Imazamox ammonium salt at 53 g ae/ha applied postemergence in the fall to imidazolinone-resistant wheat controlled Italian ryegrass 98 to 100% 10 wk after treatment (WAT). Control 22 WAT was 88 to 98% at two locations and 55% at a third location. Imazamox was more effective applied in fall to three- to four-leaf Italian ryegrass than when applied in spring to one- to three-tiller Italian ryegrass. Split applications, with 27 g/ha applied in fall and spring, were no more effective than 53 g/ha applied in fall. Pendimethalin preemergence in combination with fall-applied imazamox increased control 22 WAT 10 to 33 percentage points at two of three locations. Imazethapyr ammonium salt plus imazapyr isopropylamine salt applied at 47 plus 16 g ae/ha and imazamox at 44 or 53 g/ha were similarly effective, whereas imazethapyr at 70 g/ha was ineffective. Control by imazapic ammonium salt at 70 g ae/ha was equal to or greater than control by imazamox at 44 or 53 g/ha. Imazamox, imazethapyr plus imazapyr, and imazapic controlled diclofop-resistant and -susceptible Italian ryegrass. Thifensulfuron plus tribenuron mixed with imazamox increased Italian ryegrass control in field and greenhouse experiments, whereas dicamba reduced control compared with imazamox applied alone. Control by imazamox plus 2,4-D was similar to or greater than control by imazamox alone.

Broomrapes (Orobanche spp.) are root holoparasitic plants that cause severe damage to economically important crops, especially in Mediterranean countries. Egyptian broomrape is the most troublesome weed on tomatoes grown for processing in Israel. In the present study, we tested the efficacy and selectivity of four sulfonylurea herbicides in controlling Egyptian broomrape on tomatoes grown in pots under greenhouse conditions. MON 37500, rimsulfuron, HOE 404 and SL-160 were applied postemergence (POST) and preplant incorporated (PPI) followed by POST applications. MON 37500 and rimsulfuron were more selective to tomato and controlled the parasite more effectively than HOE 404 and SL-160. MON 37500 and rimsulfuron at 50 and 100 g ai/ha and at 100, 150, and 200 g ai/ha, respectively, applied on tomato foliage 14, 28, and 42 d after planting (DAP) and followed by sprinkler irrigation to field capacity, resulted in complete control of the parasite. However, a significant reduction in control efficacy was observed when the experiment was repeated with charcoal-topped pots, suggesting that the herbicides act mainly through the soil. Except for rimsulfuron, the PPI followed by two POST treatments was more phytotoxic to tomato plants than the POST treatments. The PPI plus POST applications controlled Egyptian broomrape effectively, but tomato plants were injured by HOE 404 at all PPI application rates and by MON 37500 at the high rate at 150 g/ha. The present study determined that three POST applications or a PPI application followed by two POST applications of MON 37500 at 50 or 100 g/ha, or rimsulfuron at 100, 150, or 200 g/ha were effective and selective in controlling Egyptian broomrape on tomato, under greenhouse conditions.

The presence of row crops, such as field corn, improves herbicidal control of weeds, but the impact of crop row position on herbicide dose–response relationships for weeds is unknown. At midseason at three site-years in Missouri, total weed cover (WC) was reduced by increasing soil residual herbicide rate in a dose-dependent response and was as much as 20% lower in-row (IR) than between-row (BR). Preemergence atrazine + S-metolachlor + clopyralid + flumetsulam at different rates (0×, 0.25×, 0.5×, 0.75×, and 1×, where 1× rate was 2,240 + 1,750 + 210 + 67 g ai/ha, respectively) were applied at planting in field corn to control giant foxtail, the chief weed present, and annual broadleaf weeds, largely common waterhemp. Lower herbicide rates were required to reduce IR WC to the same extent as BR WC, but these rates varied between site-years. At all three site-years, a least squares regression equation adequately described data variability relating corn yield to IR or BR WC (or both) (i.e., Y = a + bBR2, where Y is corn yield in kg/ha, BR is BR WC [%], and a and b are coefficients).

