Tropical spiderwort (more appropriately called Benghal dayflower) poses a serious threat to crop production in the southern United States. Although tropical spiderwort has been present in the United States for more than seven decades, only recently has it become a pest in agricultural fields. Identified as an isolated weed problem in 1999, tropical spiderwort became the most troublesome weed in Georgia cotton by 2003. Contributing to the significance of tropical spiderwort as a troublesome weed is the lack of control afforded by most commonly used herbicides, especially glyphosate. Vegetative growth and flower production of tropical spiderwort were optimized between 30 and 35 C, but growth was sustained over a range of 20 to 40 C. These temperatures are common throughout much of the United States during summer months. At the very least, it appears that tropical spiderwort may be able to co-occur with cotton throughout the southeastern United States. The environmental limits of tropical spiderwort have not yet been determined. However, the rapid spread through Georgia and naturalization in North Carolina, coupled with its tolerance to current management strategies and aggressive growth habit, make tropical spiderwort a significant threat to agroecosystems in the southern United States.

Spatial patterns of the exotic riverine knotgrass (Paspalum distichum L.) were examined in Mediterranean river basins in Southwestern Iberia. The major goals of this study were to assess the degree of invasibility of riparian habitats by this species and to determine the influence of environmental factors and human-induced disturbances that this knotgrass has on both the landscape and the habitat scales. The present study demonstrates the ability of knotgrass to invade riparian habitats in Portuguese freshwater ecosystems. However, most of the spatial variation of the knotgrass cover seemed to be driven by local factors, such as fine sediment enrichment and the fragmentation of riparian woods, and by other anthropogenic interferences in relation to both the fluvial system and the surrounding landscape.

Junipers (Juniperus spp.) are native woody shrubs that have expanded beyond their normal historical ranges in the western and southwestern United States since the late 1800s. Most ecologists and resource managers agree that juniper has become a deleterious native invasive plant that threatens other vegetation ecosystems, such as grasslands, through a steady encroachment and ultimate domination. The use of fire in managing junipers is based on a management goal to increase the disturbance return interval and thereby reduce the abundance and/or competitive impact of juniper in an ecosystem. In this paper, we discuss rates of juniper encroachment in relation to presettlement fire regimes, juniper encroachment and soil health, postfire vegetation responses, and long-term potential of different juniper treatment scenarios that involve prescribed fire.

Invasive alien species (IAS) are a major threat to biological diversity on a global scale, necessitating international cooperation to address the problem. This paper gives the context in which action against IAS needs to take place, explains the need for international cooperation, and provides examples of key international instruments, strategies, and programs to deal with IAS.

The response of rice and barnyardgrass to clomazone rates (0.22, 0.45, 0.67, 0.9, and 1.12 kg ai/ha) and application timings of preplant incorporated, preemergence (PRE), and delayed PRE (DPRE) were evaluated from 1997 to 1999. Rice bleaching at 14 d after planting (DAP) increased from 5 to 35% as the clomazone rate increased. At 14 and 49 DAP, barnyardgrass control decreased with clomazone at 0.22 kg/ha compared with control at higher rates. Clomazone at 0.22 kg/ha resulted in lower grain yield. Clomazone PRE caused less rice bleaching and lower grain yield compared with DPRE timings. These results indicate that initial bleaching by high clomazone rates may not translate into yield loss. Higher clomazone rates may increase rice yield by improving weed control.

