The effect of common cocklebur interference on snap beans was investigated at Bridgeton, NJ, in 1987 and 1988. Snap bean yields were reduced by increasing weed densities. Yields were reduced 8 to 44% in 1987 and 2 to 55% in 1988 by full-season in-row weed densities ranging from 0.5 to 8/m2. One weed and 4 weeds/m2 were the damage-threshold populations of common cocklebur with full-season interference in 1987 and 1988, respectively. The weed-free requirement, after planting, was to the unifoliolate stage of snap beans. Common cocklebur at 4 weeds/m2 did not affect yield when snap beans were maintained weed free until the unifoliolate stage of snap beans. The critical duration of interference for common cocklebur emerging with snap beans was between the emergence and full-bloom stage of snap beans. Snap bean yield was not reduced with weed removal at full bloom.

The influence of relative planting date on the growth of common cocklebur (Xanthium pensylvanicum Wallr. ♯ XANST), common ragweed (Ambrosia artemesiifolia L. ♯ AMBEL), sicklepod (Cassia obtusifolia L. ♯ CASOB), and redroot pigweed (Amaranthus retroflexus L. ♯ AMARE) grown in competition with soybean [Glycine max (L.) Merr. ‘Bragg’] was studied in the greenhouse. Increases in dry matter and height were slower for the five weed species than for soybean throughout the period of the study. The root: shoot ratio of soybean was the highest of any plant in the study, while common ragweed, common cocklebur, common lambsquarters, and sicklepod were intermediate, and redroot pigweed was the lowest. Soybean dry weight was always reduced when grown in competition with a weed. Soybean dry-matter production was reduced most when weeds were planted 2 weeks before soybean, especially with common cocklebur and common lambsquarters. Weed dry-matter content was severely reduced when the weed seed were planted simultaneously with or following soybean. Soybean height was usually reduced by competition with the weeds. The height of common ragweed was increased, however, when planted simultaneously with soybean. Common lambsquarters, redroot pigweed, and common ragweed heights were increased when planted 2 weeks prior to soybean.

Field experiments were conducted in Louisiana over 2 yr to evaluate the influence of full-season interference from johnsongrass, common cocklebur, or hemp sesbania at densities of 2.5, 0.5, and 2.0 plants m–1 of row, respectively, and simulated insect defoliation of soybean on weed and soybean growth. Defoliation at R2 (full bloom) and R5 (beginning seed development) soybean growth stages was accomplished by removal of zero, one, or two leaflets per soybean trifoliate, which approximated 0, 33, and 66% defoliation, respectively. Height and dry weight of all weeds were not affected by soybean defoliation level or defoliation stage. Soybean height 3 wk after defoliation at R5 was not influenced by weed interference, soybean defoliation level, or defoliation stage in either year. Averaged across soybean defoliation levels and stages in 1994, johnsongrass, common cocklebur, and hemp sesbania reduced soybean yields 30, 15, and 14%, respectively. In 1995, johnsongrass reduced soybean yield 35%. As soybean defoliation level increased, a linear decrease in soybean yield was observed. Averaged across weeds and soybean defoliation stages, 33 and 66% defoliation reduced soybean yield 6 and 20% in 1994 and 12 and 33% in 1995, respectively. Defoliation at R5 resulted in 10% lower yield than defoliation at R2 in one of two years. Yield reduction due to combinations of weeds and soybean defoliation was additive.

Two field experiments were conducted to examine the competitive effect of common cocklebur and sicklepod in soybean. Factors examined included sap flow of both the weed and the crop, as well as the traditional parameters of weed and crop growth and crop yield. The intent was to determine to what extent competitive effects could be attributed to differential water utilization. In the first study, soybean planted at 20 plants m−1 row was infested with either sicklepod at 10 plants m−1 row or common cocklebur at two plants m−1 row. Sicklepod reduced soybean sap flow and yield 53 and 49%, respectively. Common cocklebur reduced soybean sap flow and yield 31 and 38%, respectively. Within a weed species, weed-induced yield and sap flow reductions were comparable, indicating that water deprivation was the primary detriment that these weeds inflicted on soybean. Individual common cocklebur plants were 3.9 times more competitive than sicklepod with respect to reducing soybean yield. However, sap flow of individual common cocklebur plants was only 1.4 times more than that of sicklepod, indicating that water deprivation was not the only causal factor in weed-crop competition. In the second experiment, sicklepod was planted in soybean (fixed density) and clipped to either half the height, same height as soybean, or left unclipped, in an attempt to simulate herbicide-induced stunting. Clipping sicklepod had a positive effect on soybean sap flow and yield. Thus, the benefits of reduced weed competition were achieved without killing sicklepod.

