Improved cultivars of zoysiagrass established by seed are now available, but little is known about the safety of herbicides on zoysiagrass seedlings. Our objective was to determine the turf safety of various herbicides when applied from emergence to 4 wk after emergence (WAE) of ‘Zenith’ zoysiagrass. Oxadiazon (3.4 kg ai/ha), MSMA (2.3 kg ai/ha), and pronamide (1.1 kg ai/ha) did not reduce coverage 7 WAE when applied at emergence or later and caused only temporary discoloration of seedlings. Foramsulfuron (0.03 kg ai/ha) injured seedling zoysiagrass both years of testing and reduced cover in the final year. Fluazifop (0.07 kg ai/ha) caused significant injury in all 3 yr of the study and reduced coverage in the final year. Fenoxaprop (0.14 kg ai/ha) caused visible injury and reduction in zoysiagrass coverage in all 3 yr of the study. Our studies indicate pronamide, MSMA, or oxadiazon are the safest herbicides to use over Zenith zoysiagrass seedlings, and selection among these three depends on the primary weed species present.

Studies were conducted to evaluate absorption and translocation of 14C-glyphosate in glyphosate-resistant (GR) cotton. Both commercial GR cotton events [glyphosate-resistant event 1, marketed as Roundup Ready®, released 1997 (GRE1), and glyphosate-resistant event 2, marketed as Roundup Ready Flex®, released 2006 (GRE2)] were evaluated at the four-leaf and eight-leaf growth stages. Plants were harvested at 1, 3, 5, and 7 d after treatment (DAT). Glyphosate absorption, as a percentage of applied, increased over time with 29 and 36% absorption at 7 DAT in four-leaf GRE1 and GRE2 cotton, respectively. In eight-leaf cotton, glyphosate absorption (33% at 7 DAT) was not different between events. Glyphosate translocation patterns were not different between events or harvest timings and exhibited a source–sink relation. Observed translocation differences between cotton growth stages were probably due to reduced glyphosate export from the treated leaf of eight-leaf cotton. An additional study compared absorption and translocation of 14C-glyphosate and 14C-sucrose in 5- and 10-leaf GRE2 cotton. Averaged over trials, 14C compounds, and growth stages, cotton absorbed 28% of the applied dose at 14 DAT. On the basis of the percentage of 14C exported out of the treated leaf, glyphosate and sucrose translocation patterns were similar, indicating that glyphosate may be used as a photoassimilate model in GRE2 cotton.

Only two spinach herbicides are currently available to producers, and with limited choices in herbicide mode of action (MOA), overuse of the current herbicides can result in dominance of uncontrolled weeds. Therefore, spinach producers need more herbicide options. Trials were conducted in processing spinach to evaluate the crop safety of dimethenamid-p (0.56 kg ai/ha), EPTC (2.94 to 3.40 kg ai/ha), or ethofumesate (0.84, 1.12 or 2.24 kg ai/ha) applied pre-emergent (PRE), and ethofumesate (0.09 or 0.18 kg ai/ha) applied early postemergent (EPOST) for potential use as alternatives to s-metolachlor (0.73 kg ai/ha) and cycloate (2.52 kg ai/ha). The control of London rocket was excellent with s-metolachlor, dimethenamid-p, and ethofumesate. Weed control with cycloate and EPTC was fair, and generally inferior to all others. Cycloate and s-metolachlor were safe to spinach, and only minor crop injury was observed with all other herbicides, except the high rate of ethofumesate PRE, which resulted in high levels of injury. Spinach outgrew all early herbicide injury with no significant yield losses. Ethofumesate applied EPOST caused no injury in year 1, although in year 2 injury was higher in all plots where it was applied twice, regardless of rate. In high-density plantings, dimethenamid-p caused significant crop injury to spinach, but only at one location on a sandy loam soil. In that trial, yields in dimethenamid-p plots were reduced an average 30% compared to the hand-weeded and s-metolachlor plots. As a result of this research, dimethenamid-p, EPTC, and ethofumesate should be considered candidates for expanded-use registrations in processing spinach production. More research is needed to determine additional rates and use patterns for improved crop safety, as well as an evaluation of soil types and spinach varieties.

