Legislatively mandated reductions in open field burning have increased grass seed growers reliance on herbicides to control seedling grasses in established stands of perennial species. In nonburned fields, a dense flush of seedling weeds and volunteer crop emerges with the onset of fall rains, and additional germination of some species occurs throughout the fall, winter, and spring. Because rainfall patterns in western Oregon are erratic during late summer and early fall, the choice of when to apply preemergence herbicides is difficult. Herbicides applied too early may dissipate before the rains arrive, whereas herbicides applied too late may not prevent germination and seedling establishment. Pendimethalin was least affected by a 3- to 4-wk exposure on dry soil waiting for rain, followed in order of increasing sensitivity by oxyfluorfen, metolachlor, and trifluralin. Most treatments controlled California brome less effectively than perennial ryegrass. Duration of 85% or greater control of subsequently oversown perennial ryegrass averaged 69 d for 2.2 kg/ha pendimethalin, 11 d for 0.42 kg/ha oxyfluorfen, and 4 d for 2.2 kg/ha metolachlor, and duration of 50% or greater control averaged 98, 33, and 18 d for the same treatments. Doubling of herbicide rates doubled the duration of control in 15 out of 27 cases but increased the duration only an average of 75% in the other 12 cases. Average time to doubling of weed populations over those occurring when herbicides and weed seeds were applied on the same day was 12, 10, and 11 d after application for pendimethalin, oxyfluorfen, and metolachlor, respectively. The similarity of these periods suggests that the major difference in performance of these herbicides with time was how close to complete control they had initially achieved. Pendimethalin was the superior preemergence herbicide for controlling California brome and perennial ryegrass in these established stands, but oxyfluorfen and metolachlor also were useful if applied near germination.

Field studies were conducted at five locations in North Carolina and Virginia in 1996 and 1997 to evaluate weed control and peanut (Arachis hypogaea) response to diclosulam that was applied preemergence (PRE) and in systems with commercial standards. All plots received a preplant incorporated (PPI) treatment of ethalfluralin at 840 g ai/ha. Diclosulam controlled common lambsquarters (Chenopodium album L.), eclipta (Eclipta prostrata L.), entireleaf morningglory (Ipomoea hederacea var. integriuscula Gray), ivyleaf morningglory [Ipomoea hederacea (L.) Jacq.], pitted morningglory (Ipomoea lacunosa L.), and prickly sida (Sida spinosa L.) as well as and frequently better than the commercial standards of acifluorfen plus bentazon applied postemergence (POST), paraquat plus bentazon early POST followed by (fb) imazapic POST, or imazapic POST. Systems with ethalfluralin PPI plus diclosulam PRE at 26 g ai/ha fb acifluorfen plus bentazon POST controlled a broader spectrum of weeds and yielded greater than systems of ethalfluralin PPI fb imazapic POST or ethalfluralin PPI fb acifluorfen plus bentazon POST. Peanut exhibited excellent tolerance to diclosulam PRE at 17, 26, or 35 g/ha.

Olive jift is a solid by-product of olive (Olea europea) oil processing. Greenhouse experiments were conducted to evaluate olive jift effect on broomrape (Orobanche spp.) infections on three crops. Soil—jift mixtures were used as potting medium in ratios of 1:0, 1:1, and 3:1 soil to jift. Broomrape seeds were evenly incorporated in the potting media at 0, 150, 300, 450, 600, 750, and 900 seeds/kg. Pots planted with faba bean or pea were inoculated with seeds of O. crenata Forsk., whereas pots planted with tomato were inoculated with seeds of O. lavandulacea Reichenb. Jift in soil reduced broomrape germination and infection on all three hosts regardless of inoculation densities. Pea was not infected with broomrape in jift-containing media at any inoculation density, whereas only sporadic broomrape infections were observed in faba bean and tomato grown in jift-mixed soils. Fresh and dry weights of all crops were not adversely affected by mixing jift with soil. These results suggest a possible use of jift as an inexpensive organic material for broomrape control.

