Crop Oil Concentrate Research Articles

Formulation and Adjuvant Effects on Uptake and Translocation of Clethodim in Bermudagrass (Cynodon dactylon)

The effect of formulation and adjuvants on absorption and translocation of 14C-clethodim was determined at 1, 4, 12, 24, 48, and 72 h after treatment (HAT) in bermudagrass under greenhouse conditions. Absorption of 14C-clethodim with the 0.12 kg L−1 (15 to 85%) formulation was higher than with the 0.24 kg L−1 (5 to 40%) formulation, regardless of presence or absence of adjuvant. There was considerable variation in the effect of adjuvant on 14C-clethodim absorption. When either ammonium sulfate (AMS) or AMS plus crop oil concentrate (COC) was added to the 0.12 kg L−1 formulation, 14C-clethodim absorption increased significantly at all harvest times except at 12 HAT compared with 0.12 kg L−1 formulation alone, whereas, 14C-clethodim absorption after addition of COC to the 0.12 kg L−1 formulation was similar to the 0.12 kg L−1 formulation alone up to 24 HAT. Conversely, COC enhanced 14C-absorption at all harvest times when added to 0.24 kg L−1 formulation. Most of 14C-clethodim (79 to 100% of absorbed) remained in the treated leaf, independent of formulation or adjuvant. Formulation did not have an impact on distribution of absorbed 14C-clethodim; however, presence of an adjuvant increased movement of 14C-clethodim out of treated leaf. Of the absorbed 14C-label, most remained in the treated leaf. 14C-clethodim that translocated out of the treated leaf remained in the shoot, and negligible amount of 14C-clethodim translocated to roots. These results demonstrated improved absorption of clethodim with formulations containing half the active ingredient (0.12 kg L−1) and inclusion of both AMS and COC.

DEFOLIATION OF WOODY CUT STEMS WITH PREHARVEST, LESS TOXIC CHEMICAL AND POSTHARVEST ENVIRONMENTAL METHODS

Six defoliants were applied in fall and tested for their efficacy in preharvest defoliation of field grown curly willow (Salix matsudana `Tortuosa'), american bittersweet (Celastrus scandens), and american beautyberry (Callicarpa americana). Defoliants included acetic acid, chelated copper, crop oil concentrate (COC), ethephon, dimethipin plus COC, pelargonic acid, and a tap water control. For chelated copper, a concentration of 800 mg·L–1 was most effective at promoting defoliation, providing 100% defoliation of american bittersweet and 76% defoliation of american beautyberry. For curly willow and american beautyberry, all concentrations of dimethipin produced good or excellent defoliation. Increasing concentrations of ethephon from 200 to 2500 mg·L–1 increased defoliation from 0% to 67%. Pelargonic acid was not effective at promoting defoliation of woody plants at the concentrations used. In an experiment conducted during spring using containerized curly willow, irrigation was stopped for 0, 3, or 6 days before defoliants were applied, but none of the irrigation treatments promoted defoliation. In a postharvest study using cut curly willow, stems were held in distilled water at 5, 20, or 35 °C for 1, 3, 5, or 7 days. Holding cut stems of curly willow at 20 °C promoted 68% defoliation, compared to 53% or 28% for 5 or 35 °C, respectively.