Postemergence-applied diuron effectively controls yellow woodsorrel in nursery crops grown in pine bark–based container substrate. Whether the phytotoxicity of diuron on yellow woodsorrel is exclusively the result of foliar activity or is partially the result of root-based activity has not been determined. Application in which diuron was allowed to contact both the foliage and the pine bark–based substrate provided 84% control as determined by shoot fresh-weight reduction relative to that of a nontreated control. Foliar-only and root-only applications provided 52 and 12% shoot fresh-weight reduction, respectively. Absorption and translocation of foliar-applied diuron by yellow woodsorrel was evaluated using radiotracer techniques. After 24 h, 86% of the applied diuron had been absorbed, and 76% of the amount applied remained in the treated leaflet, indicating minimal translocation. Diuron sorption by the pine bark–based substrate was evaluated using radiotracer techniques. After 3 h, less than 6% of applied diuron remained in the aqueous phase, indicating 94% sorption. Exposing yellow woodsorrel roots to diuron concentrations as low as 0.50 mg/L resulted in injury, and concentrations equal to or greater than 10 mg/L resulted in death. Calculations described herein indicate the concentration that probably would occur within the aqueous solution held within the substrate following a 1.12-kg ai/ha application is sufficient to be phytotoxic to yellow woodsorrel. Thus, root-based absorption is a contributing factor in the overall efficacy of postemergence-applied diuron in controlling yellow woodsorrel.

Several experiments were conducted to evaluate the utility of an in vivo acetolactate synthase (ALS) assay for comparing sensitivity to imazamox among imidazolinone-resistant wheat cultivars/lines. Ten single-gene imidazolinone-resistant winter wheat cultivars/lines, one two-gene and four single-gene imidazolinone-resistant spring wheat cultivars/lines, and three pairs of heterozygous and homozygous imidazolinone-resistant winter wheat lines were evaluated in the assay experiments. Additionally, a dose-response assay was conducted to evaluate the tolerance of several imidazolinone-resistant wheat cultivars to imazamox on a whole plant level. The I50 value (i.e., the imazamox dose that inhibited ALS activity by 50%) of the winter wheat cultivar ‘Above’ was 54 to 84% higher than the I50 values of 99-420, 99-433, and CV-9804. However, based on the results of this study, it is unclear whether genetic background or market class (hard red winter vs. soft white winter) influences the level of ALS inhibition by imazamox. Teal 15A, the two-gene imidazolinone-resistant spring wheat cultivar, had an I50 value that was two to three times greater than the I50 value of the single-gene imidazolinone-resistant spring wheat cultivars/lines. The heterozygous imidazolinone-resistant wheat lines had I50 values that were 69 to 81% less than the I50 values of the homozygous lines. In the whole plant dose response, the R50 values (i.e., the imazamox dose that reduced biomass by 50%) of the susceptible cultivars Brundage 96 and Conan were 15 to 17 times less than the homozygous single-gene imidazolinone-resistant winter and spring cultivars/lines, whose R50 values were about 1.7 times less than the R50 value of the two-gene imidazolinone-resistant spring wheat line, Teal 15A. The results of the in vivo ALS imazamox assays and the whole plant imazamox dose-response assay were similar, indicating that the in vivo assay can be used to accurately and quickly compare resistance between imidazolinone-resistant wheat cultivars/lines.

