Wheat Cultivar Tolerance to Atrazine

Abstract

Winter wheat (Triticum aestivum L.) in the Texas High Plains often follows a crop or fallow period where atrazine was used for weed control. A study was conducted in 1991–1992 and repeated in 1993–1994 to determine if differences exist among commonly grown winter wheat cultivars in their tolerance to atrazine. Eighteen hard red winter wheat cultivars common to the region were planted on 13 Nov. 1991, and 26 Oct. 1993, in plots treated with 0, 0.25, 0.5, 0.75, and 1.0 lb a.i. /acre atrazine. Variation in atrazine tolerance was observed among cultivars and years, but cultivar differences in atrazine tolerance were identified. Cultivars that exhibited tolerance to atrazine were ‘Triumph’, ‘Scout’, ‘Siouxland 89’, ‘TAM 107’, and ‘Quantum 588A’. Most susceptible cultivars were ‘TAM 109’, ‘TAM 200’, ‘TAM 201’, and ‘TAM 202’. These data suggest cultivars are available to minimize yield loss for planting in fields where atrazine residues in soil are suspected. Alternatively, where atrazine is applied to wheat stubble after harvest, cultivars that are susceptible to atrazine could be planted to aid in control of volunteer wheat. Research Question Atrazine is commonly used to control weeds in sorghum, corn, and during fallow periods in the Texas High Plains. When wheat is planted in soil previously treated with atrazine, the potential for crop injury exists, especially in soils that have a high pH and low organic matter content. Little research has been done to determine if hard red winter wheat cultivars differ in their tolerance to atrazine under field conditions. The objectives of this study were to determine if commonly grown hard red winter wheat cultivars differ in their tolerance to atrazine and to develop a database for guidance to producers faced with atrazine residues in fields to be planted to wheat, or who desire to plant cultivars susceptible to atrazine. Literature Summary Studies have shown that wheat cultivars differ in tolerance to metribuzin and cyanazine under field conditions. Because of chemical similarities of atrazine to these herbicides, it seems likely that differences in cultivar tolerance to atrazine may exist. A greenhouse study in Arkansas revealed differences in wheat cultivar seedling response to atrazine. Study Description Field studies were conducted during 2-yr cycles near Bushland, TX during 1991–1992 and 1993–1994. Soil was a Pullman clay loam and is typical of the soils found in the southern Great Plains. Soil organic matter at the site was 1.2% and pH was 7.5. The experimental area had been neither cropped nor treated with herbicides during the previous 2 yr. In order to simulate residual carryover, atrazine was applied in strips (blocks) prior to wheat planting at 0, 0.25, 0.5, 0.75, and 1.0 lb a.i/acre. Eighteen hard red winter wheat cultivars (Table 1) common to the region were planted across the atrazine blocks in three replications in a split-plot arrangement. Differences in wheat cultivar tolerance to atrazine were determined by collecting data for percent stand and grain yield reduction. Applied Questions Do differences exist between winter wheat cultivars in their tolerance to atrazine? In both years tested there were clearly differences in wheat cultivar tolerance to atrazine. Which cultivars consistently showed the most tolerance and susceptibility to atrazine? Cultivars that exhibited tolerance to atrazine in both years were Triumph, Scout, Siouxland 89, followed by TAM 107 and Quantum 588A (Table 1). Most susceptible cultivars in both years were TAM 109, TAM 200, TAM 201, and TAM 202. Recommendation How can producers utilize wheat cultivar tolerance differences to atrazine? Producers who desire to plant wheat in fields that may contain atrazine residue can minimize atrazine injury by planting tolerant cultivars while avoiding those that are most susceptible. If a cropping system involves the use of atrazine after wheat harvest, it may be desirable to plant one of the susceptible TAM cultivars in order to improve control of volunteer wheat. Table 1. Quantitative summary of wheat cultivar tolerance to atrazine from studies conducted during the 1991–1992 and 1993–1994 growing seasons at Bushland, TX. Tolerant Intermediate Susceptible Siouxland 89 Karl TAM 202 Triumph Mesa TAM 200 Scout Thunderbird TAM 201 Quantum 588A 2158 TAM 109 TAM 107 Abilene Hawk Bronco 2157 Chisholm