Experiments were conducted with isolated protoplasts of wild oat (Avena fatua L. # AVEFA) and isolated chloroplasts of wild oat and wheat (Triticum aestivum L.), to determine if the methyl sulfate salt of difenzoquat (1,2-dimethyl-3,5-diphenyl-1H-pyrazolium) might influence photoreactions in these species. Difenzoquat did not affect CO2 fixation, uncoupled electron transport, or proton uptake. At concentrations of 0.5 mM and 1 mM, difenzoquat caused a slight, but statistically significant, inhibition of photophosphorylation. Experiments assaying coupled electron transport indicated that inhibition of photophosphorylation occurred not through uncoupling, but by an energy-transfer inhibition. This same effect was observed in isolated mitocondria of both species, with about 50% inhibition of state 3 respiration rates occurring with 10 μM difenzoquat. However, no important differentials were observed in the relative susceptibilities of wheat and wild oat mitochondria. Difenzoquat also functioned as a weak autooxidizing electron acceptor in photosynthetic electron transport. Therefore, difenzoquat-induced leaf chlorosis and necrosis may result from a bipyridilium-type electron acceptor activity if sufficient herbicide is absorbed.

Chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} at rates of 140 g ai/ha and lower did not reduce wheat (Triticum aestivum L. 'Stephens’) grain yield, but soil residues from 35 g/ha injured snap beans (Phaseolus vulgaris L.), alfalfa (Medicago sativa L. ‘DuPuits’), sweet corn (Zea mays L. ‘Jubilee’), Italian ryegrass (Lolium multiflorum Lam.), sugarbeets (Beta vulgaris L. ‘Giant Western’), and rape (Brassica napus L. ‘Dwarf Essex’). Chlorsulfuron at 35 g/ha reduced foliage weight of sugarbeets seeded 26 months after application. Phytotoxic levels of the herbicide were present 10 to 20 cm deep, 168 days after application to a silt loam soil. Chlorsulfuron reduced alfalfa petiole length and fresh weight in the greenhouse when mixed in soil at rates as low as 0.025 ppb (w/w).

Weed-control evaluations in ratoon-cropped grain sorghum [Sorghum bicolor (L.) Moench.] indicated that acceptable broadleaf weed control (>80%) in the second crop could be achieved by the use of a contact herbicide plus a residual herbicide applied after first harvest. Annual grasses, especially volunteer grain sorghum, were controlled in the second crop with metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] plus propazine [2-chloro-4,6-bis(isopropylamino)-s-triazine] applied preemergence at planting and followed by metolachlor, cyanazine {2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile}, or pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] applied after first harvest. Second-crop grain yields were not adversely affected by any treatments, and it appeared that satisfactory weed control in the first crop lessened the need for a residual herbicide in the second crop.

Hypocotyl callus cultures were established from six tomato (Lycopersicon esculentum L.) cultivars that exhibited differential tolerance to preemergence and postemergence metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] at 0.5 kg ai/ha in the greenhouse. Metribuzin in a low sucrose growth medium inhibited callus growth, but calli were not highly sensitive to the herbicide Differences between cultivars in the response of calli to 50 ppm metribuzin were observed. The degree of tolerance of tomato cultivars to postemergence metribuzin at 0.5 kg/ha was similar to the degree of tolerance of their hypocotyl calli to 50 ppm metribuzin in the growth medium.

Oxyfluorfen [2 - chloro -1 - (3 - ethoxy - 4 - nitrophenoxy) -4 - (trifluoromethyl)benzene] and RH-8817 {ethyl 5 - [2-chloro - 4 -{trifluoromethyl) phenoxy] - 2 - nitrobenzoate} require light for activation. Removal of carotenoids by treating corn (Zea mays L.) seedlings with norflurazon [4 - chloro - 5 - (methylamino) - 2 - (α, α, α - trifluoro -m - tolyl) - 3 (2H) - pyridazinone] rendered them partially tolerant of oxyfluorfen and RH-8817 even when grown in the light. The activation of substituted diphenylether herbicides may occur as a result of the absorption of light energy by carotenoids.

Annual bluegrass (Poa annua L.) was controlled in bermudagrass [Cynodon dactylon (L.) Pers.] turf when ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate] was applied at 1.1 kg/ha in October and again in November, but not when applied in February and March. A single, October ethofumesate treatment, did not affect spring growth of nonoverseeded bermudagrass, but the growth of selected cultivars was delayed slightly from October + November treatment. Turf growth was severely delayed for all bermudagrass cultivars when ethofumesate treatments were delayed until February and March. The October and November ethofumesate treatments reduced the quality of overseeded perennial ryegrass [Lolium perenne (L.) ‘Medalist VI’] slightly, but did not injure it permanently and the turf recovered fully. The transition from ryegrass back to bermudagrass turf was good in the spring regardless of ethofumesate treatment. Even though turf cover was excellent throughout the transition period, bermudagrass cover during June and July was less when ethofumesate was applied in October than when application was delayed until after bermudagrass became dormant.

