This article was written by Dr. Bob Hunger, Extension Wheat Pathologist
Department of Entomology & Plant Pathology
Oklahoma State University – 127 Noble Research Center
Powdery mildew (Figure 1) continued to be the primary wheat foliar disease this past week in Oklahoma. Around Stillwater, I have seen powdery mildew on the lower and mid-leaves with severities reaching 90% on the lower leaves. A preponderance of powdery mildew also was indicated by the scouting reports sent in from counties across the central tier of Oklahoma to Zack Meyer (Extension Educator; Kingfisher County) where mildew was reported in Washita and Kingfisher Counties at a light (<25%) severity on lower and mid-leaves. Across the northern tier of counties in Oklahoma, powdery mildew was reported to Josh Bushong (Area Extension Agronomy Specialist; northwest district) from Noble and Garfield Counties at light and heavy (>25%) severities on the lower and mid-leaves. Wheat in central Oklahoma was reported at growth stages 8-9 (flag leaf emerging to flag leaf fully emerged). In northern Oklahoma, wheat was extremely variable with growth stages from 2-8 (tillering to flag leaf emerging) being reported. Again, I want to thank all the educators that participated in this pilot program for reporting powdery mildew, leaf rust and stripe rust, and I would encourage more participation to facilitate the warning of these three foliar diseases of wheat.
Figure 1. Severe powdery mildew on lower wheat leaves.
There were not any reports this last week regarding foliar diseases from Texas, and there still have not been any significant reports of stripe or leaf rust across Oklahoma. There was one report of stripe rust in south central Oklahoma from Anderson Farms located near Ardmore, OK. As you can see in Figure 2, the lower leaf shows a heavy infection of active stripe rust while the top leaf shows a heavily infected leaf that has transitioned to the dormant (telial) spore stage of stripe rust. This happens as temperature rises with both day and night temperature being important. Typically day temperature needs to consistently be above about 75-80 F and night temperature about about 65 F. This transition along with very limited reports of stripe rust in Texas and Oklahoma indicate that stripe rust should not be a major factor in wheat this year in Oklahoma. Leaf rust could still develop, but inoculum will need to increase, and to date, there has not been widespread weather (cool and moist) that favors either rust.
Figure 2. Active wheat stripe rust (lower leaf) and stripe rust that has transitioned to the telial (dormant) stage on wheat in south-central Oklahoma. (Photo credit: Anderson Farms near Ardmore, OK).
The only other observation this week has been “spots” of barley yellow dwarf as reported last week. However, after the recent freeze events, these barley yellow dwarf “spots” are more difficult to discern because there is widespread burning of leaf tips from the freeze, which has a masking effect.