Stripe Rust of Cereal Grains

In the past decade, a massive resurgence of Stripe Rust (Puccinia striiformis) has been observed
in Northwest grain crops.  In severely infected fields, yield losses of over 50% are not uncommon.  There has been much speculation on the cause of these recent outbreaks of Stripe Rust. For a Stripe Rust infection to occur, there must be a favorable environment, the right pathogen races and a susceptible grain variety.

What is a favorable environment for stripe rust?  If outbreaks of rust occurred in the past year, conditions will definitely be more conducive to infection this year.  Early fall seeded small grains are
susceptible to the rust spores from previous crops.  Fall rains and warm weather allow the rust to spread in the fall.  Stripe rust infection can happen in temperatures ranging from 40 degrees Fahrenheit to 80 degrees Fahrenheit.  Free moisture is also necessary for stripe rust.

Stripe Rust has undergone a transformation this past decade.  There has been a new set of Stripe Rust races that have moved around the world in the past few years.  This rust is able to attack a different spectrum of wheat varieties, and it seems to be more aggressive than past races.  These races are able to withstand higher temperatures, overwinter better and seem to have worsened in 2010-2014.

In the past, we have relied heavily on high temperature adult plant resistance (HTAP) of cereal grains to control Stripe Rust.  Lately, this has not been sufficient protection against rust in some cases. Significant yield loss may occur from early infection while waiting for higher temperatures to control rust.

The good news is that Stripe Rust can be managed very effectively with fungicide applications.  Frequent scouting and timed fungicide applications are very effective at controlling Stripe Rust. Most of the university recommendations are to wait for at least 10% infection before spraying.  This is problematic because the disease may lay latent in a plant for 7-21 days before symptoms appear.  At 10% symptom
expression, there may actually be a 50-60% infection by the time an application is made.  This can drag yield down to unacceptable levels.

The two best windows for fungicide application are broadleaf herbicide timing and at flag leaf emergence on wheat.  Herbicide timed applications will generally provide effective control for 10-21 days. Grain flag leaf fungicide applications are critical for yield optimization.  Over 50% of grain fill is directly correlated with flag leaf health.

For effective control of Strip Rust and other cereal crop diseases, Helena offers Avaris and newly introduced Avaris 2XS. Please contact your Helena sales representative to discuss these products if you are concerned about cereal disease management.

- Casey Hughes, Northwest Division Agronomist