Field studies were conducted from 2009 through 2011 at the Sustainable Agriculture Research and Extension Center near Lingle, Wyoming, to evaluate great northern bean response to PRE flumioxazin mixed with either trifluralin, pendimethalin, or ethalfluralin. Seven treatments were arranged in a randomized complete block with three or four replicates y−1. The soil texture of the study site was loam in 2009 and 2011, and sandy loam in 2010. Soil organic matter ranged from 1.4% to 1.8%. Treatments included flumioxazin plus trifluralin, flumioxazin plus pendimethalin, flumioxazin plus ethalfluralin, ethalfluralin plus EPTC, imazamox plus bentazon (POST), hand-weeded control, and nontreated control. Dry bean density 4 wk after planting differed among herbicide treatments (P < 0.001). Treatments that included flumioxazin reduced dry bean density 54% compared with treatments without flumioxazin. Dry bean yield was influenced by dry bean density; on average, yield in flumioxazin-containing herbicide treatments was 30% less than treatments not containing flumioxazin, even though weed control was generally greater in flumioxazin treatments.

Pinoxaden is a POST acetyl coenzyme A carboxylase (ACCase) inhibitor in the phenylpyrazolin chemical family and is labelled for turfgrass use at broadcast rates of 35.5 to 71 g ai ha−1 and spot spray rates of 156 to 310 g ai ha−1. A greenhouse rate-response study was conducted to characterize the efficacy of pinoxaden against common grassy weeds. Weed species examined in this study were yellow foxtail, southern sandbur, annual bluegrass, roughstalk bluegrass, large crabgrass, dallisgrass, bahiagrass, goosegrass, and perennial ryegrass. Nonlinear regressions were modelled to determine visible injury rates (the application rate at which 50% of the weed species were injured and the 90% [I90] rate) and weight reduction rates (the application rate at which there was a 50% reduction in fresh weight and 90% reduction [WR90]) for each weed species. Only annual bluegrass, bahiagrass, and goosegrass had visible injury I90 values greater than the maximum labelled spot spray rate of 310 g ai ha−1. Annual bluegrass, bahiagrass, southern sandbur, and goosegrass all had WR90 values greater than the maximum labelled spot spray rate of 310 g ai ha−1. Results from this study indicate that the evaluated weed species can be ranked, according to visible injury I90 values, from most to least susceptible: perennial ryegrass > yellow foxtail > dallisgrass > large crabgrass > southern sandbur > roughstalk bluegrass > bahiagrass > goosegrass > annual bluegrass.

Giant reed recently was promoted as a biofuel crop in Oregon. Because giant reed is a highly invasive plant in North American rivers, the planting of this species in Oregon is a cause for concern to scientists and local land managers. However, some growers in the area were interested in producing giant reed as a rotational crop. To find potential herbicides to control the giant reed or to control it as a volunteer, 13 foliar and 13 cut-and-spray herbicide treatments were preevaluated in greenhouse studies. We chose 10% and 85% reduction in aboveground biomass for either crop safety or control, respectively. When applied at the standard rates, acetochlor and dimethenamid-p reduced aboveground dry biomass of the crop by 10% or less. Acetochlor+atrazine, atrazine, flufenacet, and mesotrione reduced aboveground biomass of the crop by at least 85%, indicating that these compounds have the potential to serve as controls against giant reed.

