Glyphosate was compared with other commonly used corn herbicides at three locations in Kentucky in 1998 and 1999. Sequential glyphosate treatments provided greater than 87% control of common cocklebur, ivyleaf morningglory, common lambsquarters, and giant ragweed. Control of these species with glyphosate treatments was similar to the control with atrazine plus other postemergence (POST) herbicides. Generally, treatments containing s-triazines and chloracetamides applied to the soil surface were not as effective as sequential glyphosate or atrazine plus POST herbicides. Corn yield was not significantly different at any location or for any year, whereas differences in net return occurred at one location in 1998.

Field experiments were conducted in 1997 and 1998 to evaluate the effect of mowing followed by hexazinone for West Indian dropseed/giant smutgrass (Sporobolus indicus var. pyramidalis) (hereafter referred to as dropseed) control. The experimental design was a split plot, with mowing (nonmowed [mature] and 35-cm regrowth) as the whole plot and hexazinone rate (0.0 [control], 0.56, 0.84, 1.12, 1.40, and 1.68 kg ai/ha) as the subplot treatments. The application of 0.84 kg/ha hexazinone provided 94 and 81% dropseed control, 365 d after treatment (DAT) during 1997 and 1998, respectively. Increasing application rate to 1.12 kg/ha hexazinone provided 87 and 88% dropseed control, 365 DAT during 1997 and 1998, respectively. Both the 0.84 and 1.12 kg/ha rates provided the same average control (87.5%); however, the 1.12 kg/ha rate provided consistent control over years. Mowing dropseed, followed by hexazinone application at 35-cm regrowth, provided no additional control when compared with no mowing treatments. Rates of hexazinone at 1.40 and 1.68 kg/ha caused phytotoxicity to bahiagrass and increased bare soil surface area, especially 90 and 120 DAT. Phytotoxic effect on bahiagrass and on bare soil decreased 365 DAT, resulting in 75 to 80% total forage cover. Concentration and yield of total nonstructural carbohydrates were significantly lower for the mowed 35-cm regrowth treatment than for the nonmowed plants; however, even in its weakened condition this reduction had no effect on dropseed control.

Field studies were conducted at two locations in North Carolina in 1999 and 2000 to evaluate weed and bromoxynil-resistant cotton response to bromoxynil, pyrithiobac, and MSMA applied early postemergence (EPOST), alone or mixtures in all combinations (two way and three way), and to prometryn plus MSMA applied late postemergence directed (LAYBY). Trifluralin preplant incorporated followed by fluometuron preemergence controlled common lambsquarters, eclipta, and smooth pigweed at least 90%. These herbicides also provided greater than 90% common ragweed control at two locations but only 65% control at a third location. Pyrithiobac and pyrithiobac plus MSMA EPOST increased sicklepod control more than did bromoxynil or bromoxynil plus MSMA EPOST. Bromoxynil and pyrithiobac were more effective for sicklepod control when applied in mixture with MSMA. Bromoxynil plus pyrithiobac EPOST or with MSMA controlled (≥ 90%) common lambsquarters, common ragweed, entireleaf morningglory, prickly sida, and smooth pigweed early season. But the LAYBY treatment of prometryn plus MSMA frequently improved late-season control of entireleaf morningglory, large crabgrass, prickly sida, and sicklepod. A tank mixture of MSMA plus bromoxynil or pyrithiobac and the three-component tank mixture (bromoyxnil, MSMA, plus pyrithiobac) provided a broader weed control spectrum than did either bromoxynil or pyrithiobac alone. Cotton lint yields were increased with all postemergence systems, and the LAYBY treatment of prometryn plus MSMA increased cotton yields in 13 out of 16 comparisons. High cotton yields were indicative of high levels of weed control.