Incorporating Foramsulfuron into Annual Weed Control Systems for Corn1

Field studies were conducted in 2000, 2001, and 2002 at Brownstown, DeKalb, Perry, and Urbana, IL, to evaluate weed control and corn tolerance from postemergence (POST) applications of foramsulfuron in sequential and total-POST herbicide programs. Foramsulfuron applied alone controlled giant foxtail, fall panicum, and redroot pigweed 88, 99, and 99%, respectively, 28 d after treatment (DAT), which was comparable with the standard treatment of nicosulfuron. However, control of common cocklebur, velvetleaf, and common lambsquarters was significantly higher with foramsulfuron compared with nicosulfuron. Sequential herbicide programs of atrazine, S-metolachlor, or isoxaflutole applied preemergence (PRE) followed by a POST application of foramsulfuron provided greater than 85% control of giant foxtail, fall panicum, common cocklebur, velvetleaf, common waterhemp, and redroot pigweed. Of the sequential herbicide treatments, atrazine applied PRE followed by a POST application of foramsulfuron provided the greatest Pennsylvania smartweed control. A PRE application of either atrazine or isoxaflutole was needed before a POST application of foramsulfuron to control common lambsquarters. POST tank mixtures of foramsulfuron with atrazine, dicamba, and dicamba plus diflufenzopyr improved control of Pennsylvania smartweed, common cocklebur, velvetleaf, common lambsquarters, and common waterhemp when compared with foramsulfuron applied alone. The tank mixture of foramsulfuron with mesotrione improved control of all species, except Pennsylvania smartweed, common lambsquarters, and common cocklebur. Foramsulfuron tank mixtures with carfentrazone did not improve control of any weed species to commercial acceptance. Adjuvant selection was important for POST tank mixtures. Control of giant foxtail and fall panicum was reduced when atrazine was tank mixed with foramsulfuron and crop oil concentrate (COC). However, when methylated seed oil (MSO) was added to the atrazine–foramsulfuron tank mixture instead of COC, giant foxtail and fall panicum control were similar to foramsulfuron applied alone.Nomenclature: Atrazine; carfentrazone; dicamba; diflufenzopyr, 2-[1-[[[(3,5-difluorophenyl)amino]carbonyl]hydrazono]ethyl]-3-pyridinecarboxylic acid; foramsulfuron, 2-[[[[(4,6-dimethoxy-2-pyrimidiny)amino]carbonyl]amino]sulfonyl]-4-(formylamino)-N,N-dimethylbenzamide; isoxaflutole; mesotrione; S-metolachlor; common cocklebur, Xanthium strumarium L. #3 XANST; common lambsquarters, Chenopodium album L. # CHEAL; common waterhemp, Amaranthus rudis Sauer. # AMATA; fall panicum, Panicum dichotomiflorum Michx. # PANDI; giant foxtail, Setaria faberi Herm. # SETFA; Pennsylvania smartweed, Polygonum pennsylvanicum L. # POLPY; redroot pigweed, Amaranthus retroflexus L. # AMARE; velvetleaf, Abutilon theophrasti Medicus # ABUTH; corn, Zea mays L.Additional index words: Antagonism, tank mixture, total-POST.Abbreviations: ALS, acetolactate synthase (EC 4.1.3.18); COC, crop oil concentrate; DAT, days after treatment; MSO, methylated seed oil; NIS, nonionic surfactant; POST, postemergence; PRE, preemergence; UAN, urea ammonium nitrate.

Broadleaf Weed Control and Potato Crop Safety with Postemergence Rimsulfuron, Metribuzin, and Adjuvant Combinations

The effects of postemergence rimsulfuron, metribuzin, and adjuvant combinations on potato crop safety and weed control were evaluated in field studies conducted at the University of Idaho Aberdeen Research and Extension Center in 1999 and 2000. Rimsulfuron at 26 g ai/ha plus metribuzin at 0, 140, or 280 g ai/ha was combined with nonionic surfactant (NIS), crop oil concentrate (COC), or methylated seed oil (MSO) in a 3 by 3 factorial with two controls. Under cool, cloudy conditions in 1999, initial ‘Russet Burbank’ potato injury was greater when metribuzin was included in the tank mixture than when rimsulfuron was applied alone, regardless of adjuvant. Under warmer conditions in 2000, however, adding MSO or COC to the tank mixture caused more injury than adding NIS. Rimsulfuron did not provide acceptable season-long common lambsquarters control in 1999 (76%) or in 2000 (88%), regardless of adjuvant. Rimsulfuron combined with metribuzin at 140 or 280 g/ha provided ≥95% common lambsquarters control both years, regardless of adjuvant. Among adjuvants, using MSO (1999 and 2000) or COC (2000) in the spray mixture improved common lambsquarters control compared with using NIS. Tuber yield and quality were not reduced as a result of metribuzin rate or adjuvant treatments either year compared with the weed-free control.