Living mulches can provide many sustainability benefits. However, living mulch–cash crop competition and unreliable weed control are major challenges in living mulch systems. In this study, we evaluated the potential of herbicides used at reduced rates in combination with living mulch to suppress weeds, while simultaneously reducing living mulch vigor. Herbicide treatments were a combination of two POST applications, each consisting of a single, different herbicide. Field trials were conducted in Freeville, NY, USA, using: fresh market field tomato as cash crop; sesbania and sunn hemp as living mulch; and the herbicides fomesafen, halosulfuron, metribuzin, and rimsulfuron. In 2015, when water was not limiting, tomato yield and living mulch biomass were positively correlated. This relationship was negative in 2016, likely because of drought during the growing season. Compared with the untreated living mulch check, using the herbicide treatments in combination with living mulch reduced tomato yield losses by up to 71% in 2015 and 51% in 2016. In these herbicide plus living mulch plots, weed biomass was reduced by up to 97%, compared with the weedy check. Living mulch in herbicide treatments generated up to 2500 kg ha−1 of dry matter during both 2015 and 2016, with an average ground cover of 63% in 2015 and 85% in 2016. A predominantly PRE herbicide with residual soil activity (metribuzin), followed by a herbicide with greater POST activity (halosulfuron/rimsulfuron) was the most effective herbicide application sequence. Results from our study indicate that well-designed herbicide applications may enhance the practicability of living mulch systems.

Giant miscanthus has the potential to move beyond cultivated fields and invade noncrop areas, but this can be overshadowed by aesthetic appeal and monetary value as a biofuel crop. Most research on giant miscanthus has focused on herbicide tolerance for establishment and production rather than terminating an existing stand. This study was conducted to evaluate herbicide options for control or terminating a stand of giant miscanthus. In 2013 and 2014, field experiments were conducted on established stands of the giant miscanthus cultivars ‘Nagara’ and ‘Freedom.’ Herbicides evaluated in both years included glyphosate, hexazinone, imazapic, imazapyr, clethodim, fluazifop, and glyphosate plus fluazifop. All treatments were applied in summer (June or July) and September. For both years, biomass reduction ranged from 85% to 100% when glyphosate was applied in June or July at 4.5 or 7.3 kg ae ha−1. No other treatment applied at this timing provided more than 50% giant miscanthus biomass reduction 1 yr after application. September applications of glyphosate were not consistent: treatments in 2013 reduced biomass by 40% or less, whereas in 2014, at all rates provided at least 78% biomass reduction. Glyphosate applied in June or July was the only treatment that provided effective and consistent control of giant miscanthus 1 yr after treatment.

Nutsedge species are problematic in plastic-mulched vegetable production because of the weed’s rapid reproduction and ability to penetrate the mulch. Vegetable growers rely heavily on halosulfuron to manage nutsedge species; however, the herbicide cannot be applied over mulch before vegetable transplanting due to potential crop injury. This can be problematic when multiple crops are produced on a single mulch installation. Field experiments were conducted to determine the response of broccoli, cabbage, squash, and watermelon to halosulfuron applied on top of mulch prior to transplanting. Halosulfuron at 80 g ai ha−1 was applied 21, 14, 7, and 1 d before planting (DBP), and 160 g ai ha−1 was applied 21 DBP. In all experiments, extending the interval between halosulfuron application and planting reduced crop injury. For squash and watermelon, visual injury, plant diameters/vine runner lengths, marketable fruit weights, and postharvest plant biomass resulted in similar values when applying 80 g ha−1 21 DBP and with the nontreated weed-free control. Reducing this interval increased injury for both crops. Visual crop injury and yield reductions up to 40% occurred, with halosulfuron applied 14, 7, or 1 DBP in squash and 1 DBP in watermelon. Broccoli and cabbage showed greater sensitivity, with injury and plant diameter reductions greater than 15%, even with halosulfuron applied at 80 g ha−1 21 DBP. Experimental results confirm that halosulfuron binds to plastic mulch, remains active, and is slowly released from the mulch over a substantial period, during rainfall or overhead irrigation events. Extending the plant-back interval to at least 21 d before transplanting did overcome squash and watermelon injury concerns with halosulfuron at 80 g ha−1, but not broccoli and cabbage. Applying halosulfuron over mulch to control emerged nutsedge before planting squash and watermelon would be beneficial if adequate rainfall or irrigation and appropriate intervals between application and planting are implemented.

