A two-year experiment was conducted to determine if tank-mixes of postemergence (POST) herbicides would consistently control large crabgrass and goosegrass in common bermudagrass turf compared to herbicide alone treatments. Tank-mixes of MSMA plus quinclorac at 2.2 + 0.6 kg/ha effectively controlled large crabgrass (≥ 81%) for 10 to 11 weeks during 1993 and 1994. The control from MSMA plus dithiopyr at 2.2 + 0.3 kg/ha was higher during this period than when each herbicide was applied alone at the same rate. There was no increase in large crabgrass control from tank-mixes of MSMA and diclofop applied in a single application, when compared with two applications of MSMA applied at 2.2 kg/ha. Goosegrass control at 9 wk after tank-mixed treatments of MSMA (2.2 kg/ha) and diclofop (≥ 0.3 kg/ha) in 1994 was lower (12 to 28%) than when diclofop at 1.1 kg/ha was applied alone (85%). Tank-mixes of MSMA with quinclorac or dithiopyr did not control goosegrass. In general, common bermudagrass injury was no higher from herbicide combinations than when each was applied alone. An exception occurred at 1 wk after treatment in 1993 when common bermudagrass injury was higher from tank-mixes of MSMA plus diclofop at 2.2 + 1.1 kg/ha, than when either herbicide was applied alone.

A 2-yr field study was conducted from 2002 to 2003 on a Dundee silt loam soil at the Southern Weed Science Research Unit Farm, Stoneville, MS (33°26′N latitude), to examine the effects of hairy vetch cover crop (hairy vetch killed at corn planting [HV-K], hairy vetch killed in a 38-cm-wide band centered over the crop row at corn planting [HV-B], hairy vetch left alive [HV-L], and no hairy vetch [NHV]) and glyphosate postemergence (broadcast, banded, and no herbicide) application on weed control and yield in glyphosate-resistant corn. Two applications of glyphosate at 0.84 kg ae/ha were applied 3 and 5 wk after planting (WAP) corn. Hairy vetch dry biomass was higher in HV-L (4,420 kg/ha) and HV-B (4,180 kg/ha) than in HV-K (1,960 kg/ha) plots at 7 WAP. Hairy vetch reduced densities of pitted morningglory, prickly sida, and yellow nutsedge in HV-B and HV-L compared with NHV plots, but hairy vetch had no effect on densities of barnyardgrass, johnsongrass, and large crabgrass at 7 WAP regardless of desiccation. Total weed dry biomass at 7 WAP was lower in HV-B and HV-L than in HV-K and NHV plots. Corn yield was higher in HV-K (10,280 kg/ha) than in HV-B (9,440 kg/ha) and HV-L (9,100 kg/ha), and yields were similar between HV-K and NHV (9,960 kg/ha). Glyphosate applied broadcast resulted in the highest corn yield (11,300 kg/ha) compared with a banded application (10,160 kg/ha). These findings indicate that hairy vetch cover crop has the potential for reducing the density of certain weed species in glyphosate-resistant corn production systems; however, optimum weed control and higher yield were obtained when glyphosate was used.

An experimental turfgrass growth regulator, V-10029, was compared with trinexapac-ethyl, a growth regulator used commonly on highly maintained turfgrasses, to evaluate growth suppression patterns and suppression of seedhead formation; the latter was evaluated on turfgrass species and annual bluegrass, a weedy species that appeared and developed seedheads in tall fescue. Plugs of creeping red fescue, Kentucky bluegrass, perennial ryegrass, and creeping bentgrass were taken from the field into a greenhouse. V-10029 at three rates (0.015, 0.029, and 0.059 kg/ha) was compared to an untreated control and trinexapac-ethyl at a label rate (0.382 kg/ha for perennial ryegrass and 0.287 kg/ha for the other four species). Of the eight replications for each treatment, four were not mowed for the purpose of evaluating suppression of seedhead formation, and four were used for weekly clipping collection to evaluate growth suppression. Compared to the untreated control, V-10029 at all three applied rates caused significant seedhead suppression in both tall fescue infested with annual bluegrass (> 90%) and perennial ryegrass (50 to 80%). Trinexapac-ethyl was not as effective, causing seedhead suppression levels of 57% in annual bluegrass found in tall fescue and 43% in perennial ryegrass. V-10029 caused unacceptable levels of discoloration (> 20%) in all turfgrass species, and discoloration increased with increasing rates of application. Patterns of growth suppression for tall fescue, Kentucky bluegrass, and perennial ryegrass, in response to V-10029 at all rates and to trinexapac-ethyl, were similar on a percent of suppression basis. Growth of creeping bentgrass was suppressed by V-10029 only at high rates. In contrast, creeping red fescue was significantly injured by V-10029 at all rates. The greatest growth suppression, in response for all treatments, occurred 2 to 3 wk after application. The effect of trinexapac-ethyl dissipated after 4 wk, while V-10029 was effective until 5 to 7 wk after treatment. Observed effects of V-10029 were consistent with its activity as an ALS-inhibiting herbicide and, therefore, as a Class D turfgrass growth regulator.

