Barnyardgrass 7 to 25 cm tall was controlled 48 to 74% with paraquat (420 g/ha), 83 to 87% with glyphosate (1120 g/ha), and 85 to 91% with glufosinate (840 g/ha). In most cases barnyardgrass control was not enhanced with addition of residual herbicides metribuzin plus chlorimuron, metribuzin, or imazaquin. Barnyardgrass and seedling johnsongrass no more than 13 cm tall was controlled at least 90% regardless of herbicide treatment. When rhizome and seedling johnsongrass were present, control with glyphosate was 96% compared with 55% for paraquat and 86% with glufosinate. Tank-mixtures of non-selective and residual herbicides generally enhanced control of entireleaf and pitted morningglory, hemp sesbania (15 to 30 cm), and prickly sida (15 to 18 cm). Soybean yields in most cases were not increased with addition of residual herbicides. Yield following glufosinate applied alone was 25% higher than following paraquat, and for all herbicide treatments yields were at least 45% greater than when a non-selective herbicide was not applied.

Foramsulfuron has recently been registered for weed control in corn in Ontario, but there is very little information on the rate of foramsulfuron required to obtain at least 90% weed control. Our objective was to determine the foramsulfuron rates giving at least 90% weed control while maintaining crop yield loss due to weed interference and injury at less than 5%. Ten field trials were conducted at five Ontario locations (Exeter, Harrow, Ridgetown, Woodslee, and Woodstock) in 2001 and 2002 to evaluate the effectiveness of foramsulfuron at rates ranging from 8.75 to 140 g ai/ha. To obtain a reduction in biomass of 90% (I90) at 78 d after treatment (DAT), foramsulfuron must be applied to common lambsquarters at 68 g/ha and to common ragweed at 86 g/ha, respectively. For green foxtail a foramsulfuron rate of 25 g/ha was required to achieve 90% control. The application of foramsulfuron caused injury to corn at 7 DAT at Ridgetown and Woodstock only, but did not exceed a rating of 10%; by 14 and 28 DAT no corn injury was recorded at any location. Corn yield of at least 95% of a weed-free check was obtained at Woodstock when foramsulfuron was applied at 70 g/ha. At Exeter and Woodslee yield was 90% of the weed-free check at a foramsulfuron rate of 35 g/ha. Finally, at Harrow and Ridgetown, corn yield was lowered at all foramsulfuron rates because of broadleaved weed interference. Tank-mixing foramsulfuron with dicamba plus prosulfuron improved common lambsquarters and common ragweed control and final corn yield was improved by more than 20% when compared with an application of foramsulfuron alone. Thus, these results show that weed control with foramsulfuron is species specific and that tank mixtures with a broadleaf herbicide may be required for broad-spectrum weed control and to protect the full yield potential of corn.

Greenhouse and laboratory studies were conducted to determine the effect of 22 postemergence corn broadleaf herbicide combinations on the efficacy of sethoxydim applied to giant foxtail, large crabgrass, and shattercane. Eighteen combinations caused a reduction in sethoxydim efficacy on at least one grass species. Dicamba, atrazine plus dicamba, atrazine plus bentazon, bromoxynil, primisulfuron, CGA-152005 plus primisulfuron, MON 12000, and flumetsulam plus clopyralid plus 2,4-D (NAF-73) were evaluated further on the efficacy and foliar absorption of sethoxydim applied to giant foxtail, large crabgrass, and shattercane. In timing studies, applying all herbicide combinations at 7 or 3 d before sethoxydim application eliminated significant antagonistic interactions. However, applying NAF-73, primisulfuron, or CGA-152005 plus primisulfuron 1 d prior resulted in a reduction in sethoxydim efficacy on at least one grass species. Dicamba, atrazine plus dicamba, and atrazine plus bentazon decreased 14C-sethoxydim absorption 9 to 63% across grass species. Replacing crop oil concentrate (COC) with DASH increased sethoxydim absorption when applied with these herbicides but not to the full extent of sethoxydim applied alone with DASH. Sethoxydim efficacy was retained or improved with DASH when applied with dicamba, atrazine plus dicamba, atrazine plus bentazon, or bromoxynil. When primisulfuron, CGA-152005 plus primisulfuron, MON 12000, or NAF-73 was applied with 14C-sethoxydim no effect on sethoxydim absorption was observed. DASH was less effective than COC at restoring sethoxydim efficacy when applied with these herbicides.

