Twelve sequential herbicide treatments were compared to cycloate (S-ethyl N-ethylthiocyclohexanecarbamate), a standard treatment, for control of annual weeds in sugarbeets (Beta vulgaris L.) in three field experiments conducted from 1971 through 1977. At harvest, seven sequential treatments had less than 10 annual broadleaf weeds per 30 m of row, whereas there were 40 broadleaf weeds per 30 m of row for the cycloate treatment. Four of these sequential treatments had significantly higher root yields and net returns than the cycloate treatment. Dependent on the sequential treatment and year, tonnage was increased 7.3 to 20.3 t/ha, and net returns $150 to $515/ha above those with cycloate. The most effective sequential treatment for control of weeds was a preplanting mixture of 2.2 kg/ha of ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate] plus 1.7 kg/ha of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} followed by a postemergence mixture of 0,6 kg/ha each of desmedipham [ethyl m-hydroxycarbanilate carbanilate (ester)] plus phenmedipham (methyl m-hydroxycarbanilate m-methylcarbanilate). This sequential herbicide treatment increased root yields by an average of 20.3 t/ha and net returns by $515/ha above those with cycloate.

Field and laboratory studies were conducted to examine effects of prior butylate use on biodegradation of subsequent applications of butylate and four other carbamothioate herbicides. Bioassays were used to demonstrate reductions of butylate and EPTC activity in four soils preconditioned by annual butylate applications. Combining these herbicides with dietholate, an enzyme inhibitor, prolonged persistence and restored normal herbicidal activity. Expected herbicidal efficacy occurred in adjacent plots with no history of carbamothioate use. Prior applications of butylate resulted in cross-adapted degradation of EPTC but not vernolate, pebulate, or cycloate. When samples of Cecil soil were treated in the laboratory with 14C-butylate, evolution of 14CO2 was significantly higher from soils that had received repeated field applications of butylate. The use of 14C-herbkides could be used to predict problem soils and potential herbicide failure.

Preplant applied herbicides were compared for their effect on three varieties of sugarbeets when seeds were planted at six depths during 1987 through 1989. More sugarbeet seedlings emerged and at a faster rate as the depth of seeding decreased from 4.5 to 1.6 cm. Herbicide injury to sugarbeet seedlings increased as depth of seeding increased from less than to greater than 2.5 cm. Herbicide treatments reduced sugarbeet stand and decreased early season sugarbeet height but had little effect on root yield or sucrose content.

Greenhouse and field experiments were conducted to investigate degradation rates and efficacy of EPTC (S-ethyl dipropyl carbamothioate), butylate [S-ethyl bis(2-methylpropyl)carbamothioate], vernolate (S-propyl dipropylcarbamothioate), and cycloate (S-ethyl cyclohexylethylcarbamothioate) in soils with and without prior history of thiocarbamate use. Herbicide persistence was measured by an oat (Avena sativa L.) bioassay, and giant foxtail (Setaria faberi Herrm. # SETFA) control was visually estimated in field studies. Both greenhouse and field studies indicated that enhanced thiocarbamate degradation occurred when the same herbicide (EPTC, butylate, or vernolate) was applied over successive years. Addition of dietholate (O,O-diethyl O-phenyl phosphorothioate) or fonofos (O-ethyl-S-phenylethylphosphonodithioate) increased thiocarbamate persistence and giant foxtail control in soils with prior thiocarbamate exposure. Use of dietholate or fonofos two or three consecutive years with EPTC or butylate again resulted in enhanced degradation. EPTC persistence and giant foxtail control were not affected by prior treatments or tank mixes with carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate). Rotation away from successive applications of the same thiocarbamate herbicide (EPTC, butylate, or vernolate) improved herbicide efficacy.