Studies were conducted in the summer and fall of 2001 in North Brunswick, NJ, and Marion County, Oregon, to evaluate the response of glyphosate-resistant and glyphosate-susceptible creeping bentgrass hybrids, colonial bentgrass, redtop, and dryland bentgrass grown as individual plants to postemergence (POST) herbicides. Glyphosate at 1.7 kg ae/ha, glufosinate at 1.7 kg ai/ha, fluazifop-P at 0.3 and 0.4 kg ai/ha, clethodim at 0.3 kg ai/ha, sethoxydim at 0.5 kg ai/ha, and a combination of glyphosate and fluazifop-P were applied 6 wk after planting. Glyphosate provided almost complete control of all susceptible bentgrass species at 4 weeks after treatment (WAT). Glufosinate provided 95% or greater control of all bentgrass species at 4 WAT, but regrowth was observed on all species in the summer experiment in Oregon. Fluazifop-P, clethodim, and sethoxydim provided slower control of bentgrass species, which ranged from 38 to 94% at 4 WAT, depending on species, herbicide, and experimental location. By 8 WAT, fluazifop-P at 0.4 kg/ha applied alone or in combination with glyphosate showed the highest levels of control (>90%) across all bentgrass species. Studies were also conducted in 2002 in the spring and summer in North Carolina to evaluate the response of a mature stand of glyphosate-susceptible ‘Penncross’ creeping bentgrass to POST herbicides. Two applications of glyphosate at 1.7 kg/ha were required to achieve 98% bentgrass control at 8 WAT. Fluazifop-P at 0.4 kg/ha, clethodim at 0.3 kg/ha, and sethoxydim at 0.4 kg/ha exhibited herbicidal activity, but two applications were required to reach (>82%) control of bentgrass at 8 WAT. Two sequential applications of clethodim or the combination of glyphosate and fluazifop-P provided 98% control of bentgrass at 8 WAT. Of the other herbicide treatments evaluated, only atrazine and sulfosulfuron provided (>80%) control at 8 WAT. The results of these studies demonstrate that fluazifop-P, clethodim, and sethoxydim have substantial herbicide activity on bentgrass species and may be viable alternatives to glyphosate for control of glyphosate-resistant creeping bentgrass and related bentgrass species in areas where they are not wanted. Glufosinate, atrazine, and sulfosulfuron also exhibited substantial herbicidal activity on bentgrass, and further research with these herbicides is warranted.

Field studies were conducted to evaluate residual herbicides applied alone and with a contact weed control program in peanut in Georgia and Alabama. Residual herbicide treatments included pendimethalin preemergence (PRE) at 924 g ai/ha, diclosulam PRE at 18 and 26 g ai/ha, flumioxazin PRE at 70 and 104 g ai/ha, sulfentrazone PRE at 168 and 280 g ai/ha, and imazapic postemergence (POST) at 71 g ai/ha. All herbicides were applied alone and in combination with an early postemergence (EPOST) application of paraquat plus bentazon. Peanut injury ranged from 0 to 7% for diclosulam, from 0 to 28% for flumioxazin, from 0 to 59% for sulfentrazone, from 0 to 15% for imazapic, and from 4 to 12% for paraquat plus bentazon. Across locations and years, Florida beggarweed control was 92% or greater with flumioxazin PRE at 104 g/ha, 77% or greater with diclosulam PRE at 26 g/ha, 80% or greater with sulfentrazone PRE at 280 g/ha, ranged from 54 to 86% for imazapic POST, and was 68% or less for paraquat plus bentazon EPOST. For diclosulam, sulfentrazone, and imazapic, including paraquat plus bentazon EPOST improved Florida beggarweed control vs. these treatments alone. However, flumioxazin alone provided consistent and season-long Florida beggarweed control without paraquat plus bentazon EPOST. Sicklepod control with imazapic was consistently greater than 90%, but it was 70% or less with diclosulam, flumioxazin, and sulfentrazone. Paraquat plus bentazon EPOST used with the residual herbicide treatments resulted in variable sicklepod control ranging from 40 to 99%. Yellow nutsedge control was 95% or greater with sulfentrazone, varied from 56 to 93% with diclosulam, and was 87% or greater with imazapic. Tall and smallflower morningglory, wild poinsettia, Palmer amaranth, and bristly starbur control varied by residual herbicide treatment. Yields were similar for diclosulam, flumioxazin, sulfentrazone, and imazapic treated peanut.

Cogongrass continues to be one of the most invasive weeds in the subhumid savanna. Herbicide application expenses depend on equipment costs, costs of water transport for spraying, and chemical costs. In three on-farm experiments on land heavily infested with cogongrass, the effectiveness of a knapsack sprayer (KS), a very low volume sprayer (VLV), and a rope wick (RW) applicator was tested at Ijaye, Nigeria, from 2000 to 2001. The sprayers differed in application method, price, and carrier volume required. The dose–response curves for the three applicators were identical in all parameters except at very high doses for the RW. Consequently, there were no apparent differences in glyphosate effectiveness, even when it was applied with different equipment and different carrier volumes. However, even at very high doses, the RW was not as efficient as was the KS and VLV. Actual biomass reduction of cogongrass was greater with the KS and VLV. Even though the KS and VLV generally gave better control levels than the RW, the latter is more user-friendly because it does not require protective masks, which are often unavailable in sub-Saharan Africa. In a situation with labor scarcity, weeding with the RW was cheaper than hand weeding with hoes. The VLV was more economical when used on areas larger than 10 ha than was the RW. The KS was more economical than all other methods when used on areas larger than 2 ha.