SN 533 [1-(N-ethyl-N-propylcarbamoyl)-3-propylsulphonoyl-1,2,4-triazole] toxicity, uptake, translocation, and degradation were studied in soybeans [Glycine max (L.) Merr. ‘Williams’] and peanuts (Arachis hypogaea L. ‘GK 19′). Soybeans were more sensitive than peanuts to SN 533 applied in the nutrient solution. 14C-SN 533 was absorbed by the roots of both species, and the 14C was translocated into the shoot acropetally. Although differences in the uptake and translocation of 14C-SN 533 by soybeans and peanuts were observed, these were not large enough to account for its differential toxicity. Root-absorbed 14C-SN 533 was rapidly degraded in both species, with less than 2% of the radiolabel present in either species occurring as unaltered SN 533 8 days after treatment. Excised leaflets of both species also rapidly degraded 14C-SN 533. The data indicate that the herbicide is more rapidly degraded in peanuts than in soybeans, and thin-layer chromatography of leaflet extracts showed that different polar products were formed from 14C-SN 533 in soybeans and peanuts.

A modified analytical procedure involving gas-liquid chromatography was used to investigate the relative amounts of 2,4-D [(2,4-dichlorophenoxy)acetic acid] and two of its amino acid conjugate metabolites, 2,4-D-Asp [(2,4-dichlorophenoxy)acetylaspartic acid] and 2,4-D-Glu [(2,4-dichlorophenoxy)acetylglutamic acid], in soybean [Glycine max (L.) Merr. var. Amsoy] plants, soybean callus tissue and red oak (Quercus rubra L.) plants at 2, 4, and 10 days after application of either 2,4-D, its ester, or its salts. 2,4-D-Asp and 2,4-D-Glu were found as major metabolites in all soybean tissues analyzed and their amounts varied depending upon the days following treatment, the formulation of treatment, and the plant substrate (0.03 to 57 ppm for 2,4-D-Asp and 0.05 to 75 ppm for 2,4-D-Glu). The amount of amino acid conjugates peaked at 2 days after treatment of callus tissue and 4 days after treatment of soybean plants. Much higher amounts of these amino acid conjugates were obtained from soybean plants treated with the propylene glycol butyl ether ester of 2,4-D than plants treated with amine salts of 2,4-D. No amino acid conjugates were observed with red oak plants.

Live root material of leafy spurge (Euphorbia spp.) was collected from 38 locations across northern United States, southern Canada, and from 1 location in Austria. These materials were established in a nursery at Lincoln, Nebraska along with E. agraria M. Bieb. and E. cyparissias L. # EPHCY. Nineteen vegetative and reproductive characters, taken from various taxonomic keys, were measured on plants established for a period of 3 yr. Data were compared with previous taxonomic keys of Euphorbia species. A key developed by A. Radcliffe-Smith was used to separate the nursery entries. Leaf width measurements were the most useful taxonomic criteria. Five morphologically separable taxa were observed: E. × pseudovirgata (Schur) Soó, E. esula L. # EPHES, E. uralensis Fisch. ex Link., E. agraria M. Bieb., and E. cyparissias L.

Storage of intact Texas gourd [Cucurbita texana (A.) Gray] pepos for 21 days after harvest increased germination of seeds from pepos collected 15 to 47 days after flowering. Germination increased as day length decreased and as osmotic potential of germination media increased. Temperatures of 20, 25, and 30C resulted in 72, 93, and 99% germination, respectively. No seeds germinated at 10 or 40C. Seedling emergence decreased as planting depth increased, with no emergence from 12.5 cm. Control of Texas gourd in soybeans [Glycine max (L.) Merr.] was achieved with preemergence applications of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one], metribuzin plus alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)-acetanilide], and oxadiazon [2-tert-butyl-4 (2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one], with successful control partially dependent on soil and climatological conditions. Postemergence treatments that resulted in adequate control included applications of acifluorfen {5-[2-chloro-4-(trifluoromethyl)-phenoxy]-2-nitrobenzoic acid}, oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl) benzene], and metribuzin plus 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid] applied at an early soybean growth stage and repeated.

