Think about stripe rust again!
Robert M. Harveson, Extension Plant Pathologist, Panhandle R&E Center, Scottsbluff, and Stephen Wegulo, Extension Plant Pathologist, University of Nebraska, Plant Pathology Dept., Lincoln
As spring approaches and wheat crops begin to merge from dormancy, wheat farmers in Nebraska need to begin scouting for stripe rust again. This is particularly true in fields where the rust was identified last fall. The purpose of this article is to provide a reminder of the disease and what to be looking for at this point.
What to look for
Stripe rust begins as small, yellow pustules that are aligned between and running parallel with leaf veins (Figure 1). You will not immediately see the long linear streaks (Figure 2) that are so characteristic of the disease in early infections. That occurs later as the small, individual pustules merge.
If stripe rust is detected, do not panic. A number of factors should be considered before making a management decision, including how widespread it is in the field, where on the plant it has progressed, and 10- to 14-day forecasted weather conditions (required temperatures of at least 50-60 degrees Fahrenheit). Irrigated fields are at a higher risk for stripe rust development due to the presence of more moisture.
1) If stripe rust was present in the fall, start scouting early in the spring to determine if it overwintered.
2) Scout fields regularly, starting in April. Look at both lower and upper leaves for yellow pustules.
3) Monitor the weather closely. If dry, warm weather is predicted, it is unlikely that stripe rust will develop to damaging levels in dry-land fields, and therefore there will be little or no benefit from applying a fungicide to control the disease.
4) Monitor reports from states south of Nebraska (Texas, Oklahoma, Kansas, Colorado).
5) If you see stripe rust on the lower leaves early in the spring, apply a fungicide preventively at early jointing (Feekes 5-6) followed by another spray at 50-100 percent flag leaf emergence to protect the flag leaf. If weather is dry after the early spray, it may not be necessary to apply the flag leaf spray.
TOP: Figure 1 – early stripe rust infection (small individual yellow pustules).
BOTTOM: Figure 2 – mature infection with large linear pustules parallel with leaf veins.