Stripe Rust is Showing Up in Missouri Wheat By Laura Sweets

Southern states have been reporting unusually high levels of stripe rust in wheat for over a month. Over the last week, reports have been coming in from southeastern and southwestern Missouri that stripe rust is showing up in some wheat fields. There appears to be some variation in severity with some fields showing rather severe symptoms on the flag leaves.

Stripe rust, caused by the fungus Puccinia striiformis, develops as yellow or yellowish red stripes or streaks that run lengthwise on wheat leaves. This disease is more commonly associated with lower temperatures (especially lower night temperatures) and intermittent rain or dew.

Varieties vary greatly in their susceptibility to stripe rust. Some varieties have good resistance and may show little disease development. Other varieties are rather susceptible and may show severe symptom development and, in some cases, yellowing and premature death of leaves. On these varieties yield may be impacted significantly.

Stripe rust is controlled primarily through the use of resistant varieties or the use of foliar fungicides. A table of foliar fungicides labeled for use on wheat was published in the April 15 issue of the Integrated Pest and Crop Management Newsletter. Most of these materials may be applied up to Feekes growth stage 10.5 which is full head emergence. Once flowering has started it is too late to apply most of these materials.

If there is a question on whether or not to apply a foliar fungicide to manage stripe rust of wheat this season, it would be wise to scout fields very closely as quickly as possible for stage of growth and disease severity.

If the crop is flowering it is too late for legal application.

If a significant number of the flag leaves are showing high levels of infection and the forecast is for warm, dry weather, it is probably too late for the fungicides to be of much benefit.

If most flag leaves have little to light infection and the forecast is for cool or cool, wet weather (or if there is a chance that weather conditions might favor an extended grain fill period), there might still be some benefit from a fungicide application. But the fungicide application would need to be done immediately.

This would also be a good year to check out any wheat variety trials in your area and evaluate varieties for reaction to stripe rust or other diseases.

Laura Sweets, Plant Pathologist
573-884-7307