A seedling bioassay was developed for the rapid diagnosis of resistance to clethodim and fluazifop-P in johnsongrass. The assay was based on differences in the coleoptile length of susceptible (S) and resistant (R) seedlings exposed to clethodim and fluazifop-P in petri dishes for 5 d. Bioassay concentrations of 0.09 mg/L clethodim and 0.18 mg/L fluazifop-P were chosen as discriminant based on rate responses of each biotype to increasing herbicide dose. At 5 d after treatment (DAT), the amounts of clethodim required to reduce coleoptile length by 50% (GR50) for the R and S seedlings were 462.5 and 24.8 mg/L, respectively, resulting in an R:S ratio of 18.7. The fluazifop GR50 values for the R and S seedlings were 618.7 and 17.5 mg/L, respectively, resulting in a R:S ratio of 35.4.

Spatial patterns of the exotic riverine knotgrass (Paspalum distichum L.) were examined in Mediterranean river basins in Southwestern Iberia. The major goals of this study were to assess the degree of invasibility of riparian habitats by this species and to determine the influence of environmental factors and human-induced disturbances that this knotgrass has on both the landscape and the habitat scales. The present study demonstrates the ability of knotgrass to invade riparian habitats in Portuguese freshwater ecosystems. However, most of the spatial variation of the knotgrass cover seemed to be driven by local factors, such as fine sediment enrichment and the fragmentation of riparian woods, and by other anthropogenic interferences in relation to both the fluvial system and the surrounding landscape.

The response of trifluralin-susceptible (S) and -resistant (R) green foxtail biotypes to herbicides belonging to several chemical groups was compared to determine the cross-resistance pattern of the R-biotype. Dose-response experiments conducted in the growth chamber indicated that R-green foxtail was resistant to other dinitroanilines and a chemically unrelated mitotic disrupter herbicide, but not to nine other herbicides belonging to seven chemical families. The response of S- and R-green foxtail to increasing dosages of ethalfluralin, applied PPI in rapeseed, was investigated in a field experiment in 1989 and 1990. The R-biotype was 7 times more resistant to ethalfluralin than the S-biotype based on density determinations 4 wk after emergence. Seven times higher dosage was required to reduce R-seed production by 50% than to reduce S-seed production by the same amount. The initial reductions in density of R- and S-plants at the recommended dosage of ethalfluralin in rapeseed (1.4 kg ha−1) was 35% and 95%, respectively. The effective kill (seed yield reduction) of R- and S-biotypes was 55% and 99%, respectively. The results indicate that ethalfluralin will not effectively control R-green foxtail. However, several other herbicides with different mechanisms of action can be used to effectively control R-foxtail, thereby reducing any adverse effects of their interference on crop production.

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.

Twelve grass genotypes were evaluated for competitiveness with leafy spurge and herbage yield in two sites in North Dakota. ‘Rebound’ smooth brome, ‘Rodan’ western wheatgrass, ‘Bozoisky’ Russian wildrye, and ‘Arthur’ Dahurian wildrye reduced leafy spurge stem density an average of 63% after 3 yr in a silty clay soil at Fargo. ‘Reliant’ intermediate wheatgrass reduced leafy spurge stem density every year for 3 yr, including an 85% reduction the second year after planting, and consistently produced high herbage yields. Rebound smooth brome and Reliant intermediate wheatgrass averaged 72% leafy spurge reduction 3 yr after seeding in a loamy sand soil at Jamestown. Reliant intermediate wheatgrass and ‘Manska’ pubescent wheatgrass provided the most consistent herbage production, which averaged about 2,000 kg/ha annually for 3 yr.