Current plant bioassays included in the guidelines for testing pesticides do not include the measurement of reproduction endpoints. A bioassay, based on reduction of flowering of cress was developed to detect soil residues of hexazinone and simazine at levels of 0.02 and 0.10 ppm, respectively. The endpoint used in the described bioassay is the percentage of plant viability that implies that the tested plants have reached the flowering stage. It was found that sensitivity of cress is lower in soils containing higher organic matter.

Integrated weed management practices, such as crop rotation and increased seeding rates, potentially improve weed management. Yet, few studies compare competitive interactions of weeds with different crops. This research quantified the impact of Persian darnel on spring wheat, canola, and sunflower yield across different seeding rates. Increasing crop density increased yield when Persian darnel affected crop yield early in physiological development. Crop yield loss was estimated to reach 83, 70, and 57% for spring wheat, canola, and sunflower, respectively, at high Persian darnel densities. Persian darnel reduced spring wheat yield by limiting the number of tillers per plant and seed per tiller; reduced canola yield by limiting the number of branches per plant, pods per branch, and seed per pod; and reduced sunflower yield by limiting the number of seed per plant. Persian darnel affected crop growth early in physiological development, indicating that interspecific interference occurred early in the growing season. Cultural and resource management aimed at reducing Persian darnel impact on resource availability and crop yield components will reduce Persian darnel impact on crop yield.

Field studies were conducted to examine the effects of the sulfonylurea-tolerant (ST) soybean and fall tillage on reducing rotational soybean response to soil-applied prosulfuron across a range of soil pH values. Prosulfuron (10 and 20 g ai/ha) was applied in the fall to simulate the maximum amount of carryover theoretically possible from corn weed control systems. ST soybean reduced effects of prosulfuron soil residues on soybean grain yield. Increased soil pH led to greater prosulfuron carryover as indicated by the differential in ST and non-ST soybean and grain yield responses. Tillage (chisel plow) did not decrease non-ST soybean response to prosulfuron soil residues. Soybean injury 30 d after emergence was well correlated with eventual yield losses in non-ST soybean. Greater soybean injury and yield loss was observed on a silt loam soil with 0.8% organic carbon than on silt loams with greater than 2.5% organic carbon.

Field studies were conducted to determine the sensitivity of conventional ‘Motte’ and ‘Pioneer 9831’ soybean to simulated glyphosate drift rates applied during vegetative and reproductive development and the effect of glyphosate on progeny. Glyphosate at 8, 84, and 420 g ae/ha was applied to soybean at the V3, V6, R2, and R5 growth stages. Glyphosate at 8 and 84 g/ha did not reduce soybean plant population, growth, or yield or cause deleterious effects on progeny, regardless of the growth stage at application. Soybean population, growth, and yield were reduced as much as 99 to 100% after application of 420 g/ha glyphosate at the V3 growth stage. Glyphosate at 420 g/ha applied at V6 was less detrimental to soybean compared with the V3 timing. Delaying the application of 420 g/ha glyphosate until R2 and R5 reduced soybean yields 22 to 49% and 43 to 44%, respectively. Soybean injury from 420 g/ha glyphosate was generally transient or less severe when applied at the V6 growth stage or later. However, 420 g/ha glyphosate at R5 (initial podfill) caused a 390 to 450 kg/ha yield reduction compared with the V6 application, which indicated greater soybean vulnerability to glyphosate drift during podfill than in the late-stage vegetative development. Although glyphosate at 420 g/ha was injurious to soybean, regardless of application timing, progeny was not affected.

