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.
Figure 1. Stripe rust on wheat. Photo by Erik DeWolf, K-State Research and Extension.
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.
In the case of Pratt County, mentioned above, the forecast was calling for fog on May 17 but only a slight chance of rain showers (20% chance of rain), with lows in the 60’s for the next two days. This situation is a tough call, but I think I would error on the side of caution and spray a field that had considerable stripe rust on the flag leaf at heading. Fields with poor yield potential or that have no rust may not need the application.
Jeanne Faulk, Sunflower District Agronomist in northwest Kansas, reported a trace of stripe rust in the white wheat variety Platte in Thomas County. Like many reports this year, only one field with low levels of disease was reported after checking many fields. A lot of wheat in this area of the state is under considerable drought stress and some fields are struggling to recover from freeze injury. However, fields that still have good yield potential should be checked for signs of stripe rust.
Don’t overreact to this report. But do make sure to check your fields. Stripe has the potential to cause losses of 40 percent or more when the disease becomes established on susceptible varieties before heading. For more information, see K-State’s Plant Pathology Fact Sheet on stripe rust at: http://www.plantpath.ksu.edu/doc1174.ashx
-- Erick De Wolf
Extension Plant Pathologist