Field experiments were conducted at Manhattan and Hesston, KS, in 2004, and at Manhattan, KS, in 2005, to evaluate cotton response to seven hormonal-type herbicides. Herbicides 2,4-D amine, 2,4-D ester, clopyralid, picloram, fluroxypyr, triclopyr, and dicamba were each applied at 0, 1/100, 1/200, 1/300, and 1/400 of the herbicide use rates on cotton in the six- to eight-leaf stage. Herbicide use rates were 210 and 280 g ae/ha for fluroxypyr and clopyralid and 561 g ae/ha, for 2,4-D amine, 2,4-D ester, dicamba, picloram, and triclopyr. At 14 d after treatment (DAT), all herbicides caused leaf cupping and epinasty, except triclopyr and clopyralid, which caused severe bleaching and chlorosis. The order of visual injury ratings was 2,4-D ester > 2,4-D amine > picloram > dicamba > fluroxypyr > triclopyr > clopyralid. By 56 DAT, slight injury symptoms were observed on plants treated with all herbicides, except all rates of 2,4-D, from which symptoms were severe. All rates of 2,4-D and the highest rate of picloram caused more than 60% flower abortion. Ranking of fiber yield reduction after herbicide treatment was 2,4-D ester > 2,4-D amine > picloram > fluroxypyr > dicamba > clopyralid > triclopyr. This research demonstrated that cotton is extremely susceptible to simulated drift rates of 2,4-D and picloram, whereas clopyralid and triclopyr caused early injury, with minimal effect on cotton yield.

Studies were conducted in 2003 and 2004 to determine the effect of application timing and halosulfuron rate on sweetpotato yield and quality. Halosulfuron was applied 1, 2, and 4 wks after transplanting (WAP) sweetpotato in 2003, and 2, 3, and 4 WAP in 2004. Treatments within each timing included halosulfuron at 13, 26, 39, 52, and 65 g ai/ha plus a weed-free control. Combined over year, site, cultivar and rate, halosulfuron applied at 1, 2, 3, and 4 WAP stunted sweetpotato 32, 15, 11, and 14%, respectively, rated 2 wks after treatment. The stunting observed with the 1 and 2 WAP timings caused a 17 and 10% reduction in yield of No. 1 roots, respectively, compared with the weed-free control. The 3 and 4 WAP timings of halosulfuron did not reduce yield of No. 1 roots. Total yield was reduced approximately 11% at the 1, 2, and 3 WAP application timings. Halosulfuron at 4 WAP did not reduce total yield. Combined over year, site, and cultivar, halosulfuron applied at 39 g/ha did not reduce the weight of No. 1 roots or total crop yield and thus could be an effective POST option for weed control in sweetpotato.

Weed control and potato response to halosulfuron applied alone POST and with rimsulfuron or S-ethyl dipropyl carbamothioate (EPTC) were evaluated in 2004 and 2005 near Paterson, WA. Potatoes were injured and exhibited chlorosis and stunted growth after halosulfuron applications of 18, 26, and 35 g/ha. Potato height was reduced 33 and 20% in late May by halosulfuron at 18 or 26 g/ha in 2004 and 2005, respectively. Halosulfuron applied alone failed to control hairy nightshade and large crabgrass. Total tuber yield and U.S. no. 1 yield were reduced 10% in halosulfuron-treated plots because of poor weed control and possibly herbicide injury. Tank-mixing rimsulfuron with halosulfuron improved control of hairy nightshade and large crabgrass and increased potato yield. Tank-mixing EPTC at 2 kg/ha with halosulfuron improved early-season hairy nightshade control, but weed control was poor at row closure. Rimsulfuron applied alone at 18 or 26 g/ha controlled hairy nightshade and large crabgrass without potato injury and resulted in the greatest potato yields.

