Following foliar application of 14C-bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4)3H-one 2,2-dioxide], a promising selective postemergence herbicide for the control of broadleaf weeds in soybean [Glycine max (L.) Merr.] and navy bean (Phaseolus vulgaris L.), the movement of the 14C-label was primarily acropetal in both species, with some basipetal movement. Metabolism was more rapid in the trifoliate navy bean leaf than in the unifoliate navy bean leaf and the trifoliate soybean leaf. Prior treatment with several other herbicides did not decrease metabolism of bentazon in navy bean. The metabolites in navy bean and soybean appeared similar. Four apparent 14C-conjugates were isolated from soybean plants harvested at full maturity.

The trifoliate leaf of tolerant navy bean (Phaseolus vulgaris L.) retained less bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4)3H-one 2,2-dioxide] from foliar applications than the unifoliate leaf, or the leaves from susceptible cocklebur (Xanthium pensylvanicum Wallr.) and moderately susceptible black nightshade (Solarium nigrum L.) seedlings. The 14C from 14C-bentazon applied to the foliage of black nightshade moved throughout the entire plant. In cocklebur, the 14C moved throughout the treated leaf, whereas, in the trifoliate leaf of navy bean, very little acropetal movement occurred from the site of application. However, in the unifoliate leaf of navy bean, acropetal and basipetal movement of 14C from the leaf was observed. The species differed in the 14C-metabolites formed from 14C-bentazon 1 and 5 days after treatment. The rapid metabolism of bentazon in the trifoliate leaf of navy bean appears to be related to tolerance.

In greenhouse studies root absorption after postemergence applications of cyanazine 2-[[4-chloro-6-(ethylamino)-s-triazine-2-yl] amino]-2-methylpropionitrile enhanced phytotoxicity to fall panicum (Panicum dichotomiflorum Michx.), green foxtail (Setaria viridis L.), and corn (Zea mays L.). Less 14C-cyanazine was taken up by the foliage of corn than by the weed species. A lower concentration of parent cyanazine in corn leaves was also evident. The addition of a phytobland oil to the treatment solution increased foliar cyanazine absorption 1 and 5 days following treatment. Although rapid metabolism occurred in corn roots, the large amount of cyanazine absorbed via the root system resulted in internal concentrations of parent cyanazine similar to that observed in the weed species. Cyanazine translocation was mainly acropetal from the point of application. The basis of selectivity is not solely based on the differential foliar uptake of cyanazine, but also on the proportion taken up by the foliage and roots. Under conditions favoring uptake by roots, the margin of selectivity may be reduced.

Triallate [S-(2,3,3-trichloroallyl)diisopropylthiocarbamate] mixed with soil (1.5 ppmw) stimulated coleoptile extension, reduced the length of the primary leaf, but had no effect on mesocotyl development of wild oat (Avena fatua L.) grown in soil in a growth chamber. Incubation of the triallate-treated soil for as long as 20 weeks at constant temperatures (10 C, 16 C, and 20 C) did not reduce phytotoxicity. Triallate phytotoxicity was similar at soil moisture levels of either 5% greater than wilting point or 5% less than field capacity. The phytotoxicity remained the same after a freezing cycle during an 8-week soil incubation. Phytotoxic effects of triallate were markedly reduced as soil organic matter increased.

Specially constructed runoff plots were used to study the effect of simulated rainfall intensity, antecedent soil moisture, and subsequent rainfall on prometryn [2,4-bis(isopropylamino)-6-methylthio-s-triazine] movement across and through a field soil with a 1% slope. The first cm (45.4 L) of runoff was collected and subdivided. The initial 3.8 L of runoff water generally contained a higher concentration of prometryn than did a composite from the next 41.6 L. The sediment contained a higher prometryn concentration than did the runoff water. However, due to the greater volume of water lost compared to sediment, over 90% of the prometryn lost was in the water fraction. When prometryn was applied to a dry soil and rainfall simulated, runoff losses of prometryn were 0.5% or less of the total amount initially applied. The first runoff producing simulated rainfall caused the largest prometryn losses, but prometryn could not be detected in the runoff 1 month subsequent to application. Prometryn was never detected at soil depths greater than 5 cm. Prometryn runoff was greater from plots in which the soil was wet at the time of application.

