Stacy Campbell: Stripe rust distribution and risk assessment
With the wheat crop soon moving into the flag leaf stage in our area, now is a critical time to assess the need for a foliar fungicide application. Scouting efforts from across Kansas have reported several new occurrences of stripe rust this week, although incidence remains extremely low in many counties such as Russell, Ellsworth, Saline, Rice, and Geary. At the time of writing this I have not seen any stripe rust yet in Ellis County.
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” by typing this into your internet browser box.
Deciding on a fungicide application to control stripe rust - scouting is a critical first step for stripe rust control. Stripe rust can be identified by characteristic orange lesions that form in straight lines on mature plants. When you run your finger over a stripe rust pustule, the orange spores will be easily dislodged.
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. To find K-State “Wheat Growth and Development” chart, simply do an internet search for it. 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. To see the latest fungicide ratings, do an internet search for “Foliar Fungicide Efficacy Ratings for Wheat Disease, KSU”. 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.
Information provided by Kelsey Andersen Onofre, & Eric DeWolf, K-State Extension Plant Pathologists.
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@example.com or calling 785-628-9430.