May 13, 2021

CAMPBELL: Stripe rust update

Posted May 13, 2021 11:02 AM
Stripe rust / courtesy photo
Stripe rust / courtesy photo

By STACY CAMPBELL
Cottonwood Extension District

The cooler wet weather has been good for our wheat, but also very conducive for a fungus in wheat called stripe rust. Late last week and early this week. I have been able to find trace to low amounts of stripe rust mainly in the lower canopy in susceptible varieties in both Ellis and Barton Counties. As I am writing this article, I strongly suspect that stripe rust will continue to increase, especially given the extended weather forecast. So scouting your wheat fields is advised. 

Stripe rust is most yield-limiting when it advances to the upper canopy, particularly the flag leaf. The risk of stripe rust causing yield loss is a function of three things:

  1. Timing of first local disease detection in relation to crop growth stage (earlier detection = higher risk)
  2. Weather conditions: specifically, moisture and relative humidity after first detection
  3. Variety genetics: varieties with better resistance ratings will, in general, benefit less from a fungicide application. Variety ratings can be found in the K-State Wheat Variety Disease and Insect Rating Guide: https://bookstore.ksre.ksu.edu/pubs/MF991.pdf

Scouting is a critical first step for stripe rust control. Fungicide applications are most beneficial when the level of disease in the field is below 10% severity. University research has demonstrated that applications that protect the fully emerged flag leaf (between Feekes 8 and Feekes 10) are most effective. Applications applied prior to flag leaf emergence will not adequately protect the flag leaf or the head. Always check and follow product label recommendations to ensure full compliance with growth-stage limitations and pre-harvest intervals.

There are many products that are rated very good or excellent for stripe rust control (http://www.bookstore.ksre.ksu.edu/pubs/EP130.pdf), but it is important to know that fungicides in the strobilurin family (Group 11) are not as effective when applied as single product after symptoms have already appeared.

The products listed in the K-State fungicide efficacy publication will generally provide at least 14-21 days of protection. This can vary between products and is also influenced by environmental conditions. 

The decision to apply a fungicide should be balanced with the yield potential of the crop, variety disease rating and current grain price. Fields with the potential to yield greater than 40 bushels per acre should be prioritized for a fungicide application.

If you have any questions, please do not hesitate to give me a call, 785-628-9430. 

Stacy Campbell is an Agriculture and Natural Resources agent in the Cottonwood District (which includes Barton and Ellis counties) for K-State Research and Extension. You can contact him by e-mail at [email protected] or calling 785-628-9430.