In Australia, widespread evolution of multi-resistant weed populations has driven the development and adoption of harvest weed seed control (HWSC). However, due to incompatibility of commonly used HWSC systems with highly productive conservation cropping systems, better HWSC systems are in demand. This study aimed to evaluate the efficacy of the integrated Harrington Seed Destructor (iHSD) mill on the seeds of Australia’s major crop weeds during wheat chaff processing. Also examined were the impacts of chaff type and moisture content on weed seed destruction efficacy. Initially, the iHSD mill speed of 3,000 rpm was identified as the most effective at destroying rigid ryegrass seeds present in wheat chaff. Subsequent testing determined that the iHSD mill was highly effective (>95% seed kill) on all Australian crop weeds examined. Rigid ryegrass seed kill was found to be highest for lupin chaff and lowest in barley, with wheat and canola chaff intermediate. Similarly, wheat chaff moisture reduced rigid ryegrass seed kill when moisture level exceeded 12%. The broad potential of the iHSD mill was evident, in that the reductions in efficacy due to wide-ranging differences in chaff type and moisture content were relatively small (≤10%). The results from these studies confirm the high efficacy and widespread suitability of the iHSD for use in Australian crop production systems. Additionally, as this system allows the conservation of all harvest residues, it is the best HWSC technique for conservation cropping systems.

A study was conducted to evaluate the response of glyphosate- and dicamba-tolerant (GDT) soybean and weed control from cover crop different termination intervals before and after soybean planting. Cover crop biomass was highest when terminated at planting, decreased with the 7- and 14-d preplant (DPP) and day-after-planting (DAP) timings, and again at the 14 DPP and DAP timings. Glyphosate+dicamba provided total control of cover crops by 21 DAP. Cover crop termination timing did not influence soybean population or yield. Palmer amaranth control at the 21 and 28 d after termination (DAT) was 97% to 99%. Differences in Palmer amaranth control were not detected among herbicide programs or termination intervals at the end of season rating, and all treatments provided ≥97% control. Although differences in Palmer amaranth control were not apparent at the end of the season, the delay in cover crop affected the number of days until 10-cm Palmer amaranth was present. When utilizing a wheat+hairy vetch cover crop in DGT soybeans, producers should delay cover crop termination until 11 to 14 DPP and make at least one POST application of glyphosate+dicamba+an additional herbicide mode of action (MOA) to maximize Palmer amaranth control and soybean yields.

Soybean consultants from Arkansas, Louisiana, southeast Missouri, Mississippi, and Tennessee were surveyed in 2016 to assess weed management practices and the prevalence of herbicide-resistant weeds in midsouthern U.S. soybean production. The consultants surveyed represented 13%, 28%, 8%, 16%, and 5% of the total soybean area planted in Arkansas, Louisiana, southeast Missouri, Mississippi, and Tennessee, respectively. Of the total scouted area, 78% of the consultants said their growers planted glyphosate-resistant soybean in 2016, with 18% planting glufosinate-resistant (LibertyLink®), primarily due to familiarity with and cost of the technology. Although 94% of the consultants determined that glufosinate was most effective on killing Palmer amaranth, the primary concern associated with controlling herbicide-resistant weeds was the associated cost, followed by return profit and time constraints. Palmer amaranth, morningglory species, horseweed, barnyardgrass, and Italian ryegrass were the five most problematic weeds in soybean across the five states. Palmer amaranth was the most problematic and important weed in each state individually. The increased concern (77% of consultants) with this species was attributed to the rising concern with and occurrence of protoporphyrinogen oxidase–resistant Palmer amaranth. Consultants were of the opinion that more research was needed on cover crops and the new traited technologies in order to improve weed management in soybean.

Florpyrauxifen-benzyl is a new herbicide under development in rice that will provide an alternative mode of action to control barnyardgrass. Multiple greenhouse experiments evaluated florpyrauxifen-benzyl efficacy on barnyardgrass accessions collected in rice fields across Arkansas, and to evaluate its efficacy on herbicide-resistant biotypes. In one experiment, florpyrauxifen-benzyl was applied at the labeled rate of 30 g ai ha−1 to 152 barnyardgrass accessions collected from 21 Arkansas counties. Florpyrauxifen-benzyl at 30 g ai ha−1 effectively controlled barnyardgrass and subsequently reduced plant height and aboveground biomass. In a dose-response experiment, susceptible-, acetolactate synthase (ALS)-, propanil-, and quinclorac-resistant barnyardgrass biotypes were subjected to nine rates of florpyrauxifen-benzyl ranging from 0 to 120 g ai ha−1. The effective dose required to provide 90% control, plant height reduction, and biomass reduction of the susceptible and resistant biotypes fell below the anticipated labeled rate of 30 g ai ha−1. Based on these results, quinclorac-resistant barnyardgrass as well as other resistant biotypes can be controlled with florpyrauxifen-benzyl at 30 g ai ha−1. Overall, results from these studies indicate that florpyrauxifen-benzyl can be an effective tool for controlling susceptible and currently existing herbicide-resistant barnyardgrass biotypes in rice. Additionally, the unique auxin chemistry of florpyrauxifen-benzyl will introduce an alternative mechanism of action in rice weed control thus acting as an herbicide-resistance management tool.

