Wheat Diseases Creeping North

What is the status of diseases in the 2012 wheat crop? Erick De Wolf (dewolf1@ksu.edu), plant pathologist for K-State Research and Extension, lends his insight in a guest blog this week.

Most parts of Kansas experienced warm temperatures last week, and with rain this week, the wheat is growing rapidly. I continue to receive reports of leaf rust and stripe rust from Texas with wheat breeders reporting the leaf rust is severe on susceptible varieties in research plots near College Station and San Antonio. Stripe rust is also active at these locations but it does not appear to be as severe as in 2010. In Oklahoma, low levels of stripe rust are occurring near Stillwater.

To date, I have not been able to find leaf rust or stripe rust in Kansas. However, the weather this past week likely favored movement and establishment of these diseases in our region. I have seen some fields and research plots with of low levels of Septoria tritici blotch and powdery mildew, but currently these diseases are restricted to the lower leaves. The risk of severe disease yield losses is currently low in Kansas, but disease activity may increase if the weather remains favorable for disease development.

Farmers should be checking fields carefully in the next 10 to 14 days make sure disease remains at low levels. If diseases have moved into Kansas, we’ll likely start seeing symptoms then. And at the rate the wheat crop is growing, that could put southern Kansas wheat right at the flag leaf emergence stage, a great time to apply fungicide.

Farmers may be interested in applying foliar fungicides to wheat. There are two basic categories of foliar fungicides:

  • Strobilurins (Headline, Quadris) prevent diseases only and must be applied before symptoms appear. They have somewhat longer residual activity than triazoles.
  • Triazoles (Bumper, Caramba, Folicur, Proline, PropiMax, Prosaro, Tilt) are a better choice when diseases are already present. They can inhibit infections that have already started, and are more upwardly mobile in the plant than are strobilurins. However, movement within the plant is limited.
  • Combination products (Quilt, Stratego, TwinLine) contain both triazole and strobilurin modes of action.

Most fungicide applications should be made between full flag leaf extension and full head emergence.

Here is a list of popular fungicides, the class these products represent, and the Pre-Harvest Interval (days required based on the label, between application and harvest). This comes from the 2011 “Know Your Wheat” booklet, provided by Kansas Wheat and The Wheat Farmer newsletter.

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