The influence of adjuvants, inorganic salts, and herbicide formulations on the antagonistic effect of Na-bentazon on sethoxydim absorption was studied in quackgrass. Adjuvant BCH 815 00, at 2.4 L ha−1 alone or at 1.2 L ha−1 combined with 1.1 kg ha−1 of ammonium sulfate, added to the sethoxydim and Na-bentazon spray mixture overcame the antagonism on 14C-sethoxydim absorption in quackgrass. Crop oil concentrate at rates up to 9.6 L ha−1 did not overcome the antagonism. Adding ammonium phosphate or ammonium nitrate to the spray solution was as effective as adding ammonium sulfate in overcoming the antagonism caused by reduced absorption of sethoxydim even from the combination of Na-bentazon plus Na-acifluorfen. Ammonium salts and NH4-bentazon overcame the antagonism of Na-bentazon by forming readily absorbed NH4-sethoxydim.

Field studies were initiated in 1985 and 1986 to evaluate the effects of dalapon, glyphosate, imazapyr, and sulfometuron applications to established cogongrass alone or in combination with either mowing or discing. Mowing and discing treatments were performed 4 mo before and 8 months after the herbicide treatments in the 1985 experiments and 2 months before and 7 months after the herbicide treatment in the 1986 experiments. When applied alone, glyphosate at 3.4 kg ai/ha and imazapyr at 0.8 kg ai/ha caused the greatest reduction in shoot and rhizome biomass about 2 yr after application. However, the rhizome infestation was reduced only 43% by glyphosate and 51% by imazapyr, as compared to the nontreated control. With no herbicide, two mowing or discing were generally more effective than a single mowing or discing treatment. The reduction in shoot and rhizome biomass for two mowing without herbicide was 65 and 38% and for two discing, 73 and 66%, respectively. Acceptable (> 80%) levels of cogongrass control, based on reductions in rhizome biomass occurred only when applications of dalapon, glyphosate, or imazapyr were made in combination with two discing despite the fact that mowing before and after treatment reduced shoot biomass by at least 89%.

Effectiveness of the common soil fungus Sclerotinia sclerotiorum as a biological control for spotted knapweed and its effect on competitive interactions between spotted knapweed and bluebunch wheatgrass were evaluated in a growth chamber study using addition series methods. Total seeding densities ranged from 2000 to 60 000 seeds/m2. Mean bluebunch wheatgrass plant weight was 3.5 times greater than spotted knapweed weight per plant, respectively. Coefficient ratios estimating species interaction showed bluebunch wheatgrass density had a greater influence than spotted knapweed density on both bluebunch wheatgrass and spotted knapweed weights (2.11 and 0.51, respectively) when not under the influence of S. sclerotiorum. Niche differentiation ratios indicated a lack of resource partitioning between species (1.11). S. sclerotiorum reduced spotted knapweed density by 68 to 80% without reducing bluebunch wheatgrass density. Spotted knapweed weight per plant also was reduced by the addition of 5. sclerotiorum (1.4 to 1.2 mg) but there was not a corresponding increase in bluebunch wheatgrass weight. S. sclerotiorum decreased competition between spotted knapweed and bluebunch wheatgrass. This study provides evidence that establishment of bluebunch wheatgrass on spotted knapweed infested rangeland may be improved by combining S. sclerotiorum with high grass seeding rates.

Field studies were conducted at two locations in 1997 and 1998 to evaluate crop injury, weed control, yield, and net economic returns of single and sequential postemergence applications of labeled and reduced rates of glyphosate to no-till, glyphosate-resistant soybean planted in narrow rows. Sequential applications provided at least 91% control of giant foxtail, while single applications provided at least 86% control with labeled rates and 68–93% control with reduced rates. Common waterhemp control was slightly higher with sequential vs. single treatments and with labeled rates vs. reduced rates. Velvetleaf control was greater than 96% with all treatments. Common cocklebur control was 90% or higher with all treatments except a single application of glyphosate at 210 g/ha. Lower control of giant foxtail and common waterhemp with single-application, reduced-rate treatments in two of the four trials resulted in lower yields. Overall, sequential applications, regardless of rate, provided greater weed control, yield, and net income and lower coefficients of variation (C.V.s) of net income than reduced-rate single applications. Single-application treatments showed a trend of decreased weed control, yield, and net income and higher C.V.s of net income with reduced rates of glyphosate.

