Field and greenhouse dose-response experiments were conducted to investigate the potential for resistance in a johnsongrass biotype from New Kent County, VA that survived repeated applications of quizalofop and quizalofop-P. During 1996 and 1997, foliar injury (30 to 60%) was initially observed on the johnsongrass at the New Kent field site, but this biotype eventually recovered and survived applications of fluazifop-P, quizalofop-P, and sethoxydim at twice the recommended field use rates. However, applications of clethodim at twice the recommended field use rates during 1997 provided essentially complete control of the New Kent johnsongrass biotype. In greenhouse dose-response experiments, the amount of quizalofop-P required to inhibit shoot growth by 50% (GR50) was 13.6 g/ha in the New Kent johnsongrass biotype and 0.8 g/ha in the susceptible johnsongrass biotype. In response to sethoxydim, the GR50 for the New Kent biotype was 122.5 g/ha while that of the susceptible biotype was 21.6 g/ha. Additionally, the New Kent biotype was least sensitive to fluazifop-P, which provided a GR50 value of 148.7 g/ha for the New Kent biotype and 5.1 g/ha for the susceptible biotype. As in the field trials, the New Kent biotype was sensitive to clethodim, which provided a GR50 value of 49.8 g/ha and 69.1 g/ha for the susceptible biotype. These values indicate that the New Kent biotype was 17 times more resistant to quizalofop-P, 5.7 times more resistant to sethoxydim, and 29.5 times more resistant to fluazifop-P than the susceptible biotype, and that the New Kent and susceptible johnsongrass biotypes are equally sensitive to clethodim. These GR50 values for the New Kent johnsongrass biotype are inconsistent with the much higher GR50 values most commonly observed in graminicide-resistant weed biotypes, and suggest a mechanism of resistance other than an insensitive ACCase in the New Kent johnsongrass biotype.

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 premix atrazine + S-metolachlor is commonly used to control a wide range of weeds in corn, but it is weak on velvetleaf and several other broadleaf species. RPA 201772, used at reduced rates in combination with atrazine + S-metolachlor, may improve the weed control spectrum. In field studies at Urbana and Dekalb in 1998 and 1999, RPA 201772 was combined with a premix of atrazine at 1,820 g ai/ha and S-metolachlor at 1,408 g ai/ha to compare RPA 201772 rate effects on corn injury, weed control, and yield. RPA 201772 was applied at 0, 26, 53, 78, 105, and 132 g ai/ha early preplant (EPP), preplant incorporated (PPI), and preemergence (PRE). Compared with atrazine + S-metolachlor alone, RPA 201772 combinations did not improve giant foxtail control. However, RPA 201772 at 26 or 53 g/ha increased control of redroot pigweed, common lambsquarters, ivyleaf morningglory, common ragweed, giant ragweed, and velvetleaf in some environments. At Urbana in both years, RPA 201772 at 26 g/ha in combination with atrazine + S-metolachlor increased velvetleaf control 15% compared with the premix alone. RPA 201722 at 26 to 78 g/ha decreased velvetleaf densities with all application methods. Greater weed control and higher corn yield occurred in treatments applied PRE or PPI compared with EPP applications, except where conditions were dry after PRE applications. This research demonstrates the benefit of RPA 201772 at low rates for broadleaf weed control with less potential for crop injury compared with high RPA 201772 rates.

Field and laboratory experiments were conducted in New Jersey to investigate the influence of spray adjuvants on foliar absorption and efficacy of bispyribac–sodium on annual bluegrass, creeping bentgrass, and perennial ryegrass. In laboratory experiments on annual bluegrass, 14C–bispyribac–sodium without an adjuvant had 25% foliar absorption by 8 h after treatment, whereas absorption increased to 45, 46, and 75% when applied with crop oil concentrate, nonionic surfactant, and methylated seed oil, respectively. In creeping bentgrass fairways, sequential bispyribac–sodium applications at 37 g ai/ha with spray adjuvants controlled annual bluegrass similarly to 74 g ai/ha applied sequentially without adjuvants. In perennial ryegrass, treatments with methylated seed oil and nonionic surfactant required 25 and 41% lower bispyribac–sodium rates, respectively, to obtain annual bluegrass control levels comparable to bispyribac–sodium rates without adjuvants. Spray adjuvants did not exacerbate turf-grass discoloration from bispyribac–sodium. Overall, spray-adjuvant use with bispyribac–sodium may allow practitioners to reduce application rates and enhance efficacy for annual bluegrass control.

