Relationships between production of cotton (Gossypium birsutum L. ‘Westburn M’) and full-season interference from tumble pigweed (Amaranthus albus L. ♯ AMAAL) at densities ranging from 0 to 64 plants/10 m of row were measured in three replicated experiments in the field. Dry weight of harvested tumble pigweed increased by 0.149 to 0.402 kg/plot for each additional weed/10 m of row. Intraspecific competition among tumble pigweed plants was observed at the higher weed densities. Cotton plant height was reduced in all three experiments at the 32 or 64 weed densities, but harvesting difficulties were not encountered in these studies. The threshold density where initial lint yield reductions occurred ranged from 4 to 16 tumble pigweed plants/10 m of row in the three experiments. Lint yields were reduced from 8 to 11 kg/ha for each additional tumble pigweed plant/10 m of row. Interference from tumble pigweed did not significantly affect cotton fiber length, uniformity, strength, or micronaire of hand-harvested bolls.

Growth and regeneration of field horsetail (Equisetum arvense L. ♯ EQUAR) were investigated under field and greenhouse conditions. Field horsetail produced shoots during the entire summer but its growth was detrimentally affected by the presence of corn (Zea mays L.). Field horsetail regrew as well whether it had been hoed once or 16 times during the growing season; and during the subsequent summer, there were no significant differences between horsetail growth in plots kept weed-free the previous growing season and in plots where field horsetail grew freely. In the greenhouse, rhizome segments 1 cm long placed 15 cm deep easily regenerated plants. Simulations were done using the growth and regenerative ability of field horsetail to estimate its potential spread in agricultural fields. The results of these simulations indicate that this weed can infest a hectare within 6 yr of its introduction into a new area.

Space-planted johnsongrass [Sorghum halepense (L.) Pers. ♯ SORHA] was clipped back to a height of 26 cm after flowering and, when 45 to 61 cm in height, was treated with various rates of the sodium salt of dalapon (2,2-dichloropropionic acid), MSMA (monosodium methanearsonate), or the sodium salt of asulam (methylsulfanilylcarbamate). Treatments were reapplied as needed during the growing season whenever a majority of surviving plants in a plot had initiated new foliar growth. Most plants were not killed by a single application of any herbicide, although rhizome development, as measured by the number of rhizome buds, was inhibited by the initial herbicide treatments. MSMA at 4.5 kg ai/ha was more phytotoxic to johnsongrass than other herbicide treatments or MSMA at 2.3 kg ai/ha; a single application at the higher rate reduced the original number of rhizome buds on plants by 50 to 60%, and two applications killed 86 to 93% of the plants. Asulam at 4.5 and 6.7 kg ae/ha and dalapon at 6.7 and 9.0 kg ae/ha primarily controlled plants by inhibiting growth for an extended period. After two or three applications of asulam or dalapon at 6.7 kg ae/ha, only about 40% of the plants had been killed, but the original number of rhizome buds on surviving plants had been reduced by about 80%.

Greenhouse studies were initiated to identify potential interactions of the postemergence herbicide acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} with the postemergence grass herbicides sethoxydim {2-[1-(ethoxyimino) butyl]-5-[2-(ethylthio) propyl)-3-hydroxy-2-cyclohexen-1-one}, diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy]propanoic acid}, and RO-13-8895 [acetone 0-(D-(2-(p-[(α,α,α-trifluoro-p-tolyl)oxy) phenoxy)propionyl)oxime}. Greatest control of barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG] was obtained with the combination of acifluorfen and sethoxydim plus a crop oil concentrate. This combination increased foliar absorption of 14C-acifluorfen by barnyardgrass but not by soybean [Glycine max (L.) Merr. ‘Corsoy’]. The combination of acifluorfen with diclofop appeared to reduce phytotoxicity to barnyardgrass and increase it to soybean. Little or no interaction was observed in combinations of acifluorfen and RO-13-8895.

