Synergistic interaction between the insecticide terbufos and the herbicide nicosulfuron may result in severe injury to corn. Greenhouse and laboratory experiments were conducted to determine if using the imidazolinone-resistant corn ‘Pioneer-3343 IR’ (P-3343 IR) or coating corn seeds with naphthalic anhydride (NA) would reduce herbicidal injury imposed by the nicosulfuron-terbufos interaction. Greenhouse experiments showed nicosulfuron-terbufos interactions resulting in herbicidal injury in both P-3343 IR and ‘DeKalb 689’ (D-689) corn varieties, but the D-689 was more sensitive than the P-3343 IR corn. The greenhouse experiments also demonstrated protection against the nicosulfuron-terbufos interaction by NA seed treatments. Studies with radiolabeled nicosulfuron showed that terbufos inhibited the metabolism of nicosulfuron, but pretreatment of D-689 and P-3343 IR corn seed with NA decreased the inhibition in excised corn leaves. The differences in sensitivity to nicosulfuron in the two corn varieties resulted in part from the differential metabolism and primarily from the differential sensitivity of the target enzyme, acetolactate synthase, to the herbicide.

The influence of metribuzin [4-ammo-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] on net photosynthesis of goosegrass [Eleusine indica (L.) Gaertn. ♯3 ELEIN] and six cultivars of bermudagrass [Cynodon dactylon (L.) Pers. ♯ CYNDA cvs. ‘Common’, ‘Tufcote’, ‘Vamont’, and ‘Midiron’, Cynodon transvaalensis Davy., and Cynodon dactylon X Cynodon transvaalensis ‘Tifway’] was evaluated. Metribuzin rapidly inhibited carbon dioxide (CO2) uptake within 1 h after application in both goosegeass and bermudagrasses. Very often, net photosynthesis was completely inhibited. Net photosynthesis in goosegrass was inhibited by lower rates of metribuzin than those required for similar reduction in bermudagrasses. Common, Tufcote, Tifway, and C. transvaalensis bermudagrasses were less sensitive to metribuzin than Midiron and Vamont based upon the degree of inhibition of net photosynthesis, the rate of its recovery, and the level of foliar injury. Recovery from inhibition of net photosynthesis was observed in both species 24 h after treatment with low metribuzin rates. High rates caused several days lag period before net photosynthesis resumed. After 10 days, 95% of the goosegrass foliage was injured (either chlorosis or necrosis) from 2 kg ai/ha metribuzin treatment. The threshold concentration for inducing leaf injury in bermudagrasses was 1 kg ai/ha. Inhibition of photosynthesis was initially rapid in both grasses; however, recovery was evident earlier and there was less foliar injury in bermudagrasses than in goosegrass. Selective control of goosegrass in bermudagrass may therefore be partially dependent upon rapid metabolism and/or inactivation of metribuzin in the bermudagrass.

The phenoxy herbicides, 2,4-D, 2,4,5-T, MCPA, silvex and related materials, are selective herbicides widely used in crop production and in the management of forests, ranges and industrial, urban and aquatic sites. These chemicals are related to naturally occurring plant growth regulators. They kill plants by causing malfunctions in growth processes. Broad-leaved plants are generally susceptible to the phenoxy herbicides, whereas most grasses, coniferous trees and certain legumes are relatively resistant.

The phenoxy herbicides are used to control broad-leaved weeds in wheat, barley, rice, oats, rye, corn, grain sorghums and certain legumes. Such uses increase yields, improve product quality and reduce production costs. The phenoxy herbicides are used in forests to suppress unwanted hardwood trees and brush, to reduce competition with conifers already established or to prepare sites for the regeneration of conifers. They are used on grazing lands to control unpalatable and noxious plants and to kill brush and small trees that reduce the productivity of pastures and ranges. 2,4-D and other phenoxys are used in canals, ponds, lakes and waterways to kill floating weeds such as water hyacinth, submerged weeds such as pond-weeds, and emergent and shoreline plants such as cattails and willows. Industrial and urban uses include control of brush on utility and transportation rights of way, control of dandelions, plantains and other weeds in turf and suppression of ragweed, poison ivy and other plants of public health importance.