Absorption and activity of foramsulfuron in giant foxtail (Setaria faberi) and woolly cupgrass (Eriochloa villosa) with various adjuvants

Greenhouse and laboratory studies were conducted to examine the activity and foliar absorption of foramsulfuron in giant foxtail and woolly cupgrass with various adjuvants. Adjuvant selection was important for giant foxtail control. Foramsulfuron provided 90% or greater giant foxtail control with the addition of methylated seed oil (MSO) or MSO plus 28% urea ammonium nitrate (UAN). When a crop oil concentrate (COC) or a nonionic surfactant (NIS) was added to foramsulfuron, giant foxtail control was only 20%. However, when 28% UAN was added to COC or NIS, control was increased to 90 and 85%, respectively. Foramsulfuron absorption and control were closely related in giant foxtail. Foliar absorption of14C-foramsulfuron in giant foxtail ranged between 35 and 90% 24 h after treatment (HAT) depending on adjuvant selection. The rate of absorption was greatest when MSO plus 28% UAN was added to foramsulfuron and absorption was maximized 4 HAT. Foramsulfuron absorption in woolly cupgrass reached its maximum levels 2 HAT with all adjuvant combinations. Although the rate of foramsulfuron absorption was quicker in woolly cupgrass, absorption trends by adjuvants were similar to those in giant foxtail. Maximum absorption of14C-foramsulfuron in woolly cupgrass was 84% with the addition of MSO plus 28% UAN. However, even with high levels of absorption, woolly cupgrass control with foramsulfuron was poor and may be related to rapid metabolism to nonphytotoxic compounds.

Physiological basis for cotton tolerance to flumioxazin applied postemergence directed

Previous research has shown that flumioxazin, a herbicide being developed as a postemergence-directed spray (PDS) in cotton, has the potential to injure cotton less than 30 cm tall if the herbicide contacts green stem tissue by rain splash or misapplication. In response to this concern, five-leaf cotton plants with chlorophyllous stems and older cotton, 16-leaf cotton plants, with bark on the lower stem were treated with a PDS containing flumioxazin plus crop oil concentrate (COC) or nonionic surfactant (NIS). Stems of treated plants and untreated plants at the respective growth stage were cross-sectioned and then magnified and photographed using bright-field microscopy techniques. More visible injury consisting of necrosis and desiccation was evident in younger cotton. Also, there was a decrease in treated-stem diameter and an increase in visible injury with COC compared with NIS in younger cotton. The effects of plant growth stage and harvest time on absorption, translocation, and metabolism of14C-flumioxazin in cotton were also investigated. Total14C absorbed at 72 h after treatment (HAT) was 77, 76, and 94% of applied at 4-, 8-, and 12-leaf growth stages, respectively. Cotton at the 12-leaf stage absorbed more14C within 48 HAT than was absorbed by four- or eight-leaf cotton by 72 HAT. A majority (31 to 57%) of applied14C remained in the treated stem for all growth stages and harvest times. Treated cotton stems at all growth stages and harvest times contained higher concentrations (Bq g−1) of14C than any other tissues. Flumioxazin metabolites made up less than 5% of the radioactivity found in the treated stem. Because of the undetectable levels of metabolites in other tissues when flumioxazin was applied PDS, flumioxazin was foliar applied to determine whether flumioxazin transported to the leaves may have been metabolized. In foliar-treated cotton, flumioxazin metabolites in the treated leaf of four-leaf cotton totaled 4% of the recovered14C 72 HAT. Flumioxazin metabolites in the treated leaf of 12-leaf cotton totaled 35% of the recovered14C 48 HAT. These data suggest that differential absorption, translocation, and metabolism at various growth stages, as well as the development of a bark layer, are the bases for differential tolerances of cotton to flumioxazin applied PDS.

Influence of Adjuvants on Cotton (Gossypium hirsutum) Response to Postemergence Applications of CGA 3626221