Field trials were conducted to determine the effect of fumigant-pebulate combinations on purple nutsedge density in fresh market tomato. Treatments consisted of methyl bromide plus chloropicrin (MBr plus Pic) [67:33] at rates of 270 and 130 kg/ha, respectively; Pic plus pebulate at 400 and 4.5 kg/ha, respectively; metham (MNa) plus pebulate at 485 and 4.5 kg/ha, respectively; dazomet plus pebulate at 950 and 4.5 kg/ha, respectively; and 1,3-dicholopropene plus Pic (C-17) [87:13] plus pebulate at 392 and 4.5 kg/ha, respectively. At 12 wk after treatment, MBr plus Pic controlled purple nutsedge more effectively (10 plants/m2) than the fumigant-pebulate combinations (50 to 70 plants/m2). Compared to MBr plus Pic, Pic plus pebulate had a 14% lower marketable yield. No differences in marketable yield were noted with dazomet plus pebulate or C-17 plus pebulate compared to MBr plus Pic. However, MNa plus pebulate produced a 15% higher yield than MBr plus Pic. Additionally, MNa plus pebulate had 15% higher marketable fruit weight than MBr plus Pic.

The impact of the management variables soybean cultivar, row spacing, population density, and shading was evaluated on the incidence of Sclerotinia stem rot (SSR) on glyphosate-resistant soybeans in an irrigated glyphosate-resistant soybean management system. Soybean canopy development, flower number, soil moisture, disease severity, and soybean yield were evaluated on three glyphosate-resistant cultivars, Pioneer ‘92B71’ (upright), Asgrow ‘AG2701’ (bushy), and Asgrow ‘AG2702’ (bushy). Three different row spacing–target population combinations of 76 cm, 430,000 seeds/ha; 19 cm, 430,000 seeds/ha; and 19 cm, 560,000 seeds/ha were evaluated. Cultivars 92B71 and AG2701 had 42 and 15% lower disease severity indexes and 38 and 19% greater yields than AG2702, respectively. The actual average population of 92B71 was 9 and 20% lower than actual average populations of AG2701 and AG2702, respectively. Disease severity indexes were lower and yield was higher when population was reduced from 560,000 seeds/ha to 430,000 seeds/ha in 19-cm rows. When averaged over the entire study, population was positively correlated with disease severity index (r2 = 0.33; P < 0.0001) and negatively correlated with yield (r2 = −0.13; P = 0.0140). Reduction of soybean population was more important than increasing row spacing to manage SSR in an irrigated system. Average actual spacing between plants within a row was 18 and 4 cm for 19- and 76-cm rows, respectively, at a target population of 430,000 seeds/ha, which may have contributed to greater plant-to-plant transfer of the Sclerotinia sclerotiorum pathogen in the 76-cm rows.

