A herbicide safener, CGA-43089 [α-(cyanomethoximino)-benzacetonitrile], has been discovered which will allow the safe use of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethylacetamide] in grain sorghum [Sorghum bicolor (L.) Moench]. Experiments revealed that sorghum is protected from injury by metolachlor when it is applied at rates as high as 4 kg/ha. Better protection was achieved when sorghum seed were treated directly with the safener than when it was mixed with the herbicide. A CGA-43089 rate of 1.25 to 1.5 g per kg of sorghum seed was adequate for protection. Sorghum tolerance to metolachlor was maintained with CGA-43089 when metolachlor was combined with several s-triazine herbicides. Metolachlor effectively controlled several annual grasses with an increase in sorghum yield.

CGA-43089 [α-(cyanomethoximino)-benzacetonitrile] applied as a seed treatment enables sorghum [Sorghum bicolor (L.) Moench] to tolerate metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide]. Improved tolerance of alexandergrass [Brachiaria plantaginea, (Link) A. Hitchc.] Eleusine spp., proso millet (Panicum miliaceum L.) and rice (Oryza sativa L.) to metolachlor also was demonstrated. Seven sorghum cultivars, representing widely divergent types of germplasm, responded similarly to the safening effect of CGA-43089 when the cultivars were exposed to metolachlor. Treated sorghum seed may be stored more than 1 yr without a loss of safening activity. In these growth chamber experiments, neither extremes of soil moisture nor temperature reduced the effectiveness of the safener. The predominant site of uptake of CGA-43089 is the coleoptile of sorghum seedlings.

Fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4 (1H)-pyridinone} and R-4-0244 [1-(m-trifluoromethylphenyl)-3-chloro-4-chloromethyl-2-pyrrolidone], herbicides that block carotenoid synthesis, increase the sensitivity of corn (Zea mays L. ‘Merit’) to exogenously-applied gibberellic acid (GA). Increase in shoot length due to the application of GA to imbibing corn seeds was considerably enhanced by simultaneously applying either fluridone or R-40244. Fluridone was more active in this respect than R-40244.

Low recoveries of total applied 14C in translocation studies and erratic control of hemp dogbane (Apocynum cannabinum L.) in the field showed a need for a balance-sheet study of absorption, translocation, and metabolism of 14C-2,4-D [(2,4-dichlorophenoxy) acetic acid] and 14C-glyphosate [N-(phosphonomethyl)glycine]. Total recovery of 14C-herbicides applied to hemp dogbane in the laboratory was 97% for 2,4-D and 105% for glyphosate. Of the 14C recovered after 12 days in the hemp dogbane, 34 to 55% was parent-2,4-D after 2,4-D treatment, and 93 to 96% was parent glyphosate after glyphosate treatment. Only negligible amounts of 14C were lost via volatilization or evolution as 14CO2. A broadcast treatment with unlabeled herbicide did not significantly affect subsequent absorption, translocation, or metabolism of either herbicide. Total herbicide absorbed and translocated out of the treated area of the leaf generally increased during the subsequent 12 days for 2,4-D but only 3 days for glyphosate. A greater percentage of the total applied 2,4-D (31 vs. 14%) and glyphosate (14 vs. 8%) was translocated from upper rather than lower leaves of hemp dogbane, respectively. Higher temperatures (30 vs. 25 C) resulted in greater translocation of glyphosate (39 vs. 18%) but not 2,4-D (35 vs. 39%). Higher light intensities resulted in greater accumulations of 2,4-D into roots and of glyphosate into untreated areas of the treated leaf. Autoradiographs showed that both herbicides moved through hemp dogbane in a typical symplastic pattern and accumulated in roots and new leaves.

