Texas Root Rot in Alfalfa-University of Arizona Research.

Texas root rot Mostafa Alfalfa Specialist with University of Arizona is conducting field trials on another threat to Arizona alfalfa growers in the low desert – Texas root rot (TRR). This pathogen, caused by the fungus Phymatotrichopsis omnivore, is more commonly known for its impact in cotton and alfalfa fields in the Southwest where it attacks plant roots including the tap root, leading to wilted leaves and plant death since diseased plants cannot uptake adequate amounts of water. Following initial TRR trials conducted by Texas A&M researchers, a UA team including retired plant pathology specialist Mary Olsen, statewide cotton specialist Randy Norton, and Mostafa conducted numerous TRR trials in cotton with the herbicide active ingredient Flutriafol (Topguard) by FMC since 2012 with good success. A Section 18 Emergency Exemption was granted for Topguard use in cotton for use in 2013, followed by a full label for the same crop in 2014. Efforts to enhance the method and timing of applications continue under the expertise of Norton and UA’s Mark Siemens. Mostafa is testing Flutriafol for TRR control in alfalfa, now in his second year of on-farm trials. So far, the early findings suggest Flutriafol is effective. TRR thrives in areas with high soil pH, low organic matter (most of Arizona) and old mesquite tree areas reclaimed for commercial agriculture. Mostafa estimates about 20 percent of all alfalfa acreage in the state have TRR, perhaps more acreage than Arizona cotton. “Once a field has Texas root rot it ruins it for alfalfa production,” Mostafa said. The only other crops which can be grown in infected ground are several grains and grasses.” In the field trial this year near Arlington (Maricopa County), Mostafa has applied the new label Topguard Terra over the top at three different application rates – two ounces, four ounces, and eight ounces. “From the 2015 results and those obtained so far in 2016, there are significantly higher yields using Flutriafol Terra at all the rates compared to the untreated check,” Mostafa said. It’s free – Western Farm Press Daily – agricultural news delivered to your Inbox. Mostafa says discussions are underway with FMC for the farm chemical company to apply for a one-year Section 18 Emergency Exemption for Topguard Terra use in alfalfa, in part with Mostafa’s alfalfa field trial findings to support it. “If we can get a label for alfalfa, Topguard Terra could be a good option for growers to increase yields despite the disease, and possibly bring abandoned fields back into production.” Mostafa plans to conduct trials next year again in Arlington, plus in Parker (La Paz County) and the Gila Bend area (Maricopa County).