Horseweed has become increasingly common and difficult to control in San Joaquin Valley vineyards, due in part, to the evolution of glyphosate resistance. The development of weed-suppressive vineyard designs in which the trellis design, spacing, and row orientation combine to cast dense shade on the weed canopy zone (WCZ) may reduce weed growth. The relevance of such a system to horseweed, which can grow to be as tall, or taller, than a typical grapevine trellis, is uncertain. Also unknown is whether a glyphosate-resistant (GR) biotype and glyphosate-susceptible (GS) biotype would perform similarly under such conditions. Therefore, we compared the growth and development of two potted horseweed biotypes (GR and GS) in vinerows oriented east–west (EW) and north–south (NS). Rows oriented EW allowed less light penetration to the WCZ than NS rows throughout the study, and horseweed biotypes responded to low light levels by producing leaves with larger specific leaf area and leaf area ratios than those in the NS rows. Also, the leaf, stem, and root dry weight of the horseweed plants in the EW rows was reduced by 30% compared to the horseweed plants in NS rows. Leaf number was also reduced in the horseweed plants in the EW rows, but only for the GS biotype. Row orientation did not affect phenological development or the number of seeds produced by the GR or GS biotypes, but the GR biotype budded, flowered, and set seed approximately 1 wk earlier than the GS biotype. Thus, shade associated with the EW vinerows reduced horseweed growth, but not fecundity, and the GR biotype reached reproductive maturity earlier than the GS biotype.

Various chemical and cultural treatments were evaluated for smutgrass [Sporobolus poiretii (R.&S.) Hitchc], control and their effects on pangolagrass (Digitaria decumbens Stent.) and bahiagrass (Paspalum notatum Flügge). Herbicide treatments were dalapon (2,2-dichloropropionic acid) at 1.7, 3.3, and 5.0 kg/ha with Sunoco HE spraying oil at 0, 9.4, 19.0 and 37.0 L/ha. Five weeks after herbicide treatment plots were clipped (clipped vs. nonclipped) and fertilized (0 vs. 112 kg/ha N). Increasing dalapon from 1.7 to 5.0 kg/ha increased smutgrass control and decreased the number of smutgrass plants/plot. Pangolagrass ground cover generally increased with fertilization, as the rate of dalapon increased up to 3.9 kg/ha. Bahiagrass ground cover decreased with rates of dalapon above 1.7 kg/ha. Increasing the rate of oil increased bahiagrass ground cover after 90 days. Nitrogen applied 5 weeks after dalapon treatment and semi-annually for 5 yr generally decreased ground cover of smutgrass and bahiagrass, but increased pangolagrass. Clipping treated smutgrass plants increased pangolagrass and bahiagrass ground cover while decreasing the ground cover of smutgrass.

The responses of established, spaced-planted strains of johnsongrass (Sorghum halepense (L.) Pers.) to repeated, foliar applications of herbicides were studied under irrigated desert conditions. Monosodium methanearsonate (MSMA) and disodium methanearsonate (DSMA) were the most effective herbicides. Six to 10 applications with 3 to 6 lb aihg of either herbicide (totaling 24 to 60 1b/A) killed johnsongrass in most experiments. Treatments initiated in the fall were more effective than similar treatments started in the spring. Higher rates of organic arsenicals were required to destroy topgrowth of johnsongrass in the spring and fall than during the summer. DSMA applications at 4 and 6-week intervals were more effective than applications at 8-week intervals. Six 1b/A of DSMA in 100 gpa of water applied broadcast was as effective as 400 gpa containing 6 lb aihg of DSMA applied as a spot treatment. Removing topgrowth of johnsongrass 4 or 24 hr after treatment did not reduce the effectiveness of DSMA. Combining or alternating organic arsenicals with 2,2-dichloropropionic acid (dalapon) reduced the effectiveness of the arsenicals. Susceptible strains were destroyed by five or six applications of DSMA and MSMA while 9 or 10 applications were needed to kill more resistant strains.

The growth of wild oat (Avena fatua L. ♯3 AVEFA) under different moisture regimes was investigated under field conditions and in a growth chamber. In the field, growth of wild oat under low moisture conditions (0.6 cm water per week – Regime 1) was significantly reduced compared to growth under high moisture conditions (2.5 cm water per week – Regime 2). Maximum reductions of 49, 33, and 38% were recorded in the leaf area, dry weight, and number of viable tillers, respectively. The growth of wild oat in soil watered daily to a soil moisture content (SMC) of 10% (water potential −6.5 bars) in the growth chamber was less than for plants in soil watered daily to 20% SMC (-0.3 bars). Maximum reductions of 55, 57, and 38% were recorded in the leaf area, dry weight, and number of viable tillers, respectively. Wild oat growth was more adversely affected by reducing the SMC from 20 to 10% after, rather than before, the four-leaf stage. By the last sampling date, stomatal diffusion resistance of the most severely water-stressed plants was 25 s·cm-1 compared to between 5 and 10 s·cm-1 for the plants receiving more water.