Three microcapsule formulations, two starch xanthate formulations, and one commercial formulation of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) were evaluated in the greenhouse and field for their relative herbicidal efficacy and persistence. Biological assays with Italian ryegrass (Lolium multiflorum Lam.) revealed significant differences among the formulations in phytotoxicity and persistence. The commercial formulation of trifluralin was generally more phytotoxic than the others to Italian ryegrass sown the week of herbicide application. The two starch xanthate formulations and one microcapsule formulation of trifluralin were generally more phytotoxic and more persistent than the commercial formulation to Italian ryegrass sown from 1 through 19 weeks after herbicide application.

In field plots, Japanese millet [Echinochloa crus-galli (L.) Beauv. var. frumentacea (Link) W. F. Wight] competed strongly with yellow nutsedge (Cyperus esculentus L.), reducing its dry weight and the number of plants and tubers with no loss of dry weight to the millet. Because Japanese millet did not shade the nutsedge for more than half the day, the main competition was thought to be ‘root’ competition (nutrient and water) with light competition as a minor factor. The greenhouse studies verified that roots were the primary area of competition. However, light competition between the two species was stronger in the greenhouse than in field plots. Also, when confined to limited light and soil volumes with a 1-month growing period, Japanese millet was reduced in dry weight by nutsedge competition.

The host specificity of mullein moth (Cucullia verbasci L.) [Lepidoptera: Caradrinidae (Noctuidae)] and its suitability as a biological control agent of the common mullein (Verbascum thapsus L.) (Scrophulariaceae) were investigated. Thirty-six plant species in 10 families were tested but sustained feeding by the insect and consistent development occurred only on mullein species. Nibbling on plants other than on mulleins did not prolong the life of the insect significantly longer than larvae without food. Thus, the mullein moth is considered to be a safe agent to release against mullein.

When glyphosate [N-(phosphonomethyl)glycine] was fed through the transpiration stream of excised bean (Phaseolus vulgaris L. ‘Red Kidney’) shoots, it was readily absorbed and transported to the leaves where it inhibited transpiration. Maximum inhibition (40 to 50%) resulted from tissue concentrations of 50 to 3000 nmoles glyphosate/g fresh weight, while transpiration was significantly inhibited (20%) by as little as 15 nmoles/g fresh weight. A combination of 5 X 10-4M tyrosine (Tyr) and 5 x 10-4M phenylalanine (Phe) supplied continuously through the transpiration stream prevented the inhibition of transpiration by glyphosate during the course of 8-h experiments. Tyrosine (10-3M) alone delayed the transpiration response to glyphosate by 2 to 3 h but 10-3M Phe alone did not affect the inhibition by glyphosate. Levels of endogenous Tyr and Phe were about 50% lower in glyphosate-treated leaves than in the controls 6 h after treatment.

Field trials conducted in the three major peppermint-producing regions of Oregon showed that repeated applications of bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] at 2.2 kg/ha controlled Canada thistle [Cirsium arvense (L.) Scop.] in peppermint (Mentha piperita L.) selectively. Repeat applications of 2.2 kg/ha controlled Canada thistle better than single applications of 3.4, 4.5, or 6.7 kg/ha. Late May or June applications were more effective than early May applications. The number of Canada thistle shoots was reduced 82% 10 months after repeat applications but had almost returned to the original number 22 months after application. Basipetal translocation of bentazon was demonstrated by observing bentazon injury symptoms on untreated Canada thistle shoots which were attached by a root to bentazon-treated shoots.

The relationship between herbicide injury and soybean [Glycine max (L.) Merr. ‘Amsoy 71’] yield response was studied under weed free conditions at three locations. Reduced crop vigor at early growth stages was not an adequate indicator of yield response. Yield reduction was greater when soybean stand was reduced by herbicides than when stand was reduced to the same level by hand thinning. Yield response was a function of the degree and persistence of crop vigor reduction in a reduced stand of soybeans.