Experiments were conducted at three locations to evaluate the efficacy of fall and spring herbicide treatments for vegetation control and enhancement of alfalfa (Medicago sativa L.) establishment. on a sward dominated by quackgrass [Agropyron repens (L.) Beauv.], fall and spring glyphosate [N- (phosphonomethyl) glycine] treatments were equally effective in reducing competition from quackgrass and in establishing alfalfa. on a mixed grass sward, spring and fall glyphosate treatment resulted in similar alfalfa yields with early spring seeding; however, alfalfa yields were lower with delayed seeding on fall-treated plots, compared with spring treatment, because of greater weed competition. Pronamide [3,5-dichloro(N-1,1-dimethyl-2-propynyl) benzamide] applied in the fall controlled perennial grasses, and when it was followed by paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) in the spring controlled broadleaf weeds as well, resulting in greater alfalfa yields compared with pronamide alone. Alfalfa established more slowly in the paraquat-treated and check plots, than in glyphosate-treated plots.

Comparative growth, development, and resource allocation of triazine - susceptible and triazine - resistant biotypes of common groundsel (Senecio vulgaris L.), grown under two light regimes, were studied over a 7 - week period. Dry-matter production, height, number of leaves, and leaf area of the susceptible biotype were greater than those of the resistant biotype at all harvests under both light regimes. Root/shoot ratios were lower in the resistant than in the susceptible biotype under high light. Lower values for these parameters in resistant plants are due to lowered photosynthetic capacity, which limits growth and lowers relative root production. Net assimilation rate (NAR) was lower in resistant than susceptible plants when grown under high light, but mean leaf area ratio over a harvest interval (L) of resistant plants was higher than that of susceptible plants under high light. Relative growth rate (RGR) was higher for susceptible plants before day 42 and higher for resistant plants after day 42 under high light. A lower plastochron index (PI) of resistant plants up to 5 weeks old, relative to susceptible plants of the same age, suggests that, when grown under high light, resistant plants are developmentally at least 2 days behind susceptible plants. Shading lowered dry-weight production, height, number of leaves, leaf area, NAR, RGR, PI and root/shoot ratios of both biotypes. Values for these growth parameters for susceptible plants were similar to or larger than for resistant plants when grown under low light. In both biotypes, resource allocation patterns and L shifted towards increased shoot and leaf production in response to shading.

Four forest watersheds (1 ha each) in the upper piedmont of Georgia were treated with hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H, 3H)-dione] pellets3 at a rate of 1.68 kg ai/ha. From the end of April, 1979, until May, 1980, 26 storms were monitored to determine movement of hexazinone and two of its metabolites [A: 3-(4-hydroxycyclohexyl)-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H, 3H)-dione, and B: 3-cyclohexyl-6-(methylamino)-1-methyl-1,3,5-triazine-2,4(1H, 3H)-dione] in runoff water. Residues in runoff peaked in the first storm after application (mean concentration of 442 ± 53 ppbw), and declined with subsequent storms in a power curve function: Conc. (ppbw) = 405 × rate × (1 + 0.44 × days)-1.1. Loss of hexazinone in storm runoff averaged 0.53% of the applied herbicide, with Storms 1 and 17 accounting for 59.3% of the chemical exported. Storm 1 had high residue concentrations and low runoff volume, while Storm 17 contained only low residue levels but a very large stormflow. Hexazinone was the predominant compound in the runoff of all 26 storms. Metabolites A and B occurred in runoff in low-to-trace concentrations (<23 ppbw) for up to 7 months after application. Subsurface movement of hexazinone appeared in streamflow 3 to 4 months after application and produced an additional loss of 0.05%. A second-order perennial stream below the treated watersheds periodically contained hexazinone residues of <44 ppbw.

Gibberellin-enhanced response of bean plants (Phaseolus vulgaris L. ‘Black Valentine’) and Canada thistle [Cirsium arvense (L.) Scop.] to bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] and glyphosate [N-(phosphonomethyl)glycine] was determined on both species under controlled photoperiods in the growth chamber and on Canada thistle under natural conditions in the field. Pretreatment of bean plants in the growth chamber with 10 mg/L gibberellin (GA3 or GA4/7) more than doubled the herbicidal effect of 1600 mg/L bentazon treatments. Pretreatment of Canada thistle plants in the growth chamber with 100 mg/L GA4/7 increased the herbicidal effect of 50 mg/L bentazon applications more than four-fold, and that of 400 mg/L glyphosate applications by more than two-fold. The phytotoxicity of bentazon to field-grown Canada thistle increased 10% or more in populations pretreated with 25 g/ha gibberellin; and that of 840 g/ha glyphosate was similarly increased. The effectiveness of a higher glyphosate dosage (1680 g/ha) was not significantly increased by GA pretreatment. Plants induced to bolt with gibberellin (GA4/7) were injured more by bentazon than were plants that bolted naturally.

