An experiment was conducted to evaluate the translocation pattern of 14C-glyphosate and 14C-quizalofop in five quackgrass biotypes at two stages of growth. Whole plant translocation differed between stages for each herbicide. The percentage of 14C-glyphosate and 14C-quizalofop in the leafwash and in the treated leaf did not differ among biotypes, but differences occurred for the translocation to the underground parts. The partitioning of the 14C-glyphosate and 14C-quizalofop in the treated crown, other crowns, propagating rhizomes, and other rhizomes differed among biotypes. On a disintegration per minute (DPM) mg-1 basis, differences among biotypes were found with 14C-glyphosate but much less with 14C-quizalofop. Metabolism of 14C-quizalofop in the treated leaf was similar in the two biotypes tested except for the percentage of polar metabolites 1 d after treatment. The percentage of 14C-quizalofop available for translocation was the same in both biotypes.

Interference between jimsonweed and soybean was investigated. Jimsonweed growing within the soybean row had little influence on vegetative characteristics of soybean during the first 12 wk of the growing season. The influence of an individual jimsonweed plant was first detected 10 wk after planting and extended 20 cm within the row. At harvest, interference extended 50 cm from individual jimsonweed plants, and yield within the 1.2 m of row surrounding a single jimsonweed plant was reduced 12%. Jimsonweed spaced 60 cm apart within the row reduced yield 18%. Soybean interference with jimsonweed growth increased steadily during the season, reducing the size of jimsonweed plants within the soybean row 80 to 93% compared with jimsonweed plants free of soybean interference. Jimsonweed grown within the soybean rows produced an average of 4900 seeds per plant whereas jimsonweed grown crop-free produced nearly 69 000 seeds per plant.

Control of Texas panicum and southern crabgrass with sethoxydim was reduced under field conditions when bentazon, acifluorfen, bentazon + acifluorfen, pyridate, or naptalam plus 2,4-DB was added. The addition of lactofen to sethoxydim did not result in antagonism. Complete control of annual grasses did not appear to be a necessity in order to improve peanut yields. Peanut yields in plots with 70 to 80% control of annual grasses were comparable to those where annual grass control was 99%.

Greenhouse and field experiments were conducted to identify alternative herbicide treatments for the control of a biotype of American black nightshade which has been shown to tolerate paraquat. In greenhouse experiments the combination of paraquat and the metal chelator diethyldithiocarbamate at either 1% w/v or 3% w/v, and diquat alone significantly lowered I50 values, based on dry weight, when compared with paraquat alone. None of these treatments provided acceptable control (>90%) in field experiments. Treatments that controlled American black nightshade under field conditions were: monocarbamide dihydrogensulfate at 9 kg ai ha-1, monocarbamide dihydrogensulfate at 9 kg ha-1 + paraquat at 0.6 kg ha-1, lactofen at 0.6 kg ha-1, oxyfluorfen at 0.6 kg ha-1, and acifluorfen at 0.6 kg ha-1. Addition of tridiphane at 1.7 kg ha-1 to paraquat at 0.6 kg ha-1 did not improve control of American black nightshade under field conditions.

Field trials were conducted from 1986 to 1988 at Clarkedale, AR, to evaluate selective POST grass herbicides for johnsongrass control in soybeans. Herbicide treatments were trifluralin PPI followed by single and sequential POST applications of fenoxaprop, fluazifop, quizalofop, or sethoxydim. In 1986, sequential applications of sethoxydim and fenoxaprop controlled more johnsongrass 4 WAT than single treatments. In 1987 and 1988, all herbicides except fenoxaprop controlled more than 79% of johnsongrass. The number of johnsongrass stems was reduced by cultural practices and herbicides after 2 yr. The lowest cost of control and the highest average net return over the 3-yr period was obtained with quizalofop.