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.

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.

Research was conducted to determine percentage excretion and germination or viability of common crupina (Crupina vulgaris Cass. # CJNVU) achenes fed to sheep (Ovis aries), cattle (Bos taurus), deer (Odocoileus hemionus), horses (Equus cabullus), and Chinese pheasants (Phasianus colchicus). No achenes were found in the feces of sheep. Horses (nonruminant), deer, and cows (both ruminant animals) excreted 5, 3, and 25%, respectively, of the achenes consumed. The mean percentage achene excretion for pheasants was 23%; however, excretion was highly variable among individuals. All achenes excreted by any test species were detected within 5 days after consumption. The percentage germination or viability of excreted achenes ranged from 29% (cows) to 81% (deer). The percentage of consumed achenes that were excreted and viable ranged from 2 to 7% for large animals, whereas it was 17% for pheasants.

Greenhouse-grown kochia [Kochia scoparia (L.) Schrad. # KCHSC] seedlings from populations having either a 13-yr triazine history or no triazine history were sprayed postemergence with 0, 2, or 20 kg/ha atrazine [6-chloro-N-ethyl-N′-[1-methylethyl)-1,3,5-triazine-2,4-diamine]. Fresh weight was reduced 20% in triazine history kochia treated with 20 kg/ha atrazine. Seedlings with no triazine history were killed by 2 kg/ha atrazine. Biotypes resistant to atrazine were also resistant to five other triazine herbicides. Biotypes susceptible to atrazine were susceptible to the other triazines. Atrazine-resistant biotypes were more susceptible to 2,4-D [(2,4-dichlorophenoxy)acetic acid] than atrazine-susceptible biotypes, but atrazine history had no effect on response to diuron [N′-(3,4-dichlorophenyl)-N,N-dimethylurea].

The phytotoxicity of barban (4-chloro-2-butynyl m-chlorocarbanilate) applied 14 days after emergence to wheat (Triticum aestivum L. ‘Waldron’) and wild oat (Avena fatua L.), at constant, fluctuating or alternating day-night temperatures was determined in controlled environmental chambers. Wheat and wild oat susceptibility to barban increased as post-treatment temperature decreased. Maximum barban selectivity for wild oat in wheat occurred with a constant 18 C or an alternating 18 C day and 10 C night post-treatment temperature. At least three days of 10 C immediately following barban application were necessary to cause wheat injury. However, two days at 29 C immediately after barban application in an otherwise 10 C post-treatment regime reduced wheat injury. Further, a night temperature lower than the day temperature after barban application increased wild oat control but did not correspondingly increase wheat injury compared to the constant temperature treatments.

Ridge-till is an integrated weed management system that involves the physical movement of soil containing weed seeds away from the row with ridge-clearing equipment on the planter. Corn, grain sorghum, and soybean are the major crops planted using the ridge-till system. Weeds can be controlled with cultivation, competitive row crops, and herbicides. Weeds have adapted to the system but have been controlled through alternative management. Through modernization of equipment and herbicides, ridge-till has become an economic crop production practice. Integrating cultivation and herbicides controls a broader spectrum of weeds than cultivation or herbicides alone.

The effects of 3,5-dibromo-4-hydroxybenzaldehyde O-(2,4-dinitrophenyl)oxime (hereinafter referred to as C-9122), 3,5-dibromo-4-hydroxybenzonitrile (bromoxynil), 3,5-dibromo-4-hydroxybenzaldoxime (hereinafter referred to as bromoxime), and 2,4-dinitrophenol (hereinafter referred to as DNP) on phosphorylation and electron transport were measured in mitochondria isolated from white potato tubers (Solarium tuberosum L.) and in chloroplasts from spinach leaves (Spinacia oleracea L.). Mitochondrial oxygen utilization was monitored polarographically. All four chemicals stimulated ADP-limited oxygen utilization, inhibited non-ADP-limited oxygen uptake, and relieved oligomycin-inhibited oxygen uptake. C-9122 produced responses at lower molar concentrations than did bromoxynil, bromoxime, and DNP. The I50 value for inhibition of state 3 respiration by C-9122 was 2.7 × 10−6 M.

