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Kansas Wheat Innovation Center

Wheat Disease Potential Merits Crop Scouting

Apr 5, 2012

MANHATTAN, Kan. - With stripe rust moving as far north as Salina as of April 5, and leaf rust found as far north as Riley County in eastern Kansas and Ness County in western Kansas, it’s a race to the finish line for the Kansas wheat crop, according to Erick DeWolf, plant pathologist for K-State Research and Extension.

Recent rains have farmers and crop consultants on alert for the spread of these diseases, and DeWolf says farmers need to be checking fields for possible infestations.

For instance, the crop is heading out in southern Kansas. If farmers see active rust lesions in wheat fields now, be prepared to spray the crop with a fungicide.

If you don’t see rust lesions at heading, a fungicide application may not be warranted. “But you do need to continue scouting those fields,” recommends DeWolf, who adds that growers need to remain vigilant and take steps to protect the crop until after the crop has flowered.

Diligent field scouting will help farmers overcome the uncertainty of this year’s race of stripe rust. “It appears that some varieties that looked vulnerable during our last stripe rust outbreak are not developing stripe rust this year,” he says. “However, many varieties, including Tam 111, Everest, Armour and Cedar – all of which showed resistance in 2010 – are appearing susceptible to the variant of stripe rust that is showing up this year.”

Growers have until a given fungicide’s Pre-Harvest Interval, or the growth stage restriction on the label, to apply a fungicide. DeWolf advises farmers that for best results, apply fungicide between the growing stages of flag leaf fully extended (Feekes 9), and fully headed (Feekes 10.5). Some fungicides can be applied during the flowering stages of growth but generally have a 30-day pre-harvest interval. Once the flag leaf has emerged, farmers will have about two weeks to scout for disease and make a final decision about fungicide application.

Farmers have a choice of two basic categories of foliar fungicides:

  • Strobilurins prevent diseases only and should be applied before symptoms appear. They have somewhat longer residual activity than triazoles.
  • Triazoles are a better choice when diseases are already present. They can inhibit infections that have already started, and some of these products are more upwardly mobile within the leaves, than are strobilurins. However, movement within the plant is limited.
  • Combination products contain both triazole and strobilurin modes of action.

In several years of yield trials, the application of fungicides to susceptible varieties between flag leaf and flowering resulted in a yield boost of 4-14%. This research was conducted at K-State.

In summary
Growers should use the best available information about varieties to determine that variety’s resistance to diseases. Then, make an application decision based on the activity of disease in the fields. If diseases are present prior to heading, and the field has good yield potential, a fungicide application is more likely to pay off. Seed production fields are also a priority, DeWolf says.

“The decision to apply a fungicide product is reinforced by a forecast for moderate temperatures and f requent rain, because these conditions favor continued disease development,” DeWolf adds. “A forecast for extreme temperatures, either cold or heat, or prolonged dry conditions might enable farmers to delay a decision to use a fungicide.”

More information is available online at: www.ksre.ksu.edu/library/plant2/mf3057.pdf

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