Development of herbicide-tolerant plants is the focus of considerable research. Some projects aim to increase herbicide use or promote use of particularly environmentally damaging chemicals, and thus may lead to environmental degradation. Other projects aim to develop herbicide-tolerant plants that allow substitution of newer less environmentally damaging chemicals for older more damaging ones. To the extent they divert research dollars from development of other weed control strategies, these projects may also jeopardize environmentally sound weed control. The paper concludes with policy recommendations concerning a) public sector research priorities, b) planting of herbicide-tolerant trees in forests, and c) regulation of herbicide-tolerant crops.

Corn gluten meal (CGM) and white mustard seed meal (MSM) can release biologically active allelochemicals and have been demonstrated to be useful as PRE alternative weed control products. The objective of this study was to compare the effects of CGM and MSM on the emergence and aboveground dry weight of five broadleaf and two grass weed species. Greenhouse experiments were conducted using 26 by 53 cm plastic trays filled with a mix of field soil and potting soil (4 : 1 by wt). CGM and MSM were mixed with 1.5 kg of soil mix and applied at rates equivalent to 2,240, 4,480, and 6,720 kg ha−1. Overall, MSM was more effective than CGM for controlling weeds. Averaged over application rates and compared to the nontreated control, emergence rates were 17, 27, and 34% for kochia, common lambsquarters, and barnyardgrass, respectively, in CGM-amended soil, and 14, 13, and 6% for kochia, common lambsquarters, and barnyardgrass, respectively, in MSM-amended soil. Averaged over application rates, green foxtail and common lambsquarters aboveground dry biomass were 40 and 25% of the nontreated control, respectively, in CGM-amended soil. Green foxtail and common lambsquarters shoot biomass in MSM-amended soil was 13 and 5% of the nontreated control, respectively. Significant interactions were observed for meal by rate on redroot pigweed seedling emergence and redroot pigweed, barnyardgrass (Moscow), and annual sowthistle (Moscow) aboveground dry biomass. These interactions can be attributed to the fact that herbicidal effects were less evident in response to higher application rates using MSM compared to higher CGM application rates. Overall, this greenhouse study indicates MSM is more effective than or at least equal to CGM for broadleaf and grass weed control at the same application rate.

Approximately 50% of the genetically modified herbicide-resistant corn hectares in the United States are treated only with POST-applied herbicides for weed management. Although a high degree of efficacy can be obtained with POST-applied herbicides, delayed timing of application may result in substantial corn yield loss. Our goal was to characterize on-farm corn–weed communities prior to POST herbicide application and estimate potential corn-yield loss associated with early-season corn–weed competition. In 2008 and 2009, field surveys were conducted across 95 site-years in southern Wisconsin and recorded weed species, density, and height in addition to crop height, growth stage, and row spacing. WeedSOFT® was used to predict corn yield loss. Common lambsquarters, velvetleaf, dandelion, common ragweed, and Amaranthus species were the five most abundant broadleaf weed species across site-years, present in 92, 86, 59, 45, and 44% of all fields, respectively, at mean densities of 19, 3, 3, 4, and 3 plants m−2, respectively. Mean plant heights among these species were 17 cm or less. Grass and sedge species occurred in 96% of fields at a mean density of 25 plants m−2 and height of 7 cm. The mean and median of total weed density across site-years were 96 and 52 plants m−2, with heights of 14 and 13 cm, respectively. Mean predicted corn yield loss was 4.5% with a mean economic loss of $62 ha−1. However, predicted yield loss was greater than 5% on one-third of the site-years, with a maximum of 26%. These results indicate that delayed application of POST herbicides has led to corn yield loss due to early-season weed-crop competition on a substantial number of fields across southern Wisconsin, and suggest that management tactics need to be improved to protect corn yield potential fully.