Studies were conducted in 1999, 2000, and 2001 to evaluate cotton response to CGA 362622 applied postemergence with various adjuvants. In field studies, CGA 362622 was applied at 3.8 or 7.5 g ai/ha with nonionic surfactant, crop-oil concentrate (COC), or a urea-based adjuvant. A nontreated control was maintained weed free for comparison. Crop injury over all years at 1 wk after treatment (WAT) was 27 and 34% from 3.8 and 7.5 g/ha CGA 362622, respectively, when rates were pooled over adjuvants. At 4 WAT, injury was 6 to 14% with 3.8 g/ha and 10 to 21% with 7.5 g/ha CGA 362622 during the 3-yr study. Cotton heights at 2 WAT were reduced by 16 to 31% of nontreated cotton heights by CGA 362622. Heights of treated cotton did not differ and were generally equivalent to the nontreated control at 8 WAT. Cotton injury and height reduction were greatest when CGA 362622 was applied with COC. Cotton lint yields and fiber quality were not affected by CGA 362622 rate or adjuvant treatment. Cotton injury from CGA 362622 in the greenhouse was similar to that in the field. Initial cotton injury and subsequent reduction in leaf area or shoot dry weight were generally lowest when CGA 362622 was applied with no adjuvant or UBA in the greenhouse.Nomenclature: CGA 362622 (proposed common name trifloxysulfuron sodium), N-[(4,6-dimethoxy- 2-pyrimidinyl)carbamoyl]-3-(2,2,2-trifluoroethoxy)-pyridin-2-sulfonamide sodium salt; cotton, Gossypium hirsutum L. ‘SureGrow 125.’Additional index words: Sulfonylurea herbicide.Abbreviations: ALS, acetolactate synthase enzyme (EC 4.1.3.18); COC, crop oil concentrate; MSO, methylated seed oil; NA, no adjuvant; NIS, nonionic surfactant; OSS, organosilicone surfactant; POST, postemergence; UBA, urea-based adjuvant; WAT, weeks after treatment.

Proper adjuvant selection for foramsulfuron activity

Greenhouse and field studies were conducted to evaluate the activity of foramsulfuron with various adjuvant combinations. Three annual weed species were evaluated in the greenhouse to determine 80% growth reduction (GR 80 values), and five annual weed species were evaluated under field conditions at a reduced dose of foramsulfuron (67%). In the greenhouse, Echinochloa crus-galli L. (barnyardgrass) was the most sensitive species to foramsulfuron, followed by Setaria faberi Herrm. (giant foxtail) and Abutilon theophrasti Medicus (velvetleaf). Adjuvant selection was important for control of these species. The addition of methylated seed oil (MSO) provided the greatest control of these species followed by non-ionic surfactant (NIS) and crop oil concentrate (COC). The addition of a nitrogen fertilizer had a greater effect on weed control for COC and NIS than for MSO with E. crus-galli and S. faberi. However, the addition of a nitrogen fertilizer, 28% urea ammonium nitrate (UAN) or ammonium sulfate, to MSO significantly enhanced A. theophrasti control. In the field, foramsulfuron applied with MSO plus a nitrogen fertilizer provided the greatest level of weed control. Increases in the foramsulfuron dose applied with COC or NIS with a nitrogen fertilizer did not equal the level of weed control achieved with the field dose of foramsulfuron applied with MSO plus UAN.

CGA-362622 Antagonizes Annual Grass Control by Graminicides in Cotton (Gossypium hirsutum)1

The effect of CGA-362622 on annual grass control in cotton by clethodim and fluazifop-P and crop response was determined in field studies. CGA-362622 applied postemergence at 5.3 g ai/ha injured cotton up to 34% 1 wk after treatment (WAT). Injury was similar when crop oil concentrate (COC) and nonionic surfactant (NIS) were included. Adding fluazifop-P, but not clethodim, to CGA-362622 increased crop injury. Cotton recovered by 3 WAT. CGA-362622 mixed with fluazifop-P at 210 g ai/ha reduced broadleaf signalgrass and large crabgrass control 60 to 80%. Control was similar with COC or NIS in the mixture. Increasing the fluazifop-P rate to 315 g/ha did not improve control. CGA-362622 mixed with clethodim at 105 g ai/ha reduced control 65 to 80% with NIS and 40 to 65% with COC. Increasing the clethodim rate to 175 g/ha, especially with COC, substantially increased control. However, control was still less than that with clethodim at 105 g/ha. Prometryn plus MSMA postemergence-directed 3 wk after gramincide and CGA-362622 application increased control. Cotton yield was similar with clethodim alone and clethodim at 175 g/ha plus CGA-362622. Yield was reduced 29% by CGA-362622 mixed with fluazifop-P at 350 g/ha. Control was reduced by CGA-362622 applied 1 d before or after clethodim but not 5 d before or after clethodim. Control by fluazifop-P was reduced by CGA-362622 applied 1 or 5 d before or 1 d after the graminicide. Under greenhouse conditions, CGA-362622 and pyrithiobac mixed with clethodim, fluazifop-P, quizalofop-P, or sethoxydim reduced control of large crabgrass. Greater antagonism was noted with CGA-362622 than with pyrithiobac, and with fluazifop-P and quizalofop-P than with clethodim or sethoxydim.Nomenclature: CGA-362622 (proposed common name trifloxysulfuron), N-[(4,6-dimethoxy-2-pyrimidinyl)carbamoyl]-3-(2,2,2-trifluoroethoxy)-pyridin-2-sulfonamid sodium salt; clethodim; fluazifop-P; MSMA; prometryn; pyrithiobac; quizalofop-P; sethoxydim; broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash #3 BRAPP; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; cotton, Gossypium hirsutum L. ‘Stoneville BXN 47’.Additional index words: Adjuvants, antagonism, herbicide interactions, herbicide mixtures.Abbreviations: COC, crop oil concentrate; NIS, nonionic surfactant; POST, postemergence; POST-DIR, postemergence directed; WAT, weeks after treatment.

