Wheat disease updates are written by Dr. Bob Hunger, OSU Extension Plant Pathologist
Wheat in southern/southwestern Oklahoma is maturing and will speed up with the warmer (>90 F) over the last couple of days. In central Oklahoma, around Stillwater and to the north, wheat is just finishing or has just past flowering and kernel development is starting. As you head to northwest Oklahoma, wheat also is in late flowering or has just finished flowering. I’m not sure about out toward the panhandle but know there is not much wheat that will be harvested as you move west of Woodward and Buffalo. I’ll be taking a trip to the panhandle the end of the coming week and will report more after that trip.
Disease-wise, not a lot changed over the past week in Oklahoma. Leaf rust remained practically absent although infections in the 15-40S range were observed in Jagalene (or Jagger) guard rows in breeder plots at Stillwater. However, little to no leaf rust was found elsewhere around Stillwater and no reports were observed or reported from north-central and northwestern Oklahoma. Stripe rust is slight more prevalent. Several “hot spots” were noted around trials at Stillwater and occasional “stripes” (but not hot spots) were noted at field days west of Enid, north of Ponca City, and north of Stillwater. Leaf spotting diseases, barley yellow dwarf, and wheat streak mosaic (WSM) are the most commonly observed diseases in samples seen at field days and submitted to the Plant Disease and Insect Diagnostic Clinic. This past week a few samples also tested positive for High plains virus. Several reports from ag educators, consultants, and growers have indicated that WSM has devastated wheat in fields in northern and western Oklahoma. In all cases where I talked to the person, there was an indication that volunteer wheat was involved either in the field or adjacent to it.
Reports/excerpts of reports from other states:
Arkansas – Dr. Gene Milus, (Professor/Small Grains Pathologist, Univ of Arkansas, Fayetteville, AR) 17-May-2013: Visited plots at Kibler near Fort Smith today. Wheat is in soft dough. Stripe rust is still active. Leaf rust was present at mostly low levels. Also Septoria, bacterial streak, powdery mildew, and Stagonospora on flag leaves depending on the line. Most lines in the variety test had resistance to most or all of the above diseases. Weather is hot and humid. Plenty of soil moisture.
Kansas – Dr. Erick De Wolf (Professor/Small Grains Extension Pathologist, Kansas State Univ, Manhattan, KS) 17-May-2013: Stripe rust continues to be reported at low levels in Kansas this week with new finds in Sedgwick, Kingman, Sumner, and Pratt counties. The wheat in this area of the state is still heading or flowering. Generally, only trace levels could be found in these fields. Tom Maxwell, Central Kansas District agent, reported finding low levels of stripe rust in Saline County on May 17. The wheat there is generally in the early heading stages. I have found a few fields and a demonstration plot in Pratt County where the disease is at high enough levels to justify a fungicide application. This area of the state has received more rain than others in recent weeks and some fields in Pratt County have good yield potential. The affected varieties included Everest and Armour, which were found to be susceptible in 2012. A lot of wheat in this area of the state is struggling with continued dry weather.
I encourage farmers to carefully check fields for symptoms of disease. Fields where stripe rust can be readily found on the flag leaf (one lesion every 2-3 feet) will likely benefit from a fungicide application. The wild card on this decision is the weather. Low temperatures in the upper 60’s are generally thought to be suppressive to stripe rust development. High temperatures in the upper 80’s or above for several days in a row also tend to suppress stripe rust. But if temperatures in that range last only last a few days or so, followed by cooler weather, stripe rust can resume activity.