Triazine-susceptible (S) and -resistant (R) biotypes of smooth pigweed (Amaranthus hybridus L.) were grown in the field under competitive conditions at varying initial proportions of S and R plants. R plants were less competitive than S plants as measured by accumulation of total above-ground dry weight and seed dry weight. S and R plants were also grown in the field under non-competitive conditions at 100, 40, and 10% light. Growth rate at 10% light did not differ between S and R plants. At the two higher light intensities, dry-matter accumulation 11 weeks after seeding was about 40% less in the R plants. At 100% light, relative growth rate and net assimilation rate were lower in the R plants by about 3.5 and 19%, respectively. The light- and CO2-saturated rates of CO2 fixation in intact leaves of glasshouse-grown R plants were 20% less than those in S plants. An apparent 10 and 20% greater number of chlorophyll molecules per photosystem II reaction center in R plants (as compared with S plants) grown in the field at 40 and 100% light, respectively, did not explain differences between the S and R biotypes in photo synthetic capacity. The S and R plants did not differ in specific leaf weight or chlorophyll content on a leaf-area basis. Lower growth rate of R plants may be responsible for inferior competitive ability of R biotypes and could be the result of an impaired photosynthetic capacity.

Long-term absorption of 14C-atrazine [2-chloro-4 - (ethylamino) - 6 - (isopropylamino) - s - triazine] by excised velvetleaf (Abutilon theophrasti Medic.) roots was investigated. A rapid, initial phase of absorption was followed by a long-term, linear phase of absorption, which resulted in atrazine accumulation in the tissue to concentrations above the external solution. This accumulation did not result from metabolism of the atrazine. Aging of the excised tissue appeared to be responsible for the accumulation. Dinitrophenol, but not cyanide, inhibited accumulation. Atrazine accumulation decreased as the temperature during absorption was decreased. The Q10 the absorption rate was ca. 2.5 between 15 and 25 C. Efflux of atrazine from the tissue occurred in two phases. At 25 C, loss of 80% of the atrazine occurred in 20 min. At 4C, the rate of this efflux was slower and the phase lasted longer. At both 4 and 25 C a second, slower phase of efflux occurred through at least 6 h and resulted in loss of equal amounts of atrazine at the two temperatures. These experiments show that, in addition to rapid absorption of atrazine to a passive equilibrium, excised velvetleaf roots accumulate atrazine by a metabolically dependent process over long periods of time.

Winter chilling in the field removed the primary dormancy in common ragweed (Ambrosia artemisiifolia L.) seeds and allowed them to germinate in both light and darkness. A secondary dormancy was induced in the spring and seeds again failed to germinate in light or darkness. Kinetin (K) + ethephon (E) + gibberellin A4 + A7 (GA4+7) applied to the soil in December prevented secondary dormancy. The following May only 20% of the seeds at the 15-cm depth remained viable. The rest had germinated or decayed. In contrast, 89% of the untreated seeds remained viable. Application of K + E + GA4+7 on April 22 and May 2 also broke the secondary dormancy. Gibberellin A3 (GA3) was less effective than GA4+7 in preventing or breaking secondary dormancy.

The combustion apparatus described provides a rapid and inexpensive alternative for measurement of radioisotopes in plant parts. The apparatus utilized a nickel-chromium resistance wire connected to a low-voltage transformer to generate the heat required to ignite the plant tissue. The nickel-chromium wire also served as the sample holder. Combustion was performed in an O2-flushed liquid scintillation vial, and the combustion gases containing either 14CO2 or 3H2O were trapped in situ, scintillant was added, and the vials assayed for radioactivity. The percentage of the radioactivity recovered after combustion was 96.0 for 14C and 93.4 for 3H with standard deviations of 6.8 and 3.0%, respectively.

Glyphosate [N-(phosphonomethyl)glycine] was less phytotoxic when applied in 190 L/ha of well water with ionic strengths of 0.005 or greater than in distilled water. At a carrier volume of 24 L/ha, this inhibition of glyphosate was reduced or eliminated. Glyphosate was less phytotoxic when applied in 10-mM solutions of CaCl2, FeSO4, Fe2(SO4)3, MgSO4, NaHCO3, Na2CO3, and ZnSO4 than in distilled water. Adding H2SO4, HCl, HClO4, acetic, and lactic acids at 5, 10, and 50 mM to the spray solution resulted in variable increases in glyphosate phytotoxicity. H2SO4 was the most effective acid tested in increasing glyphosate phytotoxicity when added to well water. Lowering the pH of the spray solution by using potassium biphthalate and phosphoric acid buffers did not increase glyphosate phytotoxicity.