Postemergence Weed Control with Rimsulfuron and Various Adjuvants in Potato (Solanum tuberosum)1

Field studies assessed weed control and potato injury with rimsulfuron applied postemergence at various rates in combination with various adjuvants. Weed control was influenced by choice of adjuvant and rimsulfuron rate. Rimsulfuron at 0, 9, 18, 26, and 35 g ai/ha was applied with nonionic surfactant (NIS), crop oil concentrate (COC), methylated seed oil (MSO), or silicone-polyether copolymer (SIL). Potato injury was less than 5% for all rimsulfuron rates and adjuvant combinations. Redroot pigweed was controlled greater than or equal to 93% by all treatments except rimsulfuron at 9 g/ha + SIL. Except for redroot pigweed, rimsulfuron treatments with SIL controlled kochia, hairy nightshade, common lambsquarters, and volunteer oats less than with other adjuvants. At lower rimsulfuron rates, weed control with rimsulfuron + MSO tended to be greater than with rimsulfuron + NIS or rimsulfuron + COC. Common lambsquarters control was 75% or less regardless of rimsulfuron rate or adjuvant. Tuber yield generally inc...

Absorption and fate of carfentrazone-ethyl inZea mays, Glycine max,andAbutilon theophrasti

Carfentrazone-ethyl absorption, translocation, and metabolism was determined in Glycine max, Zea mays, and Abutilon theophrasti. Glycine max absorbed greater than 90% of applied carfentrazone-ethyl within 2 h after treatment (HAT) when nonionic surfactant (NIS) or crop oil concentrate (COC) were included in the treatment solution. The addition of 28% urea ammonium nitrate (UAN) did not improve carfentrazone-ethyl absorption in G. max, but in Z. mays and A. theophrasti, UAN combined with NIS or COC increased the rate of carfentrazone-ethyl absorption. Carfentrazone absorption in A. theophrasti 2 HAT was 70% when UAN was combined with NIS or COC compared to 40% with NIS or COC alone; however, 24 HAT, absorption with NIS and COC were similar to treatments with UAN. Carfentrazone-ethyl did not translocate from the treated leaf to other plant parts in Z. mays and only small amounts of radiolabeled product were detected in the rest of the shoots of A. theophrasti (5%) and G. max (12%). Herbicide metabolism in Z. mays and G. max was greater than in A. theophrasti. All three species converted carfentrazone-ethyl to its phytotoxic metabolite carfentrazone-chloropropionic acid; therefore, the parent molecule was considered to be the sum of the ethyl ester and its hydrolysis product. Estimated half-lives of carfentrazone in Z. mays, G. max and A. theophrasti were 1, 7, and 40 h, respectively. The rate of carfentrazone metabolism corresponded to plant sensitivity (sensitivity to carfentrazone: Z. mays<G. max<<A. theophrasti); however, rapid absorption and translocation of carfentrazone may reduce the tolerance of G. max.

