Fluometuron adsorption and degradation were determined in soil collected at three depths from no-till + no cover, conventional-till + no cover, no-till + vetch cover, and conventional-till + vetch cover in continuous cotton. These combinations of tillage + cover crop + soil depth imparted a range of organic matter and pH to the soil. Soil organic matter and pH ranged from 0.9 to 2.5% and from 4.7 to 6.5, respectively. Fluometuron adsorption was affected by soil depth, tillage, and cover crop. In surface soils (0 to 4 cm), fluometuron adsorption was greater in no-till + vetch plots than in conventional-tilled + no cover plots. Soil adsorption of fluometuron was positively correlated with organic matter content and cation exchange capacity. Fluometuron degradation was not affected by adsorption, and degradation empirically fit a first-order model. Soil organic matter content had no apparent effect on fluometuron degradation rate. Fluometuron degradation was more rapid at soil pH > 6 than at pH ≤ 5, indicating a potential shift in microbial activity or population due to lower soil pH. Fluometuron half-life ranged from 49 to 90 d. These data indicate that tillage and cover crop may affect soil dissipation of fluometuron by altering soil physical and chemical properties that affect fluometuron degrading microorganisms or bioavailability.

Growth chamber research was conducted to compare the persistence of chlorimuron or imazaquin in soils from 11 locations in the southern United States at 25 C. Chlorimuron at 30 ng g-1 or imazaquin at 60 ng g-1 of soil was incorporated throughout each soil, and soils were watered to the water holding capacity and incubated in the dark. Soil samples were taken 0, 7, 14, 28, 60, and 90 d after treatment. Amount of chlorimuron or imazaquin remaining in each soil was quantified by sicklepod or corn root length bioassay, respectively. First order regression generally fit the concentration data for each herbicide. Bioactivity and persistence of chlorimuron in the soils was related primarily to soil organic matter content. Bioactivity and persistence of imazaquin was similar among the soils.

Greenhouse experiments were conducted to determine if the inheritance of bentazon susceptibility in the corn inbred ‘GA209’ is a recessive single gene trait Bentazon was applied at 4.4 kg ai ha-1 plus 1% by vol crop oil concentrate in all experiments. This treatment caused 96 and 30% visual injury and 86 and 50% dry weight loss for corn inbreds GA209 and ‘Ky226,’ respectively. Corn inbreds ‘B73,’ ‘T61,’ Mo17,’ ‘Pa91,’ and ‘CI66’ showed less than 18% injury and 10% dry weight loss and were considered tolerant of bentazon. Single crosses and reciprocal single crosses of GA209 with the other inbreds were considered bentazon tolerant with approximately 10% stunting and tissue necrosis and 20% dry weight reduction resulting from bentazon. Bentazon susceptibility was not maternally inherited. Apparent single recessive gene control of bentazon susceptibility of GA209 was observed for F2 and backcross segregations. However, subsequent analyses of F3 and selfed-backcross populations indicated that two genes, probably located on the same chromosome, controlled the bentazon susceptibility. Duplicate dominant epistasis provided the best fit for injury and dry weight reduction segregations in populations derived from the cross of inbreds GA209 and B73.

Geostatistical methods were used to describe and map nonrandom distribution and variation (standard deviation) of shoot density and root growth across a well-established patch of Canada thistle, a perennial weed. Semivariogram functions and kriging, an interpolation method, were used to prepare isoarithmic contour maps and associated error maps. Maps consisted of interpolated contours of uniform weed density and other measured or calculated regionalized variables between measured X-Y control points, as well as maps of error (standard deviation) associated with contour estimation. Mapped regions of greatest shoot density across a patch not only had the greatest underlying root biomass and, often, greatest density of adventitious root buds, but also had more deeply growing root biomass.

Greenhouse and laboratory experiments were conducted to evaluate the influence of two organosilicone surfactants and spray nozzle types on the spray deposition, absorption, translocation, and efficacy of the monoethanolamine salt of clopyralid on honey mesquite. Sylgard 309 or Silwet L-77 added to the spray solution at 0.1, 025 and 0.5% by vol did not increase spray deposition, absorption, translocation, or phytotoxicity of clopyralid applied at 140 g ae ha-1 on honey mesquite compared to no surfactant An air-assist spray nozzle at 9.4 L ha-1 by vol resulted in greater initial clopyralid deposit on honey mesquite than hydraulic nozzles at 9.4 or 187 L ha-1 by vol, but air-assist application did not increase phytotoxicity compared to hydraulic nozzles.

Waterhyacinths grown outdoors were treated with combinations of 0 or 22 kg ai ha-1 of the plant growth retardant paclobutrazol and 0, 25, or 250 waterhyacinth weevils per culture tank under conditions of low (25% coverage) or high (100% coverage) plant densities. The low plant density treatments simulated a regrowth or colonization situation. Weevil feeding activity, canopy height, plant volume, leaf production, and leaf mortality were monitored biweekly for 22 weeks or until all plants had died. In high plant densities, weevil infestations increased leaf mortality rates while decreasing production rates, causing eventual plant death. At low plant densities, waterhyacinth plants partially compensated for weevil feeding by increased leaf production rates, thus enabling them to survive until the end of the study. Paclobutrazol reduced canopy height for about 3 months but had little effect on weevil feeding intensities. Combinations of weevils and paclobutrazol gave complete control of waterhyacinths regardless of plant densities. The combined effects were synergistic, with accelerated leaf mortality rates exceeding production rates leading to early plant death. This study demonstrated the potential for increasing effectiveness of waterhyacinth weevils using integrated strategies.