Field and greenhouse trials have shown that ultra-low-volume applications (ULV) of glyphosate (N-(phosphonomethyl)glycine] exhibit a greater phytotoxic effect on barley (Hordeum vulgare L. ‘Bonanza′) at a given rate than do high-diluent-volume applications with a conventional hydraulic sprayer. Three greenhouse studies and one field trial were conducted to evaluate the influence of individual drop makeup on the effectiveness of ULV applications. Barley plants were treated at the four-leaf stage with one, three, or nine drops (1 μl each) of glyphosate and a non-ionic surfactant with the concentration of the drops adjusted so that the total amount of active ingredient applied to each plant was constant. Application of a single, concentrated drop was significantly more effective in reducing total shoot growth than were applications of more dilute drops in greater number. When the dilute drop was supplemented with additional surfactant, phytotoxicity was restored, provided there was a sufficiently high concentration of glyphosate in the drop. With the substitution of a commercial formulation of glyphosate, the response of barley to variations in drop number and drop concentrations followed a similar trend. The response of field-grown plants did not differ from plants grown under controlled conditions.

Metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] toxicity, absorption, translocation, and metabolism were investigated in corn (Zea mays L.) and yellow nutsedge (Cyperus esculentus L.). Metolachlor did not inhibit seed germination in corn or tuber germination in yellow nutsedge. It did not kill yellow nutsedge tubers that were exposed to 4 ppmw for 9 weeks. Metolachlor (10 ppmw) applied in soil above the seed significantly reduced corn shoot growth, but the same concentration around or below the seed had no effect. A soil mixture with metolachlor (1 ppmw) placed above or around yellow nutsedge tubers significantly reduced shoot growth, but placement around the tuber was the most toxic; placement below the tuber had no effect on shoot growth. The concentration of metolachlor that resulted in 50% reduction of shoot growth of 4-day-old seedlings in solution culture was > 10−4 M for corn and <10−6M for yellow nutsedge. Root-applied 14C-metolachlor was acropetally translocated to shoots of both species following a 7- to 13-day absorption period, with yellow nutsedge translocating the highest portion of the absorbed material to shoots. In 2-day-old seedlings with roots exposed to 14C-metolachlor for up to 48 h, both species absorbed and translocated the radioactivity to shoots, but corn absorbed much more than yellow nutsedge. When the 14C-metolachlor was applied to shoots of both species, the radioactivity was translocated basipetally into roots. Yellow nutsedge exuded appreciable 14C-metolachlor out of the roots and absorbed more 14C-metolachlor through shoot tissues than corn. Both corn and yellow nutsedge seedlings readily converted the 14C-metolachlor to metabolites, but corn was able to metabolize the 14C-metolachlor at a faster rate than yellow nutsedge and also produced more metabolites.

The influence of herbicide formulation and time of herbicide application on smutgrass [Sporobolus poiretii (Roem. & Schult.) Hitchc.] control and phytotoxicity to the major perennial forage-grass species were determined. Dalapon (2,2-dichloropropionic acid) applied at rates of 4.8 kg/ha and higher gave excellent control regardless of time of application. However, 4.8 kg/ha dalapon applied to Pensacola bahiagrass (Paspalum notátum Flügg ‘Pensacola′) and bermudagrass [Cynodon dactylon (L.) Pers.] in the spring, and to tall fescue (Festuca arundinacea Schreb. ‘Ky 31′) in the fall and spring, was phytotoxic. Applications of tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} 80W (80% wettable powder) formulation at 2.4 kg/ha, or fertilizer coated with tebuthiuron at 2.4 kg/ha, gave excellent smutgrass control. The pelleted formulation of tebuthiuron was less phytotoxic to the forage species than the other formulations.

In greenhouse studies, glyphosate [N-(phosphonomethyl)glycine] at 1.0 and 3.0 kg/ha and paraquat (1,1′-dimethyl-4,4-bipyridinium ion) at 0.6 kg/ha were applied to exposed seeds of six grasses and two legume species on continuously wet soil. Glyphosate reduced germination of both legumes and three grasses and reduced seedling growth of all species. Paraquat was toxic only to the grasses. Glyphosate mainly affected germination and growth of legumes when applied directly to their seeds. Reductions also were measured, however, when untreated legume seeds were transferred to glyphosate-treated soil.

