Postemergence herbicides alone and in combination were evaluated for Venice mallow control in corn and onion in Colorado during 1986 and 1987. Season-long control of 88 to 98% in corn was obtained with bromoxynil plus cyanazine or atrazine; 2,4-D amine plus dicamba or bromoxynil; or linuron, bromoxynil, or dicamba applied alone. Oxyfluorfen plus bromoxynil in a split application controlled Venice mallow 80 to 99% all season in onions. Uncontrolled Venice mallow caused higher yield reductions in onions than in corn.

Field experiments were conducted in 1983 and 1984 at two locations to determine the influence of various densities and durations of kochia interference in sunflower. Sunflower achene yield and dry weight were reduced by all densities of kochia, averaged over locations and years. Season-long competition by kochia densities of 0.3, 1, 3, and 6 plants/m of row decreased sunflower achene yield 7, 10, 20, and 27%, respectively. Sunflower achene yield and sunflower dry weight decreased as weeks of kochia competition increased. Only 2 weeks of kochia competition after sunflower emergence decreased sunflower achene yield 6%. Sunflower achene yield loss increased as the duration of kochia competition increased. Sunflower 200 achene weight, oil content, and plant height were not influenced by various densities or durations of kochia competition.

Growth room and field studies were conducted to determine if increasing use of forage aeschynomene may lead to new weed problems in rice and soybeans and to identify possible control measures in these crops. In a growth room study, flooding of ‘Florida Common’ and ‘LSU 1147’ forage aeschynomene did not reduce yield. However, forage aeschynomene seedlings did not emerge from a flooded seedbed, and 1-week-old seedlings were killed by 2.5 or 7.5 cm of flooding. Competition from interseeded forage aeschynomene reduced ‘Centennial’ soybean yields by 81%. Acifluorfen, fomesafen, and lactofen, labeled for soybeans, control forage aeschynomene. Acifluorfen, labeled for rice, may control forage aeschynomene in that crop. Forage aeschynomene might become a weed problem in rice if plants are past the seedling stage when flood water is applied and could cause weed problems in soybeans; but, in most situations, cultural and chemical control practices should provide adequate control.

Adjuvant effectiveness with imazethapyr for kochia control was generally methylated seed oil ≥ nonionic surfactant ≥ petroleum oil in the greenhouse experiments, and methylated seed oil ≥ petroleum oil nonionic surfactant in the field. Oil adjuvants were applied at 2.3 L ha-1 and nonionic surfactants were applied at 0.25% (v/v) of spray volume. None of the adjuvants overcame imazethapyr reduced phytotoxicity caused by simulated rain soon after treatment, posttreatment cold (10 C), low soil moisture, or low soil nitrogen. However, kochia fresh weight reductions usually were the greatest when imazethapyr was applied with methylated seed oil, except in the case when soil had 80 ppm or less soil nitrogen. Kochia control with imazethapyr was enhanced the most by methylated seed oil followed by nonionic surfactant and petroleum oil regardless of relative humidity. High compared to low relative humidity tended to increase control for imazethapyr alone or with nonionic surfactant and decrease control for imazethapyr with oils. Kochia fresh weight reduction following imazethapyr treatment was greatest at 20 C, intermediate at 30 C and least at 10 C posttreatment when used with any of the adjuvants.

Sixteen applications of imazapyr and other herbicides were made to field bindweed from 1982 to 1986. Control with imazapyr was 89% or more 1 yr after treatment at 0.14 kg ai ha-1 when plants were growing vigorously at application. Only 1 of 16 applications of imazapyr at 0.56 kg ha-1 controlled less than 90% regardless of plant vigor. Control at 0.56 kg ha-1 was usually superior to that obtained with dicamba at 1.1 and 2.2 kg ae ha-1, and 2,4-D at 1.1 kg ae ha-1, as well as combinations of picloram with either 2,4-D or dicamba. All herbicides were less effective when applied to field bindweed with poor vigor. Winter wheat planted in the fall up to 122 days after application was injured 20 to 88% by imazapyr at 0.14 kg ha-1. Sorghum planted the next spring was injured 15% or less by imazapyr at 0.14 and 0.28 kg ha-1.

Imazamethabenz is a selective herbicide used to control wild oat in small grains. The effects of rate, volume of carrier, and surfactant concentration on the efficacy of this herbicide in controlling wild oat were studied in field experiments. As each of the variables increased, wild oat control increased; the greatest degree of wild oat growth inhibition occurred at the highest herbicide rate, highest volume of carrier, and highest surfactant concentration.

In a petri dish assay, radicle growth of trifluralin-resistant (R) green foxtail exposed to trifluralin concentrations of up to 0.4 ppm (w/v) was not inhibited. Radicle growth of trifluralinsusceptible (S) biotypes was completely inhibited. Shoots were more sensitive to trifluralin than roots, with shoot growth being inhibited for both R and S biotypes at trifluralin concentrations of 0.2 ppm or more. Best discrimination between R and S green foxtail biotypes was achieved by measuring radicle length after incubation of pregerminated caryopses at 0.3 ppm trifluralin in the dark for 5 d at 22 C.