In chloroplasts, C-9122, bromoxime, and DNP inhibited photoreduction and coupled photophosphorylation with water as the electron donor, and with ferricyanide and NADP as electron acceptors. Cyclic photophosphorylation, with phenazine methosulfate as the electron mediator under an argon gas phase, also was inhibited. With ascorbate-2,6-dichlorophenolindophenol (hereinafter referred to as DPIP) as the electron donor, phosphorylation coupled to NADP reduction was inhibited, but not the reduction of NADP. C-9122 was the strongest inhibitor, and bromoxime was the weakest inhibitor of the several reactions. The I50 value for inhibition of the coupled ferricyanide reduction was 4.6 × 10−6 M for C-9122. C-9122 appeared to act in two different ways by (a) inhibiting electron transport at or near photosystem II and the oxygen evolution pathway, and (b) interfering with energy transfer and the generation of ATP. Bromoxynil inhibited photoreduction and photophosphorylation reactions in which water served as the electron donor; but it was a very poor inhibitor of both cyclic photophosphorylation, and photophosphorylation coupled to NADP reduction with ascorbate-DPIP serving as the electron donor. Because of the pivotal role of ATP in cellular metabolism, it is conceivable that interference with ATP generation could be a major (but not necessarily the only) mechanism through which the herbicidal activity of C-9122 is expressed.

Several herbicides were tested in the greenhouse on ivyleaf morningglory (Ipomoea hederacea (L.) Jacq.), green foxtail (Setaria viridis (L.) Beauv.), purple nutsedge (Cyperus rotundus L.), and quackgrass (Agropyron repens (L.) Beauv.) to determine the degree of enhancement in activity that could be obtained with an isoparaffinic oil carrier applied at 140 L/ha. The enhancement varied with the herbicide and with the species, ranging from 16-fold enhancement with 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) and 2-sec-butyl-4,6-dinitrophenol (dinoseb) on ivyleaf morningglory to no enhancement of atrazine activity on purple nutsedge and quackgrass or (2,4-dichlorophenoxy)acetic acid (2,4-D) activity on quackgrass and ivyleaf morningglory. An oil adjuvant was less effective in enhancing dinoseb and 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron) activity than was the isoparaffinic oil carrier. Also, the isoparaffinic oil carrier emulsified in water was less effective than the undiluted oil in enhancing dinoseb activity on green foxtail, even though equal volumes of the isoparaffinic oil were applied.

The methyl ester of thiameturon {3-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] amino] sulfonyl]-2-thiophencarboxylic acid} toxicity to kochia [Kochia scoparia (L.) Schrad. # KCHSC] increased with surfactant concentration in the spray to 0.25% (v/v). High soil nitrogen fertility (165 ppm) enhanced kochia susceptibility to thiameturon compared to low nitrogen fertility (65 ppm). Nitrogen plus surfactant in the spray only partially overcame the effect of low soil nitrogen but did enhance thiameturon toxicity to kochia at all fertilities. Petroleum oil plus surfactant enhanced thiameturon so that kochia fresh weight reduction was similar regardless of soil fertility. Thiameturon toxicity to kochia generally increased with an increase in temperature regardless of relative humidity (RH) or adjuvants. An RH of 90 to 95% enhanced thiameturon toxicity to kochia regardless of temperature or adjuvants, except for petroleum oil plus surfactant with the low (10:8 C day:night) temperature regime. A simulated rain of 2 mm within 24 h after treatment reduced thiameturon toxicity to kochia. Drought stress (≤25% of field capacity) after thiameturon application reduced toxicity regardless of spray additives. The results of the various experiments indicated that thiameturon phytotoxicity would be greatest to kochia growing with high temperature and high RH, adequate soil moisture and nitrogen fertility, and when applied with petroleum oil plus surfactant.

Experiments were conducted to compare the influence of production site and seed source on the germination of big sagebrush seeds in relation to incubation temperatures. Seeds of big sagebrush were collected from five plant communities located on the margin of the Carson Desert in western Nevada. Seedlings were grown from the seeds and transplanted back to the sites of collection in reciprocal gardens. Seeds from 1-yr-old gardens were tested for germination at a constant 15 C for three consecutive years. The greater quantity of seeds produced by 2- and 3-yr-old gardens were tested at 55 constant or alternating temperature regimes. Seeds of big sagebrush produced in reciprocal gardens had lower germination than seeds collected from native stands at the same locations. The reduced germination disappeared as the reciprocally transplanted plants grew older and larger, but seeds from these plants did not reach the same levels of germination as those collected from native stands at the same location. Moisture stress and/or freezing temperature conditions during flowering may have directly influenced the quality of seeds produced or interacted with the inherent genotypes of big sagebrush to trigger seed production of variable quality in relation to germination characteristics.