Field experiments were conducted during 1998, 1999, and 2000 in Santa Fe, Argentina, to evaluate chlorimuron, clethodim, flumetsulam, 2,4-DB, glyphosate, and haloxyfop for control of broadleaf and grass weeds in established alfalfa. Herbicides were applied to alfalfa, 6 to 10 cm in height, after first or second cuttings. Clethodim and haloxyfop were highly effective against bermudagrass, barnyardgrass, and knotroot foxtail, and alfalfa yields were increased. 2,4-DB was effective against Scotch thistle, swinecress, turnipweed, and birdsrape mustard, but no effects were observed on alfalfa yields. Chlorimuron, flumetsulam, and glyphosate were effective against burning nettle, common chickweed, common lambsquarters, spiny cocklebur, and Persian speedwell, but they injured alfalfa and decreased yields.

Field trials were conducted in 1998 and 1999 to determine the influence of harvest-aids on dry bean desiccation, seed yield, and quality. Light Red Kidney and Great Northern dry beans were pulled from the soil and placed on the soil surface to dry or treated with glufosinate at 440 g ai/ha, with glyphosate at 840 g ae/ha, or with paraquat at 560 g ai/ha at three stages during the maturation process. Dry bean seed weight and seed yield were reduced by all harvest-aid treatments applied when only 5 to 7% of the seedpods were yellow. Herbicides did not affect dry bean seed yield, weight, or germination if treatments were delayed until 77 to 85% of the seedpods had turned yellow. Application of harvest-aids at early stages of the maturation process enhanced desiccation of dry bean plants, pods, and seeds, but reduced yield. Herbicides applied at later stages of the maturation process avoided seed yield reductions, but were not as effective in desiccating plants. Therefore, applying glufosinate, glyphosate, or paraquat to reduce the time from dry bean maturation to harvest may not be beneficial when the crop is grown on the high plains of the United States.

Greenhouse studies were conducted to evaluate and compare herbicide safeners for protection of corn and sorghum from herbicidal injury from metolachlor, primisulfuron, and the interaction of primisulfuron with terbufos, an insecticide. With the exception of CGA-133205 which killed corn, the safeners oxabetrinil, flurazole, naphthalic anhydride, dichlormid, and R-29148 protected against significant injury from the interaction between primisulfuron (40 g ai ha−1) and terbufos (9.8 kg ha−1 equivalent to 750 g per 1000 m of row) and from metolachlor (6.7 kg ai ha−1). No primisulfuron-terbufos interaction was observed in sorghum and none of the safeners protected sorghum from primisulfuron injury. PRE application of the antioxidants, piperonyl butoxide and metyrapone, increased primisulfuron injury to corn. Piperonyl butoxide by itself did not influence the growth of corn seedlings, but metyrapone caused slight injury. The increased injury from piperonyl butoxide plus primisulfuron applied at 40 g ha−1 was protected by naphthalic anhydride, flurazole, and R-29148, whereas at 80 g ha−1 protection was provided by flurazole and R-29148. None of the safeners tested protected against increased injury from metyrapone. Naphthalic anhydride was also an effective safener against increased corn injury when 3000 ppm piperonyl butoxide was applied foliarly 3 d prior to primisulfuron application. 14C-Primisulfuron absorption by corn was not influenced by piperonyl butoxide or the safener, naphthalic anhydride. However, metabolism of 14C-primisulfuron was inhibited by piperonyl butoxide. This inhibition was not totally reversed by the safener, naphthalic anhydride.