The principal hazard in the use of the phenoxys is to crops and other valuable plants either within the treated area or nearby. Treated crops and forest trees can be injured through accidental overdosing, improper timing of treatments, unusual weather conditions and other causes. Injury to nearby crops and ornamentals can result from drift of droplets or vapors of the spray. Such losses are largely preventable through the use of proper formulations and spray equipment and the exercise of good judgment.

The phenoxy herbicides are predominantly toxic to green plants and are much less toxic to mammals, birds, fish, reptiles, shellfish, insects, worms, fungi and bacteria. When properly used, they do not occur in soils and water at levels harmful to animals and microorganisms. They do not concentrate in food chains and do not persist from year to year in croplands. They are detectable only rarely in food and then only in insignificant amounts.

A highly poisonous kind of dioxin called TCDD is an unavoidable contaminant in commercial supplies of 2,4,5-T and silvex. The amount present in currently produced formulations of 2,4,5-T and silvex is not enough to alter the toxicological properties of these preparations or to endanger human health or to affect plants or animals in the environment.

The phenoxy herbicides are widely used because they are more efficient and usually less hazardous and less injurious to the environment than alternative methods. Use of these chemicals is estimated to reduce the cost of production of the crops on which they are used by about 5% and to reduce overall agricultural production costs in the United States by about 1%. Uses in forests and nonagricultural situations provide additional savings. If the phenoxys were no longer available, the cost of food, forest products, electric power, transportation and governmental services would be higher. These costs would be borne by consumers.

Cytokinins break bud dormancy and apical dominance, induce basal bulb formation, and dwarf shoot growth in purple nutsedge (Cyperus rotundus L.). Perfluidone (MBR 8251) [1,1,1-trifluoro-N-[2-methyl-4-(phenylsulfonyl) phenyl] methanesulfonamide] in addition to being phytotoxic, mimics the cytokinins in these aspects. This and other herbicides which have demonstrated effectiveness in nutsedge control may derive their potency from the preconditioning effects of their cytokinin activity combined with their phytotoxicity.

Dormancy, longevity, and germination of seed of tall larkspur (Delphinium barbeyi Huth), duncecap larkspur (Delphinium occidentale S. Wats.), low larkspur (Delphinium nelsonii Greene), and western false hellebore (Veratrum californicum Durand) were investigated. Field studies were conducted in the Cache National Forest in Idaho at 8,000 ft elevation. With the exception of 12 of 400 buried duncecap larkspur seed, seed of all species in the longevity study germinated or disintegrated the first year under field conditions. No sound or viable seed was found at the end of the second year. Dormancy of most seed was broken in 13 to 19 weeks when seed were held at 33 to 34 F in moist sand in the laboratory or when seed were in contact with moist unfrozen soil under snow. Under optimum field conditions, the majority of the seed germinated by late March. Seedlings were well-established before snow-melt in June.

CGA-43089 [α-(cyanomethoximino)-benzacetonitrile] seed treatment was evaluated at three Nebraska locations during 1979 and 1980 for grain sorghum [Sorghum bicolor (L.) Moench] protection from injury by metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], four other chloroacetanilide herbicides, and three metolachlor + s-triazine combinations. Acetochlor [2-chloro-N-(ethoxymethyl)-6′-ethyl-o-acetotoluidide] caused the most frequent and severest injury to unprotected and protected sorghum. Soilincorporated metolachlor produced more consistent injury than preemergence application to unprotected sorghum, but placement did not affect CGA-43089 protection. Sorghum-stand reduction was the type of injury most frequently encountered, but crop yield was least affected. CGA-43089 always protected the grain sorghum from yield reduction with these herbicides.