Woolly cupgrass seeds are dormant at physiological maturity and lose dormancy while afterripening in winter. Field experiments were conducted with the seeds collected from the locations across Iowa in the fall of 1991 and 1992. The seeds were buried in mid-November 0, 5, and 15 cm below the soil surface. Seeds were extracted biweekly until mid-February and germination tests conducted. Seeds buried below the soil surface were less dormant when compared with seeds on the soil surface. There were also dormancy differences between locations. Differences observed between locations and variations from 1991 to 1992 indicated that the parent plant environment, and the likely genotype, had a significant effect on woolly cupgrass seed dormancy.

Field experiments were conducted at three locations in North Carolina in 1998 and 1999 and one location in Virginia in 1998 to evaluate weed management systems in peanut. Treatments consisted of diclosulam alone preemergence (PRE), or diclosulam plus metolachlor PRE alone or followed by (fb) bentazon plus acifluorfen postemergence (POST). These systems were also compared with commercial standards of metolachlor PRE fb bentazon plus acifluorfen POST or imazapic POST. Our data indicate that diclosulam PRE plus metolachlor PRE in conventional tillage peanut production usually controlled common lambsquarters, common ragweed, prickly sida, and entireleaf morningglory. But control of spurred anoda, goosegrass, ivyleaf morningglory, large crabgrass, and pitted morningglory by this system was inconsistent and may require additional POST herbicide treatments. Systems that included diclosulam plus metolachlor PRE consistently provided high yields and net returns.

Field studies were conducted over 2 yr in Louisiana to evaluate entireleaf morningglory and hemp sesbania control by glyphosate isopropylamine salt applied alone at 420, 560, and 700 g ae/ha and in combination with chlorimuron at 4, 6, 9, and 11 g ai/ha. Comparison treatments included glyphosate alone at 840 g/ha, glyphosate at 1,400 g/ha plus chlorimuron at 13 g/ha, and sethoxydim at 210 g ai/ha plus chlorimuron at 11 g/ha. Entireleaf morningglory and hemp sesbania were controlled no more than 77% with glyphosate rates as high as 840 g/ha. Chlorimuron added to glyphosate increased entireleaf morningglory control in two of the three experiments to 83 to 88% and hemp sesbania control to 86 to 98%. Response to chlorimuron was not rate dependent. In most cases, glyphosate–chlorimuron mixtures did not antagonize barnyardgrass control, and increasing rate of glyphosate did not always increase control. Soybean was injured no more than 6% by chlorimuron at one location, but injury was as great as 30% at another location, which was possibly due to smaller soybean size. Differences in weed control and soybean injury among the glyphosate and glyphosate–chlorimuron combinations were not reflected in soybean yields. Because injury occurred early season, sufficient time remained for soybean to recover and produce acceptable yields. Weed control by sethoxydim plus chlorimuron was less consistent than that by glyphosate plus chlorimuron, and soybean yield in most cases was inferior to the glyphosate treatments.

Field studies were conducted in 1995 and 1996 at three locations in North Carolina to evaluate weed control and soybean injury with postemergence (POST) treatments of cloransulam-methyl alone or in tank-mixture with acifluorfen, fomesafen, or lactofen compared with a commercial standard of acifluorfen plus bentazon. Soybean injury was 2 to 3% 7 d after treatment with cloransulam-methyl applied alone and 11 to 46% when applied with fomesafen, lactofen, acifluorfen, or acifluorfen plus bentazon. Cloransulam-methyl applied alone controlled 95% of entireleaf morningglory and ivyleaf morningglory. Control was not increased by the addition of acifluorfen, fomesafen, or lactofen. Cloransulam-methyl improved the control of common lambsquarters to at least 81% compared with dimethenamid applied preemergence alone (69% control). All diphenyl ether herbicide treatments controlled common lambsquarters at least 91%. Prickly sida control by cloransulam-methyl ranged from 14 to 73% 8 wk after treatment. Control of prickly sida was varied by diphenyl ether herbicides (73 to 100% control). Tank-mixtures of cloransulam-methyl + fomesafen and cloransulam-methyl + acifluorfen increased the control of prickly sida over either herbicide applied alone. Soybean yield was greater for all tank-mixtures than for any diphenyl ether herbicide or for cloransulam-methyl treatment applied alone. But only the acifluorfen + cloransulam-methyl treatment had higher economic returns than the cloransulam-methyl treatment alone. All other POST systems, with the exception of lactofen applied alone, had similar economic returns. Tank-mixtures of cloransulam-methyl and diphenyl ether herbicides increased the spectrum of control and soybean yield compared with these herbicides applied alone.