Greenhouse and growth chamber experiments were conducted to evaluate primisulfuron phytotoxicity to downy brome (Bromus tectorum) and Kentucky bluegrass (Poa pratensis) as a function of herbicide placement, adjuvants, and environmental conditions. Primisulfuron rates needed to produce GR50 (50% growth reduction) values were 0.97 ± 0.57 and 8.07 ± 1.85 g/ha for downy brome and Kentucky bluegrass, respectively. Primisulfuron was applied to downy brome and Kentucky bluegrass at three placement sites: foliar, soil, and foliar plus soil. Foliar or foliar plus soil applications were more effective at reducing downy brome dry weights than the soil application of primisulfuron, whereas Kentucky bluegrass was injured more from the soil or foliar plus soil applications than from the foliar application of primisulfuron. Primisulfuron at 5 g/ha applied alone reduced downy brome dry weights by 5%, whereas when an adjuvant was added, dry weights were reduced by 52 to 83%. Primisulfuron was more phytotoxic to downy brome at alternating temperatures of 8 to 16 C and 16 to 24 C than at 0 to 8 C. Phytotoxicity of primisulfuron was less when downy brome plants were stressed for soil moisture after herbicide treatments than when the plants were not stressed or only stressed before treatment.

Time of day at which a herbicide is applied can affect efficacy, and variability may be attributed to leaf angles at application. Spray interception by hemp sesbania (Sesbania exaltata), sicklepod (Senna obtusifolia), and prickly sida (Sida spinosa) under day and night conditions was quantified by measuring interception of a 2-M potassium nitrate solution. Following the night application, interception by prickly sida, hemp sesbania, and sicklepod was reduced 17, 67, and 70%, respectively. In a second study in the greenhouse, glyphosate was applied to hemp sesbania, pitted morningglory (Ipomoea lacunosa), prickly sida, and sicklepod at 6:00 and 11:00 A.M. and 4:00 and 9:00 P.M. Control of all species was dependent on the time of day treated, with night applications generally being less effective.

Field studies were conducted at Dekalb, Urbana, and Brownstown, IL, in 1996 and 1997 to evaluate corn (Zea mays) injury and weed control from preemergence applications of RPA 201772 alone and tank-mixed with metolachlor, atrazine, or both. No significant corn injury from RPA 201772 was observed at any time for all experiments. Giant foxtail (Setaria faberi) control at 60 days after treatment (DAT) was variable and ranged from 47 to 93% for RPA 201772 applied alone at 105 g ai/ ha. Giant foxtail control of at least 90% was observed by applying metolachlor at 1,120 g ai/ha with 105 g/ha RPA 201772. The addition of atrazine at either 1,120 or 1,680 g ai/ha improved control of giant foxtail compared with RPA 201772 applied alone at 105 g/ha in two of the six studies. RPA 201772 applied at 105 g/ha controlled at least 88% of velvetleaf (Abutilon theophrasti), Pennsylvania smartweed (Polygonum pensylvanicum), and smooth pigweed (Amaranthus hybridus). RPA 201772 controlled 88% or less of common waterhemp (Amaranthus rudis), common ragweed (Ambrosia artemisiifolia), and common cocklebur (Xanthium strumarium). Control of these three species was 92% or greater with RPA 201772 plus atrazine. Control of common lambsquarters (Chenopodium album) was at least 96% with RPA 201772 applied alone at any rate in four of the six studies. However, common lambsquarters control was 68 and 77% for RPA 201772 applied alone at 105 g/ha at Urbana and Brownstown in 1997, respectively, where high common lambsquarters densities were prevalent. Under these conditions, the addition of atrazine to RPA 201772 at 105 g/ha improved control of common lambsquarters. RPA 201772 has excellent potential to provide consistent control of velvetleaf compared with atrazine. In contrast, these studies indicate RPA 201772 may provide inconsistent control of certain weed species in different environments. In order to achieve consistent control of a broad spectrum of weed species, RPA 201772 must be combined with other herbicides.

