Control of natural infestations of dogfennel [Eupatorium capillifolium (Lam.) Small # EUPCP] and woolly croton (Croton capitatus Michx. # CYNCP) in a bermudagrass [Cynodon dactylon (L.) Pers. # CYNDA] – dallisgrass (Paspalum dilitatum Poir. # PASDI) sward ranged from 20 to 100% with surface-applied tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N-dimethylurea}. In general, efficacy increased with rate of application from 0.6 to 1.1 kg ai/ha, and with time to 107 days after treatment. Only 0.6 kg ai/ha controlled less than 90% of the weeds during the growing season. Dry matter yields of desirable forage ranged from 60 to 290 kg/ha more with tebuthiuron treatment than in the untreated check. There were no consistent differences in forage quality among treatments, which indicates that tebuthiuron had no detrimental effects upon the bermudagrass or dallisgrass.

Increasing the corn (Zea mays L. “CO-OP S265”) population from 33 300 to 133 300 plants per hectare in the field significantly reduced yellow nutsedge (Cyperus esculentus L. # CYPES) above-ground biomass, tuber number, tuber weight and yellow nutsedge height at the end of growing season, and significantly increased corn yield. Photosynthetically active radiation below corn canopies decreased with increasing corn population and corresponded to reductions in yellow nutsedge above-ground biomass, tuber weight and tuber number. These results demonstrate that available light is a major factor in yellow nutsedge competition with corn. The size of yellow nutsedge was also reduced at high corn densities. These results support the use of crop manipulation in an integrated yellow nutsedge management system in corn.

In four field experiments, acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} applied preemergence at 1.1 kg/ha was not phytotoxic to peas (Pisum sativum L.) and increased the yield of shelled peas by an average of 25% compared to the weedy control. Yields were highest in all four experiments at the 1.1 kg/ha rate and tended to decline at higher rates of application. Growth chamber studies demonstrated that pea tolerance to acifluorfen was not affected by temperatures of 16/10 to 27/21C (light/dark) nor by stimulated rainfall of 0.5 to 5.0 cm. Peas and soybeans [Glycine max (L.) Merr.] were more tolerant of acifluorfen than were snap beans (Phaseolus vulgaris L.) and lima beans (Phaseolus lunatus L.) when acifluorfen was applied preemergence in the greenhouse or in hydroponic nutrient solution.

Large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA] control with BAS 9052 OH {2-[1-(ethoxyimino)-butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexene-1-one} was similar whether applied alone or in combination with acifluorfen {5-[2-chloro-4-(trifluoromethyl) phenoxy]-2-nitrobenzoic acid}. Combinations of BAS 9052 OH and bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4-(3H)-one 2,2-dioxide] gave decreased grass control compared to BAS 9052 OH alone. This antagonism between BAS 9052 OH and bentazon was eliminated by applying bentazon as a separate application 1.5 h or longer before the application of BAS 9052 OH. A 0.2 h interval between applications of the herbicides decreased large crabgrass control compared to control obtained with BAS 9052 OH applied alone, but the decrease was signifciantly less than occurred with a concurrent application of the two herbicides.

Sweet corn (Zea mays L. rugosa 'Seneca Scout’) and soybeans (Glycine max L. Merr. ‘Kanrich’) were grown in nutrient solutions containing alachlor [2-chloro-2′,6-diethyl-N-(methoxymethyl)acetanilide] at 2.36 × 10-5 M, polyethylene glycol MW 6000 (PEG6000) at −2.5 bars osmotic potential, alachlor at 2.36 × 10-5 M plus PEG6000 at −2.5 bars osmotic potential or with no additions. Sweet corn and soybean roots exposed to alachlor plus PEG6000 accumulated significantly more PEG6000 than roots exposed to PEG6000 alone; increased shoot uptake occurred only in soybean. Alachlor was also shown to significantly increase root osmotic potential and decrease root electrolyte leakage.

A model for determination of economic thresholds, or minimum weed population densities justifying the use of postemergence herbicide treatment, for five weed species in soybeans [Glycine max (L.) Merr.] is presented. Sensitivity analysis was performed on the model with respect to economic, statistical, and agronomic variables. The model was refined to include uncertainty about lost field days during the spraying period. Predictions from both the simple and refined models were consistent with economic theory. It was also determined that the economic threshold is sensitive to choice of data-collection ranges and functional form in weed-interference studies.