In glyphosate-resistant (GR) cropping systems, paraquat applied in mixtures with residual herbicides prior to crop emergence offers an alternative herbicide mode of action (MOA) to aid in GR weed management. Rice is sensitive to off-target herbicide movement; however, severity of injury can vary with herbicide, rate, and formulation. Therefore, research was conducted from 2015 to 2017 in Stoneville, MS, to characterize rice response to a sublethal concentration of paraquat applied at 84 g ai ha–1 in combination with common residual herbicides. Paraquat plus metribuzin injured rice 68% to 69% 14 and 28 d after treatment (DAT), which was 10% to 13% greater than injury following paraquat alone or paraquat plus fomesafen. Pooled across metribuzin and fomesafen treatments, paraquat reduced rough rice yields 23%. Paraquat plus 10 different residual herbicides injured rice ≥51% 28 DAT and reduced rough rice yields ≥21%. These studies indicate a severe negative impact on rice growth and development following exposure to a sublethal concentration of paraquat alone or in mixture with common residual herbicides. Therefore, applications of paraquat plus residual herbicides to fields in proximity to rice should be avoided if conditions are conducive for off-target movement.

Dicamba and 2,4-D systems control many problematic weeds; however, drift to susceptible crops can be a concern in diverse production areas. Glufosinate-based systems are an alternative, but current recommended rates of glufosinate can result in variable control. Research was conducted in 2017 and 2018 to investigate the optimum time interval between sequential glufosinate applications and determine if the addition of glyphosate with glufosinate is beneficial for controlling Palmer amaranth and annual grasses in cotton. The interval between sequential applications (1, 3, 5, 7, 10, or 14 d or no second spray) was the whole plot and herbicide option (glufosinate or glufosinate plus glyphosate) was the subplot. Combined over herbicides, Palmer amaranth 15- to 20-cm tall (at four locations) was controlled 98% to 99% with sequential intervals of 1 to 7 d compared with 70% to 88% with intervals of 10 or 14 d. Lowest biomass weight and population densities were noted with 1- to 7-d intervals. Large crabgrass 15- to 20-cm tall (at five locations) was controlled 93% to 98% with glufosinate applications 3- to 7-d apart as compared with 76% to 81% with applications 10- to 14-d apart. Lowest biomass weights were observed with 1- to 7-d intervals. When glufosinate controlled grass less than 93%, adding glyphosate was beneficial. Neither interval between sequential applications nor herbicide option influenced cotton yield. Shorter time intervals between sequential application and including glyphosate can improve the effectiveness of a glufosinate-based system in managing Palmer amaranth and large crabgrass.

Growers desire more techniques to control weeds in horticultural crops that are grown organically and consumed directly, such as red raspberry. Abrasive grit emited via high air pressure is a new method for controlling weeds. Grit derived from corn cobs was examined for its efficacy during the year of raspberry establishment for 2 to 3 years at three sites (seven site-years) and compared with efficacy of hand-weeding as well as no weed control. Grit was applied once or twice weekly after raspberry transplantation in spring until weed emergence ceased in mid to late July. Weeds and raspberry growth were assessed in August. Grit was effective in controlling broadleaf weeds, averaging 94% control across site-years, but control of grass weeds was less than 10%. Total weed (broadleaf plus grass) control across site-years ranged from 51% to 96% and averaged 78%. Raspberry cane growth was affected by weeds, and grit-weeding at least partially alleviated these effects. Thus, abrasive grit allows growers to manage broadleaf weeds effectively without herbicides or soil tillage. However, additional research is needed to determine the correct amounts and timing of grit applications, as well as more efficacious types of grit, to control grass weeds.