An experiment was conducted at three sites in central Oklahoma to compare the efficacy of Italian ryegrass management options in no-till (NT) and conventional tillage (CT) winter wheat. The Italian ryegrass management options included selected herbicide treatments, wheat-for-hay, and a rotation consisting of double-crop soybean seeded immediately after wheat harvest, followed by early season soybean, and then by wheat. In continuous wheat, before application of glyphosate or tillage, Italian ryegrass plant densities in mid-September were 12,300 to 15,000 plants/m2 in NT plots vs. 0 to 500 plants/m2 in CT plots. When applied POST, diclofop controlled more Italian ryegrass than tralkoxydim or sulfosulfuron. In continuous wheat, yields were greater in CT plots than in NT plots at two of three sites. None of the Italian ryegrass management options consistently reduced Italian ryegrass density in the following wheat crop. Of the Italian ryegrass control strategies applied to continuous wheat, three herbicide treatments in NT at Chickasha and all treatments in NT at Perry reduced Italian ryegrass density in the following wheat crop. Italian ryegrass plant density in November and spike density were highly related to wheat yield at two and three sites, respectively. No management options were more profitable than rotation to soybean.

Field studies were conducted near Oxnard, CA and in two locations near Salinas, CA in 2002 and 2003 to evaluate efficacy and safety of six herbicides in celery. s-metolachlor at 0.6 and 0.7 kg ai/ha and flufenacet at 0.5, 0.6, and 0.7 kg ai/ha PRE were safe to celery and controlled 81 to 94% of yellow nutsedge at densities < 20 plants/m2. At yellow nutsedge densities > 20 plants/m2, the most efficacious treatments were 1.1 kg/ha of s-metolachlor or 0.7 kg/ha of flufenacet, which reduced nutsedge densities by 71 or 53%, respectively; however, both resulted in slight injury to celery. All other herbicides generally did not injure celery and none reduced marketable crop yield. Flumioxazin pretransplant (PRE) at 0.1 and 0.2 kg ai/ha controlled broadleaf weeds near 100% at all locations, suggesting that it can be an effective alternative to standard linuron and prometryn, which are applied post-transplant (POST) in celery.

Field studies were conducted 2004 and 2005 to evaluate weed control following POST applications of glyphosate in combination with either S-metolachlor (premix formulation), pyrithiobac, or trifloxysulfuron in conjunction with glyphosate in second-generation glyphosate-resistant cotton (Roundup Ready Flex). These herbicides were applied in combination with glyphosate in a two-application program at the 2-leaf (LF) (followed by glyphosate alone at the 10-LF growth stage), 6-LF (following glyphosate alone at the 2-LF growth stage), or 10-LF (following glyphosate alone at the 2-LF growth stage) cotton growth stages. No differences in weed control between residual herbicide were observed for goosegrass, hemp sesbania, Johnsongrass, Palmer amaranth, redroot pigweed, sicklepod, or smellmelon. Optimum control of barnyardgrass and browntop millet was achieved with glyphosate plus S-metolachlor. No differences were observed among application timings for control of goosegrass, hemp sesbania, Johnsongrass, pitted morningglory, and smellmelon. Control of barnyardgrass, browntop millet, Palmer amaranth, redroot pigweed, and sicklepod was optimized with residual herbicide application at the 2- or 10-LF timing. No yield differences were observed between residual herbicides, and seed cotton yield averaged 2,800 kg/ha. Yield was maximized when residual herbicide was applied at the 2- or 10-LF growth stage (2,960 to 2,730 kg/ha). Analysis based on numerical yield at particular residual-herbicide application timings and calculated yield for each timing based on the percentage of a standard three-application glyphosate program indicated the most consistent residual-herbicide timing for optimizing yield in a reduced-input Roundup Ready Flex weed-control program occurred at the two-leaf growth stage. All reduced-input programs, however, resulted in cotton yield of at least 93% of that obtained with the standard program.