Cotton boll weevil has been eradicated from much of the U.S. Cotton Belt. After eradication, a containment program is necessary to detect and destroy reintroduced boll weevils. Crops other than cotton are not monitored for boll weevil, hence fruit on volunteer glyphosate-resistant (GR) cotton in GR soybean could provide oviposition sites for boll weevils and allow the insects to build up undetected. An experiment was conducted at five locations to evaluate control of GR cotton and reduction in cotton fruit production by herbicides commonly used on GR soybean. Cotton control by preemergence (PRE) or postemergence (POST) herbicides alone was inconsistent across locations. Flumetsulam at 45 g ai/ha, imazaquin at 137 g ai/ha, and metribuzin at 360 g ai/ha plus chlorimuron at 60 g ai/ha applied PRE controlled cotton 55 to 100% and reduced cotton fruit production 84 to 100%. Sulfentrazone at 167 g ai/ha plus chlorimuron at 34 g/ha PRE controlled cotton 50 to 91% and reduced fruit 48 to 98%. Metribuzin PRE at 420 g/ha controlled cotton 23 to 97% and reduced fruit 32 to 100%. Flumiclorac at 30 g ai/ha, 2,4-DB dimethylamine salt at 35 g ae/ha, chlorimuron at 12 g ai/ha, and the sodium salt of fomesafen at 420 g ai/ha mixed with glyphosate and applied POST controlled cotton 48 to 100% and reduced fruit production 67 to 100%. Cloransulam at 12 or 18 g ai/ha controlled cotton 3 to 66% and reduced fruit production 5 to 85%. Cotton control and fruit reduction were greatest and most consistent with sequential applications of metribuzin plus chlorimuron PRE followed by chlorimuron, flumiclorac, fomesafen, or 2,4-DB POST. These treatments controlled cotton at least 95% at all locations. Cotton fruit was totally eliminated at three locations and reduced at least 97% at a fourth location.

Field trials were conducted in 1995 through 2002 to expand the development of chicory by determining the potential for tank mixtures of benefin, trifluralin, or pronamide applied preplant incorporated (PPI) and triflusulfuron methyl or imazamox postemergence (POST) for selective weed control in chicory. Lack of early-season weed control resulted in an 88% reduction in chicory root yield in 1995 to 1996 and an 85% reduction in 2001 to 2002 and demonstrated the susceptibility of chicory plants to early-season weed competition. In the first experiment, pronamide at 1.1 kg ai/ha PPI plus benefin at 1.3 kg ai/ha or trifluralin at 0.56 kg/ha were selective for chicory and controlled weed populations 90% on average with root yields that were 89% of the hand-weeded treatment. Triflusulfuron methyl POST at 17 g/ha caused early-season chicory injury. In the second experiment, trifluralin PPI at 0.56 kg/ha followed by imazamox POST at 36 g/ha controlled weeds 95% on average with a chicory root yield of 74 t/ha, which was 109% of the yield of the hand-weeded treatment.

Nine herbicides were tested in a field trial during 2001 and 2002 for the ability to suppress growth of established plants of yellow old world bluestem (OWB) that had invaded native vegetation in central Kansas. Herbicide treatments were applied to OWB at the V4 stage of growth using the Nebraska staging method. At 9 wk after treatment (WAT), plots treated with imazapyr at 1.40 kg ai/ ha had much lower OWB plant frequency than the untreated plots, and plots sprayed with imazapyr and bromacil at 7.84 kg ai/ha had much lower OWB tiller densities than the control plots. Imazapyr and glyphosate at 3.36 kg ai/ha provided greater OWB control than other herbicides. At the first frost after treatment application, imazapyr and bromacil treatments continued to have lower OWB frequency and tiller density than the control plots. Visible herbicide control was closely related to end-of-season yield (R = −0.97). Imazapic at 0.16 kg ai/ha, glyphosate, sulfometuron at 0.21 kg ai/ ha, bromacil, and imazapyr controlled OWB from 54 to 94%. Split applications, altered timing of herbicide application, or varied rates of herbicides that exhibited suppressive potential may further improve efficacy of these herbicides.

