Quinclorac is a systemic herbicide registered to control annual grass and broadleaf weeds in rice. Field research was conducted to determine the most effective quinclorac treatment for leafy spurge control. Leafy spurge control 12 mo after treatment (MAT) averaged 38 and 77% when quinclorac was applied at 0.56 and 1.7 kg ae/ha, respectively. Quinclorac applied with the crop-oil-based adjuvant Scoil provided similar leafy spurge control compared to quinclorac applied alone. Quinclorac plus Scoil applied with picloram provided better leafy spurge control than quinclorac plus Scoil alone. The optimum date for fall treatment with quinclorac is broad. Quinclorac at 1.1 kg/ha plus Scoil at 2.3 L/ha applied on September 1, September 15, October 1, and October 15 provided similar leafy spurge control and averaged 56% 12 MAT.

Duration and spectrum of preemergence (PRE) weed control following isoxaben application at 0.56, 0.84, and 1.12 kg ai/ha in spring, fall, or spring plus fall (double) application were evaluated by field experiments. Residual activity of isoxaben was assessed by monitoring weed counts at two locations for 12 mo after treatment (MAT). Buckhorn plantain and dandelion control from spring-applied isoxaben at 1.12 kg/ha was > 90% at 4 MAT in Blacksburg but dropped to < 51% at 12 MAT. Isoxaben at 1.12 kg/ha applied in fall provided ≥ 90% control of buckhorn plantain for 8–9 MAT, with control ranging from 69 to 91% at approximately 12 MAT. Dandelion control with fall-applied isoxaben at 1.12 kg/ha ranged from 60 to 75%, 8–9 MAT. Fall application of 1.12 kg/ ha isoxaben at Virginia Beach controlled henbit and cornspeedwell for 2–3 MAT. Multiple applications of isoxaben improved weed control at Virginia Beach, but results were inconclusive at Blacksburg. In comparison, oxadiazon controlled white sweet clover and dandelion for 1 MAT following spring application in Blacksburg, but < 65% broadleaf control was observed at 4 MAT. Broadleaf weed control following single application of oxadiazon at 3.36 kg/ha was < 60% at 9 MAT Poor weed control resulted from spring applications of isoxaben and oxadiazon when a 25-cm precipitation occurred within 2 wk after application in one study.

Leafy spurge, a long-lived perennial, grows in many habitats, from floodplains to grasslands and mountain slopes. The plant emerges in early spring and produces showy, yellow bracts that appear in late May. The true flowers emerge in mid-June. The plant spreads by both seeds and roots and contains a white sticky latex that deters grazing by many animals. Dicamba, 2,4-D, glyphosate, and picloram have commonly been used to control leafy spurge. Picloram plus 2,4-D is frequently used for leafy spurge control in North Dakota. Ten insect species for leafy spurge biocontrol have been released in North Dakota; the most successful have been the flea beetles, Aphthona nigriscutis, A. czwalinae, and A. lacertosa. The leafy spurge gall midge (Spurgia esulae) has been most successful near wooded areas. Herbicides combined with either the leafy spurge flea beetles or gall midge have controlled leafy spurge better than either method used alone. Grazing with sheep or goats is a cost-effective method for controlling leafy spurge top growth in large infestations. Grazing combined with fall-applied picloram plus 2,4-D reduced leafy spurge density more rapidly and maintained control longer than either method used alone. Several grass species are competitive with leafy spurge including ‘Rebound’ smooth brome, ‘Rodan’ western wheatgrass, ‘Pryor’ slender wheatgrass, and ‘Manska’ pubescent wheatgrass. Cultivating twice each fall after harvest for 3 yr in cropland completely controlled leafy spurge. A successful long-term management program should be designed for specific situations and should include combinations of herbicides, insects, grazing, and/or seeding competitive species.