Soybeans [Glycine max (L.) Merr.] and oats (Avena sativa L.) were grown in a rotation using reduced or no-tillage crop production systems at Lincoln, Nebraska, over a 4-yr period. Oat stubble was treated after harvest with 3.4 kg/ha of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] to reduce the growth of late summer weeds. The following spring soybeans were planted directly into the undisturbed stubble or into a seedbed prepared by tandem discing. Three seedbed preparations, two soybean cultivars, and six preemergence weed control treatments were compared. Glyphosate [N-(phosphonomethyl)glycine] applied at 0.8 kg/ha or tandem discing were equally effective in producing a weed-free seedbed. Herbicides applied preemergence on soybeans were still necessary for the reduced tillage or no-tillage production systems if weeds were to be adequately controlled in soybeans without cultivation. Differences in seed-yield occurred between cultivars only when late summer rains benefited the later maturing ‘Williams' soybeans over earlier maturing ‘Wells'. With adequate weed control, soybeans and oats can be grown in a no-tillage, crop rotation, production system in eastern Nebraska to produce high yields with a minimum of labor and soil exposure.

Soil-active herbicides were investigated for control of live oak (Quercus virginiana Mill.) on the Texas Coastal Prairie and Claypan areas with and without mechanical treatment. Roller chopping before, during, or after herbicide application had very little influence on mortality of live oak compared to the herbicide applied alone. Roller chopping did allow increased grazing of livestock for at least 3 yr after knockdown of the brush. Tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} was generally the most effective herbicide for live oak control; bromacil (5-bromo-3-sec-butyl-6-methyluracil), karbutilate [tert-butylcarbamic acid ester with 3(m-hydroxyphenyl)-1,1-dimethylurea], and picloram (4-amino-3,5,6-trichloropicolinic acid) were somewhat less effective, especailly at 2.2 kg/ha. Limited data suggested that hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl]-1,3,5-triazine-2,4(1H,3H)-dione] also was highly effective for control of live oak. Primary invaders on either mechanically or chemically treated areas were American beautyberry (Callicarpa americana L.), southern dewberry (Rubus trivialis Michx.), boneset (Eupatorium perfoliatum L.), yankeeweed (Eupatorium compositifolium Walt.), brownseed paspalum (Paspalum plicatulum Michx.), and carpetgrass (Axonopus affinis Chase). A herbicide was generally equally effective for live oak control whether applied broadcast or in rows as granules, or applied as sprays to the soil surface or subsurface.

Field experiments were conducted to determine optimum nozzle settings for applying glyphosate [N-(phosphonomethyl)glycine] in the recirculating sprayer for postemergence control of johnsongrass [Sorghum halepense (L.) Pers.] in soybeans [Glycine max (L.) Merr.]. Herbicide sprays were directed across the row to johnsongrass growing taller than soybeans in July and August. Herbicide not sprayed on johnsongrass was trapped and reused. Glyphosate at 0.56, 1.12, and 2.24 kg/ha applied with commercially available 25° spray nozzles provided johnsongrass control and soybean yields equal to those following applications with specialized uniform droplet nozzles. Glyphosate at 1.7 kg/ha applied in the recirculating sprayer using only one nozzle per row provided control of johnsongrass equal to or better than that from applications made with two, three, or four nozzles per row. Soybean yield following application of glyphosate at 1.7 kg/ha with one nozzle per row was equal to yields obtained following its application with two, three, or four nozzles per row, with or without surfactant at 0.1% in spray solutions. Soybean yield was higher with four nozzles per row than with one nozzle per row when 0.5% surfactant was included in spray solutions. Soybean injury was lower and yield was higher when glyphosate was applied in the recirculating sprayer rather than over-the-top with a conventional sprayer. Glyphosate at 1.12 kg/ha applied in the recirculating sprayer caused more injury to ‘Hill’ and ‘Bragg’ than to ‘Forrest’ or ‘Tracy’ soybeans.

