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

May 31, 2011

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

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. (Do not apply a fungicide if the wheat crop is past the stage when 50% of the heads on the main tillers are flowering.)

Dry conditions in the southern states this year considerably slowed development of rust diseases. This is the reason for the low level of stripe rust at this time (end of May) in the growing season. (Last year stripe rust started in mid to late April.)

For younger wheat fields, it is recommended that producers scout their fields 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 flowering yet) or younger, be prepared to apply any of the fungicides in the fungicide table that has 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 will also effectively control or provide protection against rust diseases. When applying any fungicide, beware of the pre-harvest interval.

Stephen Wegulo
Extension Plant Pathologist, Lincoln