Managing a New Race of Stripe Rust in Texas.

Stripe rust, caused by Puccinia striiformis is a major yield-limiting factor in wheat (Triticum aestivum L.) production areas throughout the United States.  Within the United States, stripe rust commonly begins in Texas and moves north as the crop develops.  In 2010, varieties that had previously been resistant to stripe rust began to show a susceptible reaction.  Only three hard red winter wheat varieties grown in Texas remain that are resistant to the new race of stripe rust, including Fannin, Doans and TAM 111.  Varieties that had previously been resistant, such as Jagger and Jagalene, now exhibit a susceptible reaction.  For this reason, chemical management along with varietal resistance are necessary to properly manage stripe rust.  To examine the interaction between host resistance and stripe rust management using fungicides, 4 varieties were evaluated for their reaction along with multiple fungicide timings.  The four varieties included, TAM 111, TAM 112, TAM 304 and Fannin.  Multiple fungicide timings included an untreated control and single and multiple fungicide applications beginning at flag leaf emergence and continuing until the head is fully emerged.  Each fungicide application consisted of 10.5 oz/a Quilt^® (a.i. Azoxystrolin and Propiconazole) with a 0.25% v/v of a nonionic surfactant (Dyneamic^®).  Severity ratings were recorded on weekly intervals following the first application.  Yield on all treatments was also recorded an analyzed.  Ratings and yield data indicate that varietal resistance in Fannin was enough to manage the new race of stripe rust.  However, susceptible varieties such as TAM 112 required at least one fungicide application to manage the disease.  Multiple applications were significantly more effective than a single application on a susceptible variety.  Yield results and the economics of stripe rust management will be discussed.