With the shift to earlier maturing soybean cultivars, harvest interference data are needed at low weed densities that will not reduce yield, but may affect soybean quality or harvesting efficiency. Field experiments were conducted in 1995 and 1996 to determine the density of five weeds necessary to warrant desiccation treatments. There were no consistent differences in losses of harvestable soybean due to weed density. Common cocklebur increased foreign material and soybean moisture at a greater rate than did hemp sesbania, ivyleaf morningglory, or redroot pigweed, with sicklepod intermediate among these species. Soybean test weight was reduced by 17, 13, and 59 g/L for each plant/meter of row with redroot pigweed, sicklepod, and common cocklebur, respectively, whereas hemp sesbania and ivyleaf morningglory did not affect test weight. However, all species evaluated increased damaged soybean seeds by 8.2 to 11.1% for each plant/meter of row. Combine speed was not affected substantially by the weed densities evaluated.

Seedling growth of soybean [Glycine max (L.) Merr. ‘Forrest’], common cocklebur (Xanthium strumarium L. # XANST), and tall morningglory [Ipomoea purpurea (L.) Roth. # PHBPU] was compared in field studies. Root growth was determined by measuring roots restricted to the inside of a permeable membrane that contained no soil. Leaf area duration and net assimilation rate between 4 and 9 weeks were greatest for common cocklebur compared to the other species. At 9 weeks, shoot and root dry weight and leaf area were greatest for common cocklebur compared to soybean and tall morningglory. Relative growth rate of common cocklebur roots was greater than the other species between 4 and 9 weeks. Tall morningglory had greater shoot length or height at 4 and 9 weeks and greater shoot or height elongation rate between 2 and 4 weeks, and 4 and 9 weeks than the other species.

Season-long interference of shattercane, giant foxtail, common cocklebur, and common lambsquarters in corn was evaluated in the field at weed densities from 0.4 to 13.1 plants or clumps/m of corn row during 1985, 1986, and 1987. Corn seed yields decreased linearly with increases in the density of clumps of 2 to 3 shattercane plants and 5 to 8 giant foxtail plants, reaching 22% yield loss at 6.6 shattercane clumps/m of row and 18% yield loss at 13.1 giant foxtail clumps/m of row. Increases in common cocklebur density caused corn yields to decrease curvilinearly in 1985 with a maximum predicted yield loss of 27% occurring at a density of 4.7 common cocklebur plants/m of row. In 1986 and 1987, yields decreased linearly as common cocklebur density increased to 6.6 plants/m of row, where a 10% yield loss was observed. Common lambsquarters reduced corn yields only in 1985. In this year, yields decreased curvilinearly with increasing weed density, resulting in a maximum yield loss of 12% at 4.9 common lambsquarters plants/m of row. Corn yields averaged 11600 kg/ha when grown without weed interference in these experiments.

Extension workers are sensing pressure to use soils information and chemical characteristics data to guide farmers in selecting pesticides least prone to leach into groundwater. Our objective was to estimate differences in herbicide migration to groundwater under conditions typical for the Southeast Coastal Plain, and to consider how a farmer might be advised to use such knowledge in selecting herbicides. We used a simple computer code for microcomputers to predict persistence and migration of 17 herbicides through a hypothetical, coarse-textured soil typical of the Southeast Coastal Plain. Appropriate herbicides were selected for several common crop-weed problems, such as sicklepod in soybean and Palmer amaranth in corn. Groundwater was assumed to be 3.15 m below the soil surface. Herbicides selected covered a broad range of half-lives and organic carbon partition coefficients. Only after the first-order degradation rate constant was reduced by a factor of five did predicted soil water concentrations of several herbicides at the groundwater interface reach normal detection limits. Still, predicted concentrations were below the level established for health effects advisory purposes. Due to the large number of uncertainties and the inability to estimate practical benefits, we conclude that data relating to soil and herbicide characteristics cannot be used at this time to override cost effectiveness, efficacy, and other factors normally considered by farmers and Extension professionals in herbicides for weed control.

