Two 1-yr field studies were conducted to evaluate preemergence and preplant incorporated treatments of alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide], EPTC (S-ethyl dipropylthiocarbamate), fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone}, and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] for the control of yellow nutsedge (Cyperus esculentus L.). Preemergence applications of metolachlor at 2.24, 3.36, and 4.48 kg/ha gave the best control with no significant differences observed among rates of metolachlor. Depth of herbicide incorporation did not result in any significant increase in control. Preplant incorporation of metolachlor at all rates, or fluridone at 0.56 and 0.84 kg/ha provided seasonal control of yellow nutsedge. Translocation of 14C-metolachlor applied to the root or shoot of yellow nutsedge was primarily acropetal with some limited basipetal movement. Application of 14C-metolachlor to the root or shoot of purple nutsedge (Cyperus rotundus L.) resulted in mostly acropetal translocation with little movement of 14C from the treatment site.

Reduced effectiveness of carbamothioate (thiocarbamate) herbicides in certain soils has been attributed to rapid herbicide degradation by soil microorganisms. Studies were conducted to determine if greater populations of EPTC (S-ethyl dipropyl carbamothioate)-degrading microorganisms were responsible for increased rates of degradation observed following repeated applications of EPTC to a Grenada silt loam soil. EPTC-degrading microorganism populations, measured with a 14C-MPN (most-probable-number) technique, were not larger in soils with accelerated rates of EPTC degradation, and degrader populations did not increase after application of 6 mg EPTC/kg of soil. Degrader populations increased after application of 60 mg EPTC/kg of soil only in soil previously treated for 6 yr with EPTC. Increased rates of metabolism of EPTC were apparently responsible for the increased rates of degradation, rather than increased populations of degraders.

Adsorption of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one], metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] and fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] on a Taloka silt loam (Mollic Albaqualf) and a Roxana silt loam (Typic Udifluvent) from the 10- to 20- and 40- to 50-cm soil depths was measured. The order of adsorption of the herbicides was fluometuron = metolachlor > metribuzin. Adsorptivity of the soil from the 10- to 20-cm depth was greater than from the 40- to 50-cm depth. At 7, 15, 23, and 37C, all herbicides degraded more rapidly as temperature increased. Metribuzin was least persistent and fluometuron and metolachlor were similarly persistent. The time required for the initial herbicide concentration to decrease by 50% in the Taloka silt loam from the 10- to 20-cm depth at 23C was 2.6, 9.4, and 10.1 weeks for metribuzin, fluometuron, and metolachlor, respectively.

Field studies were conducted in 1975 and 1976 at Urbana, Illinois, to evaluate soybeans [Glycine max (L.) Merr. ‘Amsoy 71′] as a potential rescue crop following the use of cyanazine{2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile} and procyazine {2-[[4-chloro-6-(cyclopropylamino)-1,3,5-triazine-2-yl] amino]-2-methylpropanenitrile} with corn (Zea mays L.). Preplant incorporated and preemergence applications of each herbicide were made at the recommended broadcast rates to Dana and Flanagan silt loams. Corn was removed and soybeans were planted 7, 13, and 21 days (1975) or 10, 15, and 23 days (1976) following herbicide application. Visual injury ratings, stands, and yields for soybeans were determined. In spite of varying degrees of visible injury and stand reductions, yields were not reduced significantly when soybeans were planted 3 weeks after cyanazine or procyazine application.

Trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), dinitramine (N4,N4-diethyl-α,α,α-rifluoro-3,5-dinitrotoluene-2,4-diamine), profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro 2,6-dinitro-N-propyl-p-toluidine], fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)aniline], pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine], butralin [4-(1,1-dimethylethyl)-N-(1-methylpropyl)-2,6-dinitrobenzenamine], and USB 3153 (N3,N3-di-N-propyl-2,4-dinitro-6-trifluoromethyl-m-phenylenediamine) were applied to evaluate weed control, cotton (Gossypium hirsutum L. ‘Dunn 119′) tolerance, and effect on rotational crops. Each herbicide was applied at 1-month intervals for 6 months prior to planting at 1, 1.25, 1.5, and 2X the recommended rates. Pigweed (Amaranthus hybridus L. and A. retroflexus L.) population counts and visual control ratings showed that weed control improved when treatments were applied closer to planting. Applications in November and December at 1.25X profluralin, 1.5X trifluralin, fluchloralin, and pendimethalin, 1X USB 3153, and 2X butralin were required to give effective weed control. Spring applications of 1X rates of profluralin, trifluralin, fluchloralin, and USB 3153, 1.25X rates of pendimethalin and dinitramine and 1.5X rate of butralin were required for adequate weed control. USB 3153 at all rates and dates of application severely limited growth and yields of wheat (Triticum aestivum L. ‘Funk 332′) planted after harvest and also the following May. Spring applications of profluralin at 1.5 and 2X rates and trifluralin at the 2X rate resulted in significant injury of rotational sorghum [Sorghum bicolor (L.) Moench ‘Dekalb E-59+’].