Sethoxydim, tralkoxydim, imazethapyr, quinclorac, propanil, glyphosate, and glufosinate were tested at rates below those recommended by the manufacturers with Pyricularia setariae Niskada under greenhouse conditions for control of green foxtail. At one-tenth of the recommended rate in a 100 L/ha carrier volume, only the sethoxydim–P. setariae combination achieved more effective green foxtail control when compared with the herbicide or pathogen alone. Selected herbicides at one-tenth, one-fourth, and one-half of the recommended rates showed variable interactions with the pathogen on plants with three and five leaves. Propanil (recommended rate 0.99 kg ai/ha) was more synergistic at higher rates, especially on larger plants, for which the combined treatment increased green foxtail mortality from zero in the herbicide alone to 100%. Quinclorac (recommended rate 0.10 kg ai/ha) acted similarly to propanil with slightly lower synergy effects. Sethoxydim (recommended rate 0.15 kg ai/ha) at one-tenth or one-quarter of the rate plus P. setariae often enhanced green foxtail control on larger plants. On smaller plants, the herbicide and pathogen alone were highly efficacious. Compared with tank mixes with P. setariae, propanil, quinclorac, or sethoxydim applied 6 h before the pathogen or earlier generally showed greater efficacy. Delaying a tank mix application for up to 2 h had little negative effect, but longer than 4 h often reduced efficacy. When combining the pathogen at different doses with propanil, quinclorac, or sethoxydim at one-tenth, one-quarter, and one-half of the rate, both fungal dose and herbicide rate affected the efficacy. Coapplying any of the herbicides at the one-quarter rate with the pathogen at the sublethal dose of 2 × 107 spores/ml achieved complete control of green foxtail.

Irrigated field experiments were conducted near Torrington, WY, during the 2001 to 2002 (year 1) and 2002 to 2003 (year 2) winter wheat growing seasons to evaluate cultivar response to different imazamox rates, adjuvants, and application timings. Five cultivars were treated postemergence in the early fall (EF), late fall (LF), or early spring (ES) with imazamox at 54 or 108 g ai/ha, including either nonionic surfactant (NIS) at 0.25% or methylated seed oil (MSO) at 1% (v/v) as adjuvants. A 28% urea ammonium nitrate solution at 1% (v/v) was included with all treatments. Spring injury was more severe in year 1 than year 2. Severe spring injury on ‘AP502 CL’, ‘Above’, ‘IMI-Fidel’, ‘IMI-Jagger’, and ‘IMI-Madsen’ was linked to fall application of 108 g/ha imazamox with MSO. Imazamox applied at 108 g/ha plus MSO applied in the fall consistently injured all cultivars more than the same rate with NIS and 54 g/ha imazamox regardless of adjuvant and timing, although severity of injury in the experiments differed between EF and LF timings in years 1 and 2, respectively. Correlation analysis supports injury reduced reproductive tillers per meter of row and wheat yields and increased the number of seeds per spike in year 1. The reduction of reproductive tillers per meter of row in year 1 was likely the result of severe injury caused by 108 g/ha imazamox applied in the EF coupled with little snow cover to protect against cold winter temperatures. Wheat yield in year 1 was reduced by 108 g/ha imazamox applied in the early fall; however, imazamox applied at 54 g/ha with either adjuvant in EF, LF, or ES were safe. Yield parameters and wheat yields in year 2 were not affected by imazamox rate, adjuvant, timing, or interactions of these factors.

Field violet is a winter or summer annual plant that is a serious weed of canola crops in Europe. It is a weed of increasing concern within reduced tillage fields in central Alberta, where its response to registered herbicides has not been evaluated. Two commercial fields within the Aspen Parkland ecoregion of Alberta were used to evaluate the efficacy of postemergence (POST) herbicides against field violet in conventional, imidazolinone-resistant (IMI-resistant) and glufosinate-resistant canola cultivars, as well as to evaluate the plant's response to various timings and rates of glyphosate in glyphosate-resistant canola. Control of field violet was lower in field experiments conducted in 2002 compared with 2003, probably because of abnormally low rainfall in 2002. The POST herbicides evaluated provided inadequate control of field violet in conventional canola. Glufosinate control at 500 g ai/ha was unacceptable unless the crop canopy closed shortly after application. In IMI-resistant canola, thifensulfuron did not significantly reduce plant density and biomass under the extremely dry conditions experienced in 2002, but in 2003, it conferred respective reductions of 79 and 86% relative to nontreated controls. Imazamox plus imazethapyr did not affect plant growth. Field violet was controlled by pre- and postcrop emergence glyphosate at 445 g ae/ha. Postharvest application of glyphosate provided good control throughout the following growing season when spring emergence was minimal. Herbicide activity was also evaluated on two- to four-leaf seedlings in a greenhouse experiment. Dose– response curves reflected the activity observed in field experiments. Strategies for effective field violet control with herbicides are dependent on cultivar selection and the management system, but are improved by timing application to young, actively growing plants.