Triazine-resistant common lambsquarters (TR-CHEAL) is a widespread weed problem in the northcentral United States. Field studies were conducted from 1995 to 1997 to determine the efficacy and consistency of metolachlor, pendimethalin, and acetochlor applied preemergence (PRE) for control of TR-CHEAL in corn. Pendimethalin provided greater (98%) and more consistent control of TR-CHEAL than metolachlor (66%) or acetochlor (86%). Studies were conducted from 1998 to 2000 to examine the potential of isoxaflutole, flumetsulam, and rimsulfuron plus thifensulfuron for control of TR-CHEAL in corn. In 1999 and 2000, isoxaflutole (35 g ai/ha), flumetsulam (35 g ai/ ha), and rimsulfuron plus thifensulfuron (26 g ai/ha) provided 98% or greater control of TR-CHEAL. In 1998 when rainfall was limited after application, isoxaflutole (70 g ai/ha) and flumetsulam (70 g ai/ha) provided 65 and 55% control, respectively, and rimsulfuron plus thifensulfuron (26 g ai/ha) provided 55% control. Results indicate that control of TR-CHEAL with currently labeled PRE herbicides is possible.

Paraquat applied from mid-February through early April over 2 yr was evaluated for sugarcane tolerance and Italian ryegrass control. Sugarcane 31 cm tall at application was injured 16 to 25% and 8 to 14% 28 and 56 d, respectively, after mid-March application of paraquat at 0.35 or 0.70 kg ai/ha. Early-April application to 61-cm-tall sugarcane caused 13 to 25% injury. The observed injury was not reflected in reduced sugarcane shoot population or height or sugarcane or sugar yield when compared with diuron, the standard herbicide treatment. Italian ryegrass control 28 d after the mid-February application of paraquat alone at 0.53 or 0.70 kg/ha was variable, ranging from 80% in 1994 to no more than 66% in 1995. For each year, diuron at 3.2 kg/ha in combination with both rates of paraquat increased Italian ryegrass control 28 d after the mid-February application 11 to 17 percentage points. At 56 d after the mid-February application, addition of diuron proved beneficial only in 1994 when the paraquat and diuron combinations controlled ryegrass 93% compared with no more than 62% for paraquat applied alone. In contrast, Italian ryegrass was controlled the second year no more than 80% 56 d after the mid-February application of paraquat alone or with diuron. Paraquat applied at 0.70 kg/ha with diuron in mid-March controlled Italian ryegrass 80 and 86% 28 d after treatment in 1994 and 1995, respectively. For the standard herbicides metribuzin, terbacil, and diuron applied in mid-March, weed control was no greater than 38%. Although differences in Italian ryegrass control among herbicide treatments were observed, efficacy was sufficient to reduce weed competition such that sugarcane growth and yield were not negatively affected.

Field experiments were conducted to evaluate chemicals for silvery-thread moss control and bentgrass turfgrass quality. Treatments included iron (Fe)-containing products, nitrogen fertilizers, Ultra Dawn dishwashing detergent (UD) at 3% (v/v), and oxadiazon. In general, greater silvery-thread moss control was achieved with Fe-containing products. Ferrous sulfate at 40 kg Fe/ha plus ammonium sulfate at 30 kg N/ha, a combined product of ferrous oxide, ferrous sulfate, and iron humates (FEOSH) at 125 kg Fe/ha, and a combined product of iron disulfide and ferrous sulfate (FEDS) at 112 kg Fe/ha reduced silvery-thread moss populations 87, 81, and 69%, respectively, 6 wk after initial treatment (WAIT). UD reduced silvery-thread moss populations 57% 6 WAIT. The addition of oxadiazon to Fe-containing treatments did not improve silvery-thread moss population reduction. Other experiments evaluated two formulations of chlorothalonil, each applied at two rates, chlorothalonil with zinc at 9.5 and 17.4 kg ai/ha and chlorothalonil without zinc at 9.1 and 18.2 kg/ ha, and two spray volumes (2,038 and 4,076 L/ha). Greater silvery-thread moss population reduction was observed at Jefferson Landing in 1999 compared with Elk River in 1999 and 2000. Rainfall events at Elk River in 1999 and 2000 within 24 h after application and no rain at Jefferson Landing may account for variation in performance of products between sites. However, no difference in chlorothalonil formulation, rate, or spray volume was observed in any location or year. These data indicate that Fe-containing fertilizers or chlorothalonil can be used to reduce silvery-thread moss populations in creeping bentgrass putting greens.

