Experiments were conducted in a growth chamber to study alachlor and metolachlor metabolism in soil and corn and to determine if alachlor and metolachlor and their metabolites are exuded from corn roots to the growth medium. Alachlor was more readily absorbed by corn than was metolachlor. The absorption of alachlor and metolachlor was 72 and 55%, respectively, 10 d after seedling emergence (DAE). Alachlor and metolachlor were rapidly metabolized in corn, although metabolism rates were higher with metolachlor than with alachlor. Ten similar alachlor metabolites were detected in roots and shoots. In addition, two metabolites were detected only in the shoots, and one metabolite was detected only in the roots. Metolachlor metabolism in corn produced fewer metabolites than did alachlor metabolism. At 5 DAE, 10 and 9 metabolites were detected in shoots and roots, respectively. The metabolism of alachlor and metolachlor in soil showed patterns similar to the metabolism in corn but produced fewer metabolites. One unique alachlor metabolite appeared in soil but not in corn. Roots of corn seedlings treated with 14C-alachlor or 14C-metolachlor released significant amounts of radioactivity to the surrounding growth medium 5 d after treatment. Plants treated with alachlor released more radioactivity than did plants treated with metolachlor.

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.

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.

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.

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 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.

Picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid) and metsulfuron {2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] amino] sulfonyl] benzoic acid} were applied to broom snakeweed (Gutierrezia sarothrae [Pursh.] Britt. and Rusby # GUESA) on two spring dates and three fall dates from October 1983 to 1985. Applications of picloram and metsulfuron in the fall more effectively controlled broom snakeweed than applications in the spring. Lower herbicide rates were necessary for 90% or greater control on a sandy loam than on a silty clay loam. Grass yield increased significantly the first, second, and third growing seasons when a majority of the broom snakeweed were killed by either herbicide, but was not different from untreated rangeland when less than 50% of the plants were killed. Reduction in broom snakeweed densities of 90% or greater following applications of picloram or metsulfuron resulted in 3- to 5-fold increases in the estimated carrying capacity of rangeland in east-central New Mexico.

The development of amylase activity controlled by the embryo in the distal halves of intact barley (Hordeum vulgare L., var. Larker) seeds during the first 2 days of germination was prevented by the presence in the culture solution of 10−4 M 7-oxabicyclo-(2.2.1)heptane-2,3-dicarboxylic acid (endothall), 3,5-dibromo-4-hydroxybenzonitrile (bromoxynil), 2,6-dichlorobenzonitrile (dichlobenil), or 3 amino-2,5-dichlorobenzoic acid (amiben) and was not overcome by the simultaneous addition of gibberellic acid. The aforementioned herbicides did not inhibit gibberellic acid-induced amylase synthesis in de-embryonated halved barley seeds. The amiben and bromoxynil inhibition of barley germination was slightly reduced by the simultaneous addition of 10−2 M glucose to the culture solution. Amiben and bromoxynil also inhibited the development of low levels amylase activity found in 2-day-old squash (Cucurbita maxima Duchesne, var. Chicago Warted Hubbard) cotyledons; however, added benzyladenine overcame the inhibition. In contrast to barley, benzyladenine was shown to induce the development of amylase activity in squash. Tolerance of squash and other seeds low in carbohydrates to amiben and bromoxynil during germination may be related to their independence from herbicide-inhibited carbohydrate degradation for energy and carbon source required for anabolic processes.

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.

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.

Season-long weed control has been a goal of some producers of irrigated corn (Zea mays L.) to reduce competition, lessen weed seed production, facilitate crop harvest, improve water efficiency (particularly with furrow irrigation), and improve aesthetic properties of fields. Field experiments were conducted for 3 yr on sprinkler-irrigated corn on a loamy fine sand. Five herbicides applied at layby generally provided season-long control of grass weeds and reduced weed seed production up to 100%. Pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] was particularly effective. Yields of irrigated corn were not increased by layby herbicide application. Use of corn rows spaced 91 cm apart and use of a shorter, early-maturing, horizontal-leaf corn cultivar resulted in greater weed growth and weed seed production than did use of 76-cm rows and a taller, full-season, upright-leaf corn cultivar. After nearly complete weed control with herbicides for 2 yr, withholding herbicide use in the third year allowed weed growth which reduced corn yield. Indications were that weed control efforts need to be continuous in irrigated corn production.

The influence of water stress on johnsongrass [Sorghum halepense (L.) Pers. ♯ SORHA] physiology was evaluated in a semiarid environment. Stomatal conductance of johnsongrass responded to more negative leaf water potential and increasing leaf temperature. The sensitivity of the leaf temperature effect was dependent on the soil water content. At low soil water content, conductance was limited by low water potential, and increasing leaf temperature had little effect. Conductance of CO2 was related to net photosynthesis in a curvilinear manner, with conductance levels greater than 0.3 mol·m-2· s-1 being in excess of that necessary for maximum photosynthesis. At both high conductance levels and low levels associated with increased water stress, intercellular CO2 concentration increased, indicating nonstomatal limitations to photosynthesis. Decreased osmotic potential provided the highest correlation with the linear decline of photosynthetic rate as stress intensified. The expression of osmotic adjustment in johnsongrass is reported during grain filling. Plants in the milkdough stage of grain filling had approximately 0.3 MPa lower osmotic potential at any relative water content than those at anthesis.

