Update on Stripe Rust in Nebraska - UNL CropWatch, June 3, 2011

Update on Stripe Rust in Nebraska - UNL CropWatch, June 3, 2011

June 3, 2011

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Photo - Stripe rust in wheat
Figure 1. Low severity of stripe rust in a small focus in a grower’s field in Polk County on May 30.
Photo - Stripe rust in wheat
Figure 2. Moderate severity of stripe rust in the same field area referred to in Figure 1.

On May 30 a small area (less than 2 feet wide) of stripe rust was found in a wheat field in Polk County in southeast Nebraska. The field was at early flowering. Severity on affected leaves ranged from low (Figure 1) to about 35% (Figure 2).

Stripe rust has since been observed in south central Nebraska and in the Panhandle. On June 2, samples of stripe rust were submitted to the diagnostic clinic at the Panhandle Research and Extension Center in Scottsbluff. The samples were from an irrigated field in Scotts Bluff County. Incidence was estimated at 10-15% of the field, with occurrence in pockets throughout the field. Flag leaves sustained severity of 10-15% of the leaf surface covered with lesions and pustules.

Dry conditions in the southern states this year considerably slowed development of rust diseases. This is why we’re seeing a low level of stripe rust now despite having optimal conditions for the disease — cool temperatures and wet weather — since April. (Last year stripe rust started in mid to late April and rapidly developed into a widespread epidemic throughout the state.)

Stripe rust has been observed at low levels in Kansas since April. Rain storms that have occurred since mid-April likely blew stripe rust spores from Kansas and other southern states into Nebraska, where cool, wet conditions have favored its development.

For wheat fields that are flowering or past the flowering growth stage, the impact of stripe rust on yield is likely to be minimal. Producers should scout for stripe rust in these fields in case a fungicide spray is needed.

For younger wheat fields, it is recommended that producers scout for stripe rust. Recent wet weather and high winds are optimal conditions for rapid development and spread of stripe rust. If you see stripe rust in your field and the wheat is fully headed but not yet flowering or younger, be prepared to apply a fungicide listed for rust in the fungicide table. All of those listed have excellent efficacy against rust diseases.

If the wheat crop is at the early flowering stage, apply a fungicide that has good efficacy against Fusarium head blight or scab. Such a fungicide also will effectively control or provide protection against rust diseases. When applying any fungicide, be aware of the preharvest interval.

Stephen Wegulo, Extension Plant Pathologist, Lincoln.
Robert Harveson, Extension Plant Pathologist, Scottsbluff
Dewey Lienemann, Extension Educator, Webster County