Oklahoma: Wheat continued rapid development across Oklahoma this past week with yield potentials still looking outstanding. Yesterday I sprayed my foliar fungicide trial (Jagger), which rangedfrom boot (GS 10) to heads nearly fully emerged (GS 10.5). Overall I would place that trial at GS 10.2 (heads about 1Ž4 emerged). This is 2-3 weeks earlier than I typically make this application. It strikes me from calls over this past week, that this is representative of where wheat is at across much of Oklahoma.
Stripe rust continues to be reported from across southwestern, central, and west central Oklahoma, but not as many reports from the north central and northwestern parts of the state. However, these reports indicate only scattered/light infections. With daytime temperatures into the 90s over the weekend (and 80s last week) and night temperatures in the 60s, stripe rust should be “shutting down.” It could be revived with strikingly cool temperatures and moisture, but I don’t see it being a major factor in most parts of Oklahoma this year.
Leaf rust also is being reported more frequently, but still in fairly low incidence and at a low severity. Around Stillwater, I can find pustules on susceptible varieties but mostly in the 10-15% severity range.
Powdery mildew is still a factor, at least on highly susceptible varieties. Jagger, which is in my foliar fungicide trial, has a severity of around 40-65% on leaves beneath the flag leaf. Some scattered powdery mildew pustules were visible on flag leaves.
Tan spot and Septoria/Stagonospora also can still be found on lower leaves, but are not moving up the canopy. A couple of wheat samples were received from northeastern (Rogers County) andnorth central OK (Noble County) with symptoms indicative of these leaf spotting diseases, and currently isolations are being made to confirm this diagnosis.
Over the last week, the Diagnostic Lab also had a sample from Kingfisher County that tested positive for wheat streak mosaic virus and High plains virus (Kingfisher County). As temperatures warm and wheat develops, these mite-transmitted virus diseaseslikely will become more prevalent.