Field studies were conducted on a Taloka silt loam (Mollic Albaqualf) to determine the effects of residual levels of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] on rice (Oryza sativa L.). Yield reductions could be overcome by increasing rice seeding rate, by decreasing seeding depth, or by applying the safeners CGA-43089 [α-(cyanomethoxyimino)-benzacetonitrile] or CGA-92194 [α-(1,3-dioxolan-2-yl-methoximino)-benzacetonitrile] to the rice seed. Greenhouse studies with the safeners and reduced seeding depths indicated that CGA-92194 was better than CGA-43089 for protecting rice from metolachlor injury, but reduced seeding depths did not reduce metolachlor injury.

Weed control in no-till soybeans [Glycine max (L.) Merr. ‘Wells’] planted into shredded corn (Zea mays L.) residue was evaluated at Concord, NE, over a 3-yr period. Herbicide factors evaluated were time of herbicide application for no-till soybeans, efficacy of glyphosate [N-(phosphonomethyl)glycine] relative to paraquat (1,1’-dimethyl-4,4’-bipyridinium ion) for control of emerged weeds, and the efficacy of alachlor [2-chloro-2’,6’-diethyl-N-(methoxymethyl)acetanilide], metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide), and pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] for residual weed control. Combination residual and contact herbicide treatments were applied either as a preplant surface application or preemergence after no-till-planted soybeans. Removal of existing weed growth was not consistently better with the preplant surface application compared to later removal after soybean planting. Paraquat and glyphosate gave nearly equal control of emerged weeds. Addition of 2,4-D [(2,4-dichlorophenoxy)acetic acid] with paraquat in the tank mix did not improve weed control. Use of narrow, ripple coulters on the no-till planter resulted in minimal disturbance of the preplant surface herbicide so that additional preemergence herbicide at planting was seldom beneficial.

Large crabgrass [Digitaria sanguinalis (L.) Scop. ♯ DIGSA] control was higher when either DCPA (dimethyl tetrachloroterephthalate) or napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] was applied to bermudagrass [Cynodon dactylon (L.) Pers. ‘Common’] growing in soil with a pH of 5 than in soil with a pH of 6.4 in 2 of 3 yr. Soil pH did not influence the response of large crabgrass to oxadiazon [2-tert-butyl-4(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin-5-one] or benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine). Herbicides alone did not produce high-quality turf unless fertilizer was applied annually at 300 kg N/ha or more. Bermudagrass quality was higher after three yearly applications of 300 kg N/ha or more of fertilizer when soil pH was 5 than when soil pH was 5.6 or 6.4.

Multiple regression analysis of data from field experiments conducted in Alberta at two locations between 1972 and 1983 indicated that there was a significant relationship between yield loss of barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.) and relative time of emergence of wild oat (Avena fatua L. ♯ AVEFA). At a given wild oat density, percent yield loss increased the earlier wild oat emerged relative to the crops and gradually diminished the later it emerged. However, the magnitude of the yield loss for both species varied with the year. Regression equations based on data pooled over years and locations were developed to provide an estimate of yield loss of barley and wheat due to relative time of wild oat emergence and wild oat density. The information should be considered when barley and wheat losses due to wild oat are being assessed.

The herbicides 2,4-D [(2,4-dichlorophenoxy) acetic acid], dalapon (2,2-dichloropropionic acid), glyphosate [(N-phosphonomethyl)glycine], paraquat (1,1’-dimethyl-4,4’-bypiridinium ion), and pronamide [3,5-dichloro-(N-1,1-dimethyl-2-propynyl)benzamide] were applied at selected rates and dates to quackgrass [Agropyron repens (L.) Beauv. ♯ AGRRE]-infested alfalfa (Medicago sativa L.) sod in 1979 and 1980 to suppress vegetation for subsequent establishment of alfalfa without tillage. The influence of herbicides on weed control, alfalfa seedling density and visual stand, and forage yield and quality was assessed for 3 yr. During establishment, all herbicides except 2,4-D effectively controlled quackgrass. Glyphosate applied broadcast increasingly suppressed the existing sod as the rate was increased from 0.6 to 1.6 kg ai/ha. The effectiveness of herbicides as measured by total (old and new) plant density was closely related to the suppression of the sward. While the substitution of new alfalfa plants for old ones was not necessary under dense (40 plants/m2) alfalfa stands, completely controlling the vegetation with glyphosate resulted in sustained productivity throughout the experimental period. After 3 yr, alfalfa percentage and yield were highest when glyphosate was broadcast at 1.6 kg/ha. Improvement in forage quality, as estimated by the concentrations of crude protein and neutral-detergent fiber, was closely related to grass control.

Chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carboxyl]benzenesulfonamide} has recently been registered for the control of several broadleaf weeds in spring wheat (Triticum aestivum L.), durum wheat (Triticum durum Desf.), and barley (Hordeum vulgare L.) in western Canada. Residue carryover of this herbicide can cause injury to subsequent sensitive crops. A bioassay technique based on growth of pregerminated corn roots was used to detect levels of chlorsulfuron as low as 0.125 ppb in three Saskatchewan soils. Confidence levels of 95% were established. These confidence bands allowed the detection of chlorsulfuron levels within a minimum and maximum variation of 3.1 and 11.5% of root development.

Field research was conducted in Arkansas to determine the effect of selected rice pesticides on the microbial herbicide Colletotrichum gloeosporioides (Penz.) Sacc. f. sp. aeschynomene (henceforth designated C.g.a.) and to integrate C.g.a. into control programs for northern jointvetch [Aeschynomene virginica (L.) B.S.P. # AESVI] in rice (Oryza sativa L.). Water suspensions of dry-formulated spores of C.g.a. at 1.9 × 1011 spores/ha were applied midseason in sequence with normal use rates of other pesticides. Carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranyl methyl-carbamate) at 0.56 kg ai/ha, propanil (3’4’-dichloropropio-anilide) at 2.2 kg ai/ha, acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} at 0.14 kg ai/ha, or fentin hydroxide (triphenyltin hydroxide) at 0.56 kg ai/ha did not reduce disease development of C.g.a. on northern jointvetch. Sequential applications of benomyl [methyl 1-(butylcarbamoyl)-2-benzimidazolecarbamate] at 0.56 kg ai/ha reduced activity of the fungus on northern jointvetch when fungicide applications began 1 week after C.g.a. application but had no effect on mycoherbicide activity when applications began 2 weeks after C.g.a.

Oxadiazon [2-tert-butyl-4(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin-5-one] applied to bermudagrasses [Cynodon dactylon (L.) Pers.] at 4.5 kg ai/ha/yr in September reduced turf quality more than when treatments were applied anytime from April through August. The quality of ‘Tifway’ was reduced more than ‘Tifgreen’, ‘Tifdwarf’, or ‘Ormond’, and Ormond was reduced less than the other cultivars 3 weeks following oxadiazon treatment. Turf cover at the end of the growing season was not reduced with annual oxadiazon application at 4.5 kg/ha, whereas the cover was less in all plots treated with 13.5 kg/ha after four and five annual treatments. When compared with respective untreated cultivars, the cover of Tifway was reduced more from 13.5 kg/ha rate of oxadiazon than the other cultivars. Bermudagrass growth was retarded in the spring following oxadiazon applied the previous year.

Herbicide treatments of tank mixtures or sequential applications were applied at different growth stages and compared with standard treatments for control of barnyardgrass [Echinochloa crus-galli (L.) Beauv. ♯ ECHCM], bearded sprangletop [Leptochloa fascicularis (Lam.) Gray ♯ LEFFA], and aquatic weeds in rice (Oryza sativa L. ‘Starbonnet’). Some herbicides injured rice more than the propanil (3’,4’-dichloropropionanilide) or molinate (S-ethyl hexahydro-1H-azepine-1-carbothioate) standards, but injury for all treatments was inconsequential. Postemergence tank mixture treatments that controlled barnyardgrass (two- to four-leaf stages), bearded sprangletop (two-leaf to tillering stages), and aquatic weeds better than standard treatments were propanil plus butachlor [N-(butoxymethyl)-2-chloro-2’,6,-diethylacetanilide], oxadiazon [2-tert-butyl-4(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one] thiobencarb {S-[(4-chlorophenyl)methyl]diethylcarbamothioate}, or pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine].