Contact, induction, and corona electrostatic charging systems for pesticide spraying are reviewed and are compared with uncharged spraying systems. When uncharged sprays are poorly intercepted by plants, charging significantly increases deposition, drawing from the reservoir normally deposited on the soil. Post-emergent herbicide spraying is the one area where the benefits of electrostatic charging are identified least easily. For insecticides and fungicides where the young crop is the ‘general’ target, increased capture of charged spray may permit reducing doses with economic and environmental benefits. While charging may not increase total capture where uncharged spray interception is good, it does alter spray distribution throughout the crop canopy. The biological consequences of modifying spray distribution depend upon the ‘real’ pesticide target. In situations where the crop acts as an electrical shield limiting spray penetraton, air assistance is necessary to augment charged spray deposition within the crop canopy. Drift of charged spray clouds should be related to drop spectra, velocities and trajectories and requires further study as do protocols for spray charge measurement and definition. In addition to biological performance, the transfer of electrostatic technology to farms is limited because of financial, legal, and practical factors. Identifying specific major crop/pest problems will help to introduce electrostatic spraying, which will complement, rather than replace, traditional spray systems.

Field research was conducted at three locations in Iowa to determine the effectiveness of glyphosate for velvetleaf control in glyphosate-resistant soybean. Velvetleaf survival ranged from 46 to 81% when treated with 420 g ae/ha glyphosate, whereas survival ranged from 13 to 37% at the 840 g/ha rate. At two locations, velvetleaf survival was greater when treated at the 12- to 17-cm height compared with application to either 8- to 10- or 20- to 30-cm-tall plants. Growth of plants surviving glyphosate application was greatly reduced, with the high glyphosate rate reducing velvetleaf aboveground biomass by over 90% compared to untreated plants. A linear relationship between biomass and capsule number was observed for both control plants and plants surviving glyphosate, both having slopes of approximately one. Velvetleaf surviving glyphosate treatment should have minimal impact on soybean yield due to reduced growth; however, surviving plants may replenish the seed bank, leading to future management problems.

The extended production of allelochemicals from a living mulch cover crop may potentially enhance weed management and crop productivity compared with traditional zucchini squash production systems. However, the efficacy of a living mulch cover crop in no-tillage (NT) systems with herbicides has not been determined for many vegetable crops. The objective of this research was to evaluate weed management and zucchini squash production using the combination of NT and a herbicide-suppressed winter rye cover crop with or without PRE herbicides. When used in combination with herbicides, the winter rye living mulch reduced the biomass of redroot pigweed compared to the herbicides applied alone, but did not influence the biomass of smooth crabgrass for any herbicide treatment. Visual estimates of weed control were similar for each herbicide treatment with and without the winter rye living mulch. The herbicide-suppressed winter rye resulted in excessive stunting of zucchini squash at 56 d after treatment which correlated with 20 and 50% squash yield reductions for the 2004 and 2005 growing seasons, respectively. Although some squash yield loss may have resulted from direct competition with the winter rye living mulch, yield reductions most likely resulted from allelopathy. The winter rye living mulch was the primary contributing factor for reduced squash yield and did not interact with herbicide treatment. All treatments containing herbicides resulted in yields similar to the weed-free treatment. Because of excessive zucchini injury, this research suggests that the use of herbicide-suppressed winter rye living mulch does not appear to be a feasible option for increased weed control in zucchini squash production regardless of the herbicide treatment.

Field experiments were conducted in 1996 and 1997 to evaluate the effects of six johnsongrass densities on picker- vs. stripper-harvest efficiency, fiber properties, loan rate, and lint yield loss of cotton. The weed densities employed were 0 (the check), 3, 4, 5, 8, and 15 plants/15 m of row. With three or fewer weeds in 1996 and four or fewer in 1997, harvest efficiencies were 4.9 to 7.6% higher for stripper- than for picker-harvested cotton. At four and higher weed densities in 1996 and at five and higher in 1997, differences in harvest efficiency between the two machines were not significant. For each weed per 15 m of row, stripper-harvest efficiency in 1996 and 1997 was reduced 0.3 and 0.6%, respectively; picker-harvest efficiency was not affected by the johnsongrass densities included herein. Fiber fineness (i.e., micronaire) was significantly reduced at densities of 8 weeds/15 m of row in 1997 and at 15 weeds in both years. A questionable increase in staple length was detected at the 3-weed density in 1996. Reductions in fiber strength were noted in 1997 at densities of 3, 8, and 15 weeds/15 m of row. No influences on fiber length uniformity were shown. In 1996 the loan rate for picker-harvested lint was 570 points/kg higher than for stripper-harvested lint at 8 weeds/15 m of row. In 1997 it was 741, 801, 1,058, 1,225, 1,074, and 1,329 points/kg higher at weed densities of 0, 3, 4, 5, 8, and 15 plants/15 m of row, respectively. In 1997 picker-harvest loan rate was reduced 49 points/kg of lint, and stripper-harvest loan rate was reduced 85 points. Over both years, picker-harvest lint yield was reduced 32 to 43 kg/ha (3.9 to 5.5%) for each weed per 15 m of row, and stripper-harvest lint yield was reduced 29 to 43 kg/ha (3.5 to 5.2%).