Thirteen-day-old common cocklebur (Xanthium pensylvanicum Wallr. # XANPE) plants were treated with 15 μg glyphosate [N-(phosphonomethyl)glycine] applied to the lowermost true leaves. Growth was inhibited rapidly following treatment. About 56% of applied 14C-glyphosate was taken up within 8 h. Within 4 days after treatment, diffusive resistance increased in treated leaves but did not change in untreated leaves. Glyphosate had little effect on nonstructural carbohydrate content of leaves, but soluble carbohydrate levels of stems and roots had increased by 130 and 180%, respectively, by 56 h after treatment. The uptake of 33P into roots was unaffected by the herbicide, but transport of P to the aerial tissues was severely inhibited. Effects such as inhibition of P movement could result from inhibition of protein synthesis.

Glyphosate [N-(phosphonomethyl)glycine], dalapon (2,2-dichloropropionic acid), or paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) applied for edging control of bermudagrass [Cynodon dactylon (L.) Pers. ‘common ‘ # CYNDA] did not injure any of the eight woody ornamental species included in a 3-yr study. Paraquat applied in seven applications per year did not effectively control bermudagrass. Bermudagrass control was variable with glyphosate and dalapon during spring and summer; but repeated treatments at approximately 4-week intervals maintained effective control. In most instances, bermudagrass control was higher with glyphosate than with dalapon during September and October.

Seeds of 20 weed species buried at depths of 8, 23, and 38 cm in 1972 and 1973 were exhumed at regular intervals and tested for viability and germination. Burial depth had little to no significant influence on longevity. After 5.5 yr 48% of johnsongrass [Sorghum halepense (L.) Pers.], 36% of velvetleaf (Abutilon theophrasti Medic.), 33% of purple moonflower (Ipomoea turbinata Lag.), 30% of spurred anoda [Anoda cristata (L.) Schlecht], 18% of hemp sesbania [Sesbania exaltata (Raf.) Cory], and 13% of pitted morningglory (Ipomoea lacunosa L.) seeds were still viable. No more than 6% of the original population for any other species was viable at 5.5 yr. Hard seeds comprised a high percentage of the longer-lived seeds. Seeds of longest-lived species were losing viability at an average of 26% of the existing population each year from 3.5 to 5.5 yr.

Yields of drill-seeded paddy rice (Oryza sativa L. ‘Lebonnet’) at optimum stands of 215 to 270 plants/m2 at Stuttgart, Arkansas, were reduced 9, 18, 20, and 36% by bearded sprangletop [Leptochloa fascicularis (Lam.) Gray] densities of 11, 22, 54, and 108 plants/m2, respectively. There was a linear decrease in rice grain yield of 21 kg/ha for each bearded sprangletop plant per square meter. Weed densities of 54 and 108 plants/m2 reduced head-rice yields (whole milled kernels) and a density of 108 plants/m2 reduced germination of rice seed. The number of bearded sprangletop panicles produced per weed plant decreased as the weed density increased.

A three-piece soil-sampling device was constructed to collect soil cores in polyvinyl chloride tubing to a depth of 92 cm with no or minimum contamination. The device with tube is driven into the soil with a hydraulic post-driver and removed with a chain attached to the bucket of a front-end loader on a tractor. Various depths can be sampled for analysis by cutting off proportionate sections of the tubing containing the soil core. This procedure is more rapid and poses less chance of contamination than by taking progressively deeper soil samples.

Increasing plant density of grain sorghum [Sorghum bicolor (L.) Moench.] from 57100 to 114300 plants/ha had no significant effect on grain yields, but significantly increased Striga hermonthica (Del.) ‘Benth’ # STRHE shoot yields by 49% in S. hermonthica infested soil of the Sudan. Addition of urea at 43, 86, and 172 kg N/ha increased grain yields by 14, 25, and 45%, respectively, above the control and S. hermonthica shoot yields were reduced by 14, 21, and 35%, respectively, below the control. Although average grain yields in 1981 were 77% less than in 1980, S. hermonthica shoot yields were significantly increased by about sixfold. Grain sorghum yields of pure stands were not consistent over both years. In 1980, the cultivar ‘Ariana’ outyielded ‘Tetron’, but in 1981 the reverse occurred. However, in both years, the 50:50 mixture of both cultivars gave intermediate grain yields. While pure stands of Tetron’ sustained the lowest infestations of S. hermonthica and ‘Ariana’ had the greatest, the mixture had intermediate infestations which were on average 31% less than those of ‘Ariana’. Thus, the results suggest that the cultivation of equiproportional mixtures of relatively resistant and susceptible grain sorghum varieties, coupled with the use of high rates of nitrogenous fertilizer and wider inter- and intra-row spacing, may be a better cultural practice under dense striga infestations.