Common bermudagrass is a problematic weed within tall fescue turfgrass. Field research was conducted from 2010 to 2012 in Knoxville, TN, evaluating the efficacy of sequential applications of topramezone (12.5 and 25 g ha−1), triclopyr (1,120 g ha−1), and mixtures of topramezone + triclopyr for bermudagrass control in tall fescue turf. Sequential applications of fenoxaprop + triclopyr (100 + 1,120 g ha−1) were included for comparison. Three applications of each treatment were applied at 21-d intervals during July, August, and September of 2010 and 2011. Plots were stripped to receive tall fescue interseeding at 0 or 490 kg ha−1 during September 2010 and 2011. Bermudagrass control with topramezone + triclopyr mixtures was greater than topramezone or triclopyr applied alone 14 wk after initial treatment (WAIT) each year. In the second year of this study, topramezone + triclopyr mixtures controlled bermudagrass 27 to 50% compared to 27% for fenoxaprop + triclopyr by 52 WAIT. However, bermudagrass control with topramezone + triclopyr mixtures increased to 88 to 92% by 52 WAIT when accompanied with tall fescue interseeding at 490 kg ha−1. Future research should evaluate effects of interseeding on the efficacy of different herbicides for weed control in cool- and warm-season turf.

Greenhouse studies were conducted to determine the response of velvetleaf, common cocklebur, and ivyleaf morningglory to mesotrione and atrazine applied PRE, and to characterize the nature of any interaction between mesotrione and atrazine. Sensitivity to mesotrione was as follows: velvetleaf > common cocklebur > ivyleaf morningglory. Sensitivity to atrazine was as follows: ivyleaf morningglory > common cocklebur > velvetleaf. Combinations of mesotrione and atrazine resulted in at least an additive interaction. The activity of mesotrione and atrazine applied in combination was generally additive for control of velvetleaf and ivyleaf morningglory but was synergistic for several rate combinations.

Dodder is a serious parasitic weed in the crops in which it is a problem (particularly citrus). Alternaria destruens is the active ingredient in a registered bioherbicide for control of dodder species. In greenhouse studies, the treatments applied to citrus parasitized with field dodder were a nontreated control; oil at 7.5% v/v in water; ammonium sulfate at 0.125% w/v in water; glyphosate at 0.02 kg ae/L; A. destruens at 1.8 × 1010 spores/L; A. destruens (1.8 × 1010 spores/L) + oil at 7.5% v/v in water; and a mixture of A. destruens (1.8 × 1010 spores/L) + oil at 7.5% v/v in water + glyphosate at 0.02 kg ae/L + ammonium sulfate 0.125% w/v (the mixture treatment). The highest disease or damage severity rating out of all treatments, measured as the area under the disease or damage progress curve (AUDPC), was obtained for the mixture treatment. By 35 d after treatment, all field dodder plants that received the mixture treatment were dead but the host plant, citrus, was not. These results indicate the feasibility of integrating glyphosate, ammonium sulfate, and A. destruens to manage dodder.

Studies were conducted at Clayton, Lewiston-Woodville, and Rocky Mount, NC, to evaluate weed and cotton response to herbicide systems in glyphosate-resistant cotton in 1995 and 1997. Herbicide systems evaluated included various combinations of soil-applied (trifluralin and fluometuron) and postemergence (POST) (glyphosate or pyrithiobac) herbicides with or without late postemergence-directed (LAYBY) treatments of cyanazine plus MSMA. Glyphosate-resistant cotton injury was less than 5% with all herbicide treatments. Glyphosate POST systems were as efficacious in weed control as other herbicide systems. Depending on location, glyphosate and pyrithiobac POST systems usually required cyanazine plus MSMA LAYBY for season-long control of common lambsquarters, goosegrass, large crabgrass, pitted morningglory, prickly sida, and Texas panicum. Glyphosate POST applied as needed provided weed control equivalent to soil-applied plus POST herbicides, although lint yield was slightly reduced depending on location. Herbicide systems that included soil-applied herbicides required one to two treatments of glyphosate POST and post-directed for season-long weed control and high cotton lint yields, whereas the same herbicide systems without soil-applied herbicides required two to three glyphosate treatments. In all herbicide systems, a residual soil-applied or LAYBY herbicide treatment increased yield compared with glyphosate POST only systems. Location influenced weed control and cotton yield. Generally, as herbicide inputs increased, yield increased.