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.

A promising approach for the control of parasitic weeds is herbicide seed priming, which consists of soaking crop seeds in a herbicide solution such that the herbicide is later present in the crop seedling to inhibit growth of attaching parasites. This technique is effective where selectivity exists between crop and parasite; for example, varieties of imidazolinone-resistant maize. However, seed priming has not been reported for sorghum or pearl millet, two crops that are greatly affected by purple witchweed. Research was initiated to evaluate herbicides for potential use as seed priming agents in these crops. Auxin-mimic and acetolactate synthase-inhibitor class herbicides were evaluated; specifically, clopyralid, 2,4-DB, dicamba, picloram, and prosulfuron. For sorghum, immersion of seed in 0.5% (w/v) ae 2,4-DB for 5 min 1 d before planting reduced purple witchweed densities to levels 20 to 50% of nontreated controls. However, this concentration was at the threshold of crop toxicity and reduced sorghum yields in some experiments. None of the herbicides tested consistently reduced purple witchweed on pearl millet. This research illustrates both the potential and limitations of adapting seed priming technology for sorghum and pearl millet.

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.

Studies were conducted in New Jersey and Virginia to evaluate the response of ‘Aurora Gold’ hard fescue, which had undergone five cycles of phenotypic recurrent selection for increased glyphosate tolerance, to direct applications of glyphosate. ‘Discovery’ hard fescue, which had not undergone recurrent selection, was also included in the study. Glyphosate treatments were initiated in early/mid-May and applied once, twice, or three times at 4- to 5-wk intervals at rates ranging from 0.1 to 1.6 kg ae/ha. Aurora Gold was more tolerant to glyphosate than Discovery in all experiments, indicating that recurrent selection was successful in increasing glyphosate tolerance in hard fescue. Single applications of glyphosate at rates ranging from 0.6 to 0.8 kg/ha could be applied to Aurora Gold with minimal injury or stand thinning (<20%), whereas multiple applications of glyphosate could be applied at rates ranging from 0.4 to 0.6 kg/ha. The use of Aurora Gold in areas planted to hard fescue, such as golf course roughs, vineyards, orchards, and landscapes, would allow the integration of direct glyphosate applications into an overall weed management program providing potential economic and environmental benefits.

Concern has been raised that herbicides often used to control perennial ryegrass in warm-season turf could move laterally or “track” and injure neighboring cool-season grasses. Rimsulfuron was applied at 17.5 or 35 g ai/ha to perennial ryegrass in the afternoon. The following morning, while dew was still present, a greens mower was driven through the perennial ryegrass and across the adjacent creeping bentgrass. When evaluated 5, 10, and 25 d after treatment, visible track length and creeping bentgrass injury were greatly reduced by irrigating perennial ryegrass 2 h after treatment or by irrigating both perennial ryegrass and creeping bentgrass prior to simulated mowing. Visible injury of tracked turfgrass persisted for 36 d after treatment when irrigation was not applied and for as few as 5 d when both perennial ryegrass and creeping bentgrass were irrigated. Irrigation had no effect on perennial ryegrass control. Gibberellic acid at 0.12 kg ai/ha and foliar iron at 1.3 kg ai/ha, applied when tracks first appeared, did not improve the recovery of injured creeping bentgrass. Our results suggest that when applying rimsulfuron near susceptible bentgrass, the lowest effective rate should be applied and that the bentgrass should be irrigated at least 2 h after treatment to prevent nontarget injury.