Sweet corn (Zea mays L. rugosa 'Seneca Scout’) and soybeans (Glycine max L. Merr. ‘Kanrich’) were grown in nutrient solutions containing alachlor [2-chloro-2′,6-diethyl-N-(methoxymethyl)acetanilide] at 2.36 × 10-5 M, polyethylene glycol MW 6000 (PEG6000) at −2.5 bars osmotic potential, alachlor at 2.36 × 10-5 M plus PEG6000 at −2.5 bars osmotic potential or with no additions. Sweet corn and soybean roots exposed to alachlor plus PEG6000 accumulated significantly more PEG6000 than roots exposed to PEG6000 alone; increased shoot uptake occurred only in soybean. Alachlor was also shown to significantly increase root osmotic potential and decrease root electrolyte leakage.

Atomizer type, spray volume, and herbicide rate influenced the effectiveness of paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) in controlling vegetation. In general, paraquat controlled vegetation more completely when applied from atomizers that discharged sprays with the angle between the edges of the pattern less than 80°. Increasing spray volume increased control for marginal herbicide rates. Increasing herbicide rate increased control and tended to overcome less effective atomizer performance or reduced spray volume. Vegetation was effectively controlled with cone- or fan-pattern-type nozzles at spray volumes as low as 50 L/ha. Cone- and fan-pattern atomizers were equal to or more effective than either rotary or flooding-type atomizers in all tests.

There was no antagonism between dalapon (2,2-dichloropropionic acid) or TCA (trichloroacetic acid) and BAS 9052 {2 - [1 -(ethoxyimino)butyl] - 5 - [2 -(ethylthio) -propyl] -3-hydroxy-2-cyclohexen-1-one} at 0.3 kg/ha for control of volunteer barley (Hordeum vulgare L. ‘Bonanza’) and wheat (Triticum aestivum L. ‘Neepawa’) in flax (Linum usitatissimum L. ‘Dufferin’). However, MCPA {[(4-chloro-o - tolyl)oxy] acetic acid} amine at 0.2 to 0.6 kg/ha had an antagonistic effect on BAS 9052, especially at 0.1 kg/ha, for control of wild oat (Avena fatua L.). BAS 9052 at 0.3 kg/ha overcame this antagonistic effect of MCPA. Field results confirmed that wild oat control with BAS 9052 at 0.3 kg/ha was not reduced by the mixtures with each of four broadleaf weed herbicides at 0.6 kg/ha. The mixtures gave excellent control of grass and broadleaf weeds. Flax seed yields were five times that of the unsprayed check and were equal to the yield of the handweeded treatment.

Fifty-day-old jimsonweeds (Datura stramonium L.) were susceptible and tomatoes (Lycopersicon esculentum Mill.) tolerant to soil-applied metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] at 0.25 and 0.50 kg/ha. Spray applications of 0.50 kg/ha metribuzin to jimsonweed foliage, or to both foliage and soil, reduced jimsonweed height growth 39 and 66%, respectively; whereas, tomato height was reduced 57 and 50% by the two placement methods, respectively. Metribuzin applied to a basal leaf appeared to move both basipetally and acropetally in jimsonweed, but only basipetally in tomato. Metribuzin applied to tomato leaves reduced growth 28% more when leaves had been abraded than when not abraded. Differential translocation appeared to be a major factor in selectivity. Directed sprays of metribuzin at 0.3 and 0.6 kg/ha on the lower 75% of jimsonweed leaves provided control in the field without injury to tomatoes.

The effect of duration of spurred anoda [Anoda cristata (L.) Schlecht.] competition on maturity and yield of three cotton (Gossypium hirsutum L.) cultivars was studied during 1975 through 1977. The seed cotton yields averaged over 3 yr for ‘DES 21326-04′, 'Stoneville 213′, and ‘Deltapine 16’ were 1850, 1570, and 1520 kg/ha, respectively. DES 21326-04 produced 50% of its yield 3 to 8 days earlier than Deltapine 16 or Stoneville 213 with no spurred anoda competition and 6 to 10 days earlier with spurred anoda competition. Spurred anoda competition from planting until July 10, August 10, and September 10 resulted in average yield decreases of 12, 37, and 38%, respectively. Yield reductions varied with cultivar. Deltapine 16 was more competitive than the other two cultivars. Early-season spurred anoda competition reduced the yield of the earliest-maturing cultivar DES 21326-04 more than that of Deltapine 16 or Stoneville 213.