Experiments were conducted to evaluate effects of various densities of bermudagrass [Cynodon dactylon (L.) Pers. ♯ CYNDA] in cotton (Gossypium hirsutum L. ‘Stoneville 213’) during the initial and second seasons following grass establishment and to evaluate bermudagrass competition in three cotton row spacings. During the season of grass establishment, densities of 1 to 16 plugs/7.5 m of cotton row had minimal effects on yield. Established, perennated bermudagrass was much more competitive. During second-season competition, 1 plug/7.5 m had formed a 76% ground cover and reduced yields by 600 kg/ha (25%) or more. The highest densities reduced yields 60 to 80%. In separate experiments, a cotton row spacing of 0.5 m reduced bermudagrass ground cover compared to 1.5 m row spacing.

In greenhouse studies, the butyl ester of fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid} applied preemergence at 0.035 kg ai/ha gave 91% control of goosegrass (Eleusine indica Gaertn. ♯ ELEIN), 79% control of large crabgrass [Digitaria sanguinalis (L.) Scop. ♯ DIGSA], and 73% control of giant foxtail (Setaria faberi Herrm. ♯ SETFA). In field studies, the butyl ester of fluazifop at 0.56 kg ai/ha applied preemergence gave 79% control of goosegrass, 76% control of large crabgrass, and 53% control of giant foxtail. The butyl ester of fluazifop at 0.07 kg/ha gave 79 to 85% control of each grass at the pretillering stage in field studies. The same rate applied at the early tillering stage gave 84% control of goosegrass but only 53 and 58% control of large crabgrass and giant foxtail, respectively. Relative species response was similar from spray and leaf-spot applications of the herbicide. The butyl ester of fluazifop at 4 μg/plant when spot-applied to leaves of the three grasses at the tillering stage resulted in 65% control of goosegrass but only 20 and 25% control of large crabgrass and giant foxtail, respectively.

On-farm field experiments were conducted in the Piedmont Plateau and Coastal Plain of North Carolina in 1981 and 1982 to investigate the integration of sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} with other chemical and cultural weed control tactics into soybean [Glycine max (L.) Merr.] weed management systems. Sethoxydim at 0.2 kg ai/ha provided control of broadleaf signalgrass [Brachiaria platyphylla (Griseb.) Nash. # BRAPP], large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA], and fall panicum [Panicum dichotomiflorum Michx. # PANDI) equal to control achieved with registered rates of the soil-applied herbicides alachlor [2-chloro-2’,6’-diethyl-N-(methoxymethyl)acetanilide] and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine). Control of broadleaf weed species with the postemergence herbicides bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4-(3H)-one 2,2-dioxide] and acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} equaled or exceeded the control obtained with the soil-applied herbicides linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] and metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5-(4H)-one]. Applications of 0.22 kg/ha of sethoxydim 2, 3, 4, and 5 weeks after soybean planting provided season-long control of fall panicum and crabgrass in 1981. In 1982, crabgrass control was 88 to 99% up to 4 weeks after planting. Later applications provided inadequate control of the grass species. Variations in volume and pressure of application had no effect on control of 10-cm goosegrass [Eleusine indica (L.) Gaertn. # ELEIN] or broadleaf signalgrass with 0.2 kg/ha of sethoxydim. Increasing pressure increased control of 30-cm goosegrass and broadleaf signalgrass. Increasing volume increased only control of goosegrass. Bentazon and acifluorfen provided better control of broadleaf weeds when applied early than when applied late. In two of four experiments tank mixtures of sethoxydim and bentazon resulted in an initial decrease in grass control compared to corresponding sequential applications. Soybean yields were comparable, however.