Field studies were conducted at two locations in 1997 and 1998 to evaluate crop injury, weed control, yield, and net economic returns of single and sequential postemergence applications of labeled and reduced rates of glyphosate to no-till, glyphosate-resistant soybean planted in narrow rows. Sequential applications provided at least 91% control of giant foxtail, while single applications provided at least 86% control with labeled rates and 68–93% control with reduced rates. Common waterhemp control was slightly higher with sequential vs. single treatments and with labeled rates vs. reduced rates. Velvetleaf control was greater than 96% with all treatments. Common cocklebur control was 90% or higher with all treatments except a single application of glyphosate at 210 g/ha. Lower control of giant foxtail and common waterhemp with single-application, reduced-rate treatments in two of the four trials resulted in lower yields. Overall, sequential applications, regardless of rate, provided greater weed control, yield, and net income and lower coefficients of variation (C.V.s) of net income than reduced-rate single applications. Single-application treatments showed a trend of decreased weed control, yield, and net income and higher C.V.s of net income with reduced rates of glyphosate.

Field studies were conducted in 1992 and 1993 to evaluate AC 263,222 applied postemergence (POST) alone and as a mixture with atrazine or bentazon for weed control in imidazolinone-resistant corn. Nicosulfuron alone and nicosulfuron plus atrazine were also evaluated. Herbicide treatments were applied following surface-banded applications of two insecticides, carbofuran or terbufos at planting. Crop sensitivity to POST herbicides, corn yield, and weed control was not affected by insecticide treatments. AC 263,222 at 36 and 72 g ai/ha controlled rhizomatous johnsongrass 88 and 99%, respectively, which was equivalent to nicosulfuron applied alone or with atrazine. AC 263,222 at 72 g/ha controlled large crabgrass 99% and redroot pigweed 100%, and this level of control exceeded that obtained with nicosulfuron alone. AC 263,222 at 72 g/ha controlled sicklepod and morningglory species 99 and 98%, respectively. Nicosulfuron alone or with atrazine controlled these two species less than AC 263,222 at 72 g/ha. Addition of bentazon or atrazine to AC 263,222 did not improve control of any species compared with the higher rate of AC 263,222 at 72 g/ha applied alone. Corn yield increased over the untreated control when POST herbicide(s) were applied, but there were no differences in yield among herbicide treatments.

The study was conducted to determine the cross-resistance of imazethapyr-resistant common sunflower (Helianthus annuus) to selected imidazolinone, sulfonylurea, and triazolopyrimidine herbicides. Whole-plant herbicide dose–response curves and in vitro enzyme studies showed that imazethapyr-resistant common sunflower was highly resistant to imazamox, slightly resistant to thifensulfuron and chlorimuron, and not resistant to cloransulam. Resistance ratios of herbicide concentrations required to inhibit growth by 25% were 310, 3.3, 2.0, and 1.4 times greater in the resistant biotype than in the susceptible biotype for imazamox, thifensulfuron, chlorimuron, and cloransulam, respectively. Similarly, herbicide concentrations required to inhibit ALS activity in vitro by 25% were 332.0, 18.6, 8.3, and 1.2 times greater in the resistant biotype than in the sensitive biotype for imazamox, chlorimuron, thifensulfuron, and cloransulam, respectively.

Field experiments were conducted in North Carolina from 1994 through 1998 to evaluate the effects of five weed management strategies and four corn (Zea mays)–peanut (Arachis hypogaea) rotation sequences on purple nutsedge (Cyperus rotundus) population development. Effects of these weed management programs on cotton (Gossypium hirsutum) and peanut production in following years were also investigated. Herbicide programs included a nontreated control, a carbamothioate preplant incorporated (PPI) combination treatment utilizing vernolate in peanut and butylate in corn, an early postemergence (EPOST) acetolactate synthase (ALS) inhibitor combination treatment utilizing imazapic in peanut and halosulfuron in corn, and EPOST treatments of imazapic and imazethapyr in both peanut and imidazolinone-resistant corn. Crop rotation sequences for the 3 yr included continuous corn (CCC), corn–peanut–corn (CPC), peanut–corn–peanut (PCP), and continuous peanut (PPP). The imazapic and ALS inhibitor combination treatments both provided excellent shoot and tuber control. After 3 yr, imazapic and the ALS inhibitor combination treatment reduced shoot and tuber population densities to less than 10% of the nontreated control. Imazethapyr provided variable but better control than the carbamothioate treatment with tuber densities (measured from 0 to 15 cm soil depth) and shoot densities increasing from 733 to 2,901 tubers/m3 of soil and 16 to 43 shoots/m2, respectively, after 3 yr. Tuber densities increased in the nontreated control from 626 to 9,145 tubers/m3 of soil and from 962 to 5,466 tubers/m3 of soil in the carbamothioate treatment during this same period. Also, shoot densities increased in the nontreated control from 22 to 159 shoots/m2 and from 8 to 92 shoots/m2 in the carbamothioate treatment. There was a 31% peanut yield reduction from 1994 to 1996 when peanut was continuously planted or rotated to corn for only 1 yr. Herbicide carryover effects were not observed in cotton during 1997.