PRE herbicides are the backbone of a successful weed management program in Christmas tree production. In a 2-yr field study, weed control efficacy and tolerance of newly transplanted Canaan fir to different PRE treatments were evaluated. Herbicide treatments consisted of two rates of each of atrazine plus mesotrione plus S-metolachlor at 561 + 150 + 1,504 and 1,122 + 300 + 3,008 g ai ha−1, flumioxazin at 214 and 429 g ai ha−1, hexazinone plus sulfometuron methyl at 289 + 27 and 480 + 46 g ai ha−1, indaziflam at 20 and 41 g ai ha−1, simazine plus oryzalin at 3,366 + 1,683 and 3,366 + 3,366 g ai ha−1, and a nontreated control. Averaged over 2 yr, all PRE treatments controlled giant foxtail, large crabgrass, and redroot pigweed at least 80% throughout the summer. Only the high rates of atrazine plus mesotrione plus S-metolachlor maintained >80% season-long control of yellow foxtail. Horseweed was controlled >85% with flumioxazin at both rates and at high rates of atrazine plus mesotrione plus S-metolachlor, hexazinone plus sulfometuron methyl, and indaziflam. The season-long PRE control of both red sorrel and wild carrot was maintained ≥80% with atrazine plus mesotrione plus S-metolachlor and hexazinone plus sulfometuron methyl regardless of application rate. By 16 wk after treatment, within-row densities of weeds evaluated in this study were reduced >75% in plots treated with atrazine plus mesotrione plus S-metolachlor at both application rates or hexazinone plus sulfometuron methyl at 480 + 46 g ai ha−1. Within-row weed densities in the nontreated control plots were 50, 32, 36, 25, 27, 31, and 19 plants m−2 for large crabgrass, giant foxtail, horseweed, redroot pigweed, red sorrel, wild carrot, and yellow foxtail, respectively. No discernible injury was observed in Canaan fir with any PRE treatment in both study years.

Cover crops can provide many benefits to peanut and cotton crops planted in rotation including suppressing weeds, conserving soil moisture after termination, increasing soil organic matter, and reducing soil erosion. However, herbicide carryover can affect cover crop establishment. The objective of this study was to investigate the responses of 6 cover crops (daikon radish, cereal rye, oat, crimson clover, winter wheat, and common vetch) to 12 soil residual herbicides. A multiyear (2016–2018), multilocation study was conducted in Macon and Henry counties, Alabama. Herbicide treatments included S-metolachlor, acetochlor, pyroxasulfone, diclosulam, imazapic, chlorimuron-ethyl, bentazon plus acifluorfen, pyrithiobac-sodium, trifloxysulfuron-sodium, diuron, prometryn, and flumioxazin, each applied at 10% of the full-labeled rate. At 42 to 52 and 145 to 149 d after planting (DAP), cover crop plant heights and stand counts were evaluated, as was biomass at 145 to 149 DAP. Treatments varied from year to year but not locations. In 2016, significant stand reductions (P ≤ 0.10) of 36% to 43% in rye and 44% to 75% in wheat were observed at 48 to 52 DAP for S-metolachlor, acetochlor, pyroxasulfone, imazapic, and bentazon plus acifluorfen compared with nontreated plants. Vetch had stand reductions ranging from 14% to 80% for all treatments 50 DAP except for plants treated with prometryn. S-metolachlor, pyroxasulfone, and acetochlor reduced stands of rye, wheat, and vetch more than any other herbicides. In 2017, at 147 to 149 DAP, clover stands were reduced by 29% with diclosulam and by 38% with trifloxysulfuron-sodium. Similarly, radish stands were reduced by 64% with diclosulam treatment. No significant biomass reductions were observed for any cover crop species either year. Oat showed the most tolerance with no treatments reducing any growth parameters either year. Although initial injury and stunting may occur, biomass at termination of cover crops were not affected by herbicide residues evaluated in this study.