Laboratory experiments were conducted to evaluate the biodegradation of 14C-labeled butylate, cycloate, EPTC, pebulate, and vernolate in three butylate-history soils that had received three to eight applications of butylate under field conditions. After 20 days, biodegradation of butylate and EPTC was accelerated and had no lag phase in all three butylate-history soils. Butylate-adapted microorganisms were cross-adapted for EPTC and degraded EPTC as readily as butylate. Biodegradation of butylate and EPTC in Dothan soil without a butylate history exhibited a lag phase of 6 days after which 14CO2 was evolved at an exponential rate. This indicated that enhanced biodegradation was induced after one application of butylate or EPTC. Butylate-adapted microorganisms were cross-adapted for vernolate and pebulate in Dothan and pebulate in Wagram soils with a butylate history. Biodegradation of vernolate and pebulate was not enhanced in Varina butylate-history soil. After 20 days, there was no cross-adaptation for cycloate in any soil. These findings indicated that biodegradation of carbamothioates was influenced by soil type and previous carbamothioate use and that caution should be exercised in use of EPTC on fields of previous butylate use.

Velvetleaf control and sugarbeet response to POST triflusulfuron applied alone and in combination with desmedipham plus phenmedipham, nonionic surfactant, and urea ammonium nitrate (50:50) were evaluated in the greenhouse (velvetleaf only) and field. In a second field study, the effect of POST applications of triflusulfuron, desmedipham plus phenmedipham, ethofumesate, endothall, or combinations of these herbicides on sugarbeet root yield and quality was determined in the absence of weeds. Triflusulfuron controlled velvetleaf only when nonionic surfactant (NIS) was added to the spray solution. Desmedipham plus phenmedipham plus triflusulfuron gave greater velvetleaf control than triflusulfuron in the absence of NIS in the field. However, adding desmedipham plus phenmedipham to triflusulfuron plus NIS decreased velvetleaf control in the greenhouse. Adding desmedipham plus phenmedipham to triflusulfuron plus NIS increased visible sugarbeet response compared to triflusulfuron plus nonionic surfactant or desmedipham plus phenmedipham 14 d after the last POST application in 1994. In the absence of weeds, POST herbicide applications that included triflusulfuron did not reduce sugarbeet root yield more than other POST herbicides.

Herbicide dissipation was monitored in soils differing in herbicide use histories. Repeated annual applications over 5 yr enhanced biodegradation of butylate [S-ethyl bis(2-methylpropyl)carbamothioate] and EPTC (S-ethyl dipropylcarbamothioate) but not alachlor {2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide}, atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine], cyanazine {2-[[(4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl]amino]-2-methylpropanenitrile}, or metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide]. Prior application of butylate or EPTC enhanced biodegradation of the other thiocarbamate herbicide but not alachlor, atrazine, cyanazine, or metolachlor. Prior application of alachlor, atrazine, cyanazine, metolachlor, or trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] did not enhance biodegradation of butylate or EPTC. Dissipation of EPTC applied with dietholate (O,O-diethyl-O-phenolphosphorothioate) was not enhanced by prior application of alachlor, atrazine, or trifluralin. Prior use of EPTC, EPTC + dietholate, butylate, or cycloate, respectively, enhanced biodegradation of EPTC in 100, 100, 71, and 50% of the experiments, of EPTC applied with dietholate in 57, 100, 60, and 33% of the experiments, of butylate in 33, 40, 100, and 20% of the experiments, and of cycloate in 0, 0, 17, and 0% of the experiments. Prior thiocarbamate herbicide applications usually did not enhance cycloate biodegradation, but soils from two locations without prior pesticide use histories rapidly degraded the herbicide. Storage of soil samples at 25 C for 6 or 12 months before application of EPTC and EPTC + dietholate resulted in less herbicide degradation than storage at 15 C. Differences in prior environmental conditions such as temperature may explain why development of enhanced biodegradation varied between years even in the same field plots.