Field trials were initiated at three Missouri locations in the fall of 2004 and 2005 to compare the efficacy of fall and early spring herbicide applications on winter and summer annual weed populations in no-till soybean. All three experiments received applications of chlorimuron plus sulfentrazone plus 2,4-D; chlorimuron plus tribenuron plus 2,4-D; and glyphosate plus 2,4-D in the fall, 60 d prior to planting (60 PP), 30 days prior to planting (30 PP), and 7 d prior to planting (7 PP). Good control of all winter annual weeds, except for common chickweed, was observed at planting from fall applications of chlorimuron plus sulfentrazone plus 2,4-D and chlorimuron plus tribenuron plus 2,4-D. Fall, 60 PP, and 30 PP applications of chlorimuron plus sulfentrazone plus 2,4-D provided relatively poor control of common chickweed. Glyphosate plus 2,4-D applied in the fall and 60 PP provided adequate control of early fall germinating winter annuals, such as common chickweed and henbit. However, these treatments provided poor control of winter annual species that exhibited some degree of spring germination. Control of summer annual weed species 7 wk after planting (WAP) was highly variable. Relatively poor control of common waterhemp was obtained from all treatments except chlorimuron plus sulfentrazone plus 2,4-D applied at all three spring timings. Giant foxtail control was highly variable ranging from 0 to 95%. Measurements of weed biomass collected 7 WAP revealed larger amounts of biomass present in the fall application timing of each herbicide treatment. Emergence of winter and summer annual weed species from early March to 7 WAP varied by herbicide treatment. Emergence of total winter and summer annual weed species was reduced with both residual herbicide treatments when compared with glyphosate plus 2,4-D and the untreated control.

Meadow foxtail is a rhizomatous grass widely grown for hay and pasture in wet meadows of the western United States and Canada. Two sulfonylurea herbicides, chlorsulfuron and metsulfuron-methyl, were evaluated for their effects on meadow foxtail biomass. Both herbicides were applied at four doses, 0.035, 0.070, 0.105, and 0.140 kg ai/ha, together with a control at each of two sites in October 2003. Treatments were replicated four times at each site and arranged in a randomized complete block design and sampled in July 2004 and 2005. Meadow foxtail biomass depended on site (P = 0.001) or year (P = 0.001), but not herbicide treatment (P = 0.182). No biomass production losses resulted from applying up to 0.14 kg/ha of either chlorsulfuron or metsulfuron-methyl on meadow foxtail, even in relatively high-pH soils.

Field and greenhouse studies were conducted to investigate the compatibility of MSMA in a tank mixture with glyphosate or glufosinate for broadleaf and grass weed control. Glyphosate, glufosinate, and MSMA were evaluated at 0.5×, 1×, and 2× rates, with 1× rates of 0.84 kgae/ha, 0.5 kgai/ha, and 2.2 kgai/ha, respectively. Glyphosate and glufosinate provided similar levels of control for most weed species and were often more efficacious than MSMA alone. Glyphosate controlled Palmer amaranth better than glufosinate. Glufosinate controlled hemp sesbania, pitted morningglory, and ivyleaf morningglory better than glyphosate at one location. Weed control was not improved with the addition of MSMA to glyphosate or glufosinate when compared with either herbicide alone. MSMA antagonized glyphosate efficacy on barnyardgrass, browntop millet, hemp sesbania, Palmer amaranth, and redroot pigweed. MSMA antagonized glufosinate efficacy on browntop millet, hemp sesbania, ivyleaf morningglory, johnsongrass, Palmer amaranth, pitted morningglory, prickly sida, redroot pigweed, and velvetleaf. Antagonism of glyphosate or glufosinate by MSMA was often overcome by applying the 2× rate of either herbicide alone. MSMA is not a compatible tank-mixture partner with glyphosate or glufosinate for weed control in cotton.

Field and greenhouse studies examined glyphosate and several ACCase-inhibitor herbicides for control of wirestem muhly. A field study evaluated application rate and timing for control in glyphosate-resistant soybean. Herbicides were applied at two rates, 4 and 6 wk after planting (WAP) of soybean when wirestem muhly was about 30 and 50 cm tall, respectively. A complimentary greenhouse experiment with the same herbicides examined wirestem muhly rhizome viability 30 days after herbicide application. A second field study examined optimum glyphosate application timing for control of wirestem muhly during a fallow rotation period. Glyphosate was applied at 14-day intervals from mid-May through early October. In the first field study, glyphosate, fluazifop, and clethodim provided better control of wirestem muhly than sethoxydim and quizalofop. Clethodim, fluazifop, and glyphosate provided 74 to 92% control over both rates and application timings, whereas quizalofop and sethoxydim were the least effective, providing only 52 to 64% control regardless of rate or timing. In the greenhouse, glyphosate was the most effective herbicide, providing at least 97% control and an 87% reduction in shoot biomass; sethoxydim and fluazifop were the least effective herbicides. All of the herbicides reduced rhizome viability compared to nontreated plants up to 71%, but no difference between herbicides was observed. In the second field study, end-of-season ratings revealed that glyphosate provided 95 to 100% control of wirestem muhly from applications made between late June and early September. The year following application, glyphosate provided 91 to 99% control of wirestem muhly from applications made between mid-June and early September. Applications earlier than mid-June or after early September resulted in less than 90% control. Overall, results show that (1) glyphosate was the most effective herbicide; (2) the ACCase-inhibitor herbicides differ in their effectiveness; and (3) rate and application timing can impact control.