A study was conducted to evaluate flumioxazin preemergence (PRE) at 71 and 105 g ai/ha, when used with dimethenamid PRE, dimethenamid preplant incorporated (PPI), or ethalfluralin PPI, for crop injury, weed control, and yield. Peanut injury from treatments including flumioxazin 2 wk after soil-applied treatment (WAST) was less than 2% at two locations and 50 to 67% at a third location. Peanut injury increased with flumioxazin rate. Soil-applied treatments that included flumioxazin at either rate controlled common lambsquarters and prickly sida at least 96 and 89%, respectively. Addition of postemergence (POST) herbicides to any soil-applied program controlled prickly sida and ivyleaf morningglory at least 94 and 98%, respectively. Treatments that included ethafluralin or dimethenamid controlled goosegrass at least 82%. With a few exceptions, peanut yields were not improved by use of POST herbicides. Where peanut injury occurred, increased flumioxazin rate resulted in lower peanut yield when averaged over PPI and POST herbicide treatments.

Field and greenhouse experiments were conducted to evaluate clethodim, CGA-362622, mixtures thereof, and sequential treatments for control of broadleaf signalgrass, fall panicum, goosegrass, and large crabgrass. In greenhouse experiments, clethodim alone provided 93 and 100% control of three- to four-leaf goosegrass at the low (105 g ai/ha) and high (140 g/ha) rates, respectively, whereas CGA-362622 did not control grasses in greenhouse or field experiments. Control of six- to eight-leaf goosegrass in the greenhouse with clethodim was 75% for the low rate and 89% for the high rate. Control of goosegrass in greenhouse studies was reduced at least 43 percentage points with CGA-362622 and clethodim at the high rate in mixture compared with control provided by clethodim at the high rate alone. When CGA-362622 and clethodim were applied in mixture in field studies, the effectiveness of the graminicide was decreased from > 97 to < 57% control for all annual grasses. Antagonism of clethodim activity was greater than that of the tank mixture when clethodim was applied 1 d after CGA-362622 on large crabgrass, goosegrass, and fall panicum. Clethodim applied 7 d before or after CGA-362622 controlled the four grass species as well as did clethodim applied alone. When CGA-362622 was applied to goosegrass alone, fresh weight accumulation stopped for a period of 4 d compared with untreated plants. Normal growth resumed after 4 d.

Control of common waterhemp in corn with chloroacetamide and dinitroaniline herbicides can be inconsistent. Common waterhemp control by dimethenamid, S-metalochlor, pendimethalin, and three formulations of acetochlor, applied alone or with atrazine as single preemergence (PRE) or sequential PRE followed by postemergence (POST) treatment, was determined. The manufacturer's suggested use rate (1 time) of PRE herbicides was compared with sequential applications (0.66 time PRE followed by 0.34 time POST) of herbicides. POST applications included dicamba to control emerged common waterhemp. Single and sequential herbicide applications controlled common waterhemp at least 98%, 28 d after planting (DAP). But herbicides applied sequentially were more effective than PRE treatments by 56 DAP. Encapsulated acetochlor formulations controlled common waterhemp at least 85% by 56 DAP regardless of application method. Sequential applications of S-metolachlor controlled common waterhemp greater than 83%. Atrazine improved common waterhemp control regardless of herbicide or application method 56 DAP. Sequential applications of dimethenamid or S-metolachlor alone or with atrazine were more effective than single PRE applications of these herbicides.