The persistence of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) residues under greenhouse conditions was affected by levels of activated carbon added to a silica sand potting medium and by up to four consecutive crops of corn (Zea mays L.). Degradation of atrazine within the sand and removal by the corn crops were both reduced by activated carbon. Atrazine removal by successive crops of corn reduced injury to oat seedlings grown on the sand alone, and absorption by 1.2 g of carbon per kilogram of sand prevented oat injury both with and without cropping. Although 0.4 g/kg of activated carbon inhibited atrazine removal by corn, oat seedlings were not protected from the residues remaining. When exposed to alternate freezing and thawing, the ability of 0.4 g/kg of activated carbon to deactivate atrazine was reduced causing increased oat injury.

Acetolactate synthase–- (ALS-) inhibiting herbicides are frequently used to control annual bluegrass in managed turfgrass systems. Recently, the number of annual bluegrass populations resistant to these herbicides has increased on golf courses. Previous research involving annual bluegrass resistance to ALS inhibitors has included elucidating the mechanism of resistance and in vivo response of ALS to ALS-inhibiting herbicides. The purpose of this research was to generate baseline information on enzymatic parameters of resistant (R) and susceptible (S) annual bluegrass biotypes and further distinguish these biotypes by comparing vegetative growth and reproductive characteristics. The R biotype contained a mutation in the ALS gene resulting in a Trp574 to Leu amino acid substitution. Compared to the S biotype, the R biotype exhibited a 27- and 10-fold resistance to trifloxysulfuron at the whole-plant level and under in vitro conditions, respectively. No significant differences were observed in substrate concentration at one-half maximum rate of enzyme activity (pyruvate) or extractable ALS activity between biotypes, but the maximum rate of enzyme activity was higher for the R biotype. The feedback inhibition of ALS activity by the branched-chain amino acids was higher for the R biotype than the S biotype, with leucine, valine, and isoleucine inhibiting ALS activity 20, 6, and 4% more in the R biotype, respectively. The R biotype produced more inflorescences and seeds per plant in comparison with the S biotype, but relative growth rates between biotypes were similar at all harvest intervals. Our research provides baseline information regarding ALS enzyme response, vegetative growth, and reproductive characteristics of annual bluegrass biotypes resistant and susceptible to ALS-inhibiting herbicides.

Grains of wild oats (Avena fatua L.) may remain dormant in the soil for several years or even for decades. The reasons for this dormancy are not known, but various hypotheses have been advanced to explain it, such as that the hull acts as a barrier to oxygen (1,7), and that a toxic substance is present in the hull as in cultivated oats (5). The tests here reported were undertaken to further explore some aspects of the problem of dormancy in wild oats.

Gross autoradiography showed that translocation of C14-labeled 3-amino-1,2,4-triazole (amitrole) from the leaf of quackgrass (Agropyron repens (L.) Beauv.) was retarded over 12 hr by ammonium thiocyanate applied as a spray or as a spot. While considerable export of C14 from the treated leaf occurred during 12, 24, and 96 hr after C14-amitrole was applied, C14-NH4SCN as a tracer was largely restricted to the treated leaf over the first 24 hr and showed only slight export over 96 hr. It was concluded that the synergistic effect of NH4SCN on amitrole is exerted in the treated areas and not at the ultimate site of amitrole action.

The butoxyethanol and propylene glycol butyl esters of 2,4-dichlorophenoxyacetic acid (2,4-D) were applied to and recovered from the leaf surfaces of garden bean and corn plants. Both the acid and the ester of 2,4-D were recovered, indicating that hydrolysis of the esters had occurred. The acid and esters of 2,4-D were also found in both leaves and stems of the bean plants, indicating that further hydrolysis had occurred within the plants. Bean plant homogenates incubated with 2,4-D esters yielded 2,4-D acid. The root exudate from corn plants treated with 2,4-D butoxyethanol ester showed the presence of both acid and ester.

The effect of fully-saturated bicyclic and partially-saturated tricyclic dimethylureas and dimethylthioureas on the photolytic activity (Hill reaction) of chloroplasts isolated from turnip greens (Brassica spp.) was studied. Photochemical activity was measured potentiometrically with ferricyanide as the electron acceptor. Chemicals tested were 3-[5-(3a,4,5,6,7,7a-hexahydro-4,7-methanoindenyl)]-1,1-dimethylurea; 3-(chloro-2-norbornyl)-1,1-dimethylurea; 1,1-dimethyl-3-(2-norbornyl)urea; and the 3 corresponding thioureas. Concentrations of the 3 polycyclic ureas required to inhibit the Hill reaction by 50 percent (I50) were respectively 4.0 × 10-6 M, 1.2 × 10-5 M, and 6.6 × 10-5 M. The thioureas were not very inhibitory to the Hill reaction; consequently, their I50 values were not determined. The fully or partially-saturated polycyclic dimethylureas were weaker inhibitors of the Hill reaction than the phenyldimethylureas. The decreased inhibitory activity of the polycyclic ureas was attributed to increased lipophilic properties, unfavorable spatial configurations, and lack of resonance interaction between the ring system and the imino nitrogen.