Greenhouse and field experiments were conducted to determine the response of corn (Zea mays), barnyardgrass (Echinochloa crus-galli), common lambsquarters (Chenopodium album), large crabgrass (Digitaria sanguinalis), velvetleaf (Abutilon theophrasti), and yellow foxtail (Setaria lutescence) to RPA 201772. Barnyardgrass, large crabgrass, velvetleaf, and common lambsquarters were more susceptible than yellow foxtail to RPA 201772. Velvetleaf was the most susceptible species and rates above 18 g ai/ha of RPA 201772 controlled 100% of the population 4 wk after treatment (WAT). Percent control of all the weed species increased with increased RPA 201772 rates. In the field, the dry weights of yellow foxtail decreased as the rate of RPA 201772 increased from 0 to 210 g/ha. However, a 60% reduction of dry weight of yellow foxtail was recorded at 140 g/ha of RPA 201772 compared to the untreated check 6 WAT, whereas at 12 WAT the dry weight of yellow foxtail was reduced to only 15% because of intraspecific competition. Yellow foxtail was moderately susceptible to RPA 201772. Corn was tolerant to RPA 201772; the GR80 value was 435 g/ha in the greenhouse. The bleaching injury to corn in the field was less than 10%, and it was found only with the 210 g/ha rate of RPA 201772. This injury was temporary and the plants recovered within 2 to 3 wk. Based on the GR80 values, velvetleaf was the most susceptible, followed by common lambsquarters, large crabgrass, barnyardgrass, and yellow foxtail.

Imazethapyr resistance in common sunflower (Helianthus annuus) was confirmed in 1996 in a field near Rossville, KS. In 1997, common sunflower achenes were collected within a 20-km radius of the field with known resistance to determine if resistance was present in nearby fields or if resistance had spread to the native population on the roadside. Collections were made from 14 soybean (Glycine max) fields, one corn (Zea mays) field, and 11 roadsides. Achenes from Konza Prairie Research Natural Area, a prairie that had received no herbicide applications in the past 25 yr, served as the susceptible control. Common sunflower seedlings were treated in a greenhouse with 71 g ai/ha imazethapyr and 11 g ai/ha chlorimuron. In all 15 fields sampled, at least 1% of the common sunflower exhibited an intermediate response to imazethapyr or chlorimuron. In 13 fields, at least 1% of the plants were resistant to imazethapyr, and in all 15 fields, at least 1% of the plants were resistant to chlorimuron. Ten roadsides had common sunflower that showed intermediate response to imazethapyr or chlorimuron. At least 1% of the plants from seven roadsides were resistant to imazethapyr or chlorimuron. Common sunflower collected from fields with repeated applications of imazethapyr showed more resistance to imazethapyr than to chlorimuron.

Antagonism of quizalofop-P efficacy on annual grasses by bromoxynil has been noted in both the field and greenhouse. Laboratory experiments were conducted on yellow foxtail (Setaria glauca) to determine the effect of mixing bromoxynil with the ethyl ester of quizalofop-P on absorption, translocation, and metabolism of 14C-quizalofop-P Applying bromoxynil in mixture with quizalofop-P reduced 14C-label absorption from 63 to 51%, 73 to 52%, 77 to 68%, and 90 to 80% at 4, 8, 24, and 96 h after treatment, respectively. Translocation of 14C-label from the treated leaf into the shoot above or shoot below was unaffected by bromoxynil. However, translocation into the roots was reduced from 0.9 to 0.4% and 1.0 to 0.5% at 4 and 8 h after treatment, respectively, but differences were not noted at 0.5, 1, 24, and 96 h after treatment. Bromoxynil increased deesterification of quizalofop-P-ethyl into quizalofop-P acid from 45 to 60% in the shoot above the treated leaf. However, bromoxynil did not affect metabolism of quizalofop-P in the treated leaf or shoot below the treated leaf. These results suggest that antagonism of quizalofop-P activity by bromoxynil is primarily due to decreased absorption of quizalofop-P, whereas effects on translocation and metabolism were minor.