Experiments were conducted at two locations in North Carolina from 1999 to 2000 to evaluate flumioxazin preplant (PP) for weed management in strip-tillage cotton planted in winter-wheat cover. Flumioxazin PP was evaluated at two rates alone and in mixture with two commonly used PP herbicides and one experimental PP herbicide. Flumioxazin PP at 71 or 105 g ai/ha tank mixed with the isopropylamine salt of glyphosate at 1.12 kg ai/ha, paraquat at 1.05 kg ai/ha, or the trimethylsulfonium salt of glyphosate at 1.12 kg ai/ha controlled common chickweed, common lambsquarters, common ragweed, Palmer amaranth, and smooth pigweed ≥ 96% 29 to 43 d after treatment (DAT). Both glyphosate formulations and paraquat alone provided ≥ 91% control of common chickweed and henbit 29 to 43 DAT, but control of common lambsquarters, common ragweed, large crabgrass, Palmer amaranth, and smooth pigweed was ≤50%. Treatments including flumioxazin injured cotton (≤ 5%) at one location. In all comparisons within a location, cotton treated with flumioxazin PP at 71 or 105 g/ha in mixture with either glyphosate formulation or with paraquat provided equivalent or higher yields than did cotton not treated with flumioxazin PP.

Greenhouse studies were initiated in 2001 to evaluate the effect of V-10029 applications on shoot and root growth of rice cultivars. V-10029 applications did not affect the shoot and root weight or shoot–root ratio of Cocodrie. Tolerance of Bengal was less than that of Cocodrie and was growth stage dependent. V-10029 treatments at the one- to two-leaf rice growth stage reduced shoot growth but had no effect on root, resulting in a lower shoot–root ratio compared with that of the nontreated 1 wk after treatment (WAT). At 2 and 3 WAT, both shoot and root growth were reduced by V-10029, with shoot–root ratio being greater than that of the nontreated, indicating a greater inhibition of roots than of shoots. V-10029 treatments at the two- to three-leaf rice growth stage reduced both shoot and root growth of Bengal across all three sampling dates. V-10029 treatments at the three- to four-leaf rice growth stage did not affect shoot growth but reduced root growth 2 and 3 WAT with no difference in shoot–root ratio. There was no difference in shoot and root weight or shoot–root ratio between the propanil comparison treatment and the nontreated. These results indicate that rice cultivars may differ in their tolerance to V-10029 and tolerance may be growth stage dependent.

Current environmental concerns demand intensive research on conservation tillage for cotton production. Studies were conducted in 1994 and 1995 at Florence, SC, to evaluate weed and cotton response to various weed management systems in cotton with reduced tillage. Broadcast application of pendimethalin at 1.1 kg ai/ha and fluometuron at 2.2 kg ai/ha preemergence (PRE) followed by pyrithiobac at 0.07 kg ai/ha early postemergence (EPOST) was more effective than was a 38-cm band of these herbicides in controlling naturally occurring populations of sicklepod, Palmer amaranth, goosegrass, and southern crabgrass and in providing cotton yields equal to yields under weed-free conditions. With the 38-cm band of PRE and EPOST herbicides, two supplemental weed treatments at 3 and 7 wk after planting using glyphosate applied at 0.84 kg ae/ha POST with a hooded sprayer or a no-till cultivator was required to achieve acceptable weed control, but cotton yields were less than yields for the broadcast treatment alone. Glyphosate- or cultivation-only systems were generally ineffective in reducing weed interference and precluding cotton yield reductions. Optimum cotton production with reduced tillage can be achieved with broadcast application of PRE and EPOST herbicides but alternative methods offer promise for reducing costs and environmental effects and deserve additional study.