Optimizing foliar activity of isoxaflutole on giant foxtail (Setaria faberi) with various adjuvants

Greenhouse, laboratory, and field studies were conducted to evaluate the potential of nonionic surfactant (NIS), crop oil concentrate (COC), methylated seed oil (MSO), and 28% urea ammonium nitrate (UAN) to enhance whole plant efficacy, absorption, and spray retention of foliar applications of isoxaflutole to giant foxtail. In greenhouse studies, isoxaflutole at 10 g ai ha−1reduced giant foxtail growth 5%, whereas the addition of a spray adjuvant reduced giant foxtail growth at least 75%. The addition of UAN improved giant foxtail growth reduction when used in combination with isoxaflutole plus NIS. Isoxaflutole spray retention on the leaf surface was increased with an adjuvant and a further increase was observed with the addition of UAN. Isoxaflutole applied with NIS, COC, and MSO resulted in 42, 60, and 91%14C absorption, respectively, compared to 21% absorption from isoxaflutole applied alone 24 h after treatment (HAT). Increased14C absorption and entry into the cuticle when an adjuvant was utilized with isoxaflutole resulted in greater translocation of14C from isoxaflutole out of the treated leaf. Significant basipetal movement from foliar applications of14C-isoxaflutole suggests phloem mobility. In field studies, isoxaflutole applied with MSO provided greater giant foxtail growth reduction compared to isoxaflutole applied with NIS and in some cases COC. The addition of UAN to isoxaflutole did not increase whole plant efficacy in field studies. These studies indicate isoxaflutole has excellent potential to be used for control of existing giant foxtail present at the time of corn planting if an adequate adjuvant is utilized.

Response of soybean cyst nematodes and soybeans (Glycine max) to herbicides

The effect of herbicides applied to V3 soybeans on race 3 soybean cyst nematode (SCN) reproduction and glyceollin production in roots was measured. Soybeans were treated postemergence with 1 × and 2 × rates of herbicides plus adjuvants or with adjuvants alone, and SCN development was measured. Acifluorfen, bentazon, lactofen, crop oil concentrate (COC), and nonionic surfactant (NIS) applications reduced SCN egg population densities 50 to 60% compared with the untreated control 4 and 8 wk after application. The SCN reproduction on plants treated with fluazifop-P, sethoxydim, and imazethapyr was similar to the untreated control. Crop oil concentrate or NIS applications alone were as effective as acifluorfen, bentazon, or lactofen applications for reducing SCN reproduction. However, no additive effect of adjuvant-herbicide combinations was observed, nor did herbicide rate affect SCN reproduction. Treatments reduced SCN reproduction only when applied to soybeans and had no effect on SCN reproduction when applied directly to the soil. No treatment stimulated SCN reproduction relative to the untreated control. Soybeans treated with COC, NIS, acifluorfen, and bentazon also had more glyceollin detected than the untreated control. Herbicide-induced glyceollin production may have increased the resistance of soybean to SCN.

Tolerance of Fine Fescues to Clethodim

Fine fescues are immune to two common graminicides, fluazifop-p-butyl and sethoxydim. This study was initiated to determine the tolerance of three fine fescues; chewings, hard, and creeping red, to clethodim alone or with a crop oil concentrate (COC) or non-ionic surfactant (NIS). Clethodim at 0.25 or 1.0 lb/a was applied on 23 Oct. 1995 and evaluated on 22 May and 9 July 1996. Clethodim at 0.25, 0.5, or 1.0 lb/a, was applied on 31 May and evaluated on 9 July 1996. Applied in the fall at 0.25 lb/a alone or with NIS, clethodim had little effect on chewings or creeping red fescue. Some injury to hard fescue was evident on 22 May, but it recovered by 9 July. The addition of COC resulted in moderate injury to all three species, with only partial recovery by 9 July. Severe injury of all species from clethodim applied at 1 lb/a was evident on 22 May. The amount of recovery that occurred by 9 July was dependent on the spray additive used. With none, all of the grasses recovered fairly well. With NIS, moderate injury to hard fescue persisted; and with COC, unacceptable injury to all species persisted. Similar results were obtained when the treatments were applied in the spring. The 0.5 lb/a rate caused an intermediate degree of injury. Though none of the clethodim treatments totally killed any of the fine fescues, unacceptable injury was caused by the 0.5 and 1.0 lb/a rates, regardless of additive, and by the 0.25 lb/a + COC treatment.

