Weed management systems using a chloroacetamide herbicide applied preplant incorporated (PPI) and at cracking (AC) plus lactofen applied AC and early postemergence (POST) controlled at least 98% of common lambsquarters. Similar systems using a chloroacetamide herbicide applied PPI and early POST plus lactofen applied early POST and postemergence (POST) controlled less than 70% of common lambsquarters. All sequential lactofen systems controlled common ragweed completely and at least 86% of morningglory species. Highest peanut yields and net returns were obtained with weed management systems consisting of sequential applications of lactofen applied AC and early POST, or systems that used acifluorfen plus bentazon POST, or lactofen plus bentazon applied early POST or POST.

An established alfalfa stand infested with quackgrass received fluazifop-P, haloxyfop, or quizalofop at single applications of 0.28 ae kg ha-1 and sequential applications of 0.14 plus 0.14 ae kg ha-1 with the second treatment being made 16 d after the first. All herbicide treatments increased diffusive resistance and decreased transpiration of quackgrass compared to control plants. These effects became apparent 16 d or more after spraying. Visual injury symptoms were noted 8 to 10 d after treatment, several days prior to changes in diffusive resistance or transpiration. The alfalfa content of the first cutting was increased from herbicide treatment; however, total forage yield was reduced. Yields and composition of later cuttings were unaffected by the various herbicide treatments.

Greenhouse experiments were conducted to determine the statistical precision of estimating herbicide dose-response treatment effects by covariance analysis (ANOCOVA) relative to standard analysis of variance (ANOVA). Analyses of corn seedling response to the translocated herbicides fluazifop-P, sethoxydim, and quizalofop at 10 to 60 g ai ha-1 indicated that treatment effects were estimated with 26 to 116% greater precision by ANOCOVA than ANOVA. Covariance analyses of treatment effects for corn response to the contact herbicides paraquat, acifluorfen, and lactofen at 50 to 300 g ai ha-1 gave 8 to 13% greater precision than ANOVA. Gains in precision by ANOCOVA for all experiments were generally greatest when shoot dry weight was analyzed as the response variable and pretreatment fifth leaf length served as the covariate.

Hemp sesbania interference in cotton was investigated in the greenhouse and in a 2-yr field experiment at Stoneville, MS. In greenhouse experiments, cotton and hemp sesbania heights and plant dry weights (PDW) were not different in ratios of cotton to hemp sesbania of 4:0, 2:2, 1:3, and 0:4 at 3 and 5 wk after emergence (WAE). Hemp sesbania PDW were less for ratios of cotton to hemp sesbania of 3:1 when compared to hemp sesbania PDW of other ratios. Early season cotton seedling vigor and growth (0 to 28 DAP) were not affected by 32 000 hemp sesbania plants ha-1 (3 plants m of row-1). Hemp sesbania plants were hand removed 28, 42, 56, 70, and 84 d after planting (DAP). White cotton blooms and yields were reduced when hemp sesbania plants were not removed by 70 DAP. Seed cotton yields were 2590, 2570, 2460, 2030, 1610, and 1070 kg ha-1 for hemp sesbania removed at 28, 42, 46, 70 and 84 DAP or not removed, respectively. The critical period of weed control or removal of hemp sesbania in cotton is ≤62 DAP.

In five field experiments from 1986 to 1988, herbicides were evaluated alone and in combinations for weed control in water-seeded rice. Combinations of bensulfuron with either molinate or thiobencarb applied into the paddy water at the 2-leaf stage of rice, controlled all broadleaf and sedge weeds, and 92% or more early watergrass. These combinations were equivalent to a commercial standard of molinate at the 2-leaf stage followed by a separate application of bentazon to the drained paddy at midtillering.

Bulbous oatgrass, a weed in parts of the United States and Europe, is an unusual grass, which forms corms at the stem base. Growth and development of this creeping perennial grass was investigated in the field and in pots outdoors. Under the mild climate of the Willamette Valley, Oregon, shoots emerged in early autumn. Plants grew vegetatively and formed corms during the winter and spring. Aboveground portions of the plant stopped growing and senesced in the summer. The absolute growth rate of the plants was highest in early May, shortly before the onset of flowering. In early May, the growth rate of corms was higher than that of the shoot.

Outdoor experiments were conducted at two locations in Minnesota to characterize the growth, development, and vegetative reproduction potential of giant burreed grown with and without wild rice. Giant burreed growth was influenced by environment more than the presence of wild rice. Shoots emerged from corms 2 to 3 wk after planting (WAP), and continued throughout the growing season. Giant burreed attained a maximum height of 135 cm with an average 36 shoots/plant. Rhizome production started 4 to 6 WAP, and continued throughout the growing season. Corm formation at the base of shoots started 8 WAP and continued throughout the growing season. Rhizomes grew to a maximum cumulative length of 2500 cm/plant spreading in all directions and produced up to 250 buds/plant. Corm and rhizome bud viability was 15 and 10%, respectively. These data suggest that giant burreed grown in wild rice should be controlled by 2 to 3 wk after emergence to prevent vegetative reproduction.

