Foliar absorption of 14-chlorimuron at 6, 12, 24, and 48 h after application to common cocklebur was reduced when applied in combination with acifluorfen. A maximum reduction of 10% was observed at 48 h. 14C translocation to meristematic tissue above the treated leaves also was reduced by acifluorfen in common cocklebur at 24 and 48 h after treatment. Absorption and translocation of 14C-chlorimuron in sicklepod was not affected by acifluorfen. Thin layer chromatographic analysis of treated leaf extracts showed two metabolites in common cocklebur (Rf values of 0.0 and 0.42) and four metabolites in sicklepod (Rf values of 0.0, 0.16, 0.33, and 0.50). All metabolites were more polar than the parent compound (Rf value of 0.64). Addition of acifluorfen did not affect chlorimuron metabolism in common cocklebur but reduced metabolism in sicklepod. Absorption, translocation, and metabolism of acifluorfen in common cocklebur or sicklepod were not affected by the addition of chlorimuron.

Two field experiments were established in 1988 and 1989 in southeast Missouri to evaluate several herbicides and herbicide combinations for giant ragweed control in soybean. In 1988, a timely rainfall was not received for soil-applied herbicides and giant ragweed control was less than 75%. However, in 1989 soil moisture was sufficient for uptake of soil-applied herbicides and early season giant ragweed control was generally greater than 80%. Chlorimuron, chlorimuron plus 2,4-DB, imazaquin plus 2,4-DB, acifluorfen followed by naptalam plus 2,4-DB, fomesafen, and imazethapyr applied to 2.5 to 5-cm giant ragweed controlled more than 85% in 1988. In 1989, all POST treatments except imazaquin controlled more than 81% of giant ragweed 2 wk after treatments. Imazethapyr controlled seedling giant ragweed at heights up to 12 to 25 cm. Giant ragweed regrowth and/or reinfestation and giant ragweed seed production occurred with all herbicide treatments.

The influence of temperature and relative humidity on the activity of acifluorfen, fomesafen, lactofen, and acifluorfen plus bentazon on prickly sida, pitted and entireleaf morningglory, and common cocklebur was evaluated in a growth chamber. Reduced control of all species was observed at 50% relative humidity as compared to 85% relative humidity when temperatures were higher (32/55 C day/night). Similar response to relative humidity was observed at the lower temperature (25/15 C) when treatments were applied 14 days after emergence (DAE). Changes in temperature at the same relative humidity did not alter herbicidal activity. Delaying application timing from 7 to 14 DAE decreased control by all herbicides except lactofen applied at high relative humidity, which controlled prickly sida at both 7 and 14 DAE.

Fluazifop-P, applied in the spring or fall and pronamide, applied in the fall only, reduced quackgrass infestation in established alfalfa and increased the dry matter yield of alfalfa. Herbicides did not improve alfalfa in vitro digestibility or crude protein content. Average residues of fluazifop-P in alfalfa treated with rates of 0.25 or 0.5 kg ai ha–1, were 0.1 mg kg–1 when harvested 280 d after application, and 0.06 mg kg–1 when harvested 295 d after application. Average residues in alfalfa harvested 41 and 55 d after application were 0.13 mg kg–1 and 0.1 mg kg–1, respectively, with a 0.25 kg ha–1 treatment and 0.19 mg kg–1 and 0.05 mg kg–1, respectively, with a 0.5 kg ha–1 treatment.

A four-state study was initiated in 1988 to evaluate the influence of cultivation frequency and initiation on the cotton plant. When cultivations were initiated at 1 or 2 wk after emergence and cultivated weekly at a frequency of zero, one, two, four, or six times, seed cotton yields were not affected on a consistent basis. When averaged over cultivation frequency, seed cotton yields were increased for three of nine year-locations when cultivations were initiated at 2 wk after emergence when compared with 1 wk after emergence. At two locations, when seed cotton yields were averaged over initiation timing, it was shown that only two cultivations were necessary to achieve optimum seed cotton yields.

Field experiments were conducted in 1989 and 1990 on silty clay and sandy loam soils to evaluate weed control and soybean yield with early-April preplant incorporation of selective herbicides in stale seedbed soybean followed by non-selective weed control measures at planting. Metribuzin applied PPI early followed by chlorimuron POST coupled with either glyphosate or paraquat PRE controlled sicklepod, pitted morningglory, and hemp sesbania to the same extent of that treatment applied PPI at planting. All stale seedbed treatments with POST applications and glyphosate, paraquat, or tillage at planting controlled pitted morningglory over 70%. However, imazaquin or metribuzin applied PPI early without a POST treatment controlled sicklepod and pitted morningglory poorly. Frequently, applying PPI herbicides at planting increased control compared with early PPI applications, but this was overcome by POST treatments. Early stale seedbed applications of metribuzin did not result in more than 60% control of hemp sesbania, whereas metribuzin applied PPI at planting controlled over 85%. However, metribuzin plus chlorimuron controlled hemp sesbania at least 74%, regardless of application timing or tillage method, whereas no imazaquin treatment achieved over 65% control. All stale seedbed herbicide treatments increased soybean yield compared with the untreated stale seedbed check. Selective herbicide treatments with either non-selective herbicide in a stale seedbed program resulted in equivalent yield to PPI at planting treatments most often, except with metribuzin.