Chlorimuron applied alone and in combination with acifluorfen or thifensulfuron was evaluated for POST control of common lambsquarters, common ragweed, common cocklebur, and a mixture of pitted, ivyleaf, entireleaf, and tall morningglory in soybean. Common cocklebur control was similar with thifensulfuron at 3 and 4 g ae ha−1 and with chlorimuron at 7 and 9 g ae ha−1, Common ragweed and morningglory control was greater with chlorimuron while common lambsquarters control was greater with thifensulfuron. Control of all species was good with combinations of chlorimuron at 7 g ha−1 plus thifensulfuron at 2 g ha−1 or acifluorfen at 140 g ae ha−1 and similar to or greater than the control with chlorimuron at 9 g ha−1. Soybean yields with all POST herbicide treatments were equivalent to that of the weed-free check.

Greenhouse studies were conducted to determine host status of weed species for Rhizoctonia solani AG-1, which causes Rhizoctonia foliar blight of soybean. Weed species were barnyardgrass, broadleaf signalgrass, common cocklebur, entireleaf morningglory, hemp sesbania, itchgrass, johnsongrass, large crabgrass, northern jointvetch, prickly sida, purple nutsedge, redweed, sicklepod, and smooth pigweed. Seedling weeds were inoculated with suspensions containing intraspecific group IA and IB isolates of the fungus. In the first study, sclerotia of IA were recovered from tissue of all weeds except smooth pigweed, and mycelia of IA were recovered from all except smooth pigweed and redweed. In that study, neither microsclerotia nor mycelia of IB were recovered from sicklepod, barnyardgrass, or large crabgrass, and only microsclerotia were recovered from itchgrass and purple nutsedge. In the second study, sclerotia of IA, microsclerotia of IB, and mycelia of each isolate were recovered from all weed species. In other studies, R. solani spread from at least six of seven weed species to a noninfected soybean plant growing in close proximity. These studies emphasize the importance of weed control, not only for reducing plant competition and increasing yield, but also for the potential impact on development of RFB.

The growth, development, and reproductive potential of several populations of organic arsenical-susceptible (S) and -resistant (R) common cocklebur biotypes were compared under noncompetitive field conditions. Plant height, leaf area, aboveground dry weights, and relative growth rate (RGR) were measured periodically during the growing season. Days to flowering, bur dry weight, and number of burs per plant were also recorded. Arsenical S- and R-biotypes were similar in all measured parameters of growth, development, and reproductive potential. Populations within each biotype varied occasionally in plant height, leaf area, aboveground dry weights, and reproductive potential.

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.

The acetolactate synthase-inhibiting herbicides chlorimuron and imazaquin, and the diphenylether herbicides acifluorfen and lactofen, were applied alone and in all possible combinations to the foliage of common cocklebur, pitted morningglory, and prickly sida to evaluate interacting effects on absorption and translocation. The addition of unlabeled acifluorfen to 14C-chlorimuron increased absorption in common cocklebur, pitted morningglory, and prickly sida. Lactofen also increased absorption of 14C-imazaquin in all species. Conversely, imazaquin reduced absorption or translocation of 14C-acifluorfen in common cocklebur or pitted morningglory, respectively. In all species, absorption was lower when unlabeled chlorimuron or imazaquin was combined with 14C-lactofen than when applied alone.

Field studies were conducted to determine the effect of common cocklebur interference in early-maturing (maturity group IV) soybean planted in April, May, and July. Common cocklebur density and length of interference did not affect soybean height, canopy width, or node number at any planting date. Removal of common cocklebur 4 weeks after emergence (WAE) prevented reduction of soybean leaf area, stem dry weight, dry leaf weight, dry pod weight, and seed yield. Aboveground biomass for common cocklebur emerging in July was less than biomass of April or May plantings. Common cocklebur planted into soybean 2, 4, or 8 wk after soybean emergence did not reduce soybean yield. Under parameters of this study, planting date was not a significant factor in yield reduction. Interference from one common cocklebur plant per 1.8, 0.9, and 0.3 m of soybean row for 8 wk reduced yields 7, 14, and 30%, and full-season interference reduced yields 16, 33, and 65%, respectively. The Arkansas Weed Management Computer program closely predicted actual yield loss for early-maturing soybean.