Glyphosate-resistant (GR) Palmer amaranth continues to be challenging to control across the U.S. cotton belt. Timely application of POST herbicides and herbicides applied at planting or during the season with residual activity are utilized routinely to control this weed. Although glyphosate controls large Palmer amaranth that is not GR, herbicides such as glufosinate used in resistance management programs for GR Palmer amaranth must be applied when weeds are small. Dicamba can complement both glyphosate and glufosinate in controlling GR and glyphosate-susceptible (GS) biotypes in resistant cultivars. Two studies were conducted to determine Palmer amaranth control, weed biomass, and cotton yield, as well as to estimate economic net return when herbicides were applied 2, 3, 4, and 5 wk after planting (WAP). In one experiment POST-only applications were made. In the second experiment PRE herbicides were included. In general, Palmer amaranth was controlled at least 98% by herbicides applied at least three times regardless of timing of application or herbicide sequence. Glyphosate plus dicamba applied at 4 and 5 WAP controlled Palmer amaranth similarly compared to three applications by 8 WAP; however, yield was reduced 23% because of early-season interference. The inclusion of PRE herbicides benefited treatments that did not include herbicides applied 2 or 3 WAP. Glyphosate plus dicamba applied as the only herbicides 5 WAP provided 69% control of Palmer amaranth. PRE herbicides increased control to 96% for this POST treatment. Economic returns were similar when three or more POST applications were applied, with or without PRE herbicides.

Horseweed is one of Kentucky’s most common and problematic weeds in no-till soybean production systems. Emergence in the fall and spring necessitates control at these times because horseweed is best managed when small. Control is typically achieved through herbicides or cover crops (CCs); integrating these practices can lead to more sustainable weed management. Two years of field experiments were conducted over 2016 to 2017 and 2017 to 2018 in Versailles, KY, to examine the use of fall herbicide (FH; namely, saflufenacil or none), spring herbicide (SH; namely, 2,4-D; dicamba; or none), and CC (namely, cereal rye or none) for horseweed management prior to soybean. Treatments were examined with a fully factorial design to assess potential interactions. The CC biomass in 2016 to 2017 was higher relative to 2017 to 2018 and both herbicide programs reduced winter weed biomass in that year. The CC reduced horseweed density while growing and after termination in 1 yr. The FH reduced horseweed density through mid-spring. The FH also killed winter weeds that may have suppressed horseweed emergence; higher horseweed density resulted by soybean planting unless the CC was present to suppress the additional spring emergence. If either FH or CC was used, SH typically did not result in additional horseweed control. The SH killed emerged plants but did not provide residual control of a late horseweed flush in 2017 to 2018. These results suggest CCs can help manage spring flushes of horseweed emergence when nonresidual herbicide products are used, though this effect was short-lived when less CC biomass was present.

Soybean cyst nematode (SCN) causes over $1.2 billion in revenue loss annually in the United States and consistently ranks as the most threatening pathogen for soybean. SCN weed hosts have been documented in other states in the eastern Corn Belt, but very little work has been done in the midwestern Corn Belt. To determine alternative SCN weed hosts in South Dakota, 670 whole weed root samples comprising 63 weed species were collected from 48 SCN-positive fields in 13 counties during fall 2016 and spring 2017. Among the 63 weed species, 12 contained SCN juveniles and 7 were confirmed hosts of SCN based on the completion of the SCN life cycle in greenhouse studies. Ranking of female index (FI) for the weed hosts were purple deadnettle (FI = 34.6) > field pennycress (FI = 26.9) > common mallow (FI = 2.04) > shepherd’s purse (FI = 1.89) > white clover (FI = 1.86) > Canada thistle (FI = 1.24) > common cocklebur (FI = 1.10). These results indicate that some weeds can support SCN, and therefore a proactive weed management approach should be employed for fields infested with SCN.