Field experiments were established in 1989 and 1990 on silty clay and sandy loam soils to evaluate selective herbicides in combination with non-selective weed control measures in conventional and stale seedbed soybean production. Metribuzin PRE followed by chlorimuron POST controlled sicklepod better with paraquat than with glyphosate. A POST application of imazaquin increased sicklepod and pitted morningglory control by imazaquin PRE alone in a stale seedbed or tillage program. Pitted morningglory control with imazaquin PRE was lower with tillage than with glyphosate or paraquat combinations in a stale seedbed program. All metribuzin plus chlorimuron PRE treatments, whether conventional tillage or stale seedbed, controlled pitted morningglory more than 75%. Hemp sesbania control was above 80% with all metribuzin followed by chlorimuron or metribuzin plus chlorimuron PRE combinations, and less than 70% with all treatments containing imazaquin. Selective herbicides increased yield in stale seedbed when glyphosate or paraquat was added. Imazaquin PRE, imazaquin PRE followed by imazaquin POST, and metribuzin PRE followed by chlorimuron POST tank mixed with glyphosate or paraquat in a stale seedbed program increased yield compared with the same treatments used with tillage.

Four field experiments were conducted during 1988 and 1989 to determine the effects of POST application of nicosulfuron on quackgrass control in conventional field corn. A single application of nicosulfuron at 35 to 70 g ha–1 applied to four- to six-leaf quackgrass controlled over 90% of quackgrass five weeks after treatment. Nicosulfuron at 35 g ha–1 applied at the one- to three-leaf stage was not as effective as the same rate applied at the four- to six-leaf stage. When nicosulfuron at 35 g ha–1 was applied to four- to six-leaf quackgrass, over 80% of the quackgrass regrowth was controlled one year later. Nicosulfuron did not injure ‘Agway 584S’ corn at the highest rate (140 g ha–1) tested and did not reduce silage or grain yield.

This study was conducted to compare foliar absorption and translocation of dicamba applied to plants as an aqueous solution or as dicamba-treated soil deposits. When applied as an aqueous solution, 65 to 95% of 14C-dicamba was absorbed by pea, alfalfa, and grape; whereas, limited absorption (0.4 to 4.7%) occurred from dicamba-treated soil. Based on dose-response evaluation, the low levels absorbed from treated soil are unlikely to cause crop damage. 14C-dicamba translocation was more than 80% of absorbed 14C in pea, alfalfa, and grape. Acropetal translocation exceeded basipetal translocation.

Some annual weeds, perennial herbs, and suffrutescent half shrubs are unique in that their populations are cyclic in nature and relatively short-lived. This variability presents a confounding factor that makes management decisions about control of these weeds difficult. This paper presents a procedure, using Markov processes, that gives additional information for managing cyclic weed populations. The Markov chain model is used to evaluate the interyear patterns of broom snakeweed survival when growing on New Mexico rangeland.

Velvetleaf from Mississippi and Wisconsin and soybean (var. Williams) were grown in five temperature regimes (12/4, 19/11, 26/18, 33/25, and 40/32 C day/night) in controlled-environment chambers. Leaf appearance rates increased with temperature in both species, ranging from 0.06 to 0.69 leaves per day in velvetleaf and 0.07 to 0.38 leaves per day in soybean. The threshold temperature for leaf appearance in both species was 5 to 6 C. The largest leaves of both species were produced at 26/18 C. By 55 d after emergence, the greatest total leaf area per plant occurred at 26/18 C or above in both species. Reproductive development occurred earliest at 33/25 C in velvetleaf and at 26/18 C in soybean. This limited vegetative growth in velvetleaf more than in soybean. The weed/crop ratio for total leaf area increased with increasing temperature, indicating that velvetleaf probably would be more competitive with soybean under higher temperatures. The two populations of velvetleaf generally responded similarly to temperatures.

Tolerances of soybean and rotational crops wheat and corn to chlorimuron (0.02 to 0.14 kg ai ha–1), clomazone (0.56 to 3.36 kg ha–1), imazaquin (0.07 to 0.42 kg ha–1) and imazethapyr (0.05 to 0.31 kg ha–1) were evaluated in field studies. No visible soybean injury was observed. No reduction in soybean population, height, or yield occurred from the use of these herbicides, in 1986 or 1987. Differences in wheat yields among treatments were not significant in 1987 or 1988. Corn population, number of ears, ear weight, or yield were not different.