Cotton (Gossypium hirsutum L.) was grown in the presence of common cocklebur (Xanthium strumarium L. # XANST) on a Lucedale fine sandy loam. Cotton was maintained weed free or allowed to compete with common cocklebur for 0, 3, 5, 7, 9, or 11 weeks after planting. Mathematical predictions of seed cotton yield were optimum when maintained free from common cocklebur interference for 8 weeks or more after cotton emergence in 1981 and 1982, and 10 weeks or more in 1980. Common cocklebur adversely affected yield when allowed to compete longer than 4 weeks in 1981 and 1982, and 2 weeks in 1980.

Herbicide systems consisting of PRE, early POST, and late POST options arranged factorially were compared for control of sicklepod in narrow-row soybean with modified acetolactate synthase (ALS) (E.C.4.1.3.18). Other weeds present included common cocklebur and mixed infestations of entireleaf, ivyleaf, pitted, and tall morningglories. PRE options were alachlor or alachlor plus metribuzin plus chlorimuron. Early POST options included chlorimuron, chlorimuron plus thifensulfuron, and no herbicide applied 3 wk after planting. Late POST options were chlorimuron and no herbicide applied 5 wk after planting. POST herbicides were more effective than PRE herbicides on all weeds. Chlorimuron and chlorimuron plus thifensulfuron applied early POST were equally effective on these weeds and usually more effective than chlorimuron applied late POST. There was no advantage of two POST applications compared with a single early POST application. Greatest net returns were obtained in systems using only early POST herbicides. There was no economic advantage from using metribuzin plus chlorimuron PRE in systems that included an early POST herbicide.

The weed control spectrum of clomazone, the influence of clomazone on the performance of other herbicides, and the performance of tank mixtures containing clomazone were evaluated from 1985 through 1987. Clomazone applied preemergence at 280 g ai/ha controlled 90 to 100% of barnyardgrass, giant foxtail, goosegrass, large crabgrass, seedling johnsongrass, prickly sida, and velvetleaf. Clomazone at reduced rates was more effective applied preemergence than preplant-incorporated for 10 of 23 weed species. Clomazone enhanced imazaquin activity on entireleaf morningglory and sicklepod in 1986. A tank mixture of clomazone, imazaquin, and metribuzin at half the labeled rates reduced soybean injury, increased soybean yield, and controlled weeds as well as the mixture at labeled rates.

Studies were conducted in Florida to evaluate interference of common cocklebur with peanut. Peanut yield reduction ranged from 0 to 88% for common cocklebur densities of 0–32 plants 8 m−1 of peanut row, and predicted loss was similar under normal moisture conditions. When moisture levels were above normal, the impact on yield was 9–24% less than when soil moisture was normal. Common cocklebur caused peanut yield loss if allowed to interfere for more than the first 2 wk after crop emergence, and peanut had to be common cocklebur free for at least 12 wk to prevent a yield reduction. These results show common cocklebur to be more competitive with peanut than other weeds evaluated previously.

Barnyardgrass and many broadleaf weeds were severely stunted by POST applications of isoxaben. Most grasses were only moderately affected by isoxaben at rates up to 1 kg/ha. POST activity was enhanced by soil interception, but evident with foliar interception alone. Cell swelling in stems and in interveinal leaf lamina was observed after foliar application. A radiotracer study in redroot pigweed showed that only a small amount (3.3% of applied) of isoxaben entered the leaf following foliar application, and that little (0.08% of applied) isoxaben migrated beyond the point of application. The potential of isoxaben as a POST herbicide may be limited, in part, by poor absorption and translocation.

Soil-water profiles of cotton, several weeds, and bare soil were compared in research conducted in 1989 and 1990 near Perkins, OK. Neutron probe access tubes were installed prior to plant establishment to facilitate nondestructive volumetric water content determinations at selected depths throughout the season. Planting was in a double-circle pattern concentric around each neutron probe access tube. Phenological and soil-water data were collected weekly. As plants began to senesce, aboveground biomass yield data were collected. In 1989, rainfall frequently replenished soil-water in the upper soil profile. The plants used the recharge water to varying degrees, particularly late in the season. Common cocklebur and johnsongrass extracted soil-water from greater depths than cotton and velvetleaf throughout the season. In 1990, the largest differences detected between bare soil and weeds early in the season were measured for common cocklebur, devil's-claw, and silverleaf nightshade. Later in the season, however, there was little difference in soil-water content in the upper soil profiles for all species. Johnsongrass emerged later than the other species in 1990 which affected its relative soil-water extraction.