Atomizer type, spray volume, and herbicide rate influenced the effectiveness of paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) in controlling vegetation. In general, paraquat controlled vegetation more completely when applied from atomizers that discharged sprays with the angle between the edges of the pattern less than 80°. Increasing spray volume increased control for marginal herbicide rates. Increasing herbicide rate increased control and tended to overcome less effective atomizer performance or reduced spray volume. Vegetation was effectively controlled with cone- or fan-pattern-type nozzles at spray volumes as low as 50 L/ha. Cone- and fan-pattern atomizers were equal to or more effective than either rotary or flooding-type atomizers in all tests.

Soil organic carbon (OC), clay content, water content, and pH often influence the bioactivity of soil-applied herbicides, and these soil properties can vary greatly within fields. The purpose of this work was to determine the influence of within-field soil heterogeneity on the efficacy of RPA-201772 where corn, shattercane, and velvetleaf were seeded as bioassays. An experimental approach was developed to quantify RPA-201772 dose–response across a range of soil conditions in an agricultural field. Based on a logistic model, crop injury was quantified with the I20 parameter, the dose eliciting 20% greenness reduction, using a series of photographic standards. Weed biomass was quantified with the I80 parameter, the dose eliciting 80% biomass reduction, relative to the untreated control. Crop and weed responses varied by two orders of magnitude. Significant correlation, as high as 0.76, was observed between measures of plant response and soil properties, namely particle size and OC. Furthermore, native velvetleaf spatial distribution at the study site was heterogeneous, and seedlings were observed in plots where seeded velvetleaf biomass was high. Spatial heterogeneity of soil affinity for herbicide results in differential weed fitness and contributes to weed “patchiness.”

To develop more effective pest-management strategies, it is essential to understand how different pests interact with each other and the crop. Field studies were conducted in 2003 and 2004 at two Nebraska locations to determine the effects of early-season crop defoliation on the critical time for weed removal (CTWR) in narrow-row soybean. Three soybean defoliation levels were selected to simulate 0, 30, and 60% leaf tissue removal by the bean leaf beetle. Weeds were allowed to compete with the crop until V2, V4, V6, R3, and R5 growth stages. There were also season-long weedy and weed-free treatments. Results indicated that the CTWR in soybean occurred earlier as defoliation levels increased from 0 to 60%. The CTWR occurred at V3, V2, and V1 growth stage for 0, 30, and 60% defoliation levels, respectively. Overall, 60% defoliation resulted in earlier CTWR by at least 14 d. Yield losses from defoliation and weed interference were primarily associated with a reduction in number of pods per plant−1.

Effects of temperature on response of transplanted tomatoes (Lycopersicon esculentum Mill. ‘Campbell 17′) to trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline], profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine], and isopropalin (2,6-dinitro-N,N-dipropylcumidine) were investigated in field studies. Trifluralin and nitralin caused greater reductions in growth and yields of tomatoes transplanted early in April than to tomatoes transplanted around May 1. Responses to profluralin were similar but total yields of early transplanted tomatoes were not reduced although initial yields were below those of tomatoes treated with isopropalin. In controlled environment chamber studies, percent phosphorus of plant tops was reduced by trifluralin at low temperatures but was not influenced by trifluralin at high temperatures. Tomoto responses to phosphorus as reflected by plant fresh weight, dry weight and phosphorus content (mg/plant) were reduced by trifluralin at low and high temperatures.

The metabolism of Sandoz 6706 [4-chloro-5-(dimethylamino)-2-α,α,α-trifluoro-m-tolyl-3(2H)-pyridazinone] in soybean [Glycine max (L.) Merr. ‘Kent’] and in sicklepod (Cassia obtusifolia L.) was examined at 1, 2, 4, and 8 days after herbicide application to explain the relative susceptibility of soybean and sicklepod to the herbicide. The 14C-labeled Sandoz 6706 was applied via the plant roots in a liquid culture medium. The primary pathway of metabolism in both plant species involved N-demethylation to norflurazon [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone and the desmethyl Sandoz 9774 [5-amino-4-chloro-2-(α,α,α-trifluoro-m-tolyl-3(2H)-pyridazinone]. Soybean was more efficient in the N-demethylation of the herbicide to less toxic metabolites than was sicklepod. A second transformation pathway which resulted in the formation of polar products was present in the roots of both species.