Interacting effects of MON 12000 and CGA-152005 with other herbicides in velvetleaf (Abutilon theophrasti)

Greenhouse and laboratory studies were conducted to determine the effects of dicamba, atrazine, and bentazon on efficacy, foliar absorption, and translocation of MON 12000 or CGA-152005 applied to velvetleaf. The efficacy of MON 12000, CGA-152005, and a combination of CGA-152005 plus primisulfuron applied at 4.5 g ai ha−1was similar when applied alone or with 140 g ha−1of dicamba. However, applying these herbicides in combination with 840 or 560 g ha−1of atrazine or bentazon, respectively, reduced velvetleaf control. Increasing the rate of MON 12000, CGA-152005, or the combination of CGA-152005 plus primisulfuron to 9 g ai ha−1or replacing crop oil concentrate (COC) with methylated seed oil (MSO) increased velvetleaf control of the atrazine and bentazon combinations but not to levels equal to these herbicides applied alone. Dicamba had no effect on the foliar absorption and translocation of14C from MON 12000 or CGA-152005. Atrazine had little effect on foliar absorption of14C from MON 12000 or CGA-152005, but bentazon reduced the foliar absorption of14C from MON 12000. Replacing COC with MSO increased the foliar absorption of14C from MON 12000 or CGA-152005 applied alone or with dicamba or atrazine, but not with bentazon. Translocation of14C from MON 12000 or CGA-152005 out of the treated leaves was 11 and 12%, respectively, averaged across adjuvants and sampling times. These values were reduced to an average of 3 to 4% for both MON 12000 and CGA-152005 when applied in combination with atrazine or bentazon. The majority of14C from MON 12000 or CGA-152005 was translocated acropetally. Atrazine and bentazon significantly reduced the acropetal translocation of14C from MON 12000 at 24 and 72 h and for CGA-152005 at 12, 24, and 72 h. The physiological basis for the observed antagonism of MON 12000 and CGA-152005 by atrazine and bentazon appears to be due to reductions in acropetal translocation of MON 12000 and CGA-152005 to velvetleaf meristems.

Sethoxydim and Crop Oil Concentrate Increase Pyridate Phytotoxicity in Transplanted Cabbage (Brassica oleracea)

Greenhouse and field studies were conducted in 1991 and 1992 to determine the potential for interaction among pyridate (0.5, 1.0 kg ai/ha), sethoxydim (0.22 kg ai/ha), and crop oil concentrate (COC) (1.25% v/v) applied alone or in two- and three-way combinations to transplanted cabbage. Additionally, the effect of applying sethoxydim and COC 1 and 2 d before and after application of pyridate was investigated. In greenhouse-grown cabbage, injury increased twofold and dry weight was reduced 15% when pyridate dose was doubled. Sethoxydim increased pyridate injury significantly, reducing dry weight 31%. When COC was applied with pyridate, injury increased and dry weight decreased linearly. Despite substantial crop injury 7 d after treatment with pyridate alone, pyridate + sethoxydim, and pyridate + COC, yields of field-grown cabbage were reduced significantly in 1 yr only when the three materials were combined. Pyridate injury decreased as time between sethoxydim + COC applications, before and after pyridate was applied, increased.

Interactions of Sethoxydim and Corn (Zea mays) Postemergence Broadleaf Herbicides on Three Annual Grasses

Greenhouse and laboratory studies were conducted to determine the effect of 22 postemergence corn broadleaf herbicide combinations on the efficacy of sethoxydim applied to giant foxtail, large crabgrass, and shattercane. Eighteen combinations caused a reduction in sethoxydim efficacy on at least one grass species. Dicamba, atrazine plus dicamba, atrazine plus bentazon, bromoxynil, primisulfuron, CGA-152005 plus primisulfuron, MON 12000, and flumetsulam plus clopyralid plus 2,4-D (NAF-73) were evaluated further on the efficacy and foliar absorption of sethoxydim applied to giant foxtail, large crabgrass, and shattercane. In timing studies, applying all herbicide combinations at 7 or 3 d before sethoxydim application eliminated significant antagonistic interactions. However, applying NAF-73, primisulfuron, or CGA-152005 plus primisulfuron 1 d prior resulted in a reduction in sethoxydim efficacy on at least one grass species. Dicamba, atrazine plus dicamba, and atrazine plus bentazon decreased14C-sethoxydim absorption 9 to 63% across grass species. Replacing crop oil concentrate (COC) with DASH increased sethoxydim absorption when applied with these herbicides but not to the full extent of sethoxydim applied alone with DASH. Sethoxydim efficacy was retained or improved with DASH when applied with dicamba, atrazine plus dicamba, atrazine plus bentazon, or bromoxynil. When primisulfuron, CGA-152005 plus primisulfuron, MON 12000, or NAF-73 was applied with14C-sethoxydim no effect on sethoxydim absorption was observed. DASH was less effective than COC at restoring sethoxydim efficacy when applied with these herbicides.