Laboratory and field studies were conducted to examine the influence of R-33865 (O, O-diethyl-O-phenol phosphorothioate) on the degradation rate of EPTC (S-ethyl dipropylthiocarbamate) in three soils that had a history of repeated EPTC application and exhibited accelerated degradation of EPTC. In field studies, addition of R-33865 to EPTC extended EPTC persistence in soil and provided increased shattercane [Sorghum bicolor (L.) Moench] control. In two soils that exhibited rapid EPTC degradation, addition of R-33865 to EPTC extended the half-life of EPTC from 9 to 18 days and from 6 to 15 days, respectively. Evolution of 14CO2 from 14C-carbonyl EPTC-treated soils with a prior history of EPTC treatment was significantly reduced when R-33865 was added; however, the initial lag period of EPTC degradation was not restored. Addition of R-33865 to EPTC on soils with no prior EPTC treatment did not extend persistence of EPTC in soil.

Experiments were conducted in 1990 and 1991 to determine bioavailability of PRE herbicides at three soil profile depths and two soil types in established common bermudagrass sods. Prodiamine and oryzalin reduced ‘Tifgreen’ bermudagrass root growth in the 5- to 7.5-cm layer of a Bosket very fine sandy loam soil at 2 and 4 wk after treatment in 1991. These herbicides decreased bermudagrass root weight in both the Bosket and Marietta sandy clay loam both years in samples taken from the 2.5- to 5-cm depth layer. In the 0- to 2.5-cm soil layer, all herbicides reduced root weight in 1990. In a bioassay, prodiamine caused decreased Tifgreen bermudagrass root growth at concentrations as low as 4 ppb by wt in the very fine sandy loam soil, while 8 ppb was necessary in the sandy clay loam soil. Prodiamine was detected in the very fine sandy loam at 4 wk after treatment at all depths in 1991 (65, 45, and 39 ppb in the 0- to 2.5-, 2.5- to 5-, and 5- to 7.5-cm soil layers, respectively). Oryzalin was also detected at all depths in 1991 when sampled at 2 and 4 wk after treatment in the very fine sandy loam. Pendimethalin was present in concentrations of 38, 39, and 37 ppb in the sandy clay loam at 2 wk after treatment in the 0- to 2.5-, 2.5- to 5-, and the 5- to 7.5-cm soil layers, respectively. Pendimethalin was also detected in the very fine sandy loam at 2 wk after treatment at concentrations of 55, 69, and 36 ppb in the 0- to 2.5-, 2.5- to 5-, and 5- to 7.5-cm soil layers, respectively.

Cotton [Gossypium hirsutum (L.) ‘Hancock’] lint yield or quality was not adversely affected under weed free conditions by three consecutive annual preemergence applications of up to 1.68 kg/ha fluometuron [1,1-dimethyl-3-(a,a,a-trifluoro-m-tolyl)urea] alone or in combination with 0.84 kg/ha trifluralin (a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) preplant incorporated on silt loam soils of the Memphis catena containing less than 1% organic matter. Similar applications of fluometuron at 3.36 kg/ha delayed maturity of cotton plants and ultimately reduced lint yields. Trifluralin treatments tended to overcome the detrimental effects of high rates of fluometuron. There was no effect on fiber development and maturation because fiber length and fineness (micronaire) were virtually identical for all treatments. The effect on maturity as determined by percent first harvest was a reflection of slower plant growth and fruiting and not of the development of the fiber itself. These results indicate no detrimental effects on cotton yield, maturity, and quality from annual applications of these herbicides at rates recommended and normally used in Tennessee.

Studies were undertaken to evaluate the phytotoxicity to yellow nutsedge (Cyperus esculentus L.), length of soil persistence, and tolerance of corn (Zea mays L.) to several acetanilide herbicides. The herbicides involved were alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide]. diethatyl [N-(chloroacetyl)-N-(2,6-diethylphenyl)glycine], H-26910 [N-(chloroacetyl)-N-(2-ethyl-6-methylphenyl)glycine-1-methylethyl ester], metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], Ortho 19790 [1-(chloroacetyl)-2,2-dimethyl-3-oxa-1-azaspiro-[4, 5]-decane], and Vel 5052 [2-chloro-N-(2,6-dimethylphenyl)-N-(1,3-dioxolan-2-ylmethyl)acetamide]. Most of these herbicides were equally active on yellow nutsedge in solution culture; only metolachlor and Vel 5052 were significantly more active than H-26910. Metolachlor and alachlor were the most toxic to yellow nutsedge in greenhouse and field experiments. Metolachlor persisted the longest of the herbicides in the field after spring applications. The tolerances of corn differed little among the herbicides at expected use rates.