Field studies were established at two Missouri locations in 2004 and 2005 to evaluate the effects of fall and early spring herbicide applications on soil temperature, soil moisture content, and insect injury in no-till corn production systems. Both experiments received applications of simazine plus 2,4-D, rimsulfuron plus thifensulfuron plus 2,4-D, and glyphosate plus 2,4-D in the fall, 45 d prior to planting (45 d EPP), 30 d prior to planting (30 d EPP), and 7 d prior to planting (7 d EPP). During a period from April 1 to April 14, simazine plus 2,4-D applied 45 d EPP resulted in higher soil temperatures at a 5-cm depth compared to the untreated control. However, there were few differences in soil temperature present from April 15 to May 1. Soil moisture readings taken during this same time period correlated with soil temperature readings. Measurements of soil moisture taken at 1 and 3 wk after planting (WAP) revealed significantly lower soil moisture readings in the untreated compared to herbicide treated plots. This lower soil moisture content allowed untreated plots to warm up more rapidly and thereby eliminated any negative impacts that dense stands of winter annual weeds may have had on soil temperature. Evaluations of corn flea beetle and lepidopteron injury taken at the V2, V4, and V6 corn leaf stages revealed significant differences in injury as a result of these treatments. When dense stands of winter and summer annual weeds were left uncontrolled, corn flea beetle injury was significantly lower than in plots treated with a herbicide. However, when a post herbicide application was made to remove all weed species prior to the V6 sampling date, differences in corn flea beetle injury between the untreated and herbicide treated plots were eliminated. Additionally, removal of all weed species led to higher lepidopteron injury in the untreated.

Studies were conducted to determine injury potential to rotational crops from carryover of herbicides used in watermelon production. Treatments included halosulfuron, ethalfluralin, and sulfentrazone alone; halosulfuron in tank mixtures with bensulide, clomazone, ethalfluralin, and naptalam; and a tank mixture of naptalam and bensulide. Sulfentrazone applied at 224 g ai/ha to watermelon severely reduced spinach emergence, but did not reduce emergence of broccoli, cabbage, or wheat. Residues of sulfentrazone applied to watermelon at 450 g/ha stunted growth of broccoli and cabbage and was the only treatment that reduced wheat stand. Injury to broccoli, cabbage, and spinach increased as the halosulfuron rate increased. Ethalfluralin did not reduce stand or cause injury to any of the four rotational crops. Naptalam plus bensulide did not reduce stand of the four crops and caused either slight or no injury. Residues of sulfentrazone and halosulfuron can injure vegetables following crops in which these herbicides are used, and caution should be taken particularly with spinach, broccoli, and cabbage in this respect.

Studies were conducted in growth chambers to characterize absorption and translocation of 14C-glyphosate applied alone or in mixture with MSMA in browntop millet and Palmer amaranth. MSMA antagonized activity of glyphosate in both weed species. Absorption of 14C-glyphosate in Palmer amaranth was rapid and increased with time from 11.1% at 0.5 h after treatment to 68.1% at 168 HAT. Absorption of 14C-glyphosate in browntop millet ranged from 1.6% at 0.5 HAT to 39.1% at 168 HAT. MSMA in mixture with glyphosate did not affect the absorption of glyphosate. In browntop millet, only 2.8% of the applied radioactivity translocated out of the treated leaf to the rest of the plant when glyphosate was applied in mixture with MSMA compared to 10.8% when glyphosate was applied alone at 72 HAT. Similarly, in Palmer amaranth, 3.2% of the applied radioactivity had translocated out of the treated leaf when glyphosate was applied in mixture with MSMA compared to 10.6% when glyphosate was applied alone. Reduced translocation appears to be the cause of the previously observed antagonism of glyphosate by MSMA.

