This article is written by Dr. Bob Hunger, Extension Wheat Pathologist.

Department of Entomology & Plant Pathology – 127 Noble Research Center

Oklahoma State University – Stillwater, OK

405-744-9958 (work) – bob.hunger@okstate.edu

This likely will be my last OK disease update for a while as diseases have mostly “run their course” in Oklahoma and harvest has started.  However, I wanted to provide a follow-up on the late season root rots we saw at several locations across northern Oklahoma.  Symptoms and a description of the setting in the field all pointed to take-all in several of the samples, and Jen Olson in the Diagnostic Lab and I did find visual signs of the take-all fungus.  With further examination, Jen found lesions indicative of Rhizoctonia root rot, and subsequently, she isolatedRhizoctonia.  In another sample with whiteheads that to me appeared to be take all, Jen isolated Parastagonospora nodorum and Fusarium (most likely acuminatum as indicated by DNA sequencing).  In a third sample in which roots appeared clean but the lower stems were discolored, Jen isolated Rhizoctonia, but also more commonly Fusarium (again most likely acuminatum), Curvularia, and Parastagonospora.  Likely some of these were secondary.  So, the exact cause of the whiteheads is somewhat uncertain with Rhizoctonia root rot, take-all, and perhaps some Fusarium-induced root rot all involved.

Reports/excerpts of reports from other states:  Just to let you know, stripe rust appears to be a major disease up through the northern Great Plains and into the mid-east as indicated below.  In many of these states, producers are facing the dilemma of needing two sprays – one to control early season stripe rust and another at flowering to help suppress Fusarium head blight (scab).  We faced a similar dilemma here in Oklahoma but with an early application to control early season stripe rust and then perhaps a later one to control later season foliar diseases and or scab (in eastern/north-eastern OK).  All with low wheat prices, but without the fungicide yield and quality (test weight) would be hurt as with what happened last year.

North Dakota:  Dr. Andrew Friskop (Ast Professor/Cereal Extn Pathologist); North Dakota State University; May 23, 2016:  “Stripe rust was confirmed in two counties in North Dakota on May 23. One sample was from a winter wheat research plot near Fargo (Cass County), and the other was from a winter wheat variety performance trial in southwest ND near Hettinger (Adams Co.). This is approximately 10 days ahead of when stripe rust was detected in North Dakota last year. Given the susceptibility in popular spring wheat and winter wheat varieties, growers will be encouraged to scout especially with rain and dew in the forecast.”

Ohio:  Dr. Pierce Paul (Aso Professor); Ohio State University; May 24, 2016:  “Stripe rust continues to spread across the state of Ohio. This is the most widespread and the earliest I have seen this disease in the state in 13 years. Several varieties in fields south of interstate 70 and west of interstate 71 are severely affected, with substantial damage to the flag leaf well before flowering in multiple hot spots in some field. As we approach flowering in more northern counties, the reports continue to come in. Several fields have already been sprayed for stripe rust, but the dilemma facing most growers is whether to spray for stripe rust or wait to spray for scab in fields not yet at anthesis.”

Severe stripe rust in Ohio – Dr. Pierce Paul

South Dakota:  Dr. Emmanuel Byamukama (Ast Professor/Extn Spec – Plant Pathology); South Dakota State University; May 27, 2016:  “I scouted several winter wheat fields this week in East (Codington, Clark) , Central (Beadle, Hyde, Hand, Hughes) and West (Stanley, Jackson, Pennington) South Dakota and I found stripe rust in almost every field I scouted. The majority of these fields have stripe rust just starting while a few have moderate to severe stripe rust. Winter wheat is beginning to head and a few fields are at flowering. With more rain in the forecast, a fungicide may be necessary to manage stripe rust. The challenge is going to be needing another fungicide shortly for scab management. And with the wheat prices not encouraging, producers are concerned applying 2-3 fungicides in winter wheat this season.”

Severe stripe rust in South Dakota – Dr. Emmanuel Byamukama