Adjuvant Effects on Imazethapyr, 2,4-D and Picloram Absorption by Leafy Spurge (Euphorbia esula)

Laboratory experiments were conducted to identify adjuvants that improve absorption of imazethapyr, 2,4-D amine, and picloram by leafy spurge. Adjuvants (0.25% v/v) included crop oil concentrate (COC), methylated seed oil (MSO), nonionic surfactant (NIS), organosilicones (Silwet L-77®, Sylgard® 309, Silwet® 408), 3:1 mixtures of acetylinic diol ethoxylates (ADE40, ADE65, ADE85) with Silwet L-77, ammonium sulfate (2.5 kg ha−1), and 28% urea ammonium nitrate (UAN, 2.5% v/v). Adjuvants were combined with14C-herbicide and commercially formulated herbicide product. Leaves were harvested 2 DAT, rinsed with 10% aqueous methanol to remove surface deposits of herbicide, and dipped in 9:1 hexane:acetone to solubilize cuticular waxes. Imazethapyr absorption increased by 38 to 68% when UAN was combined with COC, NIS, or MSO. Total absorption of imazethapyr plus COC, MSO, or NIS exceeded 86% 2 DAT when UAN was added. Urea ammonium nitrate reduced the amount of imazethapyr associated with the cuticular wax by 2.0%. Imazethapyr absorption was similar on both the abaxial and adaxial leaf surface when UAN was not added; however, 12% more imazethapyr was absorbed from the abaxial leaf surface than from the adaxial leaf surface when UAN was combined with Sylgard 309. Uptake of 2,4-D ranged from 54 to 78% and was greatest with Silwet 408 and 3:1 mixture of ADE40: Silwet L-77. Picloram absorption ranged from 3 to 19%. Buffering picloram treatment solutions to pH 7 and including 2.5 kg ha-1ammonium sulfate increased picloram absorption to 37%.

Bentazon Spray Retention, Activity, and Foliar Washoff in Weed Species

Greenhouse studies were conducted to investigate the effects of adjuvant and rainfall on bentazon spray retention, efficacy, and foliar washoff in hemp sesbania, sicklepod, smooth pigweed, and velvetleaf. Bentazon was applied at 0.28 to 2.24 kg ai/ha with Agri-Dex, a crop oil concentrate (COC) or Kinetic, an organiosilicone-nonionic surfactant blend (OSB) when weeds were at the three- to five-leaf stage. Plants were subjected to 2.5 cm simulated rainfall for 20 min at 1 and 24 h after application of bentazon. Shoot fresh weight reduction assessed 2 wk after treatment was similar with either adjuvant on velvetleaf and smooth pigweed. OSB enhanced bentazon efficacy in hemp sesbania and sicklepod as compared to COC. Rainfall at 1 h after application generally reduced bentazon activity in all weeds. OSB maintained bentazon activity in hemp sesbania when subjected to rainfall at 1 h after application as compared to COC. Overall, bentazon spray retention on plants was 9 to 550% higher with OSB as compared to COC among the species at 1 h after application. Amount of bentazon residue washed off from the foliage by rainfall within a weed species was relatively similar for both adjuvants except in smooth pigweed and ranged from 39 to 98% among the four weed species at 1 h after application. OSB exhibited specificity for certain weed species and the potential to minimize bentazon spray reaching the soil by increasing deposition.

Effect of Adjuvants on Bentazon Efficacy in Green Pea (Pisum sativum)

Bentazon efficacy was evaluated in early, normal, and late plantings of green pea with the addition of four adjuvants: crop oil concentrate (COC), LI-700, Sylgard 309, and X-77. Weed control was improved by all adjuvants in normal and late plantings of green pea, but only by Sylgard 309, X-77, and LI-700 in the early planting. In normal and late plantings, weed control with bentazon applied at 0.56 kg/ha with any adjuvant was equal to weed control with bentazon applied alone at 1.12 kg/ha. Bentazon injury on green pea plants varied from slight to severe, with the lowest injury resulting from bentazon applied with COC and LI-700 and highest injury from bentazon applied with Sylgard 309. Bentazon injury was greater in normal and late plantings than in the early planting.