Laboratory and field studies were conducted to determine the effect of the drift control adjuvants HM 2005B and HM 9752 on the droplet spectra and efficacy of spray mixtures of a potassium salt formulation of glyphosate. Droplet spectra were examined using a laser spray droplet analyzer. The addition of each adjuvant decreased the percentage of the spray volume in small diam spray droplets (<141μm) and either had no effect or increased glyphosate efficacy. These adjuvants could prove useful for providing management in potential drift situations.

Mesotrione is under evaluation for registration in turfgrass for weed control, but often requires repeat treatments. Previous research in agricultural crops indicates tank mixtures with mesotrione improve weed control. Greenhouse trials were conducted in Blacksburg, VA, with 7 mo-old white clover, and field trials in Knoxville, TN, evaluated control of 5-yr old white clover in a stand of common bermudagrass. Data from both field and greenhouse trials indicate mesotrione applied in combination with bromoxynil, carfentrazone, or simazine control white clover better than any of these herbicides applied alone. Combinations of bromoxynil, carfentrazone, and simazine with mesotrione also decreased relative chlorophyll index and white clover fresh weights in agreement with visually estimated control.

Two Italian ryegrass populations from Mississippi, Tribbett and Fratesi, were suspected to be tolerant to glyphosate. A third population from Mississippi, Elizabeth, known to be susceptible to glyphosate, was included for comparison. Plants were treated with the isopropylamine salt of glyphosate at 0, 0.11, 0.21, 0.42, 0.84, 1.68, 3.36, and 6.72 kg ae/ha. GR50 (herbicide dose required to cause a 50% reduction in plant growth) values for the Tribbett, Fratesi, and Elizabeth populations were 0.66, 0.66, and 0.22 kg/ha, respectively, indicating that the Tribbett and Fratesi populations were threefold more tolerant to glyphosate compared with the Elizabeth population. These three populations were also treated with diclofop at 0, 0.13, 0.25, 0.5, 0.75, 1, and 2 kg ai/ha. Diclofop GR50 values for the Tribbett, Fratesi, and Elizabeth populations were 0.25, 0.28, 0.21 kg/ha, respectively, indicating similar tolerance to diclofop in the three populations. Response of all three populations to clethodim rate (0, 0.02, 0.03, 0.05, 0.06, 0.08, 0.09, and 0.13 kg ai/ha) was measured. Clethodim GR50 values for the Tribbett, Fratesi, and Elizabeth populations at the small growth stages were 0.016, 0.023, 0.014 kg/ha, respectively, and at the large growth stage were 0.04, 0.034, 0.02 kg/ha, respectively.

Glyphosate at simulated drift rates representing 12.5, 6.3, and 1.6% of the usage rate of 1,120 g ai/ha (140, 70, and 18 g/ha, respectively) was applied to wheat at first node, boot stage, or at early flowering. At 14 d after treatment (DAT) wheat injury, expressed as bleaching of leaf foliage and growth inhibition, was 40 to 55% for 70 g/ha applied at first node and for 140 g/ha applied at all growth stages. Wheat height 28 DAT was reduced 47% with glyphosate applied at 140 g/ha at first node and was reduced around 26% for 70 g/ha applied at first node and 140 g/ha applied at boot stage. Wheat height was not reduced with glyphosate at 18 g/ha applied at first node or boot stage and with all rates applied at early flowering. Wheat yield was reduced 72% when glyphosate was applied at 140 g/ha at first node, 45% when applied at boot stage, and 54% when applied at early flowering. For 70 g/ha, wheat yield was reduced 25 to 30% for the three application timings. Wheat yield was not reduced for 18 g/ha glyphosate. In another study, six wheat varieties responded the same to glyphosate applied at 140 and 70 g/ha. Wheat height 28 DAT was reduced an average of 34% for 140 g/ha glyphosate and 17% for 70 g/ha applied at first node, but height was not reduced when applied at early flowering. Yield was reduced an average of 58 and 43% for 140 and 70 g/ha applied at first node and 38 and 19% for 140 and 70 g/ha applied at early flowering. In both studies yield reductions in most cases were reflected in reduced spike density, spikelet number per spike, and seed weight.