The rate of uptake and translocation of N,N-dimethyl-2,2-diphenylacetamide (diphenamid-14C) varied among different species. Apoplastic translocation of diphenamid occurred rapidly in tomato (Lycopersicon esculentum Mill.) seedlings, intermediate in bermudagrass (Cynodon dactylon L. ‘328’) and slowly in winged euonymus [Euonymus alatus (Thunb.) Seib. ‘compacta’]. Diphenamid-14C was dealkylated to give N-methyl-2,2-diphenylacetamide (MDA) in both winged euonymus and tomato plants. After 8 days, approximately 60% of the benzene-extractable labeled compounds from both plants was MDA and 39% was diphenamid. However, less of the radioactive material in winged euonymus was extracted.

The effect of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) and isopropyl m-chlorocarbanilate (chlorpropham) on in vivo levels of ATP in Chlorella sorokiniana Shihira and Krauss were compared. Diuron inhibited the photochemical, but not the oxidative, production of ATP, whereas chlorpropham inhibited both systems. Diuron equally inhibited growth and ATP synthesis, but chlorpropham had a stronger effect on ATP level than on growth.

Vapor losses of 2,6-dichlorobenzonitrile (dichlobenil) were studied under controlled laboratory conditions by trapping vapors directly in a magnesia silica absorbant. Vapor losses increased with increasing temperature. Herbicide loss from a spray formulation in 3 hr amounted to 10% at 30 C and 18% at 40 C. Volatility increased as the soil moisture level increased from air dryness to field capacity. However, as the moisture level was increased to saturation, vapor losses remained similar to losses at field capacity. Volatility from a granular formulation was reduced when compared to the spray application. Volatility decreased as the cation exchange capacity of the soils increased.

Greenhouse studies were conducted with soil columns to determine the influence of rainfall amount, intensity, and time of application on the bioactivity of 0.07 kg ae ha−1 imazethapyr in three soils of New Jersey: the Berryland sand (BLS) (sandy, siliceous, mesic Typic Haplaquod), Aura sandy loam (ASL) (mixed, mesic Typic Hapludult), and Quakertown silt loam (QSIL) (mixed, mesic Typic Hapludult). The Brockman-Duke simulated rainfall machine was used for rainfall application and smooth pigweed as an imazethapyr bioactivity indicator. As rainfall amount increased from low to high (75 to 300 mm mo−1 equivalent) imazethapyr bioactivity declined significantly in BLS and ASL but was unaffected in QSIL. Rainfall intensity from 6 to 25 mm h−1 had no effect on imazethapyr bioactivity in the three soils. A delay in rainfall application up to 14 d after herbicide application significantly reduced the bioactivity of imazethapyr in BLS but had no effect in ASL and QSIL.

Spring-applied herbicides were evaluated in the field in 1982 through 1984 in western Nebraska for selective weed control in irrigated seedling alfalfa (Medicago sativa L. ‘Appollo’). Weed densities were least in plots treated preplant with benefin [N-butyl-N-ethyl-2,6-dinitro-4-(trifluoromethyl)benzenamine] in combination with postemergence applications of 2,4-DB [4-(2,4-dichlorophenoxy) butyric acid]. Combinations of sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} with bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) and fluazifop-butyl {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} with bromoxynil provided less grass control than sethoxydim or fluazifop-butyl applied alone. Annual weeds did not reduce alfalfa stand density.

The influence of acetamide herbicide applications on efficacy of CGA-43089 [α-(cyanomethoximino)-benzacetonitrile] in grain sorghum [Sorghum bicolor (L.) Moench] was studied under field conditions. Acetamide herbicides applied preplant and incorporated on a Haynie very fine sandy loam caused more grain sorghum injury in 1979 than in 1978. Reductions in plant population, plant height and yield, along with delay in maturity, were severe for acetochlor [2-chloro-N-(ethoxymethyl)-6′-ethyl-O-acetotoluidide], metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], and alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide]; moderate for diethatyl [N-(chloroacetyl)-N-(2,6-diethylphenyl)glycine], xylachlor [2-chloro-N-(2,3-dimethylphenyl)-N-(1-methylethyl)acetamide], and butam [2,2-dimethyl-N-(1-methylethyl)-N-(phenylmethyl)propanamide]; and did not occur for propachlor (2-chloro-N-isopropylacetanilide) treatments. Acetamide herbicides caused less grain sorghum injury on a Reading silt loam than on a Haynie very fine sandy loam in 1979. CGA-43089 applied as a seed treatment protected grain sorghum grown on soils treated with metolachlor, alachlor, diethatyl, or xylachlor. Metolachlor-triazine combinations at five locations in Kansas reduced yields at two locations. CGA-43089 provided protection from metolachlor injury at those two locations.