The unimbibed crush test, in which seed viability is evaluated by crushing and visual inspection of dry seeds, was compared with tetrazolium staining, an established method of testing seed viability. The unimbibed crush test potentially provides an immediate and rapid method for determining seed viability. Six sets of seed lots, involving the four weed species, velvetleaf, common lambsquarters, redroot pigweed, and smooth pigweed, were tested by each method. For four of the six sets, results from the crush test were statistically indistinguishable from those of the tetrazolium test. For the other two sets of seed lots, the crush test indicated higher viability than did the tetrazolium test. The crush test may be most useful for seed bank surveys in which many samples are typically processed, and most of the variation in density of viable seeds is associated with number of seeds present rather than percentage viability. Its use in more exacting circumstances like seed survival studies requires caution.

Field experiments were conducted to determine the effect of shattercane interference on corn grain yield and nitrogen uptake in central Missouri. A glyphosate-resistant corn variety was planted, and atrazine was used to control all weeds except shattercane. Glyphosate was applied when shattercane was 8, 15, 23, 31, 38, or 46 cm tall, and plots were hand weeded weekly thereafter. Season-long shattercane interference resulted in an 85% yield loss in 1999 and a 43% yield loss in 2000. Yield reductions occurred when shattercane was allowed to remain with corn until it was 31 cm tall. In both years, late-season corn biomass N content was highly correlated (r = 0.95 and 0.84, respectively) with corn yield. When shattercane was allowed to reach the maximum recommended height for nicosulfuron or primisulfuron application (31 cm), significant yield losses occurred, and shattercane accumulated 10 and 20 kg N/ha, whereas corn accumulated 10 and 16 kg N/ha, respectively, in 1999 and 2000. Corn grain yield was reduced 0.66% (r2 = 0.71) for each day of interference before a postemergence (POST) application of glyphosate.

Field experiments were conducted on the Eastern Shore of Virginia from 1999 to 2001 to evaluate the effects of tank mixture applications of isopropylamine or trimethylsulfonium salts of glyphosate with two liquid formulations of manganese (Mn lignin or Mn chelate) on spray solution pH and weed control in glyphosate-resistant soybean. Additions of manganese to herbicide solutions resulted in a reduction in the acidifying effects of the herbicides as well as in the control of common lambsquarters, large crabgrass, morningglory spp., and smooth pigweed. Reduced control caused by manganese could be overcome with higher rates of the herbicides on some species, but reduced control of common lambsquarters was seen when manganese was included with any herbicide application rate. For most species, Mn chelate caused a greater reduction in control than did Mn lignin. Although manganese caused significant decreases in weed control, soybean yield was not influenced by glyphosate salt, application rate, or manganese. Reduced weed control caused by the addition of manganese to herbicide solutions may be due to the complexing of the herbicide formulations, which could result in the formation of insoluble salt complexes that are not readily absorbed through the plant cuticle, resulting in decreased glyphosate phytotoxicity.

Field experiments were conducted at four locations in Kansas and Wyoming during the 1998 to 1999, 1999 to 2000, or 2000 to 2001 winter wheat–growing seasons to compare BAY MKH 6561 and MON 37500 at four postemergence timings for weed control and crop response. BAY MKH 6561 at 45 g ai/ha and MON 37500 at 35 g ai/ha controlled cheat 95% or more when applied early-fall postemergence (EFP), late-fall postemergence (LFP), early-spring postemergence (ESP), or late-spring postemergence (LSP) at Hays, KS, in 1999 and 2001. At Manhattan, KS, in these years, cheat control was 98 to 100%, except for MON 37500 (83 to 90%) applied LSP. Downy brome control with BAY MKH 6561 or MON 37500 declined as application timing was delayed at Hays, Archer, WY, and Torrington, WY. Averaged over herbicides, downy brome was controlled 38 to 95% when herbicides were applied EFP and 10 to 79% when applied LSP. Late-season wheat stunting was 11% or less, regardless of herbicide treatment, at Manhattan each year; no late-season injury was visible at Hays, Archer, or Torrington. Yields did not differ between treated and untreated wheat at Manhattan in 1999 or 2001, at Archer in 2000, or at Hays in 1999. Wheat receiving BAY MKH 6561 EFP yielded 8% more grain than did wheat treated with MON 37500 LSP at Hays in 2001 and at Torrington. At these two locations, all herbicide-treated wheat yielded 10 to 20% more grain than did the untreated wheat.