A soil bioassay experiment was conducted in Blacksburg, VA, to determine the effect of isoxaben application timings and rates on duration of weed control. Flats containing soil were imbedded into the field. Isoxaben was applied in the spring, fall, and spring followed by fall (double application) at 0.56, 0.84, and 1.12 kg ai/ha. Flats were moved to a greenhouse at 0, 1, 3, 6, and 9 months after treatment (MAT) and seeded with yellow rocket, buckhorn plantain, and spotted spurge for the bioassays. Weed counts from treated flats were compared to those in untreated flats to determine percent control. Fall and spring followed by fall applications provided approximately 20% greater control of yellow rocket 3 MAT and 30% greater control 6 MAT, compared to a single spring application of isoxaben. Isoxaben at all rates controlled yellow rocket > 70% at 6 mo after fall application. At 3 MAT, fall and spring plus fall-applied isoxaben provided about 15 and 20% greater buckhorn plantain control, respectively, compared to spring application. The two highest rates of isoxaben controlled buckhorn plantain > 70% at 3 mo after fall application, but provided poor control at 6 MAT. Control of spotted spurge was similar among the three application timings for isoxaben and was unacceptable at most evaluation dates. Overall, isoxaben applied at 1.12 kg/ha provided better control of all three weed species for a longer time than the reference herbicide, oxadiazon, applied at 3.36 kg/ha.

Field trials were conducted during 1998 and 1999 to evaluate the effects of sequential herbicide treatment, herbicide application timing, and mowing on mugwort control. In the first field trial dicamba, triclopyr, clopyralid, picloram, metsulfuron, glufosinate, glyphosate, and the dimethylamine salt and the isooctyl ester of 2,4-D were applied to mugwort at 7-wk intervals to evaluate mugwort control after one, two, and three herbicide applications. When applied in three sequential applications, all herbicides except triclopyr, metsulfuron, and glufosinate provided at least 70% mugwort control 1 yr after treatment (YAT). At least 70% mugwort control was also achieved with just two sequential applications of dicamba, and only one application of picloram or clopyralid provided 100 and 84% mugwort control 1 YAT, respectively. In the second field trial the influence of application timing was investigated by applying herbicides to mugwort in the vegetative and the flowering stages of growth. Additionally, the effect of sequential mowing was evaluated by applying herbicides to mugwort regrowth after either one or two mowings. Generally, there was no difference in the level of mugwort control achieved with applications of these herbicides to mugwort in the flowering vs. the vegetative stage of growth. However, when averaged over all the herbicides included in these trials, two sequential mowings conducted before herbicide application enhanced the control of mugwort compared with either unmowed mugwort or mugwort that had been mowed once before herbicide application. Additionally, with the exception of picloram and glyphosate, all the herbicides evaluated in these trials provided higher mugwort control when applied to unmowed mugwort compared with mugwort that had been mowed only once. The results from these trials indicate that sequential herbicide treatment and sequential mowing are strategies that will enhance the control of mugwort when used with the majority of herbicides evaluated in these trials.

Bermudagrass [Cynodon dactylon (L.) Pers.] control for at least 1 yr is necessary to establish other forage species in pasture and hay field renovations, or to plant pine (Pinus spp.) in infested fields. Potential herbicides for hybrid Bermudagrass control were evaluated using single, repeat, and multiyear applications. Repeat applications were made 30 d after the first application beginning in mid-August each year. Imazapyr applied once at 0.56 or 1.12 kg/ha controlled hybrid Bermudagrass (cv. ‘Tifton 44’) 88 and 97%, respectively, 52 wk after treatment with no difference between rates observed. Additionally, imazapyr applied for two consecutive years controlled hybrid Bermudagrass 100%. Glyphosate isopropylamine salt and glyphosate trimethylsulfonium salt, applied for 1 yr at rates of 4.2 or 1.7 fb (followed by) 1.7 kg ae/ha and 4.8 or 1.9 fb 1.9 kg ae/ha, respectively, provided between 70 and 78% control at 52 wk after the last treatment (WALT). Hybrid Bermudagrass control from either formulation of glyphosate applied for two consecutive years ranged between 79 and 91% at 52 WALT. Relative to a 1-yr application program, either glyphosate formulation applied for two consecutive years did not significantly improve Bermudagrass control at 52 WALT. The addition of fluazifop-P at 0.42 kg ai/ha or clethodim at 0.2 kg ai/ha to glyphosate formulations did not significantly improve hybrid Bermudagrass control relative to glyphosate applied alone. However, a tank-mix of clethodim plus either formulation of glyphosate applied for two consecutive years generally improved hybrid Bermudagrass control relative to applications in only 1 yr.