Eight herbicide treatments per crop were evaluated for hairy vetch and crimson clover cover-crop control in no-till corn and cotton at two locations in North Carolina. Paraquat alone or combined with dicamba, 2,4-D, or cyanazine, and cyanazine alone, controlled clover the best in both crops. All herbicide treatments, except glyphosate alone, controlled at least 89% of hairy vetch in corn. However, only 2,4-D and cyanazine alone or combined with glyphosate controlled greater than 89% of hairy vetch in cotton. Except for poor control of hairy vetch and crimson clover by glyphosate alone, reduced legume control did not consistently decrease corn or cotton yield. Weed control was reduced in crimson clover treated with glyphosate alone, but control was similar among the remaining herbicide treatments. Effectiveness of legume control did not influence the N concentration of corn or cotton. Corn stand, height, and yield were greater in hairy vetch than in crimson clover. Seed cotton yield did not differ between vetch and clover.

Seedling alfalfa was injured by chlorsulfuron and sethoxydim plus 2,4-DB but recovered the following year as alfalfa seed yields were comparable to the hand-weeded control. Fluazifopbutyl and flamprop-methyl (active isomer) at 0.5 kg/ha did not affect seedling alfalfa adversely; however, seed yields were lower the following year compared to those treated at the 0.25-kg/ha rate. In established alfalfa, sethoxydim alone or with 2,4-DB applied annually did not affect seed yields adversely. However, 2,4-DB alone reduced seed yields in 2 of 5 yr. Alfalfa tolerated chlorsulfuron at 0.015 kg/ha but was damaged at the 0.03-kg/ha rate. Initial injury and later recovery without adverse effects on seed yield also were observed following annual treatments with bromoxynil, MCPA plus 2,4-DB and bentazon plus 2,4-DB.

The response of giant burreed to bentazon, propanil, 2,4-D (amine salt), and 2,4-D plus crop oil (0.5% v/v) was evaluated at the 2-aerial-leaf stage of wild rice. Bentazon, 2,4-D, and 2,4-D plus crop oil at 1.1 kg/ha or more in 1984, and propanil and 2,4-D plus crop oil at 4.5 kg/ha in 1985 reduced giant burreed dry weight. Generally, herbicide rates above 1.1 kg/ha injured wild rice and reduced yields compared to weed-free controls. None of the study treatments resulted in effective giant burreed control without unacceptable injury to wild rice.

Field studies were established to evaluate several new herbicides for preplant incorporated and postemergence shattercane control in soybeans. Imazethapyr applied postemergence controlled shattercane most consistently. The type of adjuvant tank mixed with sethoxydim did not influence shattercane control, panicle production, or soybean yields. Preplant incorporated applications of imazethapyr, imazaquin, or clomazone either alone or tank mixed with trifluralin or pendimethalin gave inconsistent shattercane control and soybean yields compared to handweeded plots.

Linuron, metribuzin, oryzalin, and metolachlor were applied at recommended (1X) and two-thirds (0.67X) rates to evaluate control of redroot pigweed and common lambsquarters in conventional and rye-stubble reduced-tillage potato production systems. Regardless of tillage, common lambsquarters control was satisfactory during both seasons at both rates of linuron, metribuzin, and oryzalin. Redroot pigweed control by these three herbicides, although excellent in 1988, was poor in RT plots during 1987. Yields did not differ between tillage systems. Reduced weed control with metolachlor during both seasons, and possible crop injury with linuron in 1987 resulted in significant yield reductions.

Studies were conducted to evaluate preplant incorporated (PPI), preemergence (PRE), and postemergence (POE) herbicide treatments on yellow nutsedge control and on growth and yield of transplanted onions. Most effective yellow nutsedge control (≥80%) was achieved with metolachlor applied PPI plus PRE. Metolachlor and SAN 582H were more effective applied PPI than PRE. Bentazon alone applied POE adequately controlled yellow nutsedge only 1 of 2 yr. Highest onion yields and percent jumbo bulbs were produced when treatments included metolachlor applied PPI.

Field research from 1986 to 1988 evaluated control of alfalfa, dandelion, orchardgrass, and annual weeds in corn with sequential herbicide treatments. Glyphosate applied the previous fall controlled 95% or more of the dandelion and orchardgrass before postemergence treatments. Atrazine applied early preplant or with paraquat the day before planting only partially controlled the perennial species. Atrazine applied postemergence usually controlled vegetation escaping initial treatment except orchardgrass following the atrazine treatments. Adding tridiphane increased weed control with atrazine or cyanazine applied postemergence only when fall panicum was present. Herbicides applied postemergence increased corn yield compared to the initial treatments alone, and few differences among postemergence treatments were observed. Sequential treatments which included glyphosate applied in the fall controlled 82% or more of each perennial species before the next growing season. Orchardgrass control was 81% or less the following spring when the initial treatment was atrazine or atrazine plus paraquat.