Controlled – environment studies were conducted to determine the influence of temperature, light, seed weight, depth of planting, substrate pH, and salinity on the germination and emergence of silverleaf nightshade (Solanum elaeagnifolium Cav.). The effects of planting date, top removal, and root-cutting length on establishment were studied in the field. Fluctuating temperatures of 20 to 30C produced 57% germination. Maximum germination, 59%, occurred between pH 6 and 7. NaCl concentrations greater than 2500 ppmw caused germination to decrease 85% or more compared to the control. Light was not important for germination. Mean seedling emergence was 46% from depths of 1.0 to 2.5 cm. Silverleaf nightshade seedling emergence from a 2-cm depth was 31% greater in a sandy soil than a loam. Delayed seeding caused a decline in dry-weight accumulation of above-ground parts. Fifteen percent of seedlings clipped 15 days after emergence were capable of regrowth, and after 30 days or more, 90% of the clipped plants regrew.

Pennsylvania smartweed (Polygonum pensylvanicum L.) achenes were harvested from plants growing either free from competition or in competition with corn (Zea mays L. ‘Pioneer 3780′) plants. Seeds were dormant when harvested. After 15 weeks of prechilling, 4 and 35% of the seeds germinated from plants with and without corn competition, respectively; after 30 weeks of prechilling, more than 92% of all seeds germinated. Scanning electron microscopy revealed that the carpel walls of achenes from plants with corn competition were porous with many channels. Carpel walls of achenes from plants without corn competition were without pores and channels. Transmission electron microscopy showed more lipid bodies in the embryo epidermal cells of seeds from plants with corn competition. Cell walls of embryos from non-prechilled seeds from plants with corn competition contained lipoidosomes that traversed cell walls. Lipoidosomes did not occur in cells of prechilled seeds.

Percentage canopy reduction of threadleaf snakeweed [Gutierrezia microcephala (D.C.) Gray] and common goldenweed [Isocoma coronopifolia (Gray) Greene] was substantially greater when sprays were applied during the spring of a year characterized by above-average rainfall than in a drought year. Applied at 2 kg/ha or less, 2,4-D [(2,4-dichlorophenoxy)acetic acid] only partially controlled threadleaf snakeweed in either year. Picloram (4-amino-3,5,6-trichloropicolinic acid) or triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} gave satisfactory control of threadleaf snakeweed at 0.5 or 1 kg/ha, depending upon year of application, whereas these treatments were effective against common goldenweed only in the “wet” year. Herbicide 3,6-dichloropicolinic acid tended to be less effective against either species than picloram or triclopyr. Approximately 1 and 2 yr after herbicides were applied, standing forage crop increased 37 and 25 kg/ha, respectively, with each percentage point reduction of threadleaf snakeweed canopy cover.

Addition of a surfactant (alkylaryl polyglycol ether) increased the rate and quantity of 14C-bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] absorbed by leaves of 3-week-old hydroponically grown sunflower (Helianthus annuus L.). Autoradiographs and radioassays of plant parts indicated that the surfactant enhanced acropetal movement of bentazon in sunflower, whereas bentazon applied alone remained in the treated leaves. Basipetal movement of 14C-bentazon was insignificant in sunflower. High-pressure liquid chromatography showed that 3 days after treatment 40% of the absorbed 14C-bentazon was metabolized to a methanol-soluble metabolite. Thinlayer chromatography substantiated the occurrence of a 14C-bentazon metabolite 3 days after treatment.

Field experiments were conducted over a 4-yr period to determine the influence of selected herbicides on ozone injury in tobacco (Nicotiana tabacum L.). Isopropalin (2,6-dinitro-N,N-dipropylcumidine), pebulate (S-propyl butylethylthiocarbamate), and diphenamid (N,N-dimethyl-2,2-diphenylacetamide) were applied at the recommended rates of 1.7, 4.5, and 4.5 kg/ha, respectively. Treatment of tobacco plants with isopropalin or diphenamid reduced oxidant injury for the first 2 to 4 weeks after transplanting, but not later in the season. Pebulate had no consistent affect on the sensitivity of tobacco to ozone.

Plants started with seed, 'seedlings', and established plants of silverleaf nightshade (Solanum elaeagnifolium Cav.) were grown in the field under shade levels of 0, 47, 63, and 92% of full sunlight to determine vegetative, reproductive, and physiological responses to shade. Dry-matter production of both 'seedling’ and established plants declined markedly with increasing shade levels. Established plants did not bear fruit under 92% shade, and 63% shade prevented fruit production by 'seedlings'. Taproots of plants grown in full sunlight contained 16% more total non-structural carbohydrate (TNC) per gram dry weight than taproots of plants grown under 92% shade. Leaves of established plants grown under moderate shade had significantly more chlorophyll per unit leaf fresh weight than plants grown in full sunlight; however, plants under heavy (92%) shade had 35% less chlorophyll per unit leaf area than unshaded plants. The chlorophyll a/b ratio of the 92%-shaded plants was significantly less than with other treatments. Leaf area increased, with increasing shade; however, leaf weight per unit area decreased because of thinner leaves. Photosynthetic rates of recently expanded leaves were 10.4, 4.6, 3.3, and 0.9 mg CO2 · dm−2 · h−1 for the 0, 47, 63, and 92% shade treatments, respectively.