A postemergence (POST) timing study was conducted on established populations of burcucumber (Sicyos angulatus) in corn (Zea mays), and a second study examined the residual activity of several herbicides for burcucumber control under greenhouse conditions. In the field study, flumiclorac, halosulfuron, primisulfuron, CGA 152005, and CGA 152005 + primisulfuron (45, 71, 40, 40, and 20 + 20 g ai/ha, respectively) were applied at two POST timings. CGA 152005, primisulfuron, and the combination provided greater than 85% control of burcucumber 14 wk after planting (WAP). Flumiclorac and halosulfuron provided 60% control or less by 8 WAP. Timing of the POST applications did not influence burcucumber control by 11 WAP with any herbicide. In the greenhouse, germinated burcucumber seeds were placed in soil treated with atrazine, chlorimuron, primisulfuron, or CGA 152005 at normal field use rates. All treatments provided similar residual control early; however by 4 wk after treatment (WAT), control from atrazine was less than 10% compared to 69% for chlorimuron and about 50% for primisulfuron and CGA 152005. This research suggests that CGA 152005 and primisulfuron can both be effective for managing burcucumber in corn, whereas flumiclorac and halosulfuron proved ineffective.

Studies were conducted to observe the effect of full and reduced rates of postemergence (POST) herbicides on seedling and rhizome johnsongrass (Sorghum halepense) at different growth stages. Herbicides and labeled rates included primisulfuron at 40 g/ha, nicosulfuron at 35 g/ha, fluazifop-P at 210 g/ha, and clethodim at 140 g/ha. Contour graphs to predict johnsongrass control at different growth stages and herbicide rates were developed. Excellent seedling and rhizome johnsongrass control was obtained with reduced rates of herbicides applied at the three- to five-leaf stages. Primisulfuron at 20 g/ha resulted in 90% or greater control of seedling johnsongrass in the three- to four-leaf stage. Rhizome johnsongrass at this growth stage required 30 g/ha of primisulfuron for the same level of control. Nicosulfuron at 17.5 and 26.3 g/ha provided 90% or greater control up to the four-leaf stage of seedling and rhizome johnsongrass, respectively. Fluazifop-P and clethodim were more effective than primisulfuron and nicosulfuron. Fluazifop-P at 105 g/ha resulted in 90% or greater control of seedling and rhizome johnsongrass up to the seven- and five-leaf stages, respectively. Clethodim at 35 g/ha controlled seedling johnsongrass at least 90% up to the eight-leaf stage. Clethodim at 70 g/ha provided 90% or greater control of rhizome johnsongrass if applied at the three- to four-leaf stages.

Hypocotyl and root length reduction of soybean (Glycine max) seedlings when seeds were exposed to sulfentrazone during germination were used as indices to classify cultivar response to soil-applied sulfentrazone. Seeds of ‘Stonewall’ (sulfentrazone tolerant) and ‘Asgrow 6785’ (sulfentrazone sensitive) were imbibed and allowed to germinate in 0, 1, 5, 10, and 50 ppm aqueous sulfentrazone solutions for 4 d. Hypocotyl and root lengths were reduced in both cultivars, but the reductions were greater for Asgrow 6785 than for Stonewall. Subsequently, the relative sensitivity of 28 cultivars to sulfentrazone was independently determined by two variations of the hypocotyl reduction method (both conducted in the laboratory) and by traditional full-season field evaluation. Results from laboratory and field studies were in agreement for cultivars distinctly sensitive or tolerant to sulfentrazone. However, cultivars with intermediate tolerance in laboratory studies produced variable responses in the field.