Six commercial petroleum oil (PO) adjuvants differed in their enhancement of imazethapyr phytotoxicity to green foxtail and kochia but not to redroot pigweed, when imazethapyr was applied postemergence at 17 g ha–1. Imazethapyr at 5 g ha–1 plus 27 combinations of three oils and nine emulsifiers reduced kochia growth by 61 to 88%. Optimum emulsifier concentration in a PO adjuvant ranged from 15 to 20% (v/v). All PO adjuvants tested produced fair to excellent oil-inwater emulsions with imazethapyr; however, emulsion stability did not correlate with weed control.

Field studies were conducted to examine hairy nightshade control with, and potato tolerance to, bentazon or bentazon plus nonionic surfactant (NIS), petroleum oil concentrate (POC), methylated seed oil (MSO), BCH-815, or urea-ammonium nitrate (UAN). Bentazon treatments were applied early or late POST. Hairy nightshade control with bentazon at 0.56 kg ha–1 plus POC, MSO, BCH-815, or UAN was equal to or better than bentazon alone at 1.12 kg ha–1 regardless of time of application. Potato injury with bentazon plus additives applied late POST was sometimes greater than with bentazon alone, but use of additives did not reduce potato yield or quality. Yield of US ♯1 tubers was lower when bentazon was applied late POST than when applied early POST in one of two years.

Tolerance of eight processing sweet corn hybrids to nicosulfuron was evaluated in field studies conducted at Arlington, Wis. in 1988 and 1989. Magnitude of sweet corn vigor reduction varied between years. Greater vigor reduction occurred to ‘Jubilee’ sweet corn than to the other seven hybrids. Injury to the hybrids increased as nicosulfuron rate increased. In 1988, some of the hybrids were stunted slightly by all of the herbicide rates, but within a hybrid there was no significant difference among herbicide rates. In 1989 none of the hybrids, including Jubilee, was stunted by even 140 g ai ha–1 nicosulfuron compared with the corresponding check. Effects of nicosulfuron on yields of the eight hybrids in 1988 and in 1989 are best described by a quadratic regression equation.

Studies were conducted to determine the effectiveness of 11 multiple treatment combinations of bensulide in controlling a perennial and an annual subspecies of annual bluegrass. Bensulide controlled 97% of the annual subspecies with annual applications of 11 kg ai ha–1 (Jan.) + 6 kg ha–1 (Feb.) + 6 kg ha–1 (Mar.) totaling 92 kg ha–1 in 4 yr. The annual subspecies appeared to have a germination period from mid November to early January. None of the bensulide treatments controlled the perennial subspecies acceptably. The common occurrence of these two subspecies in mixed stands may account for the erratic weed control reported by many researchers. Bentgrass showed good tolerance to bensulide totals over 4 yr of 160 kg ha–1 applied in a U.S. Golf Association rootzone green.

Chinese milkvetch is the most important green manure crop in the rice producing regions of China. The tolerance of Chinese milkvetch to 29 herbicides approved for other legume crops was determined in the greenhouse. Chinese milkvetch was tolerant to bentazon, diclofop-methyl, and EPTC at 2.0, 1.6, and 6.0 kg ai ha–1, respectively. Barban, bromoxynil, 2,4-DB, dinoseb, fluazifop, quizalofop, sethoxydim, and triallate at 0.5, 0.6, 1.0, 1.5, 0.3, 0.3, 0.5, and 1.0 kg ai ha–1, respectively, slightly injured Chinese milkvetch but did not substantially reduce biomass. Trifluralin, propham, DCPA, acifluorfen, and MCPA were moderately phytotoxic to Chinese milkvetch at 0.5, 3.0, 5.0, 0.5, and 0.5 kg ai ha–1, respectively.

Field studies were conducted from 1986 through 1988 to evaluate various herbicides for yellow nutsedge control and peanut yields. Three applications of pyridate provided control comparable to two applications of bentazon with yellow nutsedge regrowth beginning 3 to 4 wk after application depending on moisture conditions. Crop oil concentrate did not improve the activity of pyridate. Flurtamone provided control comparable with that of metolachlor. Nutsedge control with fomesafen was erratic with peanut injury noted. Peanut yields did not reflect the competitive nature of nutsedge.

CGA 163935, paclobutrazol, and paclobutrazol plus mefluidide were evaluated for their growth regulating effect on centipedegrass over 3 yr. Paclobutrazol did not effectively suppress seedhead production or vegetative growth. Paclobutrazol plus mefluidide at 1.1 + 0.3 kg ai ha–1 in each of two applications at a 2-wk interval suppressed seedhead development 77% (average of 3 yr) at 10 wk after the initial treatment without severe injury or loss of stand, but duration of vegetative growth suppression was variable (0 to 6 wk). CGA 163935 applied at 0.4 kg ai ha–1 and followed by 0.2 kg ai ha–1 2 wk later suppressed vegetative growth of mowed and nonmowed centipedegrass for 10 wk, while suppressing seedhead production for 3 to 5 wk. CGA 163935 caused severe injury and stand loss of centipedegrass.