Preemergence and postemergence application of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)-one] at 0.6 and 1.1 kg ai/ha controlled downy brome (Bromus tectorum L. ♯ BROTE) in winter wheat (Triticum aestivum L. ‘McDermid’) but caused considerable injury without the use of activated carbon over the seeded row. Activated carbon applied in 5-cm bands over the seeded row at 84, 167, and 336 kg/ha protected winter wheat at Pendleton on a silt loam soil. On a sandy loam soil, only a 336 kg/ha rate provided protection from metribuzin. Metribuzin toxicity to winter wheat was more difficult to neutralize when applied preemergence. Downy brome control was not reduced by carbon applied over the wheat row. The best treatment in this study was carbon at 336 kg/ha applied preemergence over the row followed by metribuzin at 0.6 or 1.1 kg/ha postemergence. A 10-week delay between preemergence carbon banding and postemergence metribuzin protected winter wheat from chemical injury.

Reaction of some wild oat (Avena fatua L. ♯4 AVEFA) populations to the herbicide triallate [S-(2,3,3-trichloroallyl)diisopropylthiocarbamate] was investigated in a controlled-environment chamber. Under specified conditions, 1.0 mg active ingredient of triallate incorporated in 1 kg of soil was a satisfactory diagnostic rate for 14-day-old seedlings. Five seedling growth parameters were studied. These parameters were emergence, survival to produce first leaf, mesocotyl length, first-leaf length, and seedling height. Of these, mesocotyl length was least affected by triallate treatment, and significant differences in variability for triallate reaction were found within and among historically triallate unexposed, as well as exposed populations. Within-population variation for seedling emergence and survival was higher in unexposed than in exposed populations. Populations with recurrent exposure to triallate were more tolerant to the herbicide under experimental conditions than historically unexposed populations. Triallate-tolerant lines were identified which were tolerant to two other common wild oat herbicides.

Sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} and RO-13-8895 {acetone-O-[d-2-[p-[(α,α,α-trifluoro-p-tolyl)-oxy]phenoxy]propionyl]oxime} were evaluated for quackgrass [Agropyron repens (L.) Beauv. ♯ AGRRE] control in ‘Norcen’ birdsfoot trefoil [Lotus corniculatus (L.)], ‘Monarch’ cicer milkvetch [Astragalus cicer (L.) Hook.], and ‘Arlington’ red clover [Trifolium pratense (L.)]. None of the herbicide treatments applied to weed-free legumes 3, 15, and 30 cm tall reduced crop ground cover or seed yield. Postemergence treatments of sethoxydim and RO-13-8895 applied to quackgrass in the one- to four-leaf stage, at rates from 0.56 to 1.1 kg ai/ha, gave control of 57 to 91% in September of the seedling year. Legumes in all postemergence herbicide-treated plots produced more seed than legumes in untreated plots, regardless of time of application. Sequential applications of sethoxydim, RO-13-8895, or fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid} at 0.14 plus 0.14 kg ai/ha gave more effective quackgrass control and greater legume ground cover than single applications at 0.28 kg ai/ha.

The general appearance of plants was similar for 14 accessions of velvetleaf (Abutilon theophrasti Medic. ♯ ABUTH) obtained from Stoneville, MS (33° 25’ N), Rosemount, MN (44° 43’ N), and various locations in between. All accessions were equally susceptible to bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide]. Variation in maturity characteristics was found among the accessions in the field at Rosemount; southern accessions began seed capsule production later and continued it longer than did northern accessions. Velvetleaf accessions from Stoneville and Rosemount both produced seeds in the field at Weslaco, TX (26° 09’ N), but at Fairbanks, AK (64° 49’ N), neither accession produced seeds before being killed by frost.