Picloram (4-amino-3,5,6-trichloropicolinic acid) herbicidal activity on seedlings of guava (Psidium guajava L.), strawberry guava (Psidium cattleianum Sabine), and dwarf beans (Phaseolus vulgaris L. ‘Bountiful’) was increased by adding ammonium sulfate to the spray solution. Picloram activity tended to increase with increasing ammonium sulfate concentration up to 10% (w/v), but by the end of each experiment ammonium sulfate concentrations above 0.5% were generally equally effective. The absorption of 14C-picloram by strawberry guava leaves was increased about five-fold by 0.5% and 10% ammonium sulfate. There was about four times more 14C-picloram in the upper stem and attached leaves when ammonium sulfate was added than with picloram alone. Ammonium sulfate at 0.5% increased picloram absorption by four-fold in guava, but there was no increase in the amount of picloram translocated acropetally. Picloram absorption by dwarf beans, measured by difference between the amount of picloram applied and the amount recovered, was increased by 0.5% and 10% ammonium sulfate by a similar magnitude as on guava species.

Ammonium sulfate increased the magnitude and rate of 14C-picloram (4-amino-3,5,6-trichloropicolinic acid) absorption in detached strawberry guava (Psidium cattleianum Sabine) leaves. Absorption of 14C-picloram with or without ammonium sulfate leveled off at 6 to 12 hr. The magnitude of the ammonium sulfate-induced increase in 14C-picloram absorption was not affected by picloram concentration in the range 250 to 2000 ppmw, or by leaf age. The absorption of 14C-picloram was increased by 0.1, 0.5, 1.0, and 10% ammonium sulfate; 0.01% had no effect. Increased 14C-picloram absorption resulted from adding the ammonium salts of sulfate, nitrate, chloride, or dibasic phosphate, but ammonium sulfate was the only one of six sulfate salts to increase picloram absorption. A pH adjustment of the external solution from 6 to 4 increased picloram absorption, whereas a pH change from 6 to 8 had no effect. Both ammonium dibasic phosphate at a solution pH of 7.7 and ammonium monobasic phosphate at pH 4.6 increased picloram absorption, whereas potassium dibasic phosphate at pH 9.5 had no effect, and potassium monobasic phosphate at pH 4.6 did increase absorption.

Adsorption of ethylene in four North Carolina soils and on montmorillonite, kaolinite, and organic matter was studied. Rate of ethylene diffusion through soils in the field and laboratory and its rate of loss from field soil were also examined. Ethylene was adsorbed in greater quantities on two soils which were limed as compared to their field pH. Ethylene adsorption by another surface soil and a subsoil were unaffected by pH changes. The order of adsorption of several hydrocarbon gases by two of the soils was ethylene = propylene ≫ methane ≥ ethane ≥ propane. Montmorillonite adsorbed more ethylene than did kaolinite or organic matter. Soils which adsorbed ethylene also had slower diffusion rates when ethylene was injected into a homogeneous soil column. Ethylene diffused 2.1 m horizontally and 0.7 m vertically to cause at least 50% witch weed (Striga lutea Lour.) seed germination in a Lakeland soil in the field. Witchweed seed germination as high as 90% was obtained at soil depths of 0.3 m and horizontal distances of 0.7 m from the point of ethylene injection.

Distribution patterns of foliar applied herbicides can be studied by x-ray element mapping provided the herbicide contains an atom with an atomic number of 11 (sodium) or greater. The suitability of an herbicide for element mapping increases as the number of similar detectable atoms per molecule increases. Herbicides containing one detectable atom per molecule provide usable element maps at concentrations of 1.12 kg/ha and higher. Inaccurate element maps can result from: (1) Formulation components containing detectable atoms the same as those of the active ingredient. (2) Herbicide volatility during analysis due to reduced pressures and heating. (3) Specimen topography preventing x-ray detection at some locations on the plant surface. (4) Herbicide concentrations that are below the minimum detectable limit. If adequate precautions are followed in the use of x-ray element mapping, a wide range of uses exist in weed science.

Studies were conducted to compare weed growth under lighting systems composed of metal halide (MH) lamps and fluorescent-incandescent (FI) lamps. The MH lamps provided more light intensity and over a 6-week period caused plant dry weight to be 60 to 70% more than for plants exposed to the FI lamps. One week after emergence, all plants under the higher intensity MH lamps had larger stems and cotyledons or first true leaves. Six weeks after planting, weeds grown under the MH lamps had larger leaves, shorter internodes, thicker stems, and, in general, more pubescence than plants under the conventional lighting system. Growth habits of weeds exposed to the MH lamps were similar to those observed for field growth plants.

