these products have a 30-day preharvest interval as well, so producers have to keep that in mind and make sure they’re not applying it so late that they will have to delay harvest to meet the preharvest interval.
Q: Are any other diseases a problem this year?
A: Wheat streak mosaic is relatively common this year, even in central and eastern Kansas. One factor producers should keep in mind going forward is that volunteer wheat is not always being controlled in some situations, including in stands of cover crops in some cases. Uncontrolled volunteer wheat is always a threat to cause wheat streak mosaic problems in nearby wheat fields.
Erick DeWolf, Extension Plant Pathology