Efficacy of EPTC (S-ethyl dipropylcarbamothioate), butylate [S-ethyl bis(2-methylpropyl)carbamothioate], vernolate (S-propyl dipropylcarbamothioate), and cycloate (S-ethyl cyclohexylethylcarbamothioate) applied with dichlormid (N,N-diallyl-2,2-dichloroacetamide), and the former three herbicides applied with dichlormid and dietholate (O,O-diethyl-O-phenol phosphorothioate) for wild proso millet (Panicum miliaceum L. ssp. ruderale (Kitagawa) Tzevelev. # PANMI) control in corn (Zea mays L.) was evaluated in fields previously treated with EPTC + dichlormid or EPTC + dichlormid + dietholate. Cycloate + dichlormid usually controlled millet regardless of prior herbicide use. But EPTC + dichlormid was less effective than on soils not previously treated with the herbicides, suggesting enhanced soil biodegradation. The use of EPTC + dichlormid with row cultivation or applications of selected herbicides improved millet control. Following prior use of EPTC + dichlormid, wild proso millet control was improved by the addition of dietholate to EPTC + dichlormid and vernolate + dichlormid but not butylate + dichlormid. In dissipation studies using soils previously treated with EPTC + dichlormid, the relative order of herbicide persistence was EPTC + dichlormid < vernolate + dichlormid < butylate + dichlormid < EPTC + dichlormid + dietholate < vernolate + dichlormid + dietholate = butylate + dichlormid + dietholate < cycloate + dichlormid. When EPTC + dichlormid + dietholate was applied to soils previously treated with that mixture, wild proso millet control was again reduced. Dissipation studies confirmed that dietholate slowed biodegradation of EPTC in soils previously treated with EPTC + dichlormid but not with EPTC + dichlormid + dietholate.

A 6-yr field study was conducted to determine the effect of herbicide rotations on enhanced biodegradation of EPTC applied with and without dietholate, and on long-term control of wild-proso millet in sweet corn. Alachlor plus pendimethalin plus cyanazine or cycloate plus cyanazine for 1 yr following previous EPTC plus cyanazine applications reduced enhanced EPTC biodegradation in 3 of 4 and 2 of 3 yr, respectively. Enhanced biodegradation of EPTC applied with dietholate was reduced in 1 of 2 yr when EPTC plus dietholate plus cyanazine treatments were followed for 1 yr by alachlor plus cyanazine, pendimethalin plus cyanazine, or cycloate plus cyanazine, but was not reduced in 2 of 3 yr when EPTC plus dietholate plus cyanazine treatments were followed for 1 yr by alachlor plus pendimethalin plus cyanazine. Dietholate biodegradation was enhanced in soils treated 1, 2, or 3 yr previously with one application of EPTC plus dietholate plus cyanazine. After 3 yr of repeated use, cycloate biodegradation was also enhanced. Continuous use of EPTC plus cyanazine and EPTC plus dietholate plus cyanazine over 6 yr provided an average of only 46 and 64% wild-proso millet control, respectively. When applied once every second, third, or fourth year in rotation with alachlor plus pendimethalin plus cyanazine or cycloate plus cyanazine, EPTC plus cyanazine provided 83, 86, and 95% wild-proso millet control, respectively. EPTC plus dietholate plus cyanazine applied every second, third, or fourth year in rotation with cycloate plus cyanazine, alachlor plus cyanazine, pendimethalin plus cyanazine, or alachlor plus by pendimethalin plus cyanazine provided 88, 91, and 95% wild-proso millet control, respectively.

Laboratory studies were conducted to evaluate the degradation of butylate (S-ethyl diisobutylthiocarbamate), EPTC (S-ethyl dipropylthiocarbamate), cycloate (S-ethyl N-ethylthiocyclohexanecarbamate), and vernolate (S-propyldipropylthiocarbamate) in soil with prior thiocarbamate herbicide exposure. EPTC degradation was accelerated in soil which had previously been treated with butylate, vernolate, or EPTC in 1979, 1980, and 1981. The evolution rate of 14CO2 from 14C-labeled vernolate was increased in soil which had previously been treated with vernolate or EPTC in 1979, 1980, and 1981. Cycloate degradation was not enhanced in soil with prior exposure to butylate, EPTC, or vernolate. Butylate breakdown was enhanced to the greatest extent in soil with previous exposure to butylate.