Farmers grow crops in the dryland region of the Pacific Northwest (PNW) using tillage practices ranging from moldboard plowing to no-tillage. The objective of this study was to determine the effect of tillage on persistence of imazamox herbicide in intermediate and high precipitation zones of the inland PNW. Along with a nontreated control, imazamox was applied to imidazolinone-tolerant winter wheat in the fall and spring at one, two, and three times the maximum labeled rate at locations near Genesee, ID, Davenport, WA, and Pendleton, OR. Moldboard plow, chisel plow, and no-till tillage treatments were implemented soon after wheat harvest and yellow mustard was planted the following season to determine crop response. Experiments were conducted at each location in 2005 to 2007 and 2006 to 2008. There were significant location by year and year and location interactions. There was no significant tillage by imazamox rate interaction, except at Pendleton in year 2, for all measured yellow mustard responses (crop injury, biomass, and yield). Genesee was colder than Pendleton and had more precipitation than Davenport, resulting in more injury to yellow mustard at Genesee than at Pendleton but less than at Davenport. Davenport had greater injury than the other two locations, likely due to lower soil pH, higher organic matter (OM), and cooler, drier climate, which allowed imazamox to persist longer in the soil. Overall, Pendleton had the least yellow mustard injury, which likely was related to its warmer, wetter climate and the concomitant rapid soil dissipation of imazamox. Tillage did not reduce the persistence of imazamox. Yellow mustard had the lowest injury and had greater mature biomass and seed yield in no-till seeded plots when averaged across imazamox rates compared to moldboard and chisel-plowed plots.

Volunteer horseradish plants that emerged from root segments remaining after harvest can reduce yields of rotational crops as well as provide a host for pathogens and insects, thus reducing the benefits of crop rotation. POST applications of halosulfuron in corn can be an effective component to improve management of volunteer horseradish, but the replant interval from application to safe planting of commercial horseradish has not been determined. Fall herbicide applications are another possible volunteer horseradish management strategy than can be implemented once crops are harvested. Therefore, field experiments were conducted to evaluate the safe replant interval of horseradish following halosulfuron applications and to determine the efficacy of fall herbicide applications for volunteer horseradish control. Visual estimates of horseradish injury were greatest (85%) in plantings made zero months after halosulfuron applied at two times the approved rate; moreover, for all rates, injury decreased as the time after halosulfuron application increased. No herbicide injury or root biomass reduction occurred on horseradish at any halosulfuron rate from replanting beyond 4 mo after halosulfuron application. Control of volunteer horseradish was 91% or greater for all fall herbicide applications that included 2,4-D. Furthermore, volunteer horseradish shoot density was the lowest following combinations of 2,4-D tank-mixed with halosulfuron or rimsulfuron : thifensulfuron (0.2 and 0.4 shoots m−2, respectively) compared with the nontreated control (5.1 shoots m−2). This research demonstrates the effectiveness of both halosulfuron and 2,4-D as components of an integrated management strategy for volunteer horseradish control and the potential for halosulfuron applications without soil persistence beyond 4 mo affecting subsequent commercial horseradish production.

Field studies evaluated the effect of brown patch control on preemergence herbicide efficacy in tall fescue. Pendimethalin (1.7 followed by [fb] 1.7; 3.4 kg ai/ha), prodiamine (0.7 fb 0.6; 1.3 kg ai/ha), and oxadiazon (2.2 fb 2.2; 4.5 kg/ha), applied sequentially and as a single application, were evaluated for smooth crabgrass control with and without the use of azoxystrobin, a fungicide that controls brown patch. Azoxystrobin suppressed brown patch and increased smooth crabgrass control with pendimethalin in both years. This enhanced efficacy with azoxystrobin was attributed to improved tall fescue turf density and thus increased competition between this turf species and smooth crabgrass. Longer soil-residual herbicides such as oxadiazon and prodiamine provided high levels of smooth crabgrass control (often >90%). With the exception of oxadiazon at 4.5 kg ai/ha in 2000, smooth crabgrass control with oxadiazon and prodiamine was unaffected by the use of azoxystrobin.

Proso millet is an important short-season summer cereal in western Nebraska, southeast Wyoming, and eastern Colorado. The objective of this study was to evaluate proso millet tolerance to saflufenacil applied early preplant (EPP) or PRE. Field studies were conducted in Lingle, WY and Sidney, NE in 2008 and 2009. A dose–response study was conducted in the greenhouse at the University of Wyoming in Laramie, WY to determine proso millet cultivar response to saflufenacil applied at six rates from 0 to 400 g ai ha−1. In the field, saflufenacil was applied EPP and PRE at 50 and 100 g ha−1. Proso millet stands were reduced by an average of 33 and 23% by PRE and EPP treatments compared with the nontreated check; however, proso seed yields were not affected by saflufenacil timing or rate. In the greenhouse, ‘Panhandle’ and ‘Dawn’ exhibited less tolerance to saflufenacil than ‘Sunrise’, the cultivar used in the field studies.