Cover crops (CCs) play an important role in integrated weed management. Data necessary to evaluate the role of CCs in weed management at the watershed scale with topographic positions are lacking. We evaluated the effects of cereal rye and hairy vetch CCs on weed suppression at different topographic positions (shoulder, backslope, and footslope) at a watershed scale. Watersheds with a CC treatment followed a crop rotation of corn–cereal rye–soybean–hairy vetch, whereas watersheds without a CC (no-CC) had a crop rotation of corn–winter fallow–soybean–winter fallow. A negative relationship was present between CCs and weed biomass at the shoulder, backslope, and footslope topographic landscape positions, with R2 values of 0.40, 0.48, and 0.50, respectively. In 2016, a cereal rye CC reduced weed biomass 46% to 50% at footslope and shoulder positions compared to no CC. In 2018, a cereal rye CC reduced weed biomass between 52% and 85% at all topographic positions in CC treatment watersheds compared to no-CC watersheds. Hairy vetch in 2017 reduced weed biomass 62% to 72% at footslope and shoulder topographic positions in CC watersheds compared to no-CC. The C:N ratio of weed biomass in CC treatment watersheds was generally higher compared to watersheds without CCs. In this study, several significant interactions were found between the topographic positions and CC treatments. Cover crop–induced weed suppression at different topographic positions can lead to developing better site-specific weed control strategies. Therefore, CC interactions with topography, weed germination potential, and the role of soil moisture at the watershed scale should be further evaluated.

Glyphosate-resistant (GR) canola is a widely grown crop across western Canada and has quickly become a prolific volunteer weed. Glyphosate-resistant soybean is rapidly gaining acreage in western Canada. Thus, there is a need to evaluate herbicide options to manage volunteer GR canola in GR soybean crops. We conducted an experiment to evaluate the efficacy of various PRE and POST herbicides applied sequentially to volunteer GR canola and to evaluate soybean injury caused by these herbicides. Trials were conducted across Saskatchewan and Manitoba in 2014 and 2015. All treatments provided a range of suppression (>70%) to control (>80%) of volunteer canola. All treatments with the exception of the glyphosate-treated control reduced aboveground canola biomass by an average of 96%. As well, canola seed contamination was reduced from 36% to less than 5% when a PRE and POST herbicide were both used. Moreover, all combinations of herbicides used had excellent crop safety (<10%). All PRE and POST herbicide combinations provided better control of volunteer canola compared with the glyphosate-only control, but tribenuron followed by bentazon and tribenuron followed by imazamox plus bentazon provided solutions that were low cost, currently available (registered in western Canada), and had the potential to minimize development of herbicide resistance in other weeds.

Weed control in tree nut orchards is a year-round challenge for growers that is particularly intense during winter through summer as a result of competition and interference with management and harvest operations. A common weed control program consists of an application of a winter PRE and POST herbicide mixture, followed by a desiccation treatment in early spring and before harvest. Because most spring and summer treatments depend on a limited number of foliar-applied herbicides, summer-germinating species and/or herbicide-resistant biotypes become troublesome. Previous research has established effective PRE herbicide programs targeting winter glyphosate-resistant weeds. However, more recently, growers have reported difficulties in controlling several summer-germinating grass weeds with documented or suspected resistance to the spring and summer POST herbicide programs. In this context, research was conducted to evaluate a sequential PRE approach to control winter- and summer-germinating orchard weeds. Eight field experiments were conducted in tree nut orchards to evaluate the efficacy of common winter herbicide programs and a sequential herbicide program for control of a key summer grass weed species. In the sequential-application strategy, three foundational herbicide programs applied in the winter were either mixed with pendimethalin, followed with pendimethalin in March, or applied as a split application of pendimethalin in both winter and spring. Results indicate that the addition of pendimethalin enhanced summer grass weed control throughout the crop growing season by up to 31%. Applying all or part of the pendimethalin in the spring improved control of the summer grass weed junglerice by up to 49%. The lower rate of pendimethalin applied in the spring performed as well as the high rate in the winter, suggesting opportunities for reducing herbicide inputs. Tailoring sequential herbicide programs to address specific weed challenges can be a viable strategy for improving orchard weed control without increasing herbicide use in some situations.