Velvetleaf control in sugarbeet by clomazone and commercially available sugarbeet herbicides was investigated in greenhouse and field studies. In greenhouse studies, clomazone at 0.07 and 0.04 kg ai ha-1 controlled 97 and 69% of velvetleaf, respectively, with little visible sugarbeet injury. Adding clomazone to pyrazon, TCA, ethofumesate, pyrazon plus TCA, or TCA plus ethofumesate increased velvetleaf control but increased visible sugarbeet injury. In field studies, clomazone at 0.07 kg ha-1 did not enhance sugarbeet injury. However, velvetleaf was not controlled by clomazone alone or clomazone plus pyrazon, ethofumesate, combinations of pyrazon plus TCA, pyrazon plus ethofumesate, or pyrazon plus TCA plus ethofumesate. Cycloate preplant incorporated plus pyrazon preemergence followed by postemergence herbicides controlled velvetleaf in all 3 yr of research. Postemergence herbicides increased velvetleaf control from soil-applied herbicides in 1987 and 1988.

Field experiments were conducted to compare herbicides applied preplant incorporated (PPI), preplant incorporated/preemergence (PPI/PRE), and preplant incorporated/early postemergence (PPI/early POST) to control woolly cupgrass in corn. Although good early-season control of woolly cupgrass from PPI cycloate plus cyanazine, EPTC plus dietholate or SC-0058, and butylate plus cyanazine sometimes was observed, middle- and/or late-season control was often limited. Generally, better woolly cupgrass control and higher corn yields were obtained from split PPI/PRE applications rather than from single PPI applications of alachlor, metolachlor, and acetochlor. The highest and most consistent full-season woolly cupgrass control resulted when cycloate or EPTC plus dietholate applied PPI was followed by cyanazine plus either pendimethalin, alachlor, metolachlor, or acetochlor applied early POST. However, in 1989 adverse weather conditions near the early POST application timing injured corn and reduced yields.

Laboratory studies enumerated butylate-, EPTC-, vernolate-, pebulate-, and cycloate-utilizing bacteria and actinomycetes in a Dothan loamy sand following repeated use of butylate, EPTC, or vernolate. Herbicide utilizers were isolated on a defined medium composed of minimal salts plus 200 mg/L herbicide as the primary carbon source plus 25 mg/L TTC as an indicator of organisms capable of metabolizing the herbicide substrates. Media inoculated with a butylate-history soil developed more TTC-red actinomycetes on the butylate-indicator agar than did media inoculated with a non-herbicide-history soil. Similarly, media inoculated with a vernolate-history soil developed more TTC-red bacteria on the vernolate-indicator agar. Cross-adaptation from vernolate to butylate and cycloate was evident, with inoculant from the vernolate-history soil exhibiting an increase in bacterial counts when butylate or cycloate was present as the primary carbon source. Likewise, previous butylate exposure corresponded with an increase in the number of vernolate- and pebulate-utilizing actinomycetes. Previous exposure to EPTC resulted in an increased population of butylate- and pebulate-utilizing actinomycetes.

