Stripe rust in winter wheat in Ellis County, TX on January 29, 2015.

Dr. Clark Neely, Small Grains/Oilseeds Extension Specialist – College Station, TX

2-4-15

February is typically a time of year that wheat growers are more concerned with topdressing nitrogen and controlling weeds than controlling diseases; however, this topic has been on the minds of many growers in recent weeks. It is not uncommon to see small amounts of leaf rust in the fall, particularly on early planted wheat for grazing, however, rust presence generally declines throughout the winter months for most of the state as freezing temperatures will often subdue the disease. The exception being South Texas where rust consistently overwinters. Typically, it is this overwintering rust in South Texas that then migrate northward with warming temperatures during the spring.

In the past month there have numerous reports of both stripe rust and leaf rust throughout Texas and Louisiana. Limited information exists on the impact of early fungicide applications (growth stage Feekes 5-7) on winter wheat yield, but in most cases it is generally accepted as uneconomical and has little impact on yield. This is based on the premise that rust pressure is generally low in January through early March for most of the state and there is little disease to control. With the higher than average disease pressure present in fields, it may be prudent to apply an early fungicide application. A study conducted in Louisianna (Edward and Hunger, http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-5602/PSS-2138.pdf) showed a significant yield increase on winter wheat by applying an application of propiconazole followed by a second fungicide application after flag leaf emergence.

With high presence of rust around the state this early in the season, the stage will be set for high rust infection rates later in the spring if weather conditions are favorable. Wheat growers are encouraged to scout fields often to detect “hot spots” and spread of disease throughout the remainder of the growing season, particularly if they have planted leaf or stripe rust susceptible varieties. The most current resistance ratings for wheat varieties can be found in the 2014 Texas Wheat Variety Trial Results publication (http://varietytesting.tamu.edu/wheat/docs/2014/2014%20Final%20Wheat%20Pub.pdf). For proper disease identification refer to Texas A&M AgriLife Extension publication titled “Identifying Rust Diseases of Wheat and Barley” (http://amarillo.tamu.edu/files/2010/11/RustDiseasesTexas.pdf). Additional information on fungicides and diseases in wheat can be found at http://amarillo.tamu.edu/amarillo-center-programs/extension-plant-pathology/wheat-publications/