Caryopses (seeds) of fall panicum (Panicum dichotomiflorum Michx.) have a dormancy that is not easily overcome. Although accelerated after-ripening for 4 weeks was partially successful in overcoming dormancy, a dark imbibition at 35 C for about a week was more effective and also interacted strongly with an accelerated after-ripening. In either case, activation of phytochrome by red irradiation was required to induce germination. Similarly, alternating temperatures allowed germination of red-treated seeds but constant temperatures did not. More seeds germinated in sealed flasks than in dishes. The enhancement of germination in sealed flasks appeared to be related to increased CO2 levels. The data suggested a multiple dormancy in fall panicum seeds. One dormancy, the most intense, was relieved by high-temperature imbibition. The residual dormancy was relieved by active phytochrome and alternating temperatures.

The distribution of sicklepod (Cassia obtusifolia L.) and coffee senna (Cassia occidentalis L.) in the United States is similar and both species are increasing as problems within their range. Sicklepod is a problem in 11 southern states and increasing in 12 while coffee senna is a problem in 7 states and increasing in 8 states. Both species germinated over a wide range of temperature. Germination characteristics were similar in the range of 15 to 36 C. Germination of coffee senna was drastically reduced at 39 C by Rhizopus sp. Seedling growth was similar for both species and was maximum from 30 to 36 C. Both species have a hard seedcoat. Abrasion for 5, 10, or 15 s, puncturing with a needle, and sulfuric acid were all effective in initiating germination. Both species emerged from a soil depth of 12.5 cm; however, emergence of sicklepod was more rapid than coffee senna with 63% of the sicklepod seedlings emerging from 2.5 cm after only 3 days.

Mathematical growth analysis techniques were used to evaluate the effects of CO2 concentrations of 350, 600, and 1000 ppm (v/v) on growth and biomass partitioning in corn (Zea mays L. ‘Dekalb XL 395’), itchgrass (Rottboellia exaltata L. f.), soybean [Glycine max (L.) Merr. ‘Tracy’], and velvetleaf (Abutilon theophrasti Medic). Controlled environment chambers with day/night temperatures of 28/22 C and photosynthetic photon flux densities (PPFD) of 650 μE (microeinsteins) m-2 s-1 were used. Dry matter production in the two C3 species (soybean and velvetleaf) was increased significantly by raising the CO2 concentration above 350 ppm. In corn (a C4 species), dry matter production was least at 1000 ppm CO2 and did not differ between the 350 and 600 ppm treatments. In itchgrass (also C4), dry matter production was greatest at 600 ppm CO2 and did not differ between the 350 and 1000 ppm treatments. Increasing the CO2 concentration increased the rate of dry matter production per unit leaf area (net assimilation rate or NAR) in soybean and velvetleaf but either decreased or did not alter NAR in corn and itchgrass. At 45 days after planting, the weed/crop ratios for total dry matter production for velvetleaf/corn and itchgrass/corn were significantly greater at both 600 and 1000 ppm than at 350 ppm CO2. The weed/crop ratio for itchgrass/soybean was less at 1000 ppm than at 350 or 600 ppm CO2. Compared to the value at 350 ppm, the weed/crop ratio for velvetleaf/soybean was greater at 600 ppm and less at 1000 ppm CO2. We conclude that atmospheric CO2 enrichment probably will make weeds with the C3 photosynthetic pathway more competitive with crops having the C4 pathway. Weeds with the C4 pathway may become less competitive with crops having the C3 pathway.