Ground ivy is an invasive, perennial, broadleaf weed common in turf sites. A recent survey of lawn care professionals suggests ground ivy populations respond differently to herbicides. Our study was conducted to determine the variation in response among and within ground ivy populations to 2,4-D or triclopyr application. Ground ivy populations were sampled from nine sites in the United States and Canada. Leaf width, petiole length, and internode length varied by population by as much as 31, 36, and 45%, respectively. In a greenhouse study, applying 4.5 kg/ha 2,4-D or 0.9 kg/ha triclopyr to all populations resulted in a phytotoxic response that varied according to population by as much as 47% for 2,4-D and 31% for triclopyr. Random-amplified polymorphic DNA analysis identified 52 genotypes in the nine populations, and these genotypes varied in response to 2,4-D application in some populations. Difficulty in control of ground ivy with 2,4-D or triclopyr may be because of the presence of ecotypes and biotypes.

Recent advances in genetic engineering have led to the development of glyphosate-resistant (GR) crops for genetic markers and selective weed control. The effects of glyphosate residue on turfgrass clippings could be toxic to non-GR species. The objective of this experiment was to determine whether glyphosate would retain activity within clippings of creeping bentgrass when applied to Kentucky bluegrass and perennial ryegrass. Greenhouse-grown ‘Penncross’ and GR ‘ASR-368’ were treated with glyphosate at 2.24 kg/ha. Clippings were collected 1, 3, 7, and 12 d after application and applied to greenhouse-grown Kentucky bluegrass and perennial ryegrass. Kentucky bluegrass and perennial ryegrass dry weight and percent cover were reduced by clippings receiving glyphosate that were harvested 1 and 3 d after glyphosate application from both susceptible and resistant creeping bentgrass. Results indicate that glyphosate remains active in clippings for up to 3 d after treatment within creeping bentgrass clippings. Glyphosate-applied creeping bentgrass clippings will need to be managed to prevent injury to susceptible species.

Natural product herbicides for vegetation control are being considered as alternatives to synthetic herbicides by many public agencies. Studies were conducted along roadsides at the Hopland Research and Extension Center (HREC) in 2001 and 2002 and on California State Route 29 (SR29) in 2002 to evaluate acetic acid, pine oil, and plant essentials compared with glyphosate for control of herbaceous vegetation. In 2001, annual grass control after a single application of pine oil at HREC was 40% or less effective, whereas acetic acid was at least 79% effective. A second application of pine oil or acetic acid did not control regrowth or new plants. In 2002, plant essentials was the most effective (>80%) natural product at HREC for control of annual grasses, except slender oat. Pine oil often provided similar control of slender oat as plant essentials (71 and 69%, respectively). At SR29, five applications of acetic acid provided 83% or better control of slender oat, hare barley, medusahead, and broadleaf filaree. Plant essentials and pine oil controlled hairy vetch, broadleaf filaree, and hare barley at least 83%, but yellow starthistle, soft chess, buckhorn plantain, and medusahead control never exceeded 85%. Glyphosate controlled all vegetation in these experiments with one or two applications. The cost of one or more applications of the natural products was greater than 10 times the cost of using one or two applications of glyphosate. Natural products were neither efficaciously nor economically comparable with glyphosate for control of annual roadside vegetation.