Field experiments were conducted to determine wheat injury following clomazone application in soybeans and fallow in North Dakota. Clomazone at recommended rates generally caused 10% or less visible chlorosis in spring wheat planted 11 to 12 mo after application or winter wheat planted 11 mo after application, although greater chlorosis was observed in two of seven location/year environments. Tillage preceding wheat planting increased chlorosis from clomazone residues in some environments. Clomazone residues reduced wheat grain yield only in three of seven location/year environments and usually at application rates of 1.4 kg ai ha-1 or greater. Severe drought prevailed during the study and probably increased clomazone persistence and wheat chlorosis. Drought also may have limited expression of grain yield reductions attributable to clomazone residues.

Field studies were conducted in 1984 and 1986 to identify herbicides that would control woolly croton and bitter sneezeweed on grazing land in the Blackland prairies of Texas. Herbicides included chlorsulfuron, clopyralid, dalapon, dicamba, 2,4-D, glyphosate, metsulfuron, picloram, tebuthiuron, 2,4,5-T, and triclopyr. Chlorsulfuron and metsulfuron applied at 0.018 kg ha-1 and 2,4-D, picloram, 2,4,5-T, and triclopyr at 0.28 kg ha-1 controlled >80% of the woolly croton. Metsulfuron controlled more than 90% of the bitter sneezeweed at 0.018 kg ha-1. Similar control was obtained with clopyralid, glyphosate, and picloram each at 0.28 kg ha-1. Bermudagrass cover increased with all herbicide treatments except dalapon at one of three sites.

Experiments were conducted for two years at one location and one year at a second location to determine the effects of paraquat on a range of peanut genotypes. Paraquat caused yield reductions of most Valencia-, Spanish-, and runner-market types as compared with hand-weeded checks. Virginia-market types were less affected by paraquat treatment. Most grade characteristics were adversely affected by paraquat. Because the paraquat treatments increased the proportion of other kernels, the herbicide may be affecting yield and grade by delaying maturity.

Research was conducted on a sandy clay loam in Georgia during 1987–88 and 1988–89 to determine winter wheat, oats, barley, and Italian ryegrass tolerance to flurtamone. Flurtamone was applied PPI, PRE, and early POST at 0.28, 0.56, and 1.1 kg ai ha-1. Order of tolerance of the four species was barley > wheat > oat > Italian ryegrass. Flurtamone potentially can be used to control Italian ryegrass in winter wheat and barley, but not in oats. In general, wheat and oat injury with flurtamone was PPI > PRE ≥ early POST, particularly at 1.1 kg ha-1.

Newly seeded alfalfa tolerated glyphosate applied from the 8-trifoliolate leaf stage (17 cm tall) to the pre-bud stage (34 cm tall) at 75 or 150 g ae ha-1. Injury symptoms were moderate and temporary. Glyphosate at 300 g ha-1 suppressed alfalfa severely and killed 30% of the plants when applied at the smallest (3-trifoliolate) stage of alfalfa growth. Alfalfa responded similarly to glyphosate and SC-0224.

A heavy, uncontrolled infestation of field dodder and largeseed dodder suppressed newly seeded alfalfa severely and killed many of the plants. Glyphosate at 75 or 150 g ae ha-1, sprayed over the top of the dodder-infested alfalfa, stopped the growth of dodder and did not injure alfalfa significantly. Treated dodder began to grow normally again 2 to 3 wk after treatment. This regrowth injured the alfalfa severely in spite of earlier control. Glyphosate at 75 or 150 g ha-1 applied two or three times controlled dodder effectively and protected the alfalfa. A rate of 40 g ha-1 was not effective.

Alachlor at 3.4 and 6.7 kg ha-1, metolachlor at 2.8 and 5.6 kg ha-1, and propachlor at 4.5 and 9.0 kg ha-1 were applied to grain sorghum in field experiments conducted in 1981 and 1982. ‘Dekalb E-59’ and ‘Pioneer 8311’ grain sorghum were tested with and without the seed protectants cyometrinil and flurazole in both experiments. ‘Funk's G-1350’ was tested with and without cyometrinil and CGA-92194 in one experiment. Alachlor and metolachlor caused serious injury (stunting and, in some instances, reductions in stand and yield) to grain sorghum without the seed protectants. Less severe injury to grain sorghum occurred with alachlor and metolachlor at high rates even in the presence of the seed protectants. The three seed protectants were equally effective in preventing crop injury. Only minor injury to grain sorghum, with or without the seed protectants, occurred with propachlor at both rates. Overall, early-season weed control was 81 to 100%; however, propachlor at the rates tested was noticeably weaker than alachlor and metolachlor against some annual grasses.