Field research conducted for 3 yr evaluated weed control in glyphosate-resistant soybean with glyphosate applied alone and in mixtures with reduced rates of the broadleaf herbicides acifluorfen, CGA-277476 (proposed name: oxasulfuron), chlorimuron, fomesafen, or lactofen. Barnyardgrass was controlled at least 95% with glyphosate at 840 and 1,120 g ai/ha, and control was not antagonized with any of the mixtures. At 14 d after treatment (DAT), wild poinsettia and prickly sida were controlled at least 90% with all glyphosate treatments. Control remained greater than 90% 28 DAT in one of the 2 yr, but in the other year, wild poinsettia was controlled 80%, and prickly sida was controlled 43% with the high rate of glyphosate. Acifluorfen or fomesafen (210 and 315 g ai/ha), or lactofen (112 and 168 g ai/ha) applied with glyphosate increased wild poinsettia control to 91 to 95% and prickly sida to 60 to 83%. At 14 DAT, pitted morningglory control improved in most cases when acifluorfen, fomesafen, or lactofen was applied with glyphosate. Hemp sesbania control was increased when glyphosate was applied with these same herbicides as well as CGA-277476 (39 and 59 g ai/ha) and chlorimuron (4.5 and 6.7 g ai/ha). But by 28 DAT, improvement in weed control with glyphosate and broadleaf herbicide mixtures was noted only in 1998, when pitted morningglory and hemp sesbania were larger at time of application (15 to 18 cm). Glyphosate alone in 1998 controlled these weeds no more than 30%, and only for hemp sesbania was control consistently more than 80% with the addition of acifluorfen or lactofen. At 28 DAT in 1999 and 2000, when weeds were no more than 10 cm, pitted morningglory was controlled 91 and 98%, respectively, and hemp sesbania 88 and 100%, respectively, with glyphosate alone at 1,120 g/ha. Soybean injury 28 DAT, consisting of foliar chlorosis and height reduction, was as much as 14, 13, and 23% for the acifluorfen, chlorimuron, and lactofen treatments, respectively, but no more than 6% for the CGA-277476 and fomesafen treatments. When weed control with glyphosate alone was at least 85%, addition of broadleaf herbicides did not improve soybean yield.

Identification of common weeds is fundamental in determining adequate recommendations for management practices. The aim of this study was to identify the patterns of weed management adopted by rice farmers and the perspectives of consultants who work in flooded rice areas in Rio Grande do Sul (RS) State, Brazil. Fifty-three public and 50 private consultants who worked with rice in RS in 2017 and 2018 were interviewed. Data were analyzed by descriptive statistics. Both weedy rice and Echinochloa sp. occurred and escaped more often from chemical control because they remained in the field until harvest in 59% of the area. According to consultants, the main reasons for reduced weed control were related to herbicide resistance and late herbicide application. Fifty-six percent of farmers used imidazolinone herbicides at rates that were greater than those indicated on the label for POST application. The consultants’ main challenges were weed escapes, resistance management, and guidelines on herbicide rates. Survey results show that the use of herbicide rates above label recommendations and consultants’ work on control of weed escapes are directly related to the high occurrence of herbicide resistance.