California and Michigan strains of Xanthomonas campestris pv. poannua were compared as biocontrol agents for the annual and perennial subspecies of annual bluegrass. Additionally, inoculation frequency was evaluated for improved control of the perennial subspecies in New York. The two bacterial strains were similarly virulent to annual bluegrass in both growth chamber and field tests. When inoculated once per week for 4 wk, the annual and perennial subspecies were controlled 92 and 82% in growth chamber tests, but only 11 and 7% in field tests, respectively. Control of established annual bluegrass in the field was improved to a maximum of about 40% by increasing inoculation frequency to three times per wk for 4 wk, but recovery occurred 2 to 5 wk after inoculations were discontinued. Creeping bentgrass was not affected by the bacterium.

Field experiments were conducted in Oklahoma to determine the effects of winter wheat seeding date and cheat infestation level on cultural cheat control obtained by increasing winter wheat seeding rates and decreasing row spacing. Seeding rate and row spacing interactions influenced cheat density, biomass, or seed in harvested wheat (dockage) at two of three locations. Suppressive effects on cheat of increasing wheat seeding rates and reduced row spacings were greater in wheat seeded in September than later. At two other locations, increasing seeding rate from 67 to 101 kg ha–1 or reducing row spacings from 22.5 to 15 cm increased winter wheat yield over a range of cheat infestation levels.

The effects of rainfall on the efficacy of 11 foliar-applied herbicides were evaluated for their control of seedling johnsongrass [Sorghum halepense (L.) Pers. # SORHA] in greenhouse experiments during 1984 and 1985 at Stoneville, MS. Time intervals between herbicide application and rainfall (at 1.27 cm in 10 ± 0.5 min) ranged from 5 to 60 and 30 to 240 min depending on herbicide classification. In general, the phosphonic acid herbicides glyphosate [N-(phosphonomethyl)glycine] and SC-0224 (trimethylsulfonium carboxymethylaminomethylphosphonate) at 0.99 kg ai/ha required rain-free periods ≥240 min to control seedling johnsongrass effectively. The selective postemergence grass herbicides generally required ≥60 min to control seedling johnsongrass effectively when control without rainfall was ≥85%. Among the selective herbicides tested, haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl]oxy] phenoxy] propanoic acid} and DPX-Y6202 {ethyl[2-[4-(6-chloro-2-quinoxalinyl)oxy] phenoxy] propionic acid} at 0.06 kg ae/ha required the shortest time between herbicide application and rainfall to be effective. As herbicide rates were reduced, the effects of rainfall increased.

Experiments were conducted from 2000 to 2002 at two locations each year to determine if lactofen and imazethapyr injury to soybean could be detected using digital aerial imagery and ground-based optical remote sensing. Lactofen and imazethapyr were applied at base rates of 105 and 71 g/ha, respectively, and at 0, 2X, and 4X rates. Treated plots were evaluated between 7 and 21 d after treatment for crop injury using a ground-based radiometer and a system using computer analysis of digital aerial imagery. Both the ground-based radiometer and the digital aerial imagery were effective in detecting herbicide injury under most conditions. The digital aerial imagery system was found to be more sensitive in detecting herbicide injury than the ground-based radiometer system. Herbicide or herbicide rate had a significant effect on normalized differential vegetation indices (NDVI) derived from digital aerial imagery in four of four site-years. NDVI values derived from a multispectral ground-based radiometer were significant for herbicide or herbicide rate in four of six site-years. NDVI values from treated plots were subtracted from the NDVI value of the untreated check to generate a ΔNDVI. The resulting ΔNDVI values from the ground-based radiometer system were significant for herbicide or herbicide rate in six of six site-years. Neither optical remote-sensing system was effective at estimating actual application rates of lactofen and imazethapyr across a broad range of field and weather conditions due to temporal and spatial variability in crop response to the herbicides.

