Corn (Zea mays L. ‘Pioneer 3732′) showed little to no injury following the postemergence-directed application of sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio) propyl]-3-hydroxy-2-cyclohexen-1-one} plus crop oil concentrate (COC) at 56 g/ha plus 1.25% (v/v) at nine locations across Midwestern U.S. in 1984 and 1985. Little corn injury also occurred for the postemergence-directed application of sethoxydim plus COC at 110 g/ha plus 1.25% (v/v) at most locations in both years. Considerable variation in tolerance was seen across locations for over-the-top applications of sethoxydim at all rates tested and for the directed application at 220 g/ha. Although corn at most locations showed no yield reduction with the over-the-top application of sethoxydim plus COC at 56 g/ha plus 1.25% (v/v), a 70% yield reduction occurred in one location in one year. For an over-the-top application of sethoxydim plus COC at 110 g/ha plus 1.25% (v/v), yields ranged from 3 to 95% of the untreated check in 1984, and from 3 to 88% in 1985. Stand reductions from an over-the-top application of sethoxydim plus COC at 220 g/ha plus 1.25% (v/v) ranged from 0 to 99%. A significant negative correlation was found between yield of corn treated over the top with sethoxydim and precipitation on the day of application and in the week following application. Air temperature on the day of application was positively correlated with corn injury from over-the-top and directed sethoxydim applications, but no correlation existed between percent relative humidity and corn injury. Open pan evaporation and solar radiation before and after application were not correlated with corn injury from sethoxydim.

Field persistence of imazaquin {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} applied preemergence as high as 16 times the 0.14 kg ai/ha recommended rate was studied at two locations in Arkansas in 1984 and 1985. Rapid dissipation of these high rates occurred on the Taloka silt loam under hot, dry field conditions in 1984 when no rainfall occurred for 2 weeks after application. In 1985, when furrow irrigation was applied 7 days after application, imazaquin phytotoxicity was greater and dissipation was delayed. Imazaquin persistence and soil adsorption were greater on Sharkey silty clay than on Taloka silt loam. Following 3- and 8-cm irrigation, 84 and 78%, respectively, of the 14C-labeled imazaquin remained in the surface 5 cm, but in plots covered between rainfalls and receiving 8 cm rain, 74% leached out of this top layer. Since nonincorporated imazaquin dissipated rapidly under hot, dry field conditions, carryover into the next growing season or leaching below the plow layer would not be expected. However, in cool, wet conditions immediately after application, the weakly adsorbed imazaquin molecule was readily bioavailable and mobile in the soil profile.

Herbicide dissipation was monitored in soils differing in herbicide use histories. Repeated annual applications over 5 yr enhanced biodegradation of butylate [S-ethyl bis(2-methylpropyl)carbamothioate] and EPTC (S-ethyl dipropylcarbamothioate) but not alachlor {2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide}, atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine], cyanazine {2-[[(4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl]amino]-2-methylpropanenitrile}, or metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide]. Prior application of butylate or EPTC enhanced biodegradation of the other thiocarbamate herbicide but not alachlor, atrazine, cyanazine, or metolachlor. Prior application of alachlor, atrazine, cyanazine, metolachlor, or trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] did not enhance biodegradation of butylate or EPTC. Dissipation of EPTC applied with dietholate (O,O-diethyl-O-phenolphosphorothioate) was not enhanced by prior application of alachlor, atrazine, or trifluralin. Prior use of EPTC, EPTC + dietholate, butylate, or cycloate, respectively, enhanced biodegradation of EPTC in 100, 100, 71, and 50% of the experiments, of EPTC applied with dietholate in 57, 100, 60, and 33% of the experiments, of butylate in 33, 40, 100, and 20% of the experiments, and of cycloate in 0, 0, 17, and 0% of the experiments. Prior thiocarbamate herbicide applications usually did not enhance cycloate biodegradation, but soils from two locations without prior pesticide use histories rapidly degraded the herbicide. Storage of soil samples at 25 C for 6 or 12 months before application of EPTC and EPTC + dietholate resulted in less herbicide degradation than storage at 15 C. Differences in prior environmental conditions such as temperature may explain why development of enhanced biodegradation varied between years even in the same field plots.

Twelve 20-ha stands of natural loblolly pine (Pinus taeda L.)-mixed hardwoods were harvested and site preparation treatments applied as follows: no site preparation (harvest only); glyphosate [N-(phosphomethyl)glycine] aerially applied at 0.25 kg ai/ha and the site burned 6 weeks later; roller-drum chopped, then burned; sheared and disced in one pass; sheared, then V bladed and disced; sheared, then raked; and sheared, raked, and then disced in three separate passes. Loblolly pine survival was 16% and volume 58% greater after the first two growing seasons on mechanically treated areas than on untreated stands or on areas treated with herbicide and then burned. Total vegetative cover was highest during both growing seasons on sites that had been sprayed and burned, and lowest on sites that were mechanically cleared and tilled. Grass and hardwood cover was negatively correlated with loblolly pine height and seedling volume during both growing seasons.

Research was conducted from 1979 through 1982 in east-central Alabama to determine the effect of various cropping and sicklepod (Cassia obtusifolia L. # CASOB) management systems on yields and total net returns to land and management. Intense weed management inputs resulted in higher levels of sicklepod control than did standard inputs with spring tillage, but sicklepod control was good regardless of management intensity with no spring tillage. Sicklepod control in soybean [Glycine max (L.) Merr.] – corn (Zea mays L.) rotations was similar to that in continuous soybeans regardless of planting method. Even though intense management inputs often resulted in increased sicklepod control, total net returns from these systems were often less due to increased herbicide and application costs. Total net returns from summer-fallow systems were generally low since only a winter wheat crop was produced each year.