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

Article 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 past week (Monday & Tuesday) I visited the Dr. Raymond Sidwell Station near Lahoma (Major County), and the variety trials near Cherokee (Alfalfa County) and Alva (Woods County) on my way to field days in the panhandle near Balko and Hooker (Texas and Beaver Counties).  Except for in the panhandle, wheat foliage is pretty much done for in Oklahoma.  Wheat in the panhandle was mostly in the kernel forming stage.  Diseases observed on the trip to the panhandle included stripe rust (some still actively sporulating), wheat streak mosaic/high plains, and barley yellow dwarf.  Samples submitted to the Plant Disease and Insect Diagnostic Lab also have tested positive for these viruses.  As indicated in the 14-May update, take-all/root rot has been confirmed from a couple samples received from across central and northern Oklahoma.  Take-all has been confirmed, but it appears another root rot also may be involved.  Jen Olson in the PDIDL is making isolations to help resolve exactly what is involved in terms of root rot disease.  In south-central Oklahoma Aaron Henson (Tillman County Extn Educator) indicated to me that wheat is variable in maturity but he estimates that some harvesting should begin in 1.5 to 2 weeks.  Heath Sanders (Area Extn Agron Spclt located in southwestern OK) indicated much the same – especially if the cool/wet weather becomes more seasonally hot and dry.

Reports/excerpts of reports from other states:

Cereal Rust Bulletin from the Cereal Disease Lab in Minnesota; May 18, 2016:  Highlights/reports in the Cereal Rust Bulletin include:

·        Wheat stem rust was found in a nursery in south central Georgia.

·        Wheat stripe is widespread in the U.S., now reported in 24 states.

·        Oat crown rust has now been reported in Texas, Louisiana, Mississippi, Alabama and North Carolina.

The link to this report is: http://www.ars.usda.gov/SP2UserFiles/ad_hoc/36400500Cerealrustbulletins/16CRB4.pdf

Kansas:  Dr. Erick De Wolf (Extn Plant Pathologist); Kansas State University; May 18, 2016:  “Wheat in central and south central Kansas is at the grain filling stages of growth with many fields at or near the milk stages of kernel development.  Stripe rust is severe in many fields that were not treated with fungicides this year.  Fields of susceptible varieties have stripe rust severity >80% on flag leaves in demonstration plots in Pratt, Kingman, Harper, Barber counties.  The disease was also severe in Ellsworth county were a fungicide demonstration plot had nearly 100% severity of the flag leaves.   The weather this week appears highly conducive for continued disease development and the risk of severe disease appears to be high in Northwestern and West Central KS where low levels of stripe rust have been reported on the flag leaves.  Varieties with genetic resistance are performing well with disease reactions very similar to what we saw in previous years.   To date, T-158, Gallagher, WB-Grainfield, TAM 114, WB Cedar, Sy- Monument have all had moderate levels of resistance to the disease.  This suggests that the race structure of the stripe rust fungus is similar to last year.  Low levels of leaf rust were observed in Kingman, Pratt, Barber and Harper Counties.”