Five weed management systems utilizing combinations of cover crops, herbicides, and cultivation were tested in potato in 1994 and 1995 in central Washington. A standard herbicide treatment of metribuzin applied preemergence (PRE) at 0.4 kg ai/ha (standard herbicide weed management system [STD]) was compared with (1) fall-planted winter rye followed by metribuzin at 0.4 kg/ha applied in a band in the potato hill, followed by reservoir tillage (rye cover crop with herbicide-banded and reservoir-tilled weed management system [RYESTD]); (2) cultivation with tine-tooth harrow followed by hilling with shovels and rolling cultivators (total-cultivation weed management system [CULT]); (3) fall-planted rapeseed followed by reservoir tillage (rapeseed cover crop and reservoir-tilled weed management system [RPSD]); and (4) reservoir tillage alone (reservoir-tilled weed management system [RESTIL]). In both years, early-season weed density and final weed biomass were lower in the STD, RYESTD, and CULT systems than in RPSD and RESTIL. Total tuber yield and yield of U.S. #2 or better were greatest in the RYESTD and STD systems in both years. The CULT system reduced early-season weed densities, but tuber yield was reduced 15% in 1994, and yield of U.S. #2 or better was reduced 25% in 1995 compared with the STD system. The RPSD system reduced early-season in-row weed density from 60 to 70% and final weed biomass from 29 to 40% compared with a nontreated check, i.e., a no–cover crop, no-cultivation, no-herbicide weed management system, but tuber yield was 27 to 30% lower than in the STD system. The RYESTD system was an effective alternative weed management strategy that controlled weeds, decreased PRE-applied herbicide inputs 66%, and maintained tuber yield.

Experiments were conducted to determine the productivity and the competitive ability of a large crabgrass accession (PW2) resistant to acetyl-coenzyme A carboxylase (ACCase) inhibitors relative to a susceptible accession (A310). Under noncompetitive conditions in the field, shoot dry biomass and plant height over time were similar for the two accessions. Leaf area was slightly greater for A310 than for PW2. The instantaneous relative growth rate was similar for the accessions. The instantaneous net assimilation rate was slightly greater for A310 than for PW2; however, the instantaneous leaf area ratio was slightly greater for PW2 than for A310. At maturity, the seed yield was similar for the accessions. The inter-accession competitive ability of PW2 and A310 plants in the field was similar, based on shoot dry biomass or seed yield. In the greenhouse, interspecific competitive ability of the accessions with corn was similar, based on shoot dry biomass or seed yield. These results suggest that resistance to ACCase inhibitors is not associated with reduced fitness of the PW2 accession.

Research was conducted to determine the influence of water carrier quality on grass control from sethoxydim. Water from a well near Halliday, ND, where sethoxydim failed to control grasses, contained 650 mg/L sodium and 1650 mg/L bicarbonate. Both sodium bicarbonate and sodium carbonate when included in the sethoxydim spray reduced grass species control in the greenhouse and field. Sodium carbonate in the spray generally was more antagonistic than sodium bicarbonate to sethoxydim toxicity to grasses. The antagonism from sodium bicarbonate at 6000 mg/L was overcome by diammonium sulfate or ammonium nitrate at 2.8 kg/ha or a 28% nitrogen liquid fertilizer at 9.4 L/ha in the sethoxydim spray. These compounds also overcame sodium carbonate and partly overcame the antagonism of sethoxydim by bentazon. Three commercial adjuvants for use with sethoxydim differed in their effect on wheat and oats control with sethoxydim alone or with bentazon.

Field studies were conducted in 2007 and 2008 to evaluate fall applications of herbicides to control glyphosate-resistant (GR) horseweed before planting cotton. Fall treatments were compared with spring treatments for control of GR horseweed and effect on seed cotton yield. Fall and spring treatments with and without residual herbicides were also compared. No differences were observed for control of GR horseweed or seed cotton yield between fall and spring application timings. However, a difference was observed between fall applications with and without a residual herbicide. Fall applications that contained residual herbicides provided 86% control of GR horseweed and yielded 2,360 kg/ha of seed cotton. Fall applications that did not contain a residual herbicide only provided 70% control of GR horseweed and yielded 2,010 kg/ha of seed cotton. No benefit was observed from spring applications that contained a residual herbicide. This research indicates that glyphosate-resistant horseweed can be controlled with fall- or spring-applied burndown herbicides, and fall applications should include a residual herbicide for best results.

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.

Metribuzin and the ethyl ester of chlorimuron were evaluated alone and in combination for preemergence broadleaf weed control in soybeans. Neither herbicide alone controlled all broadleaf weeds tested, but combinations showed both complementary and additive action. Two field studies quantified these interactions on broadleaf weeds and showed that low rates of either herbicide alone controlled Pennsylvania smartweed and redroot pigweed. Metribuzin was more effective than chlorimuron in controlling prickly sida and hemp sesbania, while chlorimuron was more effective on common cocklebur, sicklepod, and ivyleaf and pitted morningglories. Additive action was most important on velvetleaf, sicklepod, annual morningglories, and hemp sesbania. Because the components were both additive and complementary, a range of mixture rates and ratios were more effective for weed control than either herbicide alone.