Field research was conducted at Arlington, WI in 1984 and 1985 to determine the influence of application timing on weed control with atrazine and metolachlor in conservation tillage corn production systems. Early preplant treatments controlled fewer weeds than preemergence or early preplant/preemergence sequential treatments in a chisel plow system. Velvetleaf control was only 50% late in the growing season with early preplant atrazine compared with 88% with an early preplant/preemergence sequential treatment of the same amount of atrazine. In the no-till system, early preplant applications of atrazine and/or metolachlor had reduced weed control late in the growing season compared with preemergence and early preplant/preemergence sequential treatments of the same amount of herbicide. Giant foxtail control 110 d after corn planting was only 73% with an early preplant treatment compared with 99% when the same amount of herbicide was evenly divided between early preplant and preemergence applications.

Three seed lots each of two varieties of field corn were compared in greenhouse and field studies. Cold test germination percentages of the seed lots were as follows: 79, 85, and 93% for ‘DK656’; 77, 84, and 91% for ‘T1100’. Tank mixes of metolachlor or metolachlor with safener CGA-154281 plus atrazine or formulated metolachlor/atrazine with and without the safener were applied preemergence. Crop stand of either variety or among seed lots within a variety was not affected by herbicide treatments. In the greenhouse, fewer corn plants were injured and growth of plants was greater with herbicides with safener than herbicides without safener. Plant heights and weights at harvest from the most vigorous seed lot of DK656 were higher than those of the other two seed lots. Herbicide treatments with the safener did not cause significant injury to corn in the field. Yields of both varieties increased with herbicide treatments in one conventional planting. No significant differences in injury or yields occurred among seed lots within varieties.

Field studies were conducted to identify herbicides suitable for improved control of hairy nightshade, redroot pigweed, and common lambsquarters in pinto beans. Fomesafen at 0.25 kg ai ha-1 did not adequately control these weeds. Clomazone at 0.5 kg ai ha-1 controlled common lambsquarters but only suppressed the growth of redroot pigweed and hairy nightshade. Ethalfluralin at 0.84 to 1.1 kg ai ha-1 gave excellent initial control of these weeds but did not control later flushes of hairy nightshade. Imazethapyr applied PPI or POST at 50 to 75 g ai ha-1 controlled hairy nightshade, redroot pigweed, and common lambsquarters throughout the growing season. Imazethapyr combined with ethalfluralin gave superior weed control and resulted in greater yields than the most commonly used herbicides in pinto beans in western Canada.

Research was conducted to determine the role of uptake, distribution, and metabolism of quinclorac in differential sensitivity of southern crabgrass and Kentucky bluegrass. At 0.5 h, quinclorac uptake was 85% in southern crabgrass and 66% in bluegrass. Uptake and distribution differed between species. By 128 h, Kentucky bluegrass had uniformly distributed quinclorac and exuded 17% into the nutrient solution. Metabolism of quinclorac was limited to less than 3.6% of the applied 14C in the two species, at 128 h. Selectivity of quinclorac may be influenced by differences in uptake, distribution, and exudation by the roots but not by metabolism.

This study examined the response of corn to clomazone, chlorimuron, imazaquin, and imazethapyr the year following their application to soybeans. Herbicides were surface-applied from one-half to three times the labeled application rates. Soybeans were planted the year of application and crop tolerance was evaluated. Corn was planted in rotation the following season. Soybeans were tolerant of all four herbicides. The highest rates of clomazone, chlorimuron, and imazaquin injured the corn early in the season. Imazethapyr did not influence corn growth. Visual estimates of clomazone injury were as high as 39% chlorosis. Seedling dry weight reductions at the highest chlorimuron and imazaquin rates were 32% and 24%, respectively. Although corn was injured by higher rates of clomazone, imazaquin, and chlorimuron at the 3-leaf stage, none of the herbicides significantly reduced grain yield. This study suggests that these herbicides can carry over and injure corn, especially if labeled application rates are exceeded. However, low to moderate early season injury to corn may not affect grain yield.

Reduction of initial top growth of quackgrass with haloxyfop at 0.13 kg ai ha-1 and above in the greenhouse was comparable at the 2-, 4-, and 6-leaf stages. Quackgrass control was not affected by rhizome length in plants grown from 2-node and 10-node rhizome pieces. Removal of quackgrass shoots 6 h after treatment resulted in increased initial topgrowth, regrowth, and rhizome weight at all application rates when compared to treatments with no removal of shoots; however, growth decreased with increasing rates of haloxyfop. Later removal at 24 or 96 h after treatment did not affect quackgrass control, indicating rapid translocation. In field-grown potato, haloxyfop applied at 0.25 kg ha-1 at the 4- to 5-leaf stage controlled more than 80% of quackgrass. Lower rates controlled less than 80% when used alone; but adding cultivation improved control. No adverse effect on potato yield was noted with haloxyfop.