Solarization is a method of heating moist soil by covering it with plastic sheets to trap solar radiation. In field experiments in Israel during the summer, maximum soil temperature under plastic cover at the 5-cm depth averaged 46 to 49C. No weeds emerged under the plastic cover during solarization and weed emergence was reduced after its removal. The heating effect from solarization decreased with soil depth. Concentration of O2 in soil under plastic was similar to that in uncovered controls, but the concentration of CO2 was markedly higher than in control soil, rising up to 2.4%. Higher temperatures and better residual weed control were produced by transparent than by black plastic, with best results from thin (0.03 mm), transparent polyethylene. Under Israeli summer conditions, 2 to 4 weeks of solarization produced effective control of annual weeds that was still appreciable after 1 yr. Narrow sheets of 20 to 50 cm produced effective weed control in bands. on soil irrigated once before placing the plastic sheets, there was no need to irrigate during solarization. The response of weed species to solarization differed. Many annual weeds, both summer species such as pigweed (Amaranthus spp.) and common purslane (Portulaca oleracea L.) and winter species as henbit (Lamium amplexicaule L.) were well controlled by solarization. Broomrape (Orobanche crenata Forsk.) was controlled in one experiment. on the other hand, horseweed [Conyza canadensis (L.) Cronq.] and bull mallow (Malva niceaensis All.) were relatively resistant, and established perennials escaped the treatment.

A triazine-resistant (R) biotype of a Graminaceous weed, Brachypodium distachyon (= Trachynia distachya), was found in the lower Galilee area of Israel after repeated treatments of roadsides with simazine [2-chloro-4,6-bis (ethylamino)-s-triazine] and atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine]. It was not affected at levels up to 3.0 kg/ha of soil-incorporated atrazine or simazine. The (R) biotype was unaffected by atrazine, as ascertained by measuring whole-leaf and plastid fluorescences and the Hill reaction. The triazine-sensitive (S) biotype was inhibited in all these reactions. The data suggest that the (R) biotype has a plastid mode of resistance common to many weed species. The (R) biotype metabolized 14C-(ring)-atrazine more rapidly to both water-soluble and to chloroform-soluble compounds than the (S) biotype did, but that could not explain the immediate resistance at the plastid level. Probably there was evolution towards increased tolerance by detoxification as well as plastid level resistance.

When trifluralin [α,α,α - trifluoro - 2,6 - dinitro -N,N-dipropyl-p -toluidine] was manually incorporated in small field plots to a depth of 10 cm, ivyleaf morningglory [Ipomoea hederacea (L.) Jacq.] was controlled more effectively than when incorporation was only 5 cm deep. No significant differences in ivyleaf morningglory control were observed between different incorporation depths when trifluralin was mechanically incorporated in large field plots. Ivyleaf morningglory emerging from 10 cm deep was controlled to a greater degree than that emerging from 5 cm deep. Preplant incorporated (PPI) trifluralin plus alachlor [2 - chloro – 2′, 6’ - diethyl - N- (methoxymethyl)acetanilide ] applied preemergence (PE) controlled up to 92% of the ivyleaf morningglory compared to 33 and 15% respectively, when these herbicides were applied alone at equal rates. This indicates a synergistic interaction between these two compounds. Trifluralin PPI plus RH 8817 [5-(2-chloro-4-trifluoromethyl phenoxy) - 2 - nitrobenzoic acid ethyl ester] and alachlor applied PE controlled ivyleaf morningglory more effectively (88 to 94%) than all other treatments. Soybean [Glycine max (L.) Merr.] injury and stand reduction were less than 5% in all studies.

Greenhouse and laboratory experiments showed that the biological activity of EPTC (S-ethyl dipropylthiocarbamate) + R-25788 (N,N-diallyl-2,2-dichloroacetamide) was lost more rapidly in soils if they had been previously treated with this herbicide. Treatments which reduced or eliminated the microbial activity in the soil restored the herbicide activity in ‘problem’ soils. A combination of 2 kg/ha of the insecticide fensulfothion (diethyl-4-methylsulphinyl phenyl phosphorothionate) with EPTC + R-25788 also restored the biological activity of the herbicide. Field trials confirmed the decreased biological activity with repeated use of EPTC + R-25788; other herbicides recommended for grass weed control in corn (Zea mays L.) performed satisfactorily in these ‘problem’ soils. The performance of EPTC + R-25788 was improved by a rotation away from it for one season (using another herbicide) but the level of activity was still below that obtained in a soil treated with EPTC + R-25788 for the first time. A new formulation of EPTC + R-25788 containing a herbicide extender R-33865 (O,O-diethyl-O-phenyl phosphorothioate) was not affected by the enhanced microbiological breakdown and provided effective season-long weed control in the ‘problem’ soils.

A model for determination of economic thresholds, or minimum weed population densities justifying the use of postemergence herbicide treatment, for five weed species in soybeans [Glycine max (L.) Merr.] is presented. Sensitivity analysis was performed on the model with respect to economic, statistical, and agronomic variables. The model was refined to include uncertainty about lost field days during the spraying period. Predictions from both the simple and refined models were consistent with economic theory. It was also determined that the economic threshold is sensitive to choice of data-collection ranges and functional form in weed-interference studies.