Studies were conducted to determine the usefulness of HOE-39866 (HOE-00661) in chemical fallow systems on the Canadian prairies. HOE-39866 at 0.5 to 1.0 kg ai/ha controlled Russian thistle, kochia, green foxtail, wild oats, and wheat comparable to paraquat, glyphosate, and glyphosate plus the isopropylamine salt of 2,4-D. However, control of barley with HOE-39866 was unacceptable. HOE-39866 was compatible in tank mixtures with ammonium sulfate, paraquat, chlorsulfuron, and metsulfuron. Ammonium sulfate improved weed control when HOE-39866 was applied at 0.25 kg/ha but not at 0.75 kg/ha. Adding paraquat at 0.07 to 0.21 kg ai/ha to HOE-39866 improved control of grass species over HOE-39866 alone. Adding chlorsulfuron and metsulfuron to HOE-39866 provided greater initial control of certain species as well as residual control of many weeds. HOE-39866 alone or in conjunction with other herbicides is an alternative to the herbicides used in chemical fallow systems.

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.

Fifty-five soybean cyst nematode (SCN)–infested production fields across Indiana were surveyed in March 2004 to assess broadleaf winter weed prevalence. The most frequently occurring weeds were common chickweed (87%), speedwell (83%), buttercup (58%), and henbit (53%). Henbit and wild garlic were present at the highest average densities, both occurring at greater than 50 plants/m2. Based on relative abundance indices, common chickweed and henbit were the most prevalent winter weeds in this survey. As a composite, winter weed hosts of SCN were found in 93% of fields and occurred at an average density of 151 plants/m2. No correlation existed between weed density and SCN egg counts. Frequency, uniformity, density, and diversity indices for individual weed species were generally higher in the southern region of Indiana than in the north. Thus, the region of highest risk for SCN reproduction and population increase on winter weeds in Indiana appears to be in the southern part of the state.

A 3-yr field experiment was initiated in 2001 to evaluate weed suppression and sweetpotato productivity in three organic sweetpotato production systems. Organic systems were (1) compost and no cover crop with tillage (Org-NC), (2) compost and a cover crop mixture of hairy vetch and rye incorporated before transplanting (Org-CI), and (3) compost and the same cover crop mixture with reduced tillage (Org-RT). A conventional system with tillage and chemical controls (Conv) was included for comparison. Suppression of monocot and dicot weed density and biomass was similar between Org-NC and Org-CI each year, and were frequently similar to Conv. Org-RT was as effective as Org-NC in controlling dicot weed density and biomass each year, but did not suppress monocot weeds. At sweetpotato harvest, an increase in cover crop surface residue biomass in Org-RT was associated with a decrease in cumulative total weed density (R 2 = 0.43, P = 0.0001); however, the amount of that residue was insufficient to suppress late-emerging monocot weeds. Total sweetpotato yield in Org-RT was at least 45% lower than other systems in 2002 and was most likely due to an increase in monocot weed density and biomass concurrent with a decrease in sweetpotato vine biomass. Total sweetpotato yield was similar among all systems in 2001 and 2004; the exception was lowest yields obtained in the Org-RT system in 2002. Organically managed sweetpotato with or without an incorporated cover crop produced sweetpotato yields equal to conventionally managed systems despite difficulties controlling weeds that emerged later in the season.