Field experiments were initiated in 1973 at Fargo and Williston, ND, to evaluate wild oats seed longevity in soil at six burial depths. The number of viable seed decreased rapidly during the first 7 mo from 99% to 21 and 15% at Fargo and Williston, respectively, when averaged over depths. The number of viable seed decreased gradually over the 7- to 168-mo period at Fargo; however, at Williston, viability remained relatively constant for 84 mo and decreased rapidly after 108 mo. At both locations, several wild oats seed were viable 168 mo after burial. More viable wild oats seed were recovered from deep than shallow depths regardless of sampling date. Seed viability at the 6- to 10-cm burial depth was lost more rapidly with nitrogen fertilizer than without nitrogen fertilizer. The percentage of dormant viable seed remained constant for 33 mo at Fargo and 60 mo at Williston regardless of burial depth, but decreased gradually thereafter. Dormant seed percentages at the various depths did not relate to differences in seed viability at these depths.

‘Atlantic’ and ‘Russet Burbank’ potato cultivars were grown on mineral and organic soils either with or without weeds and were hilled at two stages of potato development (potatoes cracking through the soil and potatoes 30 cm tall). A single hilling procedure was not adequate in either year for full-season weed control. Early hilling suppressed weeds and increased tuber yields more than conventional hilling on mineral soils in 1988 only. Early hilling tended to increase the relative biomass of C4 weeds compared to C3 weeds for both soils. Weeds reduced aboveground potato biomass on mineral and muck soils. However, reduced aboveground potato biomass measurements did not predict tuber yield reductions. Marketable yield of Russet Burbank potato was reduced by weed interference more than the yield of Atlantic on mineral soils when planted according to conventional cultural practices. However, the marketable yield of Atlantic potato was reduced more than Russet Burbank yield by weeds on muck soils. Weed interference influenced tuber quality on both mineral and muck soil.

Broccoli treated with 0.07 kg ai/ha oxyfluorfen, 0.28 and 0.56 kg ai/ha pyridate, and 0.14 kg ai/ha BAS 514 at four field locations produced yields similar to the cultivated check. Oxyfluorfen at 0.14 and 0.28 kg/ha, pyridate at 1.0 and 2.0 kg/ha, and BAS 514 at 0.28 and 0.56 kg/ha reduced broccoli yield at one or more locations. Broccoli treated with BAS 514 plus the experimental adjuvant BAS 090 had increased injury and decreased yield when compared to BAS 514 applied alone. Little to no stand reduction was observed with any herbicide treatment. Direct-seeded broccoli is marginally tolerant to rates of oxyfluorfen, pyridate, and BAS 514 that control broadleaf weeds acceptably.

Field experiments were conducted to determine the influence of winter wheat seeding date and forage removal on the efficacy of cheat control herbicides, forage and grain yields, and net returns to land, overhead, risk, and management for the various cheat control strategies. Economic analysis showed that net returns were higher when wheat was seeded during the traditional seeding period (October) than when either seeded early (September) for increased forage production or delayed (November) for cultural cheat control. Some herbicides were economically beneficial at two of three locations where the initial cheat population exceeded 170 plants/m2.

Sulfonylurea herbicide resistance was crossed into a susceptible (S) prickly lettuce biotype and into ‘Bibb’ (B), a domestic lettuce cultivar, and inheritance of the resistance trait was determined. The best fit for Chi Square analysis of the metsulfuron treated F2 generations was a 1:2:1 ratio indicating the trait was controlled by a single nuclear gene with incomplete dominance. F3 generations also were treated with metsulfuron. The F3 seedlings from resistant F2 plants were resistant while the F3 seedlings from intermediate F2 plants segregated.

Alachlor, chloramben, cinmethylin, diphenamid, fluazifop, fluazifop-P, metolachlor, metribuzin, napropamide, oryzalin, and sethoxydim were applied on transplanted sweet potato at Tifton, GA, during 1982 to 1985. The weeds most prevalent were large crabgrass, Florida pusley, smallflower morningglory, and yellow nutsedge. No significant phytotoxicity was observed from any herbicide treatment over the 4 yr. Cultivation at 4 wk is advantageous to eliminate early flushes of weeds which escape control and reform the beds. Alachlor or metolachlor at 4.5 and 3.4 kg ha-1, respectively, and metribuzin controlled weeds best. Although no serious phytotoxicity was evident, these treatments tended to cause lowered yields of marketable roots while marginally affecting total yields in most cases. Metribuzin was the only compound which controlled late-season broadleaf weeds such as smallflower morningglory effectively.