Winter cover crops (CCs) provide soil conservation benefits for strip-tillage tobacco producers, but soil-residual herbicides may interfere with their establishment and growth. Tobacco is planted later than many agronomic crops, but growers often terminate CCs early to minimize CC residue at planting, and this may reduce weed suppression potential. We examined residual herbicide effects on CCs across two seasons and the potential for CC-based weed suppression within strip-tilled tobacco. Mixtures of wheat plus crimson clover and cereal rye plus crimson clover were examined, with a no-CC control. Herbicides included two rates of PRE sulfentrazone (177 or 354 g ai ha–1) plus carfentrazone (20 or 40 g ai ha–1); the higher rate was also followed by POST clomazone (840 g ai ha–1) or mixed with PRE pendimethalin (1,400 g ai ha–1). Controls with no weed management and hand weeding were also included. CC density and biomass were not reduced by weed management (WM) treatments with residual herbicides. However, CCs did not reduce density of annual grasses, small-seeded broadleaves, or perennials in the tilled in-row or untilled between-row zones. Cereal rye plus crimson clover resulted in lower weed biomass at tobacco harvest in the untilled between-row zone in 2017. WM effects were variable between the years, weed groups, and zones. Adding clomazone or pendimethalin was more consistent for reducing weed density and biomass compared to the low rate of sulfentrazone plus carfentrazone. Tobacco yield was unaffected by CCs in 2017 but lower in some WM treatments in 2018. In this study, tobacco herbicides did not interfere with wheat, cereal rye, or crimson clover establishment, but additional research should determine if these results apply to other environments and soil types. However, when these CC species were terminated 5 to 6 wk before transplanting, they did not consistently contribute to weed control.

POST weed control atop the bed during strawberry production is limited to hand weeding, clopyralid, and acetyl CoA carboxylase inhibitors. Identification of additional modes of action is desirable to increase available options for producers and alleviate herbicide resistance concerns. The study objective was to screen sulfonylurea herbicides for safety of strawberry coordinated with efficacy against Carolina geranium. Herbicide treatments included metsulfuron-methyl, flazasulfuron, foramsulfuron, thifensulfuron-methyl, trifloxysulfuron-sodium, and rimsulfuron. Strawberry plants were heavily damaged by all herbicides apart from foramsulfuron. Although the strawberry plant was dramatically affected by the evaluated herbicides, demonstrating strong epinasty, there were no differences in resultant biomass at 31 d after treatment (DAT) compared to controls. Carolina geranium was severely injured by metsulfuron-methyl, flazasulfuron, and thifensulfuron-methyl, and moderately injured by foramsulfuron. There were consistent reductions in biomass by 31 DAT by metsulfuron-methyl and flazasulfuron. Overall, metsulfuron-methyl and flazasulfuron are suitable candidates for Carolina geranium control in row-middles. Foramsulfuron is a suitable candidate for additional field-based screening for utility in POST use in strawberry production atop the bed. Consideration toward doses, surfactants, timings, and cultivar tolerance may be necessary to minimize injury as observed in the greenhouse (15% to 20%).

Research using the critical period for weed control (CPWC) has shown that high-yielding cotton crops are very sensitive to competition from grasses and large broadleaf weeds, but the CPWC has not been defined for smaller broadleaf weeds in Australian cotton. Field studies were conducted over five seasons from 2003 to 2015 to determine the CPWC for smaller broadleaf weeds, using mungbean as a mimic weed. Mungbean was planted at densities of 1, 3, 6, 15, 30, and 60 plants m−2 with or after cotton emergence and added and removed at approximately 0, 150, 300, 450, 600, 750, and 900 degree days of crop growth (GDD). Mungbean competed strongly with cotton, with season-long interference; 60 mungbean plants m−2 resulted in an 84% reduction in cotton yield. A dynamic CPWC function was developed for densities of 1 to 60 mungbean plants m−2 using extended Gompertz and exponential curves including weed density as a covariate. Using a 1% yield-loss threshold, the CPWC defined by these curves extended for the full growing season of the crop at all weed densities. The minimum yield loss from a single weed control input was 35% at the highest weed density of 60 mungbean plants m−2. The relationship for the critical time of weed removal was further improved by substituting weed biomass for weed density in the relationship.