In a 3-year study on four soil types, subsurface application just ahead of a planter with a device that removed the top from the bed, applied a band of spray, and covered the band with soil reduced weed control in cotton (Gossypium hirsutum L.) obtained with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), 2,4-bis(isopropylamino)-6-methylmercapto-s-triazine (prometryne), 3-(hexahydro-4,7-methanoindan-5-yl)-1,1-dimethylurea (norea), dimethyl-2,3,5,6-tetrachloroterephthalate (DCPA), and 1,1-dimethyl-3(α,α,α,-trifluoro-m-tolyl)urea (fluometuron) compared to applications on the soil surface. This machine improved weed control with α,α,α,-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin). Shallow incorporation, with two helical blades, after planting increased weed control with trifluralin, diuron, and DCPA by 10% or more over the surface applications. This incorporator increased weed control obtained with prometryne and norea 5%. Very shallow incorporation, with metal tines, after planting improved weed control obtained with trifluralin and DCPA 18 and 11%, respectively. Weed control with norea was increased 7%, but metal tines did not appreciably affect weed control obtained with prometryne, diuron, or fluometuron. Compared to surface applications, incorporation increased cotton injury with diuron, norea, prometryne, and fluometuron on sandy loam soil.

Isopropyl m-chlorocarbanilate (chlorpropham) at 6.7 kg/ha applied in mid April controlled dodder (Cuscuta campestris Yunck. and Cuscuta indecora Choisy) that emerged in May but did not consistently control dodder that emerged in June. Mid March applications sometimes controlled dodder that emerged in May but did not control that which emerged in June. When p-chlorophenyl N-methylcarbamate (PCMC), an inhibitor of microbial enzyme activity, at 1.7 kg/ha was applied with chlorpropham at 6.7 kg/ha in mid March or mid February, dodder that emerged in May and June was controlled consistently. A reduced rate (4.5 plus 1.1 kg/ha) of the combined materials applied in mid March also consistently controlled dodder that emerged in May and June.

The mode of action and selectivity of oxadiazon [2-tert-butyl-4(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one] were investigated in tolerant rice (Oryza sativa L.) and susceptible barnyardgrass [Echinochloa crus-galli (L.) Beauv. ♯3 ECHCG]. Oxadiazon produced only brown spots on the foliage of rice plants at higher rates (> 500 ppmv), while LC50 for barnyardgrass was 250 ppmv. Translocation of 14C-oxadiazon from the treated leaf was minimal in both species; after 7 days, about 2 and 3% of applied 14 C translocated in rice and barnyardgrass, respectively. In rice, 14C recovered in water and chloroform washings of the treated leaf was 25% in each and in barnyardgrass, 20 and 18%, respectively. After water and chloroform washings, 14C-oxadiazon present in the treated leaf of barnyardgrass and rice was 36 and 26%, respectively. In rice and barnyardgrass, unaltered 14C-oxadiazon represented 86 and 79% of applied 14C, respectively, 7 days after application. In barnyardgrass 7 days after foliar application, oxadiazon inhibited 14CO2 fixation and the export of fixed carbon. The effects were less marked in rice.

UHF energy (2450 MHz) was applied to seeds and seed-soil mixtures with a waveguide under controlled conditions. After treatment, seeds were germinated at 27 C to determine viability. Seeds were either killed or seedlings grew normally with no intermediate levels of inhibition typical of that produced with sub-lethal dosages of herbicides. The energy required to kill several species of dry seeds ranged from 88 to 183 J/cm2 and could be reduced 12 to 42% by a 24-hr imbibition period prior to treatment. When several seed-soil mixtures were treated, the greatest toxicity occurred in a moist muck and clay loam soil, with the least toxicity on a dry loamy sand soil. Although attenuation of activity occurred in dry soils of three types, less energy was required to kill seeds in moist soils than was required in the absence of soil. Increasing the power levels reduced the time of exposure necessary to kill barnyardgrass [Echinochloa crus-galli (L.) Beauv.] seeds. Less energy was required to kill seeds as the soil temperature was increased from −20 to +18 C.