Broomsedge control studies were conducted on six broomsedge-infested pastures in southeastern Oklahoma from 1995 to 1997. Glyphosate applied in spring at 2.24 kg ai/ha decreased broomsedge plant density by 58% 3 mo after treatment (MAT), on areas where the previous year's forage was grazed, and by 95% 3 MAT, where spring fire had removed the old top-growth before glyphosate application. Broomsedge plant density was not affected where glyphosate was applied in spring to sites with old-standing top-growth. Paraquat applied in spring at 0.56 kg ai/ha and spring burning without a herbicide treatment had no effect on broomsedge plant density. Glyphosate at 0.56 and 1.12 kg ai/ha applied in late summer reduced the number of broomsedge stems 1 yr after treatment (YAT) by an average of 65 and 80%, respectively. Paraquat at 0.56 kg/ha applied in late summer of 1995, followed by burning 1 wk after treatment (WAT), decreased broomsedge stem density by more than 60% 1 YAT at four of six locations when compared with mowing in late summer. Burning in November after an October frost decreased broomsedge stem density by more than 47% 1 YAT at four locations. Two consecutive years of burning after frost and paraquat applied in late summer followed by burning 1 WAT reduced broomsedge dry matter production by 68 and 96%, respectively, when compared with mowing in late summer. These data suggest that good to excellent control of established broomsedge is possible with herbicides alone, with a combination of herbicides and late-summer burning, and with fall burning after an early frost in a dry fall. However, broomsedge control was short-lived with all the treatments because of the establishment of new broomsedge seedlings. Thus, it will be important to integrate the destruction of broomsedge plants with proper fertility and grazing management in order to provide satisfactory broomsedge control.

Field trials were conducted in Virginia during 2000 and 2001 to evaluate long-term trumpetcreeper control in corn with dicamba, BAS 654 plus dicamba, 2,4-D, CGA 152005 plus primisulfuron, halosulfuron, primisulfuron, and mesotrione. Each of these herbicides was applied alone as a single postemergence (POST) treatment or as a component of a POST herbicide combination. Trumpetcreeper suppression ratings 3 mo after treatment (MAT) revealed a general trend toward higher levels of suppression with combinations of dicamba, BAS 654 plus dicamba, or 2,4-D with any of the sulfonylurea herbicides and lower levels of suppression with applications of any of the sulfonylurea herbicides alone. Combinations of dicamba, BAS 654 plus dicamba, or 2,4-D with mesotrione also provided some of the highest levels of trumpetcreeper suppression 3 MAT in both years. At 1 yr after treatment (YAT), 2,4-D alone, BAS 654 plus dicamba, CGA 152005 plus primisulfuron plus 280 g ai/ha dicamba, primisulfuron plus 280 g/ha dicamba, primisulfuron plus 2,4-D, mesotrione plus BAS 654 plus dicamba, and mesotrione plus 2,4-D reduced trumpetcreeper stem density by at least 52% when compared with that of the nontreated control. These herbicide treatments were the only ones that provided reductions in trumpetcreeper stem density 1 YAT when compared with that of the nontreated control. In 2000 and 2001, there were few differences in corn yield among the treatments evaluated in these trials, and no treatment resulted in corn yields that were lower than the nontreated control. Acceptable trumpetcreeper suppression may be achieved during the season of treatment with any of these herbicide combinations, but only a few treatments will provide long-term trumpetcreeper control.