Competition studies were conducted in Brazil during 1972 and 1973 between high populations (160 plants/0.1 m2 at 5 to 7 weeks after planting) of purple nutsedge (Cyperus rotundus L.) and the following vegetable crops: garlic (Allium sativum L. ‘Mineiro’), okra (Hibiscus esculentus L. ‘UFV 1152’), carrot (Daucus carota L. ‘Nantes’ and ‘Kuroda’), bush-type green bean (Phaseolus vulgaris L. ‘Topcrop’), cucumber (Cucumis sativus L. ‘Aldai’), transplanted cabbage (Brassica oleracea L. var. capitata ‘Louco’) and transplanted tomato (Lycopersicon esculentum Mill. ‘Santa Rita’). Purple nutsedge grew all year with irrigation, although growth was greater during the warm, wet season (October to March). Crop losses due to purple nutsedge competition during the entire cropping season were as follows: garlic 89%; okra 62%; two carrot cultivars, ‘Kuroda’ and ‘Nantes’ 39% and 50%, respectively; green bean 41%; cucumber 43%; cabbage 35%; and tomato 53%. Critical periods of purple nutsedge competition occurred between 3 and 13 weeks for garlic; 3 and 7 weeks for okra, cucumber and the carrot cultivar ‘Nantes’; 3 and 5 weeks for tomato and the carrot cultivar ‘Kuroda’; and at approximately 4 weeks for cabbage and green bean. Purple nutsedge competed for light in the slow-growing, non-competitive crops and for nutrients in all crops. Competition for water was reduced because the vegetables were irrigated regularly. The rate of leaf area development for a competitive crop, green bean, was similar to the rate for purple nutsedge, whereas the rate was much lower for the non-competitive okra.

Cotton maintained free of annual grass and broadleaf weeds for 6 or more weeks after emergence in 1969 produced maximum yields, whereas in 1970 and 1971, 8 or more weeks of weed-free maintenance were required. Nitrogen applications at planting of 67 and 100 kg/ha did not influence the weed-free requirement of cotton in any year. Cotton yields were not reduced in 1969 when weeds were allowed to compete for 4 or 2 weeks. In 1970 and 1971 weed competition for 7 or fewer weeks did not result in yield reductions. Nitrogen did not affect the competitive relationship between cotton and weeds in 1969 and 1971. In 1970, however, cotton tolerated only 6 weeks of competition at the zero nitrogen rate, whereas it tolerated 7 weeks of competition at the 67 and 100 kg/ha nitrogen rates. Height and stem diameter of cotton were less reliable indicators of the crop-weed relationship than was yield. Neither height nor stem diameter of cotton revealed a consistent difference in the competitive relationship at the three nitrogen rates.

Prometryn [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine] and dinoseb (2-sec-butyl-4,6-dinitrophenol) were applied in a non-phytotoxic undiluted oil carrier to sorghum (Sorghum bicolor L. ‘RS 610’), bean (Phaseolus vulgaris L. ‘Cascade’), and cucumber (Cucumis sativas ‘Wis. SMR-18’) simultaneously or separately, where prometryn treatment was followed by dinoseb at varying intervals of time. The simultaneous application of the two herbicides resulted in an additive response on all three plants, except that a slight antagonism was observed at one rate on both bean and cucumber. A synergistic response was observed when dinoseb treatment was delayed for at least 1 day on bean and cucumber and 2 days on sorghum. 14C-prometryn (14C) movement in bean leaves was not altered by simultaneous dinoseb application.

Yellow nutsedge (Cyperus esculentus L.) was studied to determine the relationship between physical character of tubers and sprouting habits. All tuber lots studied, which averaged from 157 to 662 mg per tuber, sprouted and grew well under greenhouse conditions. Longevity (the time between initial planting and death) increased with tuber weight. Weight of the third and fourth sprouts equalled that of the first and second sprouts for heavy tubers, but sprout weight decreased for light tubers. Detaching the plants at 2-week intervals from the tubers which produced them allowed all buds present to sprout. However, when the plants were detached at 4-week intervals, a reduction in the number of sprouts and a decrease in longevity were observed. Allowing plants to grow for 8 weeks before detaching did not cause any further decrease. Number of buds, number of sprouts, number of multiple sprouts, the time interval between first planting and first sprout, and the time interval between successive sprouts did not vary with initial tuber weight. Prolonged refrigerated storage of tubers caused an increased number of multiple sprouts, a decreased initial and subsequent sprouting interval, and a short life.