• The Interaction and Effects of Soil Moisture Regime and Yellow Nutsedge (Cyperus esculentus) Density on Cotton (Gossypium hirsutum) Growth

      Moffett, Jody E.; McCloskey, William B.; Husman, Stephen H.; Dixon, Gary L.; Silvertooth, Jeff; Department of Plant Sciences, University of Arizona, Tucson, Arizona; Cooperative Extension, Maricopa County, Phoenix, Arizona (College of Agriculture, University of Arizona (Tucson, AZ), 1995-03)
      The goal of our research is to determine the effects of yellow nutsedge competition on cotton and to examine how the competitive relationship between these two species is modulated by soil moisture. In support of this goal, a competition experiment with various nutsedge densities and three irrigation regimes was conducted at the University of Arizona, Maricopa Agricultural Center. The results of this study indicate that increasing nutsedge density caused a significant linear decrease in cotton seed yield in both 1993 (p=0.03) and 1994 (p=0.002). The cotton yield reductions caused by the highest nutsedge densities, 33 and 50 tubers /m of crop row in 1993 and 1994, respectively, were 13.5 and 15.5 percent, respectively. Stem biomass, an indicator of total above ground biomass, increased significantly with increasing soil moisture. There was also a trend of increasing seed cotton yield with increasing soil moisture with the wet treatment (i.e., irrigation at 35 percent soil moisture depletion) resulting in the highest biomass and yields. In 1994 this trend was significant (p=0.0001) but in 1993 it was not (p=0.098) probably because fewer replications were used in 1993. An important goal of this research was to determine if cotton, with its deeper tap root type of root architecture, is more competitive against yellow nutsedge, which has a fibrous root system, when irrigation is less frequent. However, analysis of variance showed that there was no significant interaction between soil moisture availability and seed cotton yield reductions caused by nutsedge competition in either 1993 (p=0.44) or 1994 (p=0.62).
    • Practical Considerations of Precision Guidance and Weed Control in Cotton

      Thacker, Gary W.; Coates, Wayne E.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1995-03)
      This paper offers practical advice to growers interested in precision guidance technologies. Various types of guidance systems are described, along with their potential applications and benefits in a farming operation. Also discussed are some of the techniques which can be employed with precision guidance, including mechanical removal of weeds in the row, improved nutsedge control, and precision herbicide applications.
    • Precision Guidance Techniques to Reduce Weed Competition and Production Costs in Cotton

      Thacker, Gary W.; Coates, Wayne E.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1995-03)
      The objective of this project is to evaluate the benefits of precision guidance systems as a means of using tillage to kill weeds, and to confine herbicide applications to narrow bands. In cotton, a precision guided close cultivation with a directed spray of MSMA significantly reduced a purple nutsedge stand early on. However this reduction was not significant by the end of the season. For controlling woolly morningglory, the use of a precision guided cultivator equipped with in -row weeding devices resulted in much lower numbers of morningglory weeds, although the differences were not significant at the 95% confidence level. The guidance system kept the implement precisely aligned to the drill rows at a higher speed than was possible with the cooperator's non - precision cultivator. This higher productivity more than offsets the cost of the guidance system and the in-row weeding devices.