Fresh market spinach has limited herbicides available and weed management in this crop is dependent on hand-weeding. Phenmedipham is a POST herbicide registered for use on spinach grown for processing or for seed, but not fresh market spinach. This study evaluates the potential use of phenmedipham alone and in combination with cycloate for weed control in fresh spinach production. Greenhouse and field studies were conducted in 2013 using two spinach varieties known to have low and high tolerance to phenmedipham. The greenhouse studies showed that phenmedipham at 270 and 550 g ai ha−1 was safe to spinach when applied at the four-leaf stage for the low- and high-tolerance varieties, respectively. Phenmedipham was evaluated alone (550 g ha−1) and applied to the four-leaf stage in two varieties. Subsequently, a second experiment evaluated cycloate (1,700 g ha−1) followed by (fb) phenmedipham at several rates (90, 180, and 270 g ha−1). Phenmedipham alone (550 g ha−1) did not result in crop injury when applied to four-leaf spinach; however, the weed control was not better than cycloate alone. When applied as a sequential treatment following cycloate, all phenmedipham rates were safe to spinach and significantly improved weed control compared to cycloate alone. Cycloate fb phenmedipham at 270 g ha−1 provided 87% weed control relative to cycloate alone. This level of weed control was similar to the cycloate plus hand-weeding treatment, which provided 98% control. Results here show that cycloate fb phenmedipham improves weed control compared to cycloate alone, and has the potential to reduce hand-weeding costs in the fresh spinach production.

Field studies were conducted with fresh market spinach to examine crop tolerance and weed control with S-metolachlor. S-metolachlor was applied preemergence (PRE) at rates of 0.56, 0.72, 1.06, and 1.41 kg/ha and compared with the commercial standard cycloate at 3.4 and 4.5 kg/ha. Spinach was generally tolerant of S-metolachlor at rates up to 1.06 kg/ha on all soil types. S-Metolachlor at 0.56 to 0.72 kg/ha and cycloate at 3.4 kg/ha provided >88% control of common purslane, nettleleaf goosefoot, and shepherd's purse. Control of common chickweed with S-metolachlor at ≥0.56 kg/ha was >80%, whereas cycloate at 3.4 to 4.5 kg/ha was ineffective. Hand-weeding times in plots treated with S-metolachlor at 0.56 and 0.72 kg/ha were similar or lower than hand-weeding times in plots treated with cycloate at 3.4 kg/ha. Greenhouse studies were conducted to compare the relative tolerance of fresh market spinach to S-metolachlor and metolachlor. The GR10 values for S-metolachlor and metolachlor were 1.57 and 2.03 kg/ha, respectively. At rates above 2.2 kg/ha S-metolachlor is less selective in spinach than metolachlor. S-metolachlor is safe for PRE use in fresh market spinach at rates up to 1.06 kg/ha.

Only two spinach herbicides are currently available to producers, and with limited choices in herbicide mode of action (MOA), overuse of the current herbicides can result in dominance of uncontrolled weeds. Therefore, spinach producers need more herbicide options. Trials were conducted in processing spinach to evaluate the crop safety of dimethenamid-p (0.56 kg ai/ha), EPTC (2.94 to 3.40 kg ai/ha), or ethofumesate (0.84, 1.12 or 2.24 kg ai/ha) applied pre-emergent (PRE), and ethofumesate (0.09 or 0.18 kg ai/ha) applied early postemergent (EPOST) for potential use as alternatives to s-metolachlor (0.73 kg ai/ha) and cycloate (2.52 kg ai/ha). The control of London rocket was excellent with s-metolachlor, dimethenamid-p, and ethofumesate. Weed control with cycloate and EPTC was fair, and generally inferior to all others. Cycloate and s-metolachlor were safe to spinach, and only minor crop injury was observed with all other herbicides, except the high rate of ethofumesate PRE, which resulted in high levels of injury. Spinach outgrew all early herbicide injury with no significant yield losses. Ethofumesate applied EPOST caused no injury in year 1, although in year 2 injury was higher in all plots where it was applied twice, regardless of rate. In high-density plantings, dimethenamid-p caused significant crop injury to spinach, but only at one location on a sandy loam soil. In that trial, yields in dimethenamid-p plots were reduced an average 30% compared to the hand-weeded and s-metolachlor plots. As a result of this research, dimethenamid-p, EPTC, and ethofumesate should be considered candidates for expanded-use registrations in processing spinach production. More research is needed to determine additional rates and use patterns for improved crop safety, as well as an evaluation of soil types and spinach varieties.