The effect of nonionic surfactant, crop oil concentrate, organosilicone surfactant, methylated seed oil, and a blend of organosilicone surfactant and methylated seed oil on absorption of 14C-clethodim was evaluated in barnyardgrass (Echinochloa crus-galli). Absorption of 14C-label was greatest during the first 40 min after application when 14C-clethodim was applied with methylated seed oil or a blend of methylated seed oil and organosilicone surfactant. These adjuvants increased the rate of absorption more than crop oil concentrate, organosilicone surfactant, or nonionic surfactant. Crop oil concentrate was more effective than organosilicone or nonionic surfactant in increasing absorption, with nonionic surfactant being more effective than organosilicone surfactant. These results generally agreed with the order of increasing efficacy of clethodim on barnyardgrass as affected by adjuvants in field experiments. Another study was conducted to determine the effect of bromoxynil on absorption and translocation of 14C-clethodim in yellow foxtail (Setaria glauca). Bromoxynil reduced absorption of 14C–clethodim 4, 8, and 24 h after application and also reduced the amount of 14C-label translocated from the treated leaf. These data suggest that antagonism of clethodim control of yellow foxtail by bromoxynil observed in previous research can be attributed partially to decreased absorption and translocation of clethodim.

The recent introduction of glufosinate-resistant and glyphosate-resistant crops provides growers with new options for weed management. Information is needed to compare the effectiveness of glufosinate and glyphosate on annual weeds. Greenhouse trials were conducted to determine the response of barnyardgrass (Echinochloa crus-galli), common lambsquarters (Chenopodium album), common ragweed (Ambrosia artemisiifolia), fall panicum (Panicum dichotomiflorum), giant foxtail (Setaria faberi), large crabgrass (Digitaria sanguinalis), and velvetleaf (Abutilon theophrasti) to glufosinate and glyphosate. The response of velvetleaf and common lambsquarters was investigated at multiple stages of growth. Glufosinate and glyphosate were applied to each weed species at logarithmically incremented rates. The glufosinate and glyphosate rates that provided a 50% reduction in aboveground weed biomass, commonly referred to as GR50 values, were compared using nonlinear regression techniques. Barnyardgrass, common ragweed, fall panicum, giant foxtail, and large crabgrass responded similarly to glufosinate and glyphosate. Common lambsquarters 4 to 8 cm in height was more sensitive to glufosinate than glyphosate. In contrast, 15- to 20-cm tall-velvetleaf was more sensitive to glyphosate than glufosinate.

Quinclorac was registered for weed control in wheat (Triticum spp.) for western Canada in 1997. Residues from quinclorac may persist in the soil and may damage following crops; therefore, field and growth chamber experiments were conducted to determine the tolerance of several following rotational crops. Cereals and bromegrass (Bromus biebersteinii) were sufficiently tolerant that they could be seeded within 16 d of quinclorac application without risk of injury. At the other extreme, marketable and total potato (Solanum tuberosum) yields were reduced by quinclorac on irrigated land 1 yr after application. Growth chamber experiments were used to rank crops in order of their tolerance of quinclorac residues and to compare the tolerance of crops that were grown in the field with additional crops. Quinclorac injured several legume and oilseed crops when the crops were seeded immediately after application, but quinclorac did not reduce the dry matter yield of two of the most sensitive legumes, faba bean (Vicia faba) and alfalfa (Medicago sativa), 1 yr after application on irrigated land. However, based on a previous study, one can conclude that injury to these crops may occur in the field under drought conditions in rain-fed agricultural systems.

Under greenhouse conditions, annual bluegrass (Poa annua L.), common groundsel (Senecio vulgaris L.), shepherd's purse [Capsella bursa-pastoris (L.) Medicus], small nettle (Urtica urens L.), canola (Brassica napus L. ssp. napus), and pea (Pisum sativa L.) differed in sensitivity to ultraviolet (UV) radiation. Of the weed species, annual bluegrass was the least sensitive; whereas, among the crop species, canola was about sevenfold more sensitive than was pea. The sensitivity of a species to UV radiation was highly dependent upon its stage of development. The study indicates some potential for using UV radiation to control weeds, but the method needs further investigation to unravel the selectivity of the methods and potential health hazards.