Stripe rust, leaf rust, and stem rust have been identified in fall planted wheat in Nebraska, extending into areas where it had previously not developed in the fall. Plant Pathologist Stephen Wegulo looks at the outbreak, conditions contributing to rust development this fall, and the economic and management issues.
By far, the greatest risk of losses from mite-vectored viruses occurs when there is a summer "green bridge" of volunteer wheat emerging before harvest. This almost always occurs as a result of wheat seed head shatter from hail storms (Figure 1).
Stripe rust has significantly increased in all wheat-growing areas in Nebraska. It is recommended that wheat be treated with a fungicide to protect the flag leaf. If the incidence (percentage of flag leaves diseased) or severity (percentage of the flag leaf area diseased) is less than 50%, spraying a fungicide will significantly reduce yield loss due to stripe rust.
A survey of wheat fields in southeast and south central Nebraska this week found most fields looking healthy with little or no disease. Fungal and virus diseases were found at varying levels in some fields. Depending on growth stage and disease present, fungicides may still be beneficial.
With wheat headed or flowering in southeast and south central Nebraska, head diseases are starting to appear, including Fusarium head blight, loose smut, white mold (scab) and barley yellow dwarf. Wheat stem maggots were also causing damage.
Wheat is heading, headed, or flowering in most fields in eastern Nebraska. The Fusarium Head Blight Prediction Center is currently showing a low risk for scab in Nebraska. However, due to the recent rains, there is a possibility that some level of scab may occur in some fields, and the risk will be higher in areas that receive rainfall in the next 10 days. Base the decision to apply a fungicide to suppress scab on the risk level, the cost of application, and the price of wheat.