The effect of irrigation and weed control by various mechanical and chemical means was evaluated over a 4-yr period on newly planted pecans [Carya illinoensis (Wang.) K. Koch]. Weed control effect on tree growth became evident in the second growing season, and became more pronounced after the third and fourth season. After the fourth season, the maximum increase in tree diameter (384%) was achieved with comprehensive, herbicide-based weed control. Mowing provided a 224% increase, which was equivalent to the untreated (229%). Disking and selective chemical control of grass weeds resulted in 339 and 292% increase, respectively. Cumulative increase in tree diameter was 316 and 271% with and without irrigation, respectively.

Imazethapyr, glyphosate-isopropylamine salt, and glyphosate-sodium sesqui salt plus 2,4-D injured bahiagrass severely for 4 to 6 wk after treatment (WAT) but effectively controlled seedheads for 10 WAT without permanently reducing turf density. Imazethapyr applied twice at 0.08 kg ha-1 suppressed vegetative growth of mowed bahiagrass by 5 WAT while unmowed turf was suppressed 62% by 6 WAT. Glyphosate-isopropylamine salt suppressed vegetative growth by 3 WAT, but did not consistently suppress unmowed bahiagrass. Bahiagrass treated with glyphosate-sodium sesqui salt injured bahiagrass more than glyphosate-isopropylamine salt when each was applied at the same rate. CGA 163935 suppressed bahiagrass seedheads for 8 WAT and vegetative growth from 2 to 4 WAT. The activity of mefluidide, MON 4620 plus paclobutrazol, paclobutrazol plus mefluidide, and flurprimidol plus mefluidide was minimal on bahiagrass.

Field experiments were conducted to evaluate the influence of application timing of imazethapyr and fluazifop-P on rhizome johnsongrass and pitted morningglory control in soybean. Herbicides were applied at three timings keyed to johnsongrass heights of 15, 30, and 60 cm and 3-, 6-, and 9-leaf pitted morningglory. Evaluations 6 wk after the final treatment indicated imazethapyr controlled both species best when applied at the 15-cm johnsongrass growth stage. Increasing imazethapyr rate did not increase control of pitted morningglory, but did increase johnsongrass control at the 15-cm application timing. However, at the 30-cm johnsongrass application timing, increasing the rate from 0.07 to 0.10 kg ha-1 improved control of both species. Johnsongrass control with imazethapyr was no more than 64% when applications were delayed to 30-cm or larger johnsongrass. Fluazifop-P controlled johnsongrass well at all timings.

Greenhouse studies were conducted to determine the effects of herbicide, herbicide rate, genetic variability, and soil moisture content on the tolerance of corn seedlings to two chloroacetanilide herbicides. Alachlor and metolachlor were applied preemergence at 2.2, 3.4, 4.5, and 6.7 kg ha-1 to 10 Great Lakes corn hybrids. Metolachlor appeared to be less injurious at the low rate and more injurious at the high rate than alachlor. Injury among the 10 hybrids tested varied significantly. Some of the hybrids appeared to tolerate alachlor more, while others tolerated metolachlor more indicating that even in a limited number of hybrids there was a spectrum of response. Six levels ranging from 8% to 22% soil moisture were evaluated for their effect on alachlor and metolachlor injury to corn seedlings. The herbicide injury ranged from no injury at the lowest soil moisture level to about 70% at the highest soil moisture level with 4.5 kg ha-1 application rate of alachlor or metolachlor.

Greenhouse experiments were conducted in 1989 at Stoneville, MS to evaluate the efficacy of fluridone and MSMA applied at 0.3 and 1.0 kg ai ha-1, respectively, either alone or in combination and with or without 0.1 M ammonium sulfate on purple nutsedge. The herbicides were applied at 19 L ha-1 in an oil-water, invert emulsion (low-volume) and at 187 L ha-1 in water with a nonionic surfactant (0.25% v/v) (high-volume). Purple nutsedge control with both herbicides alone or in combination was greater with the low-volume than with the high-volume application. Addition of MSMA to fluridone, or of ammonium sulfate to fluridone plus MSMA did not enhance purple nutsedge control over fluridone alone applied in low volume. The addition of ammonium sulfate to fluridone alone applied in low volume reduced purple nutsedge control.

Water samples from eight locations, ranging in pH from 7.1 to 8.5, were tested to determine the effect of carbon dioxide (CO2) pressurization on pH. After pressurization with CO2 the pH of the water decreased 1.8 to 4.1 pH units. An increase of 0.4 to 1.2 pH units occurred after the CO2 pressurized water exited a spray nozzle. The use of N2 or air as a pressurizing gas had very little effect on pH. The addition of diammonium phosphate, urea-ammonium nitrate (UAN)3, or ammonium sulfate had only minor effects on water pH. The addition of monoammonium phosphate reduced water pH to 4.6 to 5.5. The physical/chemical properties and activity of a herbicide may be altered with the change in spray solution pH by using CO2 to pressurize the spray solution.