Effective methods are needed to eradicate tall fescue (Festuca arundinacea) and convert tall fescue fields into habitats more suitable to wildlife species. The objectives of this study were to determine the efficacy of (1) a single glyphosate application during the spring or fall and (2) AC 263,222, alone and in combination with glyphosate, applied during four different tall fescue growth stages for control of established tall fescue. Studies were conducted during 1996 to 1998 in fields dominated by tall fescue located in central Kentucky. Pre- and posttreatment plant communities were described to quantify differences in vegetative characteristics due to herbicide applications. Glyphosate at 2.2 kg ai/ha applied during the spring or fall was effective in reducing tall fescue to less than 12% cover. AC 263,222 at 0.2 kg ai/ha, AC 263,222 at 0.2 kg/ha plus glyphosate at 0.6 kg/ha, or AC 263,222 at 0.2 kg/ha plus glyphosate at 1.1 kg/ha applied during the spring growth, boot, summer dormancy, and fall growth stages were equally effective, reducing tall fescue cover to less than 3% at 2 to 7 mo after treatment. Glyphosate and AC 263,222 are effective tools for the initial removal of tall fescue.

Field trials were established in orchardgrass and tall fescue grass pastures and hay fields during 2000 and 2001 to evaluate wild carrot, broadleaf plantain, buckhorn plantain, bladder campion, and yellow crownbeard response to a variety of herbicides and prepackaged herbicide combinations. Picloram plus 2,4-D at 0.23 plus 0.84 kg/ha and higher, triclopyr plus clopyralid at 0.96 plus 0.32 kg/ha and higher, and 2,4-D plus triclopyr at 2.20 plus 1.12 kg/ha provided greater than 84% wild carrot, broadleaf plantain, and buckhorn plantain control at 4 mo after treatment (MAT) in both years. Metsulfuron, picloram plus 2,4-D at 0.30 plus 1.12 kg/ha, and 2,4-D plus triclopyr at 2.20 plus 1.12 kg/ha provided from 56 to 61% control of bladder campion 4 MAT, which was the highest bladder campion control observed in these trials. Greater than 80% yellow crownbeard control was achieved during both years with picloram plus 2,4-D at 0.15 plus 0.56 kg/ha and higher and with triclopyr plus clopyralid at 0.96 plus 0.32 kg/ha and higher. Results from these experiments reveal that good broad-spectrum control of many biennial and perennial broadleaf weeds can be achieved with higher rates of the picloram plus 2,4-D and triclopyr plus clopyralid prepackaged combinations.

Field experiments were conducted in north-central Oklahoma to evaluate the effects of MON 37500 at 35, 70, and 140 g ai/ha applied to wheat on rotational crops seeded no-till 16 to 29 mo after treatment (MAT). Wheat yields were not reduced by MON 37500 at site 1 but at site 2 were decreased 6, 11, and 24% by 35, 70, and 140 g/ha, respectively. Wheat yield reductions at site 2 were attributed to late seeding, small wheat growth stage, and cool, wet weather during the month after application. Corn and soybean seeded approximately 16 MAT were not visibly injured by residual MON 37500 at any rate at either site. At site 1 grain sorghum seeded 17 MAT was visibly injured by residual MON 37500 applied at 70 and 140 g/ha (soil pH value 6.4), and grain yield was reduced 58% by residual MON 37500 applied at 140 g/ha. Grain sorghum seeded 17 MAT was not visibly injured at site 2 (soil pH value 5.0), and that seeded 29 MAT was not injured at either site. Sunflower seeded 17 MAT at site 1 was visibly injured by residual MON 37500 at 140 g/ha, and yield was reduced 17% but at site 2 was not affected by MON 37500. Sunflower seeded 29 MAT was not injured at either site.