Translocation of 14C-glyphosate [N-(phosphonomethyl) glycine] in tall morningglory [Ipomoea purpurea (L.) Roth., ‘Heavenly Blue’] was compared with movement of 14C-photosynthate. The flow of photosynthate was manipulated by creating assimilate sinks in mature leaves and cotyledons using combinations of stem girdling, leaf shading, and localized cytokinin application. Comparisons of 14C distribution patterns indicated minor differences between glyphosate and assimilate sink partitioning when 14C-glyphosate or 14CO2 were applied to a single leaf. Labeled glyphosate moved upward through stem girdles in greater proportions than 14C from photosynthate, suggesting a greater capacity for glyphosate to transfer from symplast to apoplast. When 14C-glyphosate was applied to the stem, 14C still moved symplastically to natural and artificial sinks, but apoplastic movement into all transpiring tissues above the site of application greatly increased. Results support the classification of glyphosate as an ambimobile rather than a phloem-mobile herbicide.

Losses of picloram (4-amino-3,5,6-trichloropicolinic acid) in water exposed to sunlight ranged from 50 to 80% after 1 days' exposure (14 h sunlight) and 95% or more after 4 days exposure (56 h of sunlight) at four locations in Southern Arizona. Samples exposed at the highest elevation (2800 m) consistently lost picloram more quickly than samples at the lower elevations. Dry, recrystallized picloram losses were 11, 47, and 67% after 1, 2, and 4 days of sunlight exposure, respectively. At the same times, picloram losses in water were 65, 89, and 99%, respectively. These results indicate that photodecomposition is an important factor for the use and residue longevity of picloram on high-altitude rangelands of the western United States.

The major reserve lipid of yellow foxtail [Setaria lutescens (Weigel) Hubb.] caryopses is triacylglyceride stored in lipid bodies. Lipid bodies are heavily concentrated in the cells of the embryo axis, scutellum, and aleurone layer and are roughly spherical (average diam 0.5 μm). Percentage lipid (hot isopropanol extract) on a fresh-weight basis of mature, unimbibed seed and caryopses collected locally was about 6.4 and 11%, respectively. About 95% of the total (0.23 mg/caryopsis) was saponifiable and distributed among fatty acid classes as follows: 16:0, 5.8%; 18:0, 1.5%; 18:1, 16.2%; 18:2, 73.7%; and 18:3, 2.8%. In nondormant caryopses, saponifiable lipid content declined (18:1 and 18:2 only) about 23% during the first 6 days after imbibition in the dark at 25 C. This modest decline was preceded by the appearance of an alkaline lipase at about 24 h after the onset of imbibition. Free fatty acids accumulated during these early stages of germination and accounted for about 22% of the total saponifiable lipid remaining (0.17 mg/caryopsis) 6 days after the onset of imbibition. Lipid content and lipase activity did not change in dormant caryopses treated similarly. The delayed initiation of lipid mobilization in germinating caryopses suggests that triacylglyceride degradation is not a pivotal metabolic pathway controlling dormancy.

Concentrations of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] in contaminated groundwater recovered from 41 monitoring wells in Hall and Buffalo counties, Nebraska range from 0.01 to 8.29 μg/L. Over a 1-year period concentrations fluctuated sufficiently in a seasonal pattern to indicate that atrazine dissipation occurs. This reduction in concentration can be attributed to adsorption, dispersion, and degradation. A limited amount of atrazine degraded chemically to hydroxyatrazine [2-hydroxy-4-(ethylamino)-6-(isopropylamino)-s-triazine] under simulated aquifer conditions; microbial degradation could not be detected. A geometrical progression model for predicting long term residue accumulation indicates that current contamination levels probably reflect a steady-state situation between the amount that yearly enters into, and the partial degradation that occurs within, the aquifer. Oat (Avena sativa L. ‘Neal’) bioassays indicate that present levels of groundwater contamination remain well below the threshold necessary for phytotoxicity.

Black nightshade (Solanum nigrum L.) planted in the field at monthly intervals from March through October at Shafter, California, began to emerge in March when soil temperatures at a depth of 5 cm reached 17C. With the exception of August plantings, emergence remained constant for all plantings. Average weights of plants of May, June, and July plantings at 12 weeks were 60% greater than March and August plantings and 30% greater than April plantings. Plants began flowering 7 to 9 weeks after planting for the March through June plantings and 5 to 6 weeks after planting for the July through September plantings. Killing frosts in November prevented black nightshade planted in October from flowering. Black nightshade planted in April through July produced an average of 1000 berries/plant, which was 40 to 95% greater than those planted in March, August, and September. Seed production ranged from 20000 to 30000 seed/plant for the May through July plantings, and 600 to 8000 seed/plant for the March, April, August, and September plantings.