To address recent concerns related to auxin herbicide drift onto soybean, a study was developed to understand the susceptibility of the reproductive stage of soybean to a new auxin herbicide compared with dicamba. Florpyrauxifen-benzyl is under development as the second herbicide in a new structural class of synthetic auxins, the arylpicolinates. Field studies were conducted to (1) evaluate and compare reproductive soybean injury and yield following applications of florpyrauxifen-benzyl or dicamba across various concentrations and reproductive growth stages and (2) determine whether low-rate applications of florpyrauxifen-benzyl or dicamba to soybean in reproductive stages would have similar effect on the progeny of the affected plants. Soybean were treated with 0, 1/20, or 1/160, of the 1X rate of florpyrauxifen-benzyl (30 g ai ha−1) or dicamba (560 g ae ha−1) at R1, R2, R3, R4, or R5 growth stage. Soybean plant height and yield was reduced from 1/20X dicamba across all reproductive stages. High drift rates (1/20X) of florpyrauxifen-benzyl also reduced soybean plant height >25% and yield across R1 to R4 stages. Germination, stand, plant height, and yield of the offspring of soybean plants treated with dicamba and florpyrauxifen-benzyl were significantly affected. Dicamba applied at a rate of 1/20X at R4 and R5 resulted in 20% and 35% yield reduction for the offspring, respectively. A similar reduction occurred from florpyrauxifen-benzyl applied at R4 and R5 at the 1/20X rate, resulting in 15% to 24% yield reduction for the offspring, respectively. Based on these findings, it is suggested that growers use caution when applying these herbicides in the vicinity of reproductive soybean.

The introduction of 2,4-D–resistant soybean will provide an additional POST herbicide site of action for control of herbicide-resistant broadleaf weeds. The introduction of this technology also brings concern of off-site movement of 2,4-D onto susceptible crops such as sensitive soybean and tomato. The 2,4-D formulation approved for use in 2,4-D–resistant soybean restricts application of the herbicide to nozzles that produce very coarse to ultra-coarse droplet spectrums. The use of larger droplet spectrums for broadcast applications can reduce herbicide deposition onto target weeds and thus influence herbicide efficacy. Field experiments were conducted to evaluate the influence of nozzle design on herbicide deposition onto target plants and the resulting efficacy of a POST application of 280 g ha−1 glyphosate plus 280 g ha−1 2,4-D. The TTI11004 nozzle produced an ultra-coarse droplet spectrum and reduced coverage and deposition density on spray cards as compared with the XR11004 and TT11004 nozzles that produced medium droplet spectrums. The AIXR11004 nozzle also reduced deposition density on spray cards but did not reduce coverage. Herbicide solution deposition onto glyphosate-resistant Palmer amaranth, tall waterhemp, giant ragweed, and horseweed ranged from 0.28 to 0.72 µl cm−2 and was not influenced by nozzle design. Herbicide efficacy was reduced by the TTI11004 nozzle on Palmer amaranth and horseweed compared with the AIXR11004, TT11004, and XR11004 nozzles when applications were made to either high densities of plants or plants exceeding the labeled height. The use of the AIXR11004 and TTI11004 nozzles that are listed as approved nozzles for glyphosate plus 2,4-D applications on 2,4-D–resistant soybean did not reduce herbicide deposition onto four of the most troublesome broadleaves and did not reduce herbicide efficacy when applied in conjunction with lower weed densities and smaller weeds.