Field experiments were conducted in 2009 and 2012 at Fayetteville, AR, to compare four herbicides across three application timings for johnsongrass control and to evaluate the effect of late-season herbicide applications on johnsongrass control, fecundity, seed viability, and progeny emergence. In the first experiment, glyphosate at 840 g ae ha−1 and clethodim at 68 and 136 g ai ha−1 provided 75 to 94% control of 15- to 60-cm tall johnsongrass and up to 98% stand reduction 4 wk after treatment (WAT). Glufosinate and nicosulfuron were generally effective on ≤30-cm tall johnsongrass; however, efficacy declined as johnsongrass size increased. In the second experiment, glyphosate at 840 g ha−1 provided at least 89% johnsongrass control when applied at boot or after panicle emergence and up to 95% stand reduction 3 WAT. Applications of glyphosate at 420 and 840 g ha−1, clethodim at 68 and 136 g ha−1, and glufosinate at 740 g ai ha−1 at the boot stage reduced viable seed production of treated plants 94 to 99%. Irrespective of rate, glyphosate and clethodim applied at boot stage reduced progeny emergence by 77 to 95% and 100-seed weight of treated plants 62 to 96% compared to the nontreated check. This research demonstrates the importance of herbicide selection, particularly for controlling johnsongrass plants larger than 30 cm. Additionally, the results demonstrate the benefits of a single application of glyphosate or clethodim at the boot stage of johnsongrass for decreasing the soil seedbank and reducing the success of johnsongrass progeny in future years.

Glasshouse research was conducted to investigate the efficacy of herbicide safeners for improving creeping bentgrass (CBG) tolerance to various herbicides. CBG injury from amicarbazone (150 g ha−1), bispyribac-sodium (110 g ha−1), fenoxaprop-p-ethyl (35 g ha−1), imazapic (45 g ha−1), quinclorac (1,050 g ha−1), or topramezone (37 g ha−1) applied in combination with the herbicide safeners naphthalic anhydride or isoxadifen-ethyl was evaluated. These safeners reduced CBG injury from topramezone only. Topramezone was then applied in combination with naphthalic anhydride, isoxadifen-ethyl, cloquintocet-mexyl (cloquintocet), fenchlorazole-ethyl, mefenpyr-diethyl, and benoxacor. These experiments determined that CBG injury was lowest from topramezone in combination with cloquintocet. Additional experiments evaluated topramezone (37 g ha−1) with several rates of cloquintocet and determined that applications at ≥ 28 g ha−1 reduced CBG injury similarly. Cloquintocet (28 g ha−1) increased topramezone I50 values against CBG, but not large crabgrass or goosegrass. The cytochrome P450 (cP450) inhibitor malathion (1000 g ha−1) reduced topramezone I50 values against CBG in one experimental run. Topramezone–cloquintocet combinations warrant further research in field settings.

Integrated strategies for management of glyphosate-resistant (GR) horseweed are needed to reduce reliance on herbicides. Planting a cover crop after corn or soybean harvest in the Upper Midwest may reduce horseweed establishment and growth. Experiments were conducted in Michigan to determine if cereal rye and winter wheat, seeded at 67 or 135 kg ha−1, and terminated with glyphosate at 1.27 kg ae ha−1 1 wk before planting (early termination) or 1 wk after soybean planting (planting green) would suppress establishment and growth of GR horseweed. Cover-crop biomass was 212% to 272% higher when termination was delayed by planting green compared with early termination. At the time of termination, cover crops reduced GR horseweed biomass 41% to 89% compared with no cover. Planting green increased the C:N ratio of cover-crop residue, which improved residue persistence and GR horseweed suppression at the time of POST herbicide application, approximately 5 wk after planting. Planting green reduced GR horseweed biomass 46% to 93% compared with no cover at the time of POST herbicide application; early termination provided less consistent suppression. Cover crops alone did not suppress GR horseweed through soybean harvest. Soybean yield was 30% to 108% greater when planting green compared with early termination at 2 site-years. Cereal rye and winter wheat, seeded at 67 or 135 kg ha−1, provided early-season GR horseweed suppression. Results from this research indicate that the practice of planting green may improve GR horseweed suppression through the time of POST herbicide application.