Field experiments were conducted to compare herbicides applied preplant incorporated (PPI), preplant incorporated/preemergence (PPI/PRE), and preplant incorporated/early postemergence (PPI/early POST) to control woolly cupgrass in corn. Although good early-season control of woolly cupgrass from PPI cycloate plus cyanazine, EPTC plus dietholate or SC-0058, and butylate plus cyanazine sometimes was observed, middle- and/or late-season control was often limited. Generally, better woolly cupgrass control and higher corn yields were obtained from split PPI/PRE applications rather than from single PPI applications of alachlor, metolachlor, and acetochlor. The highest and most consistent full-season woolly cupgrass control resulted when cycloate or EPTC plus dietholate applied PPI was followed by cyanazine plus either pendimethalin, alachlor, metolachlor, or acetochlor applied early POST. However, in 1989 adverse weather conditions near the early POST application timing injured corn and reduced yields.

Sweet corn was grown with a living mulch of white clover, a dead mulch of rye, and without mulch, in both till and no-till conditions. Unplanted controls were also included in the experimental design. Corn yields were highest in clover treatments early in the experiment but lowest in later years. The declining yields in the clover living mulch were related to the strip application of glyphosate which allowed establishment of perennial and biennial weeds, notably dandelion and horseweed. These overwintering weeds apparently prevented effective control of summer annuals, especially redroot pigweed, common lambsquarters and large crabgrass, by atrazine and metolachlor. Presence of a rye mulch decreased weed biomass and had no detrimental effect on corn yield. In general, corn yield was not affected by tillage, although the number of marketable ears was reduced in the no-till treatments during the drought year of 1988. The much greater weed biomass in the unplanted control treatments showed the importance of crop competition for weed control in sweet corn cropping systems.

Field experiments were conducted to compare efficacy of BAS 514, bromoxynil, fenoxaprop, sethoxydim, and triclopyr with standard herbicides for barnyardgrass and bearded sprangletop control in rice at four locations. Sequential applications of BAS 514 and fenoxaprop, or propanil and sethoxydim consistently controlled barnyardgrass and bearded sprangletop as well as or better than standard treatments of propanil, thiobencarb, or pendimethalin alone or combined; and rice so treated produced high yields. BAS 514 applied postemergence alone, BAS 514 applied sequentially with sethoxydim, or BAS 514 tank mixed with propanil controlled barnyardgrass but not bearded sprangletop. Bromoxynil or triclopyr tank mixed with fenoxaprop or sethoxydim antagonized activity on barnyardgrass and bearded sprangletop. Combinations of fenoxaprop with BAS 514 or propanil consistently provided barnyardgrass and bearded sprangletop control and high yields.

In the field, 14 soft red winter wheat cultivars responded differently to 1.1 kg ai ha–1 diclofop, 1.7 kg ai ha–1 BAY SMY 1500, and 0.42 kg ai ha–1 metribuzin applied POST. Diclofop and metribuzin did not injure any cultivar more than 10% on a silty clay soil. However, BAY SMY 1500 injured ‘Pioneer 2551’ and ‘Coker 983’ 39 and 21%, respectively, in March. All other cultivars were injured less than 10% by BAY SMY 1500. Early injury did not translate into yield loss in the cultivar tolerance study. In an application timing study for Italian ryegrass control, late-season ratings indicated better control with two-leaf applications than with PRE applications for all treatments. Delaying application to the three-tiller stage reduced control with BAY SMY 1500 or metribuzin, but not with diclofop. On the sandier soil at this location, wheat injury with 0.28 or 0.43 kg ha–1 metribuzin or 2.2 kg ha–1 BAY SMY 1500 was sufficient to reduce wheat yield compared with other treatments, despite good Italian ryegrass control.