Seed germination responses to temperature and osmotic stress were determined for smallflower morningglory [Jacquemontia tamnifolia (L.) Griseb.] and seven species of Ipomoea. Cypressvine (I. quamoclit L.), willowleaf (I. wrightii Gray) and smallflower morningglory germinated and seedlings developed more slowly than the other morningglories at 16 C. Maximum germination of ivyleaf [I. hederacea (L.), Jacq. var. hederacea], entireleaf [I. hederacea (L.) Jacq. var. integriuscula Gray], pitted (I. lacunosa L.), tall [I. purpurea (L.) Roth], cotton (I. trichocarpa Ell.), and smallflower morningglories occurred in 24 h at 20 C. Cypressvine and willowleaf morningglories reached maximum germination in 24 h at 24 C. Optimal root-hypocotyl development occurred at 24 C for pitted, tall, and willowleaf morningglories, while all other species required a temperature of 28 C for maximal root-hypocotyl development in 4 days. Increasing osmotic pressure decreased or delayed germination of all morningglory species. Species tolerance to osmotic stress during germination could be ranked, most to least tolerant, as follows: ivyleaf=entireleaf>pitted=cotton>tall = willowleaf>cypressvine=smallflower. Maximum germination was delayed approximately 24 h for each 2 bar increment increase in osmotic pressure.

Low species diversity accompanied high populations of Canada thistle [Cirsium arvense (L.) Scop.]. Two perennial grasses and two rushes grew with Canada thistle; annual plants did not. Canada thistle litter, ground roots, and ground foliage added to soil in greenhouse bio-assay tests reduced growth of redroot pigweed (Amaranthus retroflexus L.) and green foxtail [Setaria viridis (L.) Beauv.] more than cucumber (Cucumis sativis L.) or barley (Hordeum vulgare L.). The addition of nutrients did not mask the toxic effect. Ethanolic extracts of Canada thistle roots and foliage were similar in their ability to reduce radicle growth of barley, cucumber, green foxtail, and redroot pigweed in petri dish studies. There was no significant difference between water controls and controls adjusted to the average pH and osmotic potential of the extracts. Germination of barley and cucumber seed was not affected. Comparisons between ethanolic extractions and soil incorporation of plant residues with presumably non-allelopathic plants revealed that cucumber and barley extracts reduced redroot pigweed radicle growth whereas barley and green foxtail extracts increased green foxtail radicle growth. These effects were not observed when these plant residues were mixed in soil.

Studies were conducted in 1977 and 1978 to evaluate the impact of surface irrigation water on the dissemination of weed seed in the North Platte River Project from May through September each year. Seventy-seven different plant species were found in irrigation water, with germination averaging 26%. Two to five times more weed seed were found in two irrigation canals than in the North Platte River. As water moved through the canals, the weed seed content of the water increased dramatically. The majority of seed collected was found floating on the water surface. Amounts of seed collected varied with time with the largest amounts being collected in June and July and gradually declining in August and September. Samples also were taken to determine the amount of seed entering the field with irrigation water during the growing season. During the 1978 growing season irrigation water disseminated 48,400 seed per ha in the sampled fields.

The effects of temperature, relative humidity (RH) and light on absorption and translocation of 14C-glyphosate [N-(phosphonomethyl)glycine] in common bermudagrass [Cynodon dactylon (L.) Pers. ‘Common’] and the effect of temperature and stage of growth on glyphosate activity in horsenettle (Solanum carolinense L.) were determined. 14C-glyphosate was used to evaluate the absorption and translocation of foliar-applied herbicide in bermudagrass plants grown at 22 or 31 C and 35 or 80% RH and absorption in excised leaf tips and stem sections. Autoradiography of bermudagrass indicated that downward translocation of 14C was extensive with large accumulations in new roots and rapidly growing stolons. RH of 35% decreased 14C-glyphosate translocation to the untreated foliage of plants grown at 31 C as compared to 80% RH. RH of 35% also decreased the translocation of 14C to the rhizomes and roots of plants grown at 22 C. The absorption of 14C was greater in excised leaf tips than stem sections and was greater in the light than in the dark. Horsenettle plants grown at 32 C had shoots which were more rapidly killed by glyphosate but had more regrowth than plants treated at 13 C. Shoots of plants treated while blooming were also more rapidly killed than those treated in the prebloom stage of growth, but the regrowth was not significantly different.