Previous research has shown that some insecticide seed treatments provide safening effects in rice following exposure to low rates of the herbicides glyphosate and imazethapyr. However, no research has been conducted to determine whether a similar effect may be seen in soybean or grain sorghum, two important rotational crops across the Midsouth. To evaluate the potential safening effects of insecticide seed treatments in these two crops, field trials were conducted in Marianna, AR, in 2015 and 2016, and near Colt, AR, in 2016. In soybean, glyphosate, glufosinate, 2,4-D, dicamba, halosulfuron, mesotrione, tembotrione, and propanil were applied at low rates to simulate drift events, in combination with the insecticide seed treatments thiamethoxam and clothianidin at labeled rates. In grain sorghum, glyphosate, imazethapyr, and quizalofop were applied at low rates in combination with the insecticide seed treatments thiamethoxam, clothianidin, and imidacloprid at labeled rates. Injury reduction was seen at 1 site-year for glyphosate, glufosinate, 2,4-D, dicamba, mesotrione, and tembotrione, and at 2 of 3 site-years for halosulfuron. At 1 site-year, the safening in halosulfuron resulted in increases in both crop height and yield. In grain sorghum, reducing injury via seed treatments was generally more successful. All three herbicides applied in sorghum displayed instances of injury reduction when seed treatments were used at 1 or more site-years, including reducing injury upward of 40% in the case of quizalofop+clothianidin at Marianna in 2016. For 2 site-years, injury reduction through the use of insecticides resulted in increases in crop height and grain yield in grain sorghum compared with no insecticide use. Although the degree of safening seen varied depending on site-year in both crops, growers who use insecticide seed treatments on an annual basis may expect to see a safening effect from drift events of most herbicides evaluated in both soybean and grain sorghum.

Giant ragweed is one of the most competitive annual broadleaf weeds in corn and soybean crop production systems in the United States and eastern Canada. Management of giant ragweed has become difficult due to the evolution of resistance to glyphosate and/or acetolactate synthase (ALS)-inhibitor herbicides and giant ragweed’s ability to emerge late in the season, specifically in the eastern Corn Belt. Late-season herbicide application may reduce seed production of weed species; however, information is not available about late-season herbicide applications on giant ragweed seed production. The objective of this study was to evaluate the effect of single or sequential late-season applications of 2,4-D, dicamba, glyphosate, and glufosinate on inflorescence injury and seed production of glyphosate-resistant (GR) giant ragweed under greenhouse and field conditions (bare ground study). Single and sequential applications of glufosinate resulted in as much as 59 and 60% injury to giant ragweed inflorescence and as much as 78 and 75% reduction in seed production, respectively, under field and greenhouse conditions. In contrast, single or sequential applications of 2,4-D or dicamba resulted in ≥ 96% inflorescence injury and reduction in seed production in the field as well as in greenhouse studies. The results indicated that 2,4-D or dicamba are effective options for reducing seed production of glyphosate-resistant giant ragweed even if applied late in the season. Targeting weed seed production to decrease the soil seedbank will potentially be an effective strategy for an integrated management of GR giant ragweed.

Research was conducted from 2011 to 2015 to determine the effect of herbicide strategy on efficacy and evolution of herbicide resistance in weeds in a continuous glyphosate- and dicamba-resistant (GDr) soybean system. The nine herbicide strategies included sequential applications of glyphosate only, glyphosate plus dicamba with or without acetochlor, PRE application of residual herbicides with POST glyphosate or non-glyphosate herbicides, and their biennial rotation with one another. Giant foxtail and horseweed were the least problematic during all growing seasons. An increase in horseweed was observed by the end of the experiment especially in the plots where POST glyphosate was not used with PRE application of residual herbicides. Giant ragweed evolved resistance to glyphosate over a 4-yr period of selection with strategies that predominantly included PRE and POST glyphosate. Herbicide use strategies that included glyphosate-only and PRE application of residual herbicides fb POST glyphosate annually or in a biennial rotation were ineffective in controlling giant ragweed and glyphosate-resistant (GR) common waterhemp. Over the years, application of PRE herbicide mixtures before POST glyphosate application improved weed control and soybean yields compared with the glyphosate-only strategy. During all growing seasons, the greatest yield and reduction in total weed density before harvest was provided by herbicide use strategies that included glyphosate plus dicamba annually or in a biennial rotation regardless of the inclusion of acetochlor POST. Dicamba proved to be a valuable addition to improve the control of GR weeds. GDr soybean will provide growers with a new option for managing resistant weeds, but it needs to be used with caution, as multiple resistance in weeds, including waterhemp and giant ragweed, is already widespread.