Methyl bromide (MBr) was a widely used fumigant in plasticulture because of its effectiveness against soil-borne pests and weeds in high-value crops; however, it was found to be a class 1 ozone-depleting substance and is no longer available for use in most of the United States. A mixture of 1,3-dichloropropene and chloropicrin (Pic-Clor 60) is an alternative that has been used to control soil-borne pathogens and nematodes, and has marginal control of weeds. Virtually impermeable film (VIF) and totally impermeable film (TIF) retain fumigants in the soil longer than the low- and high-density polyethylene films typically used in plasticulture production systems. The increased retention by these films may result in greater control of recalcitrant weeds such as nutsedge. Four rates of Pic-Clor 60 (112, 168, 224, and 280 kg ai ha−1) used with TIF, 280 kg ai ha−1 of Pic-Clor 60 used with VIF, and one nontreated control with VIF were evaluated for 2 yr to assess control of yellow and purple nutsedge and to determine an efficacious Pic-Clor 60 rate used with TIF. TIF with a lower rate of 224 kg ai ha−1 of Pic-Clor 60 significantly controlled nutsedge populations compared to a high rate of 280 kg ai ha−1 with VIF.

Tolpyralate is a new Group 27 pyrazolone herbicide that inhibits the 4-hydroxyphenyl-pyruvate dioxygenase enzyme. In a study of the biologically effective dose of tolpyralate from 2015 to 2017 in Ontario, Canada, tolpyralate exhibited efficacy on a broader range of species when co-applied with atrazine; however, there is limited published information on the efficacy of tolpyralate and tolpyralate+atrazine relative to mesotrione and topramezone, applied POST with atrazine at label rates, for control of annual grass and broadleaf weeds. In this study, tolpyralate applied alone at 30 g ai ha−1 provided >90% control of common lambsquarters, velvetleaf, common ragweed, Powell amaranth/redroot pigweed, and green foxtail at 8 weeks after application (WAA). Addition of atrazine was required to achieve >90% control of wild mustard, ladysthumb, and barnyardgrass at 8 WAA. Tolpyralate+atrazine (30+1,000 g ai ha−1) and topramezone+atrazine (12.5+500 g ai ha−1) provided similar control at 8 WAA of the eight weed species in this study; however, tolpyralate+atrazine provided >90% control of green foxtail by 1 WAA. Tolpyralate+atrazine provided 18, 68, and 67 percentage points better control of common ragweed, green foxtail, and barnyardgrass, respectively, than mesotrione+atrazine (100+280 g ai ha−1) at 8 WAA. Overall, tolpyralate+atrazine applied POST provided equivalent or improved control of annual grass and broadleaf weeds compared with mesotrione+atrazine and topramezone+atrazine.

Greenhouse and field experiments were conducted to determine the response of corn (Zea mays), barnyardgrass (Echinochloa crus-galli), common lambsquarters (Chenopodium album), large crabgrass (Digitaria sanguinalis), velvetleaf (Abutilon theophrasti), and yellow foxtail (Setaria lutescence) to RPA 201772. Barnyardgrass, large crabgrass, velvetleaf, and common lambsquarters were more susceptible than yellow foxtail to RPA 201772. Velvetleaf was the most susceptible species and rates above 18 g ai/ha of RPA 201772 controlled 100% of the population 4 wk after treatment (WAT). Percent control of all the weed species increased with increased RPA 201772 rates. In the field, the dry weights of yellow foxtail decreased as the rate of RPA 201772 increased from 0 to 210 g/ha. However, a 60% reduction of dry weight of yellow foxtail was recorded at 140 g/ha of RPA 201772 compared to the untreated check 6 WAT, whereas at 12 WAT the dry weight of yellow foxtail was reduced to only 15% because of intraspecific competition. Yellow foxtail was moderately susceptible to RPA 201772. Corn was tolerant to RPA 201772; the GR80 value was 435 g/ha in the greenhouse. The bleaching injury to corn in the field was less than 10%, and it was found only with the 210 g/ha rate of RPA 201772. This injury was temporary and the plants recovered within 2 to 3 wk. Based on the GR80 values, velvetleaf was the most susceptible, followed by common lambsquarters, large crabgrass, barnyardgrass, and yellow foxtail.

