UNL CropWatch May 28, 2010: Stripe and Leaf Rust and Fusarium Head Blight in Wheat

UNL CropWatch May 28, 2010: Stripe and Leaf Rust and Fusarium Head Blight in Wheat

 Photo - Stripe rust in wheat  Photo - Fusarium head blight  Photo - Fusarium head blight in wheat
Figure 1. Stripe rust in wheat. Figure 2. Wheat head with a few spikelets  bleached by Fusarium head blight in a grower's field in Phelps County on May 27. Figure 3. Wheat head almost entirely bleached by Fusarium head blight in a grower's field in Phelps County on May 27.

May 28, 2010

A survey of wheat fields in southwestern Nebraska on May 27 found trace levels of stripe rust (Figure 1) in all fields. Fields that have been sprayed showed old lesions but no active stripe rust. Earlier in the week stripe rust was confirmed in the southern Panhandle and is likely to be in the northern Panhandle. Leaf rust is active in southeast Nebraska and is likely to increase as the weather warms up.

Photo - Lose smut in wheat

Figure 4. A wheat head with kernels replaced by loose smut in a grower's field in Phelps County on May 27.

 

In one of the fields surveyed May 27 in Phelps County, Fusarium head blight (scab) was found for the first time in Nebraska this year. Incidence was trace and severity ranged from a single bleached spikelet to several bleached spikelets (Figure 2) to entire bleached heads (Figure 3). Other diseases observed were loose smut (Figure 4) and barley yellow dwarf.

Continued warm weather should slow down stripe rust; however, the disease can still spread in irrigated fields and, if it rains, in dryland fields. Even if it does not rain and night temperatures are cool, the combination of dew and cool night temperatures will favor development and spread of the disease.

 

Producers should continue to scout their fields and be prepared to apply a fungicide to protect the flag leaf from stripe rust and other foliar diseases. If the crop is in the fully headed and/or early flowering growth stage, apply a fungicide that controls both stripe rust and scab. Fungicides effective on both stripe rust and scab are also effective on common fungal foliar diseases including leaf rust, tan spot, and Septoria tritici blotch. (See Wheat Disease Fungicide Efficacy Table.)

To Spray or Not to Spray?

For dryland wheat, base the decision to spray on the yield potential, weather forecast, and the presence of stripe rust in the field. If stripe rust is present even at trace levels, it can spread quickly under cool, wet conditions. It will be worth it to spray dryland wheat if

On this week's Market Journal the author reports on the current wheat disease situation. 

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  • the yield potential is 40 bu/ac or more
  • stripe rust is present in the field
  • weather favorable to stripe rust is forecast

For irrigated wheat, if stripe rust is present even at trace levels, it is advisable to spray.

Is Variety Resistance Enough?

This year a significant level of stripe rust has been observed on some varieties that have been known to have some level of resistance, including Jagger and Jagalene. This may be due to the fact that disease pressure has been unusually high and environmental conditions (cool and wet weather) have been very conducive to disease development. It also may be due to a new race/s of the stripe rust fungus.

Our recommendation is that even if you planted a variety listed as resistant to stripe rust, if conditions favor stripe rust development, consider spraying based on the above criteria.  (See Table 1 in the May 21 CropWatch article for a list of wheat varieties that are moderately or highly resistant to stripe rust.)

Also, note that varieties listed as resistant to stripe rust may be susceptible to other diseases such as tan spot, Septoria tritici blotch, and leaf rust.

Stephen Wegulo
Extension Plant Pathologist

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A field of corn.