The effect of site of application on uptake and translocation of the butyl ester of fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy] phenoxy] propanoic acid} by quackgrass [Agropyron repens (L.) Beauv. # AGRRE] was investigated using 14C-labeled herbicide and intact plants. Uptake and distribution of the label were significantly greater from the abaxial than from the adaxial surface of leaves. The addition of a nonionic surfactant4 to the treatment solution increased the uptake significantly only through the adaxial surface. Uptake of 14C by the apical, middle, and basal regions of the treated leaf lamina did not differ significantly. However, movement of the 14C-label to stem areas and leaves both above and below treated leaves was greater from lamina base applications than from treatments to the lamina apex and middle. The older leaves absorbed more herbicide than did younger leaves, but the pattern of translocation did not differ. Considerably greater translocation occurred from treatments to the outside of the leaf sheaths in the lower regions of the stem than from applications to the upper leaf sheaths, with the 14C-label moved to young and old leaves, roots, and rhizomes. Uptake from applications to the outside of the upper leaf sheaths also resulted in improved translocation mainly within the stem areas and into upper leaves.

Acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} applied 7 days after cowpea [Vigna unguiculata (L.) Walp.] emergence (unifoliolate leaf stage) gave better control than later applications. Cowpea control was obtained with one acifluorfen application at 7 days after cowpea emergence in 1981, but in 1980 and 1982, applications at 7 and 14 days were necessary for acceptable control (> 80%). Acifluorfen reduced cowpea plant dry weights relative to the weedy control. A single application 7 days after emergence reduced cowpea plant growth more than one at 21 days after emergence. Of all times of application, the greatest soybean [Glycine max (L.) Merr.] injury occurred when acifluorfen was applied at 7, 14, and 21 days after emergence, but seed yields were not reduced relative to the untreated weed-free control. There was no difference in response among three weedy cowpea cultivars to acifluorfen.

The growth of soybean (Glycine max (L.) Merr.) seedlings was retarded when treated with either methyl 3-amino-2,5-dichlorobenzoate (amiben methyl ester) or α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) when compared with soybeans treated with either 3-[-p-(p-chlorophenoxy)phenyl]-1,1-dimethylurea (chloroxuron) or 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea linuron. Seedling growth of soybeans also was retarded when treated with amiben methyl ester alone or applied in combination with O,O-diethyl S[2-(ethylthio)ethyl] phosphorodithioate (disulfoton). Insecticides did not influence growth of soybeans. Linuron applied in combination with O,O-diethyl S-[(ethyl-thio)methyl] phosphorodithioate (phorate). or methyl-N-[(methylcarbamoyl)oxy] thioacetimidate (methomyl) and amiben ester applied in combination with phorate produced significantly lower seedling vigor during only 1 year than when each pesticide was applied alone. Soybean stands were significantly lower only in 1 year when linuron was applied in combination with methomyl. None of the pesticides applied alone or in combination caused significant differences in date of maturity, lodging, seed yield, seed size, or seed quality during either year.

A series of experiments were conducted from 1983 through 1986 to determine the efficacy of encapsulated starch formulations of trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] in conventional and no-till soybean [Glycine max (L.) Merr.] production. The encapsulated starch formulations remaining on the soil surface were significantly more effective than the emulsifiable concentrate when applied in February, March, or April. Encapsulated trifluralin products prepared by both the starch xanthate and starch borate processes were as effective as the emulsifiable concentrate even when used in conventional-tillage systems for weed control and for maintaining soybean yields. Our data indicate that an effective and economical herbicide such as trifluralin need not be lost in no-till soybean production if new controlled-release formulation technology is used by the agricultural industry.