Field studies were conducted at Lewiston and Rocky Mount, NC, in 1996 and 1997 to evaluate weed control and peanut response to preplant incorporated (PPI) treatments of diclosulam alone and in systems with postemergence (POST) commercial standard herbicides. All plots received ethalfluralin PPI at 840 g ai/ha. In both years, ethalfluralin plus diclosulam PPI at 17 or 26 g ai/ha followed by (fb) acifluorfen plus bentazon POST, paraquat plus bentazon POST, or imazapic POST controlled common lambsquarters, ivyleaf morningglory, pitted morningglory, prickly sida, smooth pigweed, spurred anoda, and yellow nutsedge in a manner similar to or better than did the commercial standards of ethalfluralin PPI fb metolachlor preemergence (PRE) fb acifluorfen plus bentazon or ethalfluralin PPI fb acifluorfen plus bentazon POST. Yield from peanut treated with diclosulam systems that included POST herbicides was equivalent to or higher than that from peanut treated with ethalfluralin PPI fb metolachlor PRE fb acifluorfen plus bentazon POST or ethalfluralin PPI fb acifluorfen plus bentazon POST. Peanut exhibited excellent tolerance to diclosulam PPI at all rates.

Three studies were conducted in 1999 and 2000 to determine whether acetolactate synthase (ALS)–resistant common ragweed and giant ragweed biotypes were present in Ohio. Results of field studies indicated that biotypes of both species had cross-resistance to three chemical families of ALS-inhibiting herbicides. Cloransulam-methyl applied postemergence at 9, 18, and 36 g/ha controlled more than 85% of two susceptible populations of common and giant ragweed 28 d after treatment, whereas less than 35% control of resistant populations was achieved at the same rates. Fomesafen, lactofen, and glyphosate applied alone at the recommended rates provided the most effective control of ALS-resistant common and giant ragweed. Mixtures of cloransulam-methyl with either fomesafen or lactofen did not significantly increase ALS-resistant common and giant ragweed control compared with each diphenylether herbicide used alone. Dose–response bioassays conducted in the greenhouse indicated that susceptible common and giant ragweed tended to be more sensitive to cloransulam-methyl and chlorimuron than to imazamox. ALS-resistant common ragweed demonstrated a high level of resistance to all the herbicides tested because GR50 values were not reached with rates 1,000 times higher than the recommended rate. ALS-resistant giant ragweed treated with 13,000 g/ha of chlorimuron and 18,000 g/ha of cloransulam-methyl was not inhibited enough to obtain a GR50 value, thus also demonstrating a high level of resistance. The GR50 for ALS-resistant giant ragweed treated with imazamox was 1,161 g/ha. Results of these studies confirmed the presence of ALS–cross-resistant populations of common and giant ragweed in Ohio and suggest that herbicides with different mechanisms of action will be required to manage these weeds effectively.

Outside its native range, smooth cordgrass is a noxious weed in estuaries throughout the world. Trials were conducted to evaluate smooth cordgrass control with imazapyr at various timings, rates, and spray volumes, and with several surfactants; comparisons were made with glyphosate, the sole herbicide registered in the United States for estuarine use. Across years, all sites, application dates, and experiments, it was found that smooth cordgrass control with imazapyr at 1.68 kg/ha was better and more consistent than with glyphosate at 8.4 kg/ha. Control with imazapyr at 0.84 kg/ha was comparable to control with glyphosate at 8.4 kg/ha. The time between application and tidal inundation over the canopy affected the efficacy of imazapyr less than that of glyphosate. There was a lack of consistent effects across dates of application. For imazapyr, a higher application volume (467 L/ha) usually provided better control than did the low volume (93 L/ha), but excellent control was achieved using ultra-low application volumes (23 and 47 L/ha) if the dry time was greater than 12 h. Several surfactants provided comparable efficacy for imazapyr.