Few weed management options are available for juneberry, which has limited the potential for this new crop. Field trials were initiated at three locations in North Dakota to evaluate efficacy and crop safety associated with chemical and physical weed control treatments applied just before or immediately after transplanting. All treatments except norflurazon and trifluralin provided at least 85% control of redroot pigweed, common lambsquarters, common purslane, and yellow foxtail for the duration of the trial at Absaraka, ND, during 2001. Stinkgrass weed control 8 wk after treatment (WAT) dropped to unacceptable levels (<85%) with all treatments except azafenidin at 0.5 kg ai/ ha, norflurazon, and oxyfluorfen at 1.1 kg ai/ha at Dawson, ND, during 2001. However, juneberry injury 4 WAT by azafenidin at 0.5 kg/ha, flumioxazin at both locations, or azafenidin at 0.34 kg/ha and oxyfluorfen at 1.1 kg ai/ha at Absaraka, ND, was greater than observed for plants within the physical treatments. Juneberry injury generally decreased with time, yet remained >20% at 8 WAT for azafenidin and flumioxazin at Absaraka, ND, and for all treatments except the mulches at Dawson, ND. Plant injury 8 WAT at Absaraka in 2002 was 10% or less for all treatments and was lower compared with 2001. All physical treatments—azafenidin at 0.34 and 0.5 kg/ha, flumioxazin at 0.29 kg/ha, and oryzalin at 4.5 kg/ha—provided at least 85% control of all weed species at Carrington and Absaraka, ND, during 2002.

Greenhouse and field experiments were conducted in North Dakota to determine the effect of adjuvants applied with imazapic on the control of leafy spurge and production of various grass species and to determine the most effective fall-application timing of imazapic for optimum leafy spurge control with minimal effect on herbage. Imazapic applied with a methylated seed oil (MSO) adjuvant tended to provide greater leafy spurge control than when applied with other types of adjuvants. Imazapic applied alone or with adjuvants reduced production of some grass species in the greenhouse, but it did not decrease herbage production in the field. Imazapic at 140 g/ha applied with MSO or with 28% N plus MSO averaged 72% leafy spurge control 12 mo after treatment, compared to 33% control from imazapic alone and 40% control from picloram plus 2,4-D. Imazapic at 140 g/ha applied with MSO in mid-September provided greater leafy spurge control compared to August or October applications.

Diflufenzopyr is an auxin-transport inhibitor that has increased broadleaf weed control by some auxin herbicides. The effects of auxin herbicides when applied with diflufenzopyr for leafy spurge or Canada thistle control, herbage production, and herbicide absorption and translocation in leafy spurge were evaluated. The influence of diflufenzopyr on leafy spurge and Canada thistle control varied by herbicide. Diflufenzopyr applied with quinclorac increased both Canada thistle and leafy spurge control. Diflufenzopyr added to picloram increased leafy spurge but not Canada thistle control, whereas control of both weeds generally increased when diflufenzopyr was applied with dicamba. Canada thistle control slightly improved when diflufenzopyr was applied with clopyralid or clopyralid plus 2,4-D compared with the herbicides alone. Diflufenzopyr did not influence weed control from imazapic and reduced weed control from glyphosate. Weed control was not influenced by the ratio of diflufenzopyr to herbicide or by whether diflufenzopyr was tank mixed with or applied before the herbicides. Diflufenzopyr did not affect cool-season grass production in the greenhouse or field but did reduce sideoats grama and switchgrass production when applied alone and with dicamba in greenhouse trials. 14C-picloram and 14C-quinclorac absorption was increased when applied with diflufenzopyr in leafy spurge but nearly all absorbed herbicide remained in the treated leaf compared with the herbicides applied alone. 14C-dicamba absorption decreased from 60 to 14% when applied with diflufenzopyr and translocation to the roots decreased by a factor of 10. Overall, the increase in weed control from the addition of diflufenzopyr was much more pronounced with leafy spurge than with Canada thistle.

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