Concentrations of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] in contaminated groundwater recovered from 41 monitoring wells in Hall and Buffalo counties, Nebraska range from 0.01 to 8.29 μg/L. Over a 1-year period concentrations fluctuated sufficiently in a seasonal pattern to indicate that atrazine dissipation occurs. This reduction in concentration can be attributed to adsorption, dispersion, and degradation. A limited amount of atrazine degraded chemically to hydroxyatrazine [2-hydroxy-4-(ethylamino)-6-(isopropylamino)-s-triazine] under simulated aquifer conditions; microbial degradation could not be detected. A geometrical progression model for predicting long term residue accumulation indicates that current contamination levels probably reflect a steady-state situation between the amount that yearly enters into, and the partial degradation that occurs within, the aquifer. Oat (Avena sativa L. ‘Neal’) bioassays indicate that present levels of groundwater contamination remain well below the threshold necessary for phytotoxicity.

Over 9 yr, bandane (polychlorodicyclopentadiene isomers) at 67 kg/ha, bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide] at 11 and 22 kg/ha, DCPA (dimethyl tetrachloroterephthalate) at 22 kg/ha, and terbutol (2,6-di-tert-butyl-p-tolyl methylcarbamate) at 22 kg/ha applied preemergence controlled 94 to 100% of large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSP] in a lawn of common bermudagrass [Cynodon dactylon (L.) Pers. # CYNDA]. Control from benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) at 5 kg/ha, DCPA at 11 kg/ha, simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] at 5 kg/ha, and terbutol at 11 kg/ha was 90 to 99%. Bandane and bensulide persisted in soil to control large crabgrass a year after treatment.

Greenhouse and on-farm tests were conducted in North Carolina in 1979 and 1980 to evaluate sicklepod (Cassia obtusifolia L. # CASOB) management in soybeans [Glycine max (L.) Merr.]. All postemergence herbicide applications gave better sicklepod control when applied following vernolate [S-dipropylthiocarbamate) preplant incorporated than when applied following alachlor [2-chloro-2,6-diethyl-N-(methoxymethyl)acetanilide] preemergence. This resulted from decreased fatty alcohols and hydrocarbons in the epicuticle of vernolate-treated sicklepod. When applied sequentially to vernolate, toxaphene (chlorinated camphene, 67 to 69% chlorine) plus an oil concentrate and acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} applied postemergence to the first true-leaf stage of sicklepod resulted in 95 and 90% control, respectively. Linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] and metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] applied alone or as tank mixes with 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid] provided greater than 90% sicklepod control when applied postemergence-directed to soybeans. Metribuzin was more injurious to soybeans than linuron.

Field and greenhouse experiments were conducted to evaluate factors affecting johnsongrass [Sorghum halepense (L.) Pers. # SORHA] control in soybeans [Glycine max (L.) Merr. ‘Essex’] with three foliarly-applied herbicides. In 1980, johnsongrass height at treatment time had little effect on control due to inadequate soil moisture. In 1981, a wet year, best control was achieved on 15- or 40-cm-tall johnsongrass. BAS-9052 {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} at 0.6 kg/ha gave good to excellent control at all growth stages. Two applications of 0.3 kg/ha of BAS-9052 in both years and PP-009 butyl {2-[4-[5-(trifluoromethyl-2-pyridinyloxy)] phenoxy] propanoate} in 1981 increased johnsongrass control compared to only one treatment. Mixing BAS-9052 with other herbicides significantly reduced johnsongrass control. Greenhouse studies to determine the effect of soil water on herbicide response indicated that drier soils decreased johnsongrass regrowth with PP-009 and increased regrowth with BAS-9052.