Fresh market spinach has one primary herbicide, cycloate, which does not control all weeds. Previous studies demonstrated that cycloate PRE followed by (fb) phenmedipham at the four-leaf spinach stage is a safe and effective treatment. However, this treatment is not useful for the main growing season of fresh spinach due to its short crop cycle and the 21-d preharvest interval requirement of phenmedipham. This study evaluates the potential to use the combination of cycloate PRE fb phenmedipham on two-leaf spinach. Greenhouse and field studies were conducted in 2014 using three spinach varieties with low (‘Nordic' and ‘Sardinia') and high (‘Regal') tolerance to phenmedipham. Greenhouse studies revealed that phenmedipham at 90 g ai ha−1 was safe to Regal when applied at the two-leaf stage. Sardinia was more susceptible to phenmedipham injury under high (310 W m−2) light conditions than low (258 W m−2) light conditions. Impact of time of day on phenmedipham safety was evaluated in the field: day-long exposure to high light intensity following morning applications vs. evening applications fb exposure to low light intensity. Injury estimations taken 3 d after treatment (DAT) were lower for evening than for morning applications. Nonetheless, injury 11 DAT and spinach yield evaluations found no differences between morning and evening applications. Subsequently, cycloate (1,700 g ha−1) PRE fb phenmedipham (90 and 180 g ha−1) applied in the evening at the two-leaf stage was evaluated. A reference treatment was cycloate PRE fb phenmedipham (270 g ha−1) at the four-leaf stage. Treatments with cycloate fb two-leaf phenmedipham at 90 and 180 g ha−1 were safe to spinach and improved weed control compared to cycloate alone. Cycloate fb 180 g ha−1 phenmedipham at the two-leaf stage reduced weed biomass by 88% compared to cycloate alone. This level of weed control was similar to the reference treatment. Results here show that phenmedipham applied at the two-leaf stage is safe to fresh market spinach and it has the potential to be used during most of the fresh spinach growing season.

Field experiments were conducted to determine the critical period of weed interference in glyphosate- and glufosinate-resistant sugar beet, and to determine if PRE herbicides increased weed control or sugar beet root yield when glufosinate, glyphosate, or conventional POST herbicides were applied. Glyphosate- and glufosinate-resistant sugar beet root yields were reduced by up to 66 and 67%, respectively, when weeds remained all season in the weedy control treatment compared with yields when weed removal occurred as soon as the weeds were 2.5 cm tall, approximately 2 to 3 wk after planting (WAP). A critical period of weed interference did not occur in this research. The critical time of weed removal was approximately 8 WAP in 1998 and beyond 11 WAP in 1999. Weeds averaged 20 cm in height at 8 WAP and weed densities were greater in 1998 compared with 1999. The critical weed-free period for glyphosate- and glufosinate-resistant sugar beet was 4.5 to 5 WAP in 1998. In 1999, the critical weed-free period at the Michigan Sugar location was 1.5 WAP in glyphosate-resistant sugar beet, and 6.5 WAP in glufosinate-resistant sugar beet for the Michigan Sugar site. Glyphosate or glufosinate POST provided better weed control and resulted in greater sugar beet root yield compared with conventional POST herbicides when data were combined over PRE herbicide treatments. PRE herbicides improved the control of common lambsquarters and Amaranthus species in some of the site-years when data were combined over POST treatments, but sugar beet yield did not increase. Our research suggests that PRE herbicides will not be necessary in glyphosate- or glufosinate-resistant sugar beet. To avoid sugar beet yield loss, multiple POST applications of glyphosate or glufosinate will be needed until 6 to 9 WAP to prohibit yield loss from weeds emerging after the last POST application.