Dodder is a serious parasitic weed of cranberry bogs. Investigations were undertaken to determine if applications of sand to cranberry bogs might be useful as a control strategy for dodder. Sand is regularly applied to bogs as a cultural practice. In greenhouse studies, applications of sand reduced the seedling emergence, but did not affect survival time of dodder seedlings. At least 2.5 cm of sand was needed to reduce the emergence of dodder seedlings. Sanding may be used as part of a program consisting of combinations of multiple management methods directed toward the control of dodder. In addition, potential exists for using sand as a nonchemical means for obtaining some control, should present herbicidal control methods become unavailable.

Field experiments were conducted in 1989 and 1990 to evaluate seasonal effects of herbicide application, smutgrass (Sporobolus indicus) growth stage, and herbicide rate on smutgrass control. The experimental design was a split–split plot, with season (late spring, midsummer, and fall) as the whole plot, physiological stage at application (uncut, 15-, and 30-cm regrowth) the subplot, and hexazinone rate (0.0, 0.56, 0.84, and 1.12 kg ai/ha) as the sub-subplot treatment. Whole plots were arranged in three randomized complete blocks. Smutgrass control for the mean of the hexazinone treatments (1989 and 1990) was 95%. Application of 0.56 kg/ha hexazinone during late spring, midsummer, and fall seasons provided 77, 92, and 92% smutgrass control, respectively. Generally, the influence of plant stage at time of hexazinone application had no effect (P > 0.05) on smutgrass control. At 20 d after treatment (DAT), hexazinone had injured bahiagrass (Paspalum notatum) plants by yellowing them, but the plants reverted to their usual dark green color by 40 DAT. Total nonstructural carbohydrates were lower for the 30-cm regrowth than for the uncut plants, regardless of season; however, 30-cm regrowth had little effect on smutgrass control.

The Spurgia esulae gall midge was introduced in North Dakota in 1986 as a biocontrol agent for leafy spurge. Spurgia esulae causes stem tip galls thereby decreasing seed production and it has been most successful near wooded areas. However, a second control method is needed to reduce the leafy spurge infestation and prevent spread from roots. Imazethapyr, 2,4-D, or picloram application did reduce the number of S. esulae galls but not the number of larvae per gall. Long-term S. esulae population was not affected by herbicide application. The integration of herbicides with S. esulae would prevent leaf spurge spread from a wooded area and would reduce seed production within an area where herbicides generally cannot be used.

Experiments were conducted to test the accuracy of a global positioning system (GPS) in measuring the area of simulated weed patches of varying size and to determine the accuracy in navigating back to particular points in a field. Circular areas of 5, 50, and 500 m2 were established and measured using point and polygon features of a GPS. The GPS estimations of the area of those patches had errors ranging from 7 to 45%, 6 to 15%, and 3 to 6%, respectively, when compared to actual measurements. As patch size increased, errors decreased. A curve describing the relationship between GPS error and patch size had an excellent fit (r 2 = 0.92). The error remained the same in all measurements across all patch sizes, but composed a smaller percentage of large patches. The GPS had submeter accuracy in navigation to the correct quadrat 73% of the time, located the correct quadrat 27% of the time, and invariably navigated to within 1.58 m of the correct quadrat. The relationship between patch size and measurement error was applied to natural infestations of hemp dogbane.

The effect of application technology on efficacy has been thoroughly investigated for sprays of chemical pesticide but not biological pesticides. This study investigates the effect of applying conidia of Microsphaeropsis amaranthi, a candidate bioherbicide for Amaranthus spp., with a range of different hydraulic nozzle tips. The nozzle tips were selected to deliver sprays with different spectra of droplet sizes deployed at different angles. We found that sprays of large droplets gave poor coverage of the target and resulted in low levels of disease severity on common waterhemp. The most effective nozzle tip tested was a hollow cone nozzle tip, such as is commonly used for the application of fungicides. This nozzle tip deployed large numbers of fine droplets that swirled within the plant canopy, provided good coverage of all plant parts, and resulted in the highest levels of disease severity, particularly on stems.