Tebuthiuron (N-[5-(1,1-dimethylethyl)-1,3,4-thiadiozol-2-yl]-N,N′-dimethylurea} pellets (20% ai) applied at 0.6, 1.1, or 2.2 kg ai/ha in the spring at two locations and in the fall at a third location on the South Texas Plains did not significantly decrease buffelgrass (Cenchrus ciliaris L. # PESCI) standing crop or foliar cover compared to untreated areas. Buffelgrass standing crop was reduced for 8 months after application of 3.3 and 4.4 kg ai/ha of tebuthiuron to a sandy clay loam in the spring, but the same rates did not reduce standing crop after application to clay loam in the fall. However, buffelgrass foliar cover was reduced following application of 3.3 kg ai/ha or more of the herbicide, regardless of soil. Tebuthiuron applied at 2.2, 3.3, or 4.4 kg ai/ha to sandy clay loam soils killed buffelgrass plants in spots, but production by larger surviving plants compensated for reduction in plant density where 2.2 or 3.3 kg ai/ha were applied.

Live oak (Quercus virginiana Mill. # QUEVM) on the Texas Coastal Prairie was treated with herbicides using ground and aerial application methods. Tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} and pellets of buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone} at 2.2 kg ai/ha were the most effective herbicides, killing 60 to 95% of the live oak. Tebuthiuron pellets 3.2 mm in diam were more effective than the wettable powder at 1.1 kg/ha. Bay Met 1486 {N-[5-(ethylsulfonyl)-1,3,4-thiadiazole-2-yl]-N,N′-dimethylurea}, Dowco 290 (3,6-dichloropicolinic acid), hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H, 3H)-dione], and picloram (4-amino-3,5,6-trichloropicolinic acid) reduced the live oak canopy at 2.2 kg/ha whereas 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] and triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} were ineffective. Foliage-active herbicides generally were most effective in reducing the live oak canopy during the year of application. The soil-active herbicides generally were most active 1 or 2 yr after herbicide application. All herbicides reduced the live oak cover sufficiently to allow an increase in grass cover 2 to 4 months after treatment. Tebuthiuron at 2.2 kg/ha maintained a high degree of grass cover at least 2 or 3 yr after treatment.

The effects of MSMA on the development of straighthead, yields of rice, and hormonal balance in rice plants were observed in a greenhouse study. MSMA was applied to soil at 0, 6, and 9 kg ai/ha. At 6 kg/ha some straighthead and a 45% yield reduction occurred. At 9 kg/ha straighthead was evident, and yield was reduced by 85%. Analyses were made for ethylene with gas chromatography and for indoleacetic acid (IAA) with high performance liquid chromatography. Concentrations of ethylene and total arsenic detected in the tissue from rice leaves grown in MSMA-treated soil were higher at every growth stage when compared to plants grown in untreated soil. Both treated and untreated plants showed marked increases of these compounds during the reproductive stage and a decrease prior to panicle emergence. Significant changes occurred in IAA levels with the growth stage of treated and untreated samples, but MSMA had no obvious effect on IAA levels at any of the stages examined in this study.

The level of genetic variation for tolerance to herbicides was quantified in populations of slender wild oat (Avena barbata Brott. # AVEBA), wild oat (Avena fatua L. # AVEFA), and godetia (Clarkia williamsonii Lewis & Lewis) that had not been previously exposed to herbicides. Seedlings of wild oat and godetia were treated with barban (4-chloro-2-butynl-m-chlorocarbanilate) and bromoxynil (3,5-dibromo-4-hydroxybenzonitrile), respectively. The plants were rated for phytotoxic effects following treatment. A one-way analysis of variance on arcsin-transformed phytotoxicity ratings showed significant amounts of inter- and intrapopulation variability for herbicide reaction. Furthermore, the amount of genetic variance for herbicide reaction is higher than expected on the basis of mutation alone, suggesting selection favoring genes conferring herbicide tolerance occurs in natural populations.

The absorption, translocation, and metabolism of the methyl ester of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} by three sunflower (Helianthus annuus L.) lines was determined at 10 and 30C. Sunflower absorbed up to 27% more 14C-diclofop while growing at 30C and 90 ± 5% relative humidity (RH) than at 10C and 40 ± 10% RH. Absorption of diclofop by susceptible (170415) and tolerant (296292 and Hybrid 894) sunflower lines was similar. Translocation of 14C out of the treated sunflower leaf was greater at 30 (1.3%) than 10C (0.5%) 192 h after treatment when averaged across sunflower lines. The diclofop-susceptible line exported more of the applied diclofop from the treated leaf to the shoot portion below the treated leaf than the tolerant lines. Metabolism of diclofop was more rapid at 30 than 10C; however, the three sunflower lines metabolized diclofop similarly.