Field studies were conducted in South Carolina and Georgia to evaluate weed control and soybean tolerance and yield after nonionic surfactant addition to combinations of chlorimuron plus an adjuvant-containing glyphosate formulation. Treatments included glyphosate alone, at 420 or 840 g ae/ha, or in combination with 6 or 9 g ai/ha chlorimuron and all possible combinations with or without 0.25% (v/v) nonionic surfactant. Other treatments included a weed-free and nontreated check. Chlorimuron plus glyphosate improved entireleaf, smallflower, and tall morningglory control over glyphosate alone, but nonionic surfactant addition did not further improve the control of any species, except tall morningglory. Up to 31% early-season injury was observed with the three-way mixture. Soybean injury was greater, and yields were reduced in one of three trials when nonionic surfactant was added to chlorimuron plus glyphosate combinations. This research indicates that there would be no benefit from the nonionic surfactant addition to this adjuvant-containing glyphosate formulation when combined with chlorimuron.

Two experiments, one focusing on preemergence (PRE) herbicides and the other on postemergence (POST) herbicides, were conducted and repeated in time to examine the utility of hyperspectral remote sensing data for discriminating common cocklebur, hemp sesbania, pitted morningglory, sicklepod, and soybean after PRE and POST herbicide application. Discriminant models were created from combinations of multiple indices. The model created from the second experimental run's data set and validated on the first experimental run's data provided an average of 97% correct classification of soybean and an overall average classification accuracy of 65% for all species. These data suggest that these models are relatively robust and could potentially be used across a wide range of herbicide applications in field scenarios. From the data set pooled across time and experiment types, a single discriminant model was created with multiple indices that discriminated soybean from weeds 88%, on average, regardless of herbicide, rate, or species. Signature amplitudes, an additional classification technique, produced variable results with respect to discriminating soybean from weeds after herbicide application and discriminating between controls and plants to which herbicides were applied; thus, this was not an adequate classification technique.

Chemical weed control with acrolein has been shown to be a lower cost method for reducing submerged plant biomass of sago pondweed in the irrigation district of the Lower Valley of Rio Colorado, Argentina (39°10′S–62°05′W). However, no experimental data exist on the effects of the herbicide on plant growth and its survival structures. Field experiments were conducted during 3 yr to evaluate the effect of acrolein on growth and biomass of sago pondweed and on the source of underground propagules (i.e., rhizomes, tubers, and seeds). Plant biomass samples were collected in irrigation channels before and after several herbicide treatments. The underground propagule bank was evaluated at the end of the third year. Within each treatment, plant biomass was significantly reduced by 40 to 60% in all three study years. Rapid new plant growth occurred after each application; however, it was less vigorous after repeated treatments. At the end of the third year at 3,000 m downstream from the application point, plant biomass at both channels ranged from 34 to 3% of control values. Individual plant weight and height were affected by acrolein treatments, flowering was poor, and seeds did not reach maturity. After 3 yr, acrolein did not reduce the number of tubers. However, they were significantly smaller and lighter. Rhizomes fresh weight decreased by 92%, and seed numbers decreased by 79%. After 3 yr of applications, operational functioning of the channels could be maintained with fewer treatments and lower concentrations of acrolein.

Biennial wormwood has become a problem for soybean producers in the northern Great Plains of the United States. Research was conducted to evaluate control of biennial wormwood with preemergence (PRE) herbicides alone or followed by postemergence (POST) herbicides in 2000 and 2001 at Fargo, Leonard, and Wyndmere, ND. Favorable soil moisture conditions at Leonard resulted in continual emergence and greater densities of biennial wormwood, whereas the soil at Fargo and Wyndmere was dry and few biennial wormwood seedlings emerged at these locations. Biennial wormwood control with PRE herbicides was greater than 89% at Fargo and Wyndmere but was 80% or lower at Leonard. PRE biennial wormwood control was higher with flumetsulam than with sulfentrazone. When POST treatments were applied after PRE herbicides, biennial wormwood control 4 wk after treatment was 92% or better at Fargo and Wyndmere but was 76% or less at Leonard. The combination of PRE and POST herbicide treatments did not improve control greatly at Fargo or Wyndmere but at Leonard reduced the number of biennial wormwood plants.