Dicamba-resistant soybean technology provides an additional site of action for POST control of herbicide-resistant broadleaf weeds in soybean but also raises concern of off-site movement and damage to sensitive crops in adjacent fields. Dicamba formulations approved for use on dicamba-resistant soybean require applicators to use nozzles producing large droplets to reduce the risk of spray-particle drift. The use of nozzles with relatively larger droplet spectra can reduce herbicide deposition on target weeds, especially if a filtering effect from the crop canopy occurs. Experiments were conducted to evaluate the influence of broadcast nozzle design on the deposition and efficacy of 280 g ha−1 glyphosate plus 140 g ha−1 dicamba applied POST to four herbicide-resistant weed species. The TTI11004 nozzle, the original nozzle labeled for dicamba applications on dicamba-resistant soybean, reduced deposition coverage and density on spray cards compared with the TT11004 and XR11004 nozzle. The AIXR11004 nozzle produces a very coarse droplet spectrum and did not reduce coverage on spray cards, though it did reduce deposition density. Herbicide solution deposition onto Palmer amaranth, tall waterhemp, giant ragweed, and horseweed ranged from 0.41 to 0.52, 0.55 to 0.87, 0.49 to 0.58, and 0.38 to 0.41 µl cm−2, respectively. Nozzle design and droplet spectrum did not influence the deposition of herbicide solution onto the target weed, as all nozzles were equivalent for all species and site-years. Herbicide efficacy was not influenced by nozzle design, as weed control and plant height reduction were similar for all species. The results of this experiment show that the use of the TTI11004 nozzle for dicamba applications to dicamba-resistant soybean will provide acceptable herbicide deposition and efficacy when applied under the label requirements of weed height and carrier volume.

A population of buckhorn plantain with suspected resistance to 2,4-D was identified in central Indiana following 30 yr of 2,4-D–containing herbicide applications. Our objectives were to (1) confirm and quantify the level of herbicide resistance in the buckhorn plantain population using dose–response experiments and (2) find alternative herbicides that could be used to control this population. Greenhouse experiments were conducted to quantify the dose–response of resistant (R) and susceptible (S) biotypes of buckhorn plantain to both 2,4-D and triclopyr, two synthetic auxin herbicides from different chemical families. The R biotype was ≥6.2 times less sensitive to 2,4-D than the S biotype. The efficacy of triclopyr was similar on both the R and S biotypes of buckhorn plantain, suggesting the absence of cross-resistance to this herbicide. This is the first report of 2,4-D resistance in buckhorn plantain and the first report of 2,4-D resistance in turf. The resistance mechanism was limited to within a chemical family (phenoxycarboxylic acid) and did not occur across all WSSA Group 4 synthetic auxin herbicides, as the pyridinecarboxylic acid herbicides clopyralid and triclopyr and the arylpicolinate herbicide halauxifen-methyl provided control in our experiments.

Chickpea producers currently have no POST applied herbicides labeled for broadleaf weed control and rely heavily on PRE herbicides to manage weeds. Severe crop losses from broadleaf weed competition and harvest losses from weeds impeding harvest can occur when PRE herbicides perform poorly. Chickpea tolerance to POST applications of acifluorfen at 0.42 kg ai ha-1 and fomesafen at 0.28 kg ai ha-1 was tested at two sites in 2015. In 2016, both herbicides were tested on chickpeas when applied alone and in combination with pyridate at three sites. Acifluorfen and fomesafen injured chickpeas from 8 to 25% at 1 week after treatment (WAT) and 3 to 8% at 4 WAT in 2015 and from 16 to 40% at 1 WAT and 2 to 36% at 4 WAT in 2016. Pyridate applied POST at 1.00 kg ai ha-1 did not injure chickpeas or reduce yields. When pyridate was tank mixed with either acifluorfen or fomesafen, chickpea injury increased, but chickpeas recovered and yielded similar to nontreated checks or pyridate-treated plots. A low rate of metribuzin at 0.06 kg ai ha-1 tank mixed with pyridate had little impact on chickpea injury or weed control. In 2015, Russian thistle was controlled 100% by acifluorfen and fomesafen at Prosser at 28 DAT and both herbicides controlled the weed only 63% at Wilbur at 25 DAT. In 2016, all herbicide treatments reduced broadleaf weed densities equally ranging from 95 to 100% at Paterson, 50 to 100% at Prosser, and 78 to 98% at Wilbur. Chickpea yield was similar among POST herbicide treatments in all site-years. Acifluorfen, fomesafen, and pyridate have potential to improve control of susceptible broadleaf weeds that escape PRE herbicides chickpea production, but the potential for crop injury with acifluorfen and fomesafen warrant further evaluation.