Corn (Zea mays L. ‘DeKalb 640′), kidney beans (Phaseolus vulgaris L. ‘Light red’) and oats (Avena sativa L. ‘Kanota’) were grown in solution culture and the roots exposed to radioactively labeled atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine]. The radioactivity from 3H-atrazine, or its metabolites, was located in microautoradiographs of corn leaf sections, almost exclusively at the perimeter of the vascular bundles, and was primarily confined to the cell walls and intercellular spaces, with no activity associated with subcellular organelles. Radioactivity from 3H-atrazine in oat leaf section microautoradiographs was primarily associated with the chloroplasts, with no evidence of radioactivity specifically associated with other subcellular organelles. Sucrose density gradient centrifugation of homogenized leaf tissue following exposure of the plants to 14C-atrazine showed that most of the radioactivity was associated with the light cell fragments and cytoplasm for the test species. There was no accumulation of 14C-activity in any of the heavier subcellular organelles from corn leaf cells. A peak of radioactivity was associated with the chloroplast fraction from oat and kidney bean leaves.

When applied at 0.1 or 0.3 kg/ha, acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} did not reduce rough rice (Oryza sativa L. ‘Labelle’) yield, milling yield, seed weight, seed germination, or plant height, regardless of growth stage. Application of 0.6 kg/ha to rice in the boot, late boot, or panicle filling stage reduced yields, but had no effect on plant height, seed germination, or whole milling yield.

Laboratory experiments were conducted to determine the effect of moisture stress on the absorption and translocation of 14C-labeled picloram (4-amino-3,5,6-trichloropicolinic acid), dicamba (3,6-dichloro-o-anisic acid), and glyphosate [N-(phosphonomethyl)glycine] within the Canada thistle [Cirsium arvense (L.) Scop. # CIRAR] plants. The absorption and translocation of picloram and dicamba were unaffected by moisture stress. Absorption and translocation of glyphosate to the roots and apical meristem of Canada thistle was reduced by increasing moisture stress. Weekly differential irrigation of Canada thistle field plots during the summers of 1980 and 1981 established three soil moisture regimes averaging −6.6, −11.3, and −15.0 bars at the time of herbicide treatment. When Canada thistle control was evaluated 1 year after application of glyphosate, dicamba, and picloram at 2.5, 1.1, and 0.6 kg/ha, respectively, no differences in Canada thistle shoot control were found between moisture stress treatments.

Triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} was aerially applied at four locations in Texas to determine effectiveness of the amine and ester formulations for the control of honey mesquite [Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell # PRCJG]. The ester formulation was superior to the amine in most trials. Honey mesquite control with triclopyr amine was comparable to that with 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] while control with triclopyr ester was similar to that attained with a 1:1 mixture of 2,4, 5-T and picloram (4-amino-3,5,6-trichloropicolinic acid). Honey mesquite control obtained with a 1:1 mixture of 2,4,5-T and dicamba (3,6-dichloro-o-anisic acid) was intermediate between that with the 2,4,5-T and picloram mixture and that with 2,4,5-T alone. Efficacy of triclopyr increased as rates were increased from 0.3 to 0.6 kg ae/ha and from 0.6 to 1.1 kg/ha. Triclopyr formulations were effective when applied in either water or diesel oil/water emulsions. Honey mesquite control from triclopyr in combination with picloram was generally comparable to that from the mixture of picloram and 2,4,5-T.

C4 plants account for a small fraction of the total number of plant species (fewer than 1000 out of 250 000). A larger proportion of the world's weed species possess C4 physiology. There are 2000 species in 500 genera and 125 families of flowering plants listed in the WSSA composite list of weeds. of that number, 146 species in 53 genera and 10 families exhibit the C4 syndrome. This, as a percentage, is 17-fold greater than the percentage of C4 plants in the total world plant population. In this report, we have listed the C4 -weed species and provide specific information concerning various aspects of their Kranz anatomy and C4 physiology.