Continuous corn was grown for 5 consecutive yr using conservation tillage methods in the Maryland Piedmont. Herbicide treatments were applied annually at common usage rates and were compared for their effects on weed cover, species stability, and grain production. Weed flora dominance shifted from giant foxtail the first year to smooth pigweed the following year. Smooth pigweed then dominated the flora for the duration of the study. Horsenettle was ubiquitous in all treatments but never became competitive. Canada thistle occurred in measurable densities in all plots that had not received atrazine applied preemergence. Grain yields were correlated negatively with densities of smooth pigweed in 1983 (r = −0.58, P = 0.01), and Canada thistle in 1983 and 1984 (r = −0.63 and −0.62, respectively; P = 0.05). Grain yields were correlated positively with midseason precipitation (r = 0.85, P = 0.01).

Kikuyugrass was analyzed for nitrate (expressed as KNO3) and soluble oxalate concentration after it was grown for 8 wk in nutrient solution supplemented with KCl, NaCl, or NH4NO3; fertilized in the greenhouse with urea and KNO3 at 112 kg N ha-1; and fertilized in the field in Hawaii and Panama with urea at 56 and 112 kg N ha-1. Both treated and untreated kikuyugrass grown in nutrient solution contained toxic levels of nitrates and soluble oxalates. Plants treated with urea in the greenhouse contained 0.4% nitrate (nontoxic) 72 h after treatment whereas those treated with KNO3 contained 2.36% nitrate (highly toxic). Fertilization of kikuyugrass with urea in Panama and Hawaii did not significantly affect soluble oxalate concentration, but nitrate concentration increased to potentially lethal levels (over 1.5% as KNO3, dry wt) in plants from Hawaii.

Selected sweet potato clones were evaluated in greenhouse and field trials to identify clones with superior tolerance to bentazon. ‘Julian’ and NC 1519 were the most tolerant in the greenhouse. ‘Sweet Red’ exhibited foliar injury in the field, but yields were not reduced. The clone 79-BM-17 was equally tolerant in the field as Sweet Red, but in the greenhouse exhibited only intermediate tolerance. ‘Jewel,’ a widely grown commercial cultivar, was sensitive to bentazon in both the greenhouse and field. When averaged over all clones sweet potato injury increased as bentazon rate was increased from 1.1 to 2.2 kg ai ha-1, but it decreased as the season progressed. Bentazon did not reduce marketable yields at Clayton, NC. Bentazon as a split or late application at the 2.2 kg ha-1 rate, reduced yields at Clinton, NC. Percent culls among bentazon treatments did not differ at either location.

Field studies were conducted to compare the short- and long-term control of hemp dogbane by POST applications of Dowco 433, clopyralid, and 2,4-D amine. Dowco 433 at 140 g ae ha–1 controlled 81 to 93% of weeds at 8 wk after treatment. Good control (79 to 89%) was also achieved with 560 g ae ha–1 2,4-D amine at 8 wk after treatment. Twelve months after treatment, control of hemp dogbane averaged 65 to 75% where Dowco 433 was applied at rates of 140 g ha–1 or higher. Similar results were obtained with 2,4-D amine at 560 g ha–1. Control with clopyralid was minimal. Weed height and dry weight were reduced with all treatments except clopyralid. The effect of early versus late application was also evaluated in two studies. In certain situations, control 8 wk after treatment was greater when application was made during the early reproductive growth stage as opposed to the vegetative growth stage.

The influences of pH, surfactants, and nutrients on germination were investigated to develop a basis for improvement of Alternaria cassiae mycoherbicide formulations. In vitro results indicated that a formulation with a pH of approximately 6.5 containing 0.1 to 1% Tween 80, 0.02 M potassium phosphate buffer, and 1% dehydrated potato dextrose broth best promoted germination. Sicklepod plants at the 2 to 3 true-leaf stage were sprayed with test solutions, incubated in the dark at 100% relative humidity (28 C) for 6 h, and placed in a growth chamber maintained at 30 C. Assessment of the plants after 2 d indicated that the ability of the formulation components to induce germination of Alternaria cassiae in vitro corresponded well with their ability to improve infection of sicklepod seedlings.