Use of R-25788 (N,N-diallyl-2,2-dichloroacetamide) eliminated early-season corn (Zea mays L. '501D′) injury, stand loss, and yield reduction caused by EPTC (S-ethyl dipropylthiocarbamate) at 3.4, 6.7, and 13.4 kg/ha. R-25788 also eliminated early-season corn injury from butylate (S-ethyl diisobutylthiocarbamate) at 9.0 kg/ha. R-25788 did not consistently prevent corn yield reduction from 2,4-D [(2,4-dichlorophenoxy)acetic acid] or EPTC + 2,4-D. R-25788 had no effect on weed control from any of the herbicides evaluated nor any effect by itself on corn injury or corn yield. No corn injury or yield reductions occurred from vernolate (S-propyl dipropylthiocarbamate) at rates up to 6.7 kg/ha or alachlor [2-chloro-2′, 6′-diethyl-N-(methoxymethyl)acetanilide] at rates up to 13.4 kg/ha. Early-season corn injury frequently did not result in reduced corn yield.

Efficacy of atrazine [2-chloro-4-(ethylamino-6-(isopropylamino)-s-triazine] applied preemergence to no-tillage and conventional-tillage corn (Zea mays L.) was studied in the field for 2 yr at two locations. Other variables examined were lime treatments, atrazine rates, and acid-forming (NH4NO3) vs. nonacid-forming (NaNO3) nitrogen fertilizers. Mean surface soil pH levels during the growing season were higher with no-tillage than conventional tillage, because of the retention of lime in the surface in no-tillage vs. mixing it with the soil in conventional tillage, but there was no consistent increase in atrazine efficacy or longevity in one system over the other. Liming significantly increased atrazine efficacy and longevity in both no-tillage and conventional-tillage systems. Increased rates of atrazine increased weed control and longevity of the herbicide. Use of NaNO3 as a nitrogen source resulted in increased atrazine efficacy and longevity as compared with use of NH4NO3 during the first year, which was relatively dry, but had no effect during the second year, which was relatively wet.

Analysis of reciprocal F1, F2, F3, and backcross progeny from crosses between atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine]-resistant and several susceptible genotypes of Brassica campestris L. indicated that triazine resistance was inherited cytoplasmically from the female parent. A partially dominant chlorotic cotyledon was used as a genetic marker to confirm true hybrids in the reciprocal F1 progenies. Phytotoxicity of atrazine was correlated with loss of the Hill reaction.

Germination of prostrate spurge (Euphorbia supina Raf.) seeds collected in August, September, October, and November 1977 at Riverside, California was 53, 30, 18, and 16%, respectively. Stratification of seeds collected in August, September, and October at 5 C for 3 weeks or more increased germination to 70 to 80%. Prostrate spurge seeds germinated at constant temperatures of 20 to 40 C, with optimum temperatures of 25 to 30 C. Maximum germination occurred under alternating temperatures with a high temperature of 30 to 35 C and a low temperature of 15 to 25 C. Germination in the dark was much lower than in the light. Seedling establishment of seeds collected in August sown at 0.0- to 0.5-cm depths was 30 to 35%, but establishment from 2 cm declined to near 0%. Light intensity did not affect the number of seedlings established, but the seedlings established were larger under higher light intensities.

Field experiments were conducted to study the feasibility of applying glyphosate [N-(phosphonomethyl) glycine] postemergence with a recirculating sprayer and a vertical roller for the control of common lambsquarters (Chenopodium album L.), common sunflower (Helianthus annuus L.), kochia [Kochia scoparia (L.) Schrad.], redroot pigweed (Amaranthus retroflexus L.), and velvetleaf (Abutilon theophrasti Medic.) in sugarbeets (Beta vulgaris L.). Glyphosate was applied twice each year at 1.7 kg/ha with a recirculating sprayer in 1977 and 1978, or twice as a 20% (v/v) solution with a vertical-roller applicator in 1979. By harvest, 70 to 74% of the total population of treated common sunflower, kochia, and redroot pigweed, 61% of the common lambsquarters, and 30% of the velvetleaf was dead. Root yields in glyphosate-treated plots, when averaged over 3 yr, were increased 5800, 8500, 12 500, and 13400 kg/ha at densities of 6, 12, 18, and 24 broadleaf weeds (equal densities of common lambsquarters, kochia, and redroot pigweed)/30m of row, respectively. Where equal densities of common sunflower and velvetleaf competed with sugarbeets, root yields in glyphosate-treated plots, when averaged over 2 yr, were increased 4400, 11900, 11700, and 10700 kg/ha, respectively, at these same densities.

