Manipulation of crop architecture through the use of chemical bioregulators suggests the potential to improve plant water use and production efficiency. A bioregulator, mepiquat chloride (1,1‐dimethyl piperidinium chloride), was evaluated in field grown cotton (Gossypium hirsutum L.) during 1979, 1980, and 1981 to determine effects on several plant water relations parameters and crop development in a semiarid environment. All experiments were conducted on an Olton loam soil (fine, mixed, thermic family of Aridic Paleustolls). A broadcast, foliar application was made at the rate of 50 g active ingredient (a.i.)/ha during the early square (young floral bud) Stage. Increases in leaf water potential (Ψw), solute potential (Ψw), and turgor pressure (Ψp) in mepiquat chloride treated plants were recorded during midmorning and at daily minimum Ψw. The earliest Ψw increase wass measured 12 days after application. Changes in Ψw ranged from no significant differences to a 0.63 MPa increase in treated plants, 77 days after application under a high soil water level. Increased Ψs and Ψp in treated plants occurred most frequently during the midmorning period and increases Of 0.20 MPa were measured. Improvements in plant water status were not restricted to low soil water availability and occurred across a range of control Ψw from −1.43 to −3.43 MPa. Increased abaxial transpiration rate, associated with decreased diffusive resistance, was measured in treated plants, particularly during the afternoon. No difference in seasonal soil water extraction was measured between treatments, even in tests in which leaf area index (LAI) was reduced 33% by mepiquat chloride application. Leaf area index reductions were attributable to both fewer leaves per plant and reduced leaf size. Differences in the growth parameters between treated and untreated plants were most evident when conditions for growth were optimum. A maximum decrease in plant height of 25 cm was measured 43 days after application in a high soil water level experiment. Reductions of one to two mainstem nodes were measured in treated plants. The number of bolls per plant throughout the season was not altered by mepiquat chloride application, and there were no differences in lint yield as a result of treatment.

Metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] has considerable potential for yellow nutsedge (Cyperus esculentusL.) control in crops commonly produced in the Texas High Plains. Little information is available, however, concerning adsorption characteristics of metolachlor in soils of this region. Adsorption and movement of metolachlor were determined in three commonly occurring soils of the Texas High Plains. Organic carbon contents of the soils by weight varied from 0.3 to 0.5%, and the clay fraction ranged from 16 to 33%. Freundlich adsorption isotherms exhibited two linear regions for each soil, suggesting the possibility of multilayer adsorption. K′ocvalues and coefficients of determination for organic carbon and clay content vs. Freundlich K values indicated that organic matter was the predominant adsorbent for metolachlor in the soils studied. Desorption, soil column leaching, and thin-layer plate studies demonstrated metolachlor to be sufficiently mobile in scils low in organic matter to cause possible crop injury or loss of efficacy.

Field experiments conducted in 1991, 1992, and 1993 evaluated Palmer amaranth and devil's-claw control and cotton injury with pyrithiobac applied PPI, PRE, or POST. Pyrithiobac at 36 or 71 g ae/ha applied PPI, PRE, or POST did not injure cotton. Pyrithiobac at 140 g/ha applied PPI or PRE injured cotton 9 to 11% 6 wk after treatment. Cotton recovered and no injury was observed 12 wk after treatment. Pyrithiobac applied PPI and PRE at 71 g/ha controlled Palmer amaranth at least 97% 6 wk after treatment. Palmer amaranth control with pyrithiobac applied POST was more variable and influenced by environmental conditions. Palmer amaranth control with 71 g/ha of pyrithiobac exceeded that with 36 g/ha. Devil's-claw control with pyrithiobac was better with POST applications than PPI or PRE applications. Pyrithiobac applied POST at 140 g/ha controlled devil's-claw 83–97%. These studies indicate that pyrithiobac can effectively control Palmer amaranth and devil's-claw in cotton on the Texas Southern High Plains when applied at appropriate rates and timings.

Horseweed is a major weed in conservation tillage production systems. Herbicides were evaluated for horseweed control at two growth stages, rosette and 10- to 15-cm tall. Horseweed was controlled at the rosette stage with the 2,4-D ester, 2,4-D amine, dicamba, 2,4-D plus glyphosate, and glyphosate. Higher rates were needed for control at the 10- to 15-cm stage. Paraquat did not effectively control horseweed at any stage.

The Texas Southern High Plains is a major cotton (Gossypium hirsutum L.) producing region in which a conventional tillage cotton monoculture has evolved during the last 15 yr. Decreased profitability in cotton production in the region, as well as soil erosion concerns, have increased interest in conservation tillage systems. Initial adoption, acceptance, and widespread use of conservation tillage systems will depend on how their economic performance compares with current production practices. In this study, two conservation tillage systems for the Texas Southern High Plains (TSHP) were evaluated in 1986 and 1987 as a means of increasing profitability of cotton. Conservation tillage systems with and without a winter wheat (Triticum aestivum L.) cover crop were compared with conventional tillage for cotton under both irrigated and dryland conditions. The two conservation tillage systems either irrigated or dryland, increased profitability over current conventional tillage cotton practices used in the Texas Southern High Plains. Cotton production in conservation tillage systems is a viable alternative for the Texas Southern High Plains and its adoption could result in net revenue increases.