Crop management practices such as tillage can influence the dissipation of herbicides in soil. This study aimed to determine the effects of tillage systems on soil dissipation of prosulfocarb (PSC) using two assessment methods: bioassay and high-performance liquid chromatography (HPLC) analysis. PSC was applied on plots cultivated under three tillage systems (moldboard plowing, tine tillage at 8- to 10-cm soil depth, and direct drilling) at different rates (0, 500, 1,000, 2,000, 4,000 and 8,000 g ai ha−1) and two spraying times, representing early and late sowing time of winter cereals in Denmark. The experiment was conducted over 2 yr. The soil was analyzed for PSC residues by HPLC and a bioassay, using silky windgrass as the indicator plant. Neither technique revealed an effect of tillage systems on PSC dissipation, but the LD50 values estimated based on the bioassays were generally lower under direct drilling (11.7 d) than with plowing (17.5 d). Moreover, LD50 estimates based on bioassay results were generally lower than those estimated with HPLC analyses. Half-life values estimated with HPLC were low and not within the range of values reported in the literature (ca. 20 d), suggesting enhanced degradation of PSC. In addition to influencing the performance of PSC against problematic weed species, an enhanced dissipation rate could also hamper the benefits of PSC in an antiresistance strategy.

Interrow cultivation is a selective, in-crop mechanical weed control tool that has the potential to control weeds later in the growing season with less crop damage compared with other in-crop mechanical weed control tools. To our knowledge, no previous research has been conducted on the tolerance of narrow-row crops to interrow cultivation. The objective of this experiment was to determine the tolerance of field pea and lentil to interrow cultivation. Replicated field experiments were conducted in Saskatchewan, Canada, in 2014 and 2015. Weekly cultivation treatments began at the 4-node stage of each crop, continuing for 6 wk. Field pea and lentil yield linearly declined with later crop stages of cultivation. Cultivating multiple times throughout the growing season reduced yield by 15% to 30% in both crops. Minimal yield loss occurred when interrow cultivation was conducted once at early growth stages of field pea and lentil; however, yield loss increased with delayed and more frequent cultivation events.

Little information is published related to seed germination and seedling emergence of Japanese foxtail, a troublesome annual grass weed widely distributed in winter wheat fields in China. Three Japanese foxtail populations were studied under laboratory and greenhouse conditions, to determine the effects of different environmental factors on seed germination or seedling emergence. Chemical control is absolutely necessary in integrated management, and efficacy of POST herbicides against different growth stages of Japanese foxtail was evaluated. Germination rate was 90% or more when temperature ranged from 5 to 25 C, with germination onset shortened as temperature increased. Light was not required for germination to occur. For pH values ranging from 5 to10 there was no effect on seed germination. Japanese foxtail seed germination was sensitive to osmotic stress and completely inhibited at an osmotic potential of -1.1 MPa. The ‘1513’ population of Japanese foxtail demonstrated tolerance to soil salinity, with 98% germination at 80 mM NaCl compared with 25 and 40% germination for populations ‘1532’ and ‘1544’, respectively. High amounts of crop residue (10 t ha−1) suppressed Japanese foxtail emergence 38 to 55%. Germination of seeds placed at 160 C for 5 min was completely inhibited for dry seeds, with a similar effect at 130 C for pre-soaked seeds. Seed burial in the soil from 0 to 4 cm had no effect on seedling emergence, but burial at 7 cm completely inhibited seedling emergence. POST herbicides mesosulfuron-methyl (13.5 g ai ha−1), clodinafop-propargyl (67.5 g ai ha−1), pyroxsulam (13.5 g ai ha−1), pinoxaden (67.5 g ai ha−1) and isoproturon (1125 g ai ha−1) reduced plant dry weight 80% or more when applied at three- to seven-leaf stage, but control declined with application at later growth stages. The information from this study helps to develop an integrated approach to Japanese foxtail management.

The distinction between count nouns and mass nouns affects thinking and writing about various types of crops and produce. Count nouns are words that indicate discrete, countable objects (e.g., forks, viewpoints), whereas mass nouns are words that indicate some relatively undifferentiated substance (e.g., water, energy). We explain the grammar of these two forms and point out some writing pitfalls to avoid. The word seed is one of the few English nouns that is both a count noun and a mass noun. An argument is presented for using seeds as the plural when several individuals are counted and for using seed as the singular when referring to seeds in the aggregate.