Lath-house experiments were conducted to compare the effect of wild oat (Avena fatua L.) competition on two wheat (Triticum aestivum L. ‘Anza’ and T. turgidum durum group ‘Mexicali′) genotypes at three nitrate concentrations. Plants were grown to maturity in pots containing 10 wheat or wild oat plants, or mixtures of 10 wheat and 10, 25, or 50 wild oat plants. Nitrate was supplied in 500 ml Hoagland's solution with 1.5, 7.5, or 15.0 mM nitrate, as K and Ca nitrate, every 4 days. When grown without competition, Anza had more above-ground plant weight and grain yield and less whole-plant percent nitrogen than Mexicali. Wild oat competition caused larger reductions in plant weight and grain yield, and smaller reductions in percent nitrogen for Anza than for Mexicali. Wild oat competition reduced the effectiveness of nitrate in increasing plant weight, grain yield, and whole-plant percent nitrogen of wheat.

Greenhouse and field experiments were conducted with a roller applicator at Lincoln, Nebraska, during 1979 and 1980. Glyphosate [N-(phosphonomethyl)glycine] concentrations of 5, 10, and 20% and carpet saturations of 50 and 75% controlled shattercane [Sorghum bicolor (L.) Moench] when applied to the top 30 cm of the plant in greenhouse research. In the field, glyphosate concentrations of 5 to 20% with a carpet saturation of 50% controlled shattercane acceptably in soybeans [Glycine max (L.) Merr.], but a concentration of 2.5% with 25% carpet saturation did not. Weed control was comparable whether speed of application was 3.2, 6.4, or 9.6 km/h. Shattercane control in grain sorghum [Sorghum bicolor (L.) Moench.] was excellent at glyphosate concentrations of 5, 10, and 20% and at carpet saturations of 50 and 75%, and sorghum injury was minimal at 25 and 50% carpet saturations. The roller applicator was compared to a ropewick applicator for shattercane control in sorghum. Excellent weed control (90% or greater) with minimal crop injury was obtained with the roller applicator at glyphosate concentrations of 10 and 20% at application speeds of 3.2 and 6.4 km/h and with the ropewick applicator with glyphosate concentrations of 35 and 50% applied at 3.2, 6.4, and 9.6 km/h.

Aerial applications of pelleted tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} at 0.5 kg/ha reduced creosotebush [Larrea tridentata (DC.) Coville] density by up to 86% and by 99% when applied at 1 kg/ha in February or March. Grass production 32 months after treatment was 174 to 305% greater in tebuthiuron-treated plots than on untreated ran gel and, but forb production in treated plots was reduced 38% or more and the poisonous half-shrub broom snakeweed [Gutierrezia sarothrae (Pursh) Britt. and Rusby] was reduced 94% or more.

Cotton (Gossypium hirsutum L.) response was evaluated when propanil (3′,4′-dichloropropionanilide), thiobencarb {S-[(4-chlorophenyl)methyl] diethylcarbamothioate}, 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], bifenox [methyl-5-(2,4-dichlorophenoxy)-2-nitrobenzoate], acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid}, and metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] were applied over-the-top at simulated drift rates at two growth stages during 1975 to 1979. No rate of butachlor or thiobencarb injured cotton. The order of phytotoxicity for the herbicides applied to cotyledonary cotton was propanil > metribuzin > bifenox > oxadiazon > acifluorfen > butachlor = thiobencarb. Herbicides injured cotton less at the five- or eight-node stage than at the cotyledonary stage. Injury was more severe in seasons of wet or cold weather during early plant development.

Glyphosate [N-(phosphonomethyl)glycine] applied at 1.1 kg/ha to wheat [Triticum aestivum (L.) ‘Arthur 71′] plants increased height and fresh weight of soybean [Glycine max (L.) Merr. ‘Ransom′] seedlings planted in the pot at time of application of the glyphosate as the number of wheat plants treated increased from 5 to 30/pot. Height and fresh weight of the soybean seedlings also increased as the rate of glyphosate applied to wheat plants (5/pot) increased from 1.1 to 6.7 kg/ha. Increasing the rate of glyphosate from 1.1 to 6.7 kg/ha, however, reduced the height and fresh weight of soybeans when 30 wheat plants/pot were treated. In addition, when 6.7 kg/ha of glyphosate were applied to wheat plants, soybean-seedling plant height and fresh weight decreased as the density of wheat plants per pot increased from 5 to 30. The 14C-glyphosate exuded into the soil from treated wheat plants was characterized by thin-layer chromatography. Trace amounts of the radio-label were present on thin-layer plates of leaf and stem extracts of corn (Zea mays L.) plants, which were growing in the same pots with the treated wheat plants. The zone of activity had the same Rf value as the glyphosate standard.