Browsing by Subject "Weeds"
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Item Thermal dependence of pyrithiobac efficacy in Amaranthus palmeri(Texas Tech University, 1999-12) Light, Ginger G.Variability in weed control following pyrithiobac applications has been observed under field conditions. The influence of temperature on this variability was investigated. Results from field studies performed over two growing seasons identified plant and air temperatures at the time of herbicide treatment that correlated with differences in whole-plant efficacy (R^ = 0.90). Based on the field data, weed control with pyrithiobac was acceptable at application temperatures of 20 to 34° C. To investigate a potential source of thermal limitations on pyrithiobac efficacy, the thermal dependence of in vitro inhibition of acetolactate synthase (ALS), the site of action for pyrithiobac, was examined. A crude leaf extract of ALS was obtained from seedling Amaranthus palmeri. Relative inhibitor potency (I50) values were obtained at saturating substrate conditions for temperatures from 10 to 50° 0. Regression analysis of field activity against I50 values showed the two data sets to be highly correlated (F^ = 0.88). Historic air temperature data sets collected over eleven growing seasons were evaluated to assess the probability, duration, and frequency of the temperature range where acceptable weed control occurred. The recommended thermal range occurred during 59 to 93% of the daylight hours in a typical growing season. Conversely, up to 41% of pyrithiobac applications are potentially adversely affected by application temperature. Computer images of seasonal temperature data with a color oveday corresponding to the temperatures below, within, and above the recommended application temperature range were developed to provide a visualization of seasonal efficacy. The thermal dependence of enzyme/herbicide interactions may provide another means of understanding environmental factors limiting herbicidal efficacy and predicting herbicide inhibition at the whole-plant level.Item Weed management with the computer-based Herbicide Application Decision Support System (HADSS) program(Texas Tech University, 2001-05) Lyon, Leanna L.Field experiments were initiated in 1999 and continued in 2000 to evaluate the Cotton Herbicide Application Decision Support System (HADSS®) program in Texas Southern High Plains cotton production. Weed management systems in the irrigated experiment were evaluated in a natural infestation of Palmer amaranth (Amaranthus palmeri S. Wats) and devil's-claw [Proboscidea louisianica (Mill.) Thellung], while the dryland experiment had Palmer amaranth, devil's-claw, and silverieaf nightshade {Solanum elaeagnifolium Cav.). Weed management systems evaluated were: (1) a preplant incorporated (PPI herbicide followed by (fb) postemergence HADSS® recommendations (PPI fb POST HADSS®); (2) postemergence HADSS® recommendations alone (POST HADSS®); and (3) Texas Agricultural Experiment Station (TAES) recommendations for the Texas Southern High Plains. All weed management systems were evaluated in glyphosate [A/-(phosphonomethyl) lycine]-tolerant, bromoxynil 3,5-dibromo-4-hydroxybenzonitrile)-tolerant, and conventional cotton varieties and each system was compared to an untreated and weed-free check in each variety. Weed control was evaluated approximately two weeks after each treatment and at harvest and cotton lint yields and net returns over weed control costs were determined for each weed management system.