At early stages of canopy development net carbon exchange (NCE) values for redroot pigweed (Amaranthus retroflexus L.), prickly sida (Sida spinosa L.), and birdsfoot trefoil (Lotus corniculatus L.) were determined in an air-sealed leaf chamber. Regardless of light intensity, temperature, CO2 concentration, or competition level, redroot pigweed had a NCE at least 10 mg CO2/dm2 per hr higher than that of birdsfoot trefoil or prickly sida. On a total leaf area basis, CO2 utilization changed as the heteroculture canopies developed and as the microenvironmental parameters changed. Redroot pigweed's rapid attainment of leaf area and leaf display coupled with a high photosynthetic (P) rate greatly enhance its utilization of available CO2. Direct competition for CO2 does not occur between plants with low and high (P) rates under field conditions because CO2 concentrations are always greater than the CO2 compensation point (r) of plants with low (P) rates. More efficient utilization of available CO2 by weeds such as redroot pigweed with greater (P) capacity contributes to more rapid growth and development of these weeds to the ultimate detriment of a plant such as birdsfoot trefoil with lower (P) capacity.

The percentage composition of fat, protein, nitrogen-free extract (NFE), fiber, and ash was determined for 50 weed and crop species. Data on 16 additional species were compiled from the literature. Generally, within a family there was a tendency toward a certain type of storage material. Seeds of the Polygonaceae and Gramineae were low in fat, high in NFE and, with few exceptions, low in protein. Seeds of the Leguminosae family were the highest in protein and, with the exception of peanut (Arachis hypogaea L.) and soybean [Glycine max (L.) Merr] were low in fat and high in NFE. Seeds of the Compositae, Cruciferae, Cucurbitaceae, and Solanaceae were high in fat, moderately high in protein, and low in NFE. The data may be valuable in the interpretation of the mode of action or basis for selectivity of herbicides.

Effects of barban (4-chloro-2-butynl m-chlorocarbanilate) were investigated on the growth and metabolism of oat (Avena sativa L. ‘Victoria’) (susceptible) and wheat (Triticum aestivum L. ‘Ushio’) (tolerant) plants. Barban remarkably retarded the growth of oat seedlings but not that of wheat seedlings. Respiration and photosynthesis of both plant species were not inhibited. Protein and RNA synthesis of oat seedlings were remarkably inhibited even 1 day after the barban treatment, while the protein and RNA synthesis of wheat seedlings were inhibited less.

In greenhouse studies, atrazine (2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine killed Canada thistle [Cirsium arvense (L.) Scop.] when applied as preemergence or postemergence treatments. Postemergence atrazine applications caused more rapid kill when allowed to cover the ground as well as the foliage compared to only foliar atrazine applications. In three field experiments conducted in 1967, 1968, and 1969, Canada thistle was controlled with atrazine and amitrole (3-amino-s-triazole) + NH4SCN. Control resulting from atrazine was as good or superior to amitrole + NH4SCN when both were applied to foliage prior to plowing. Control from 2.2 kg/ha of atrazine applied prior to plowing was 78% for the 3-year average. Atrazine applied preemergence at 2.2 kg/ha resulted in inferior control, whereas postemergence atrazine applications resulted in thistle control similar to treatments applied prior to plowing.

First of all I would like to bring greetings from the Canada Weed Committee (CWC). Under one name or another this Committee has met every year since 1929 when it was organized by a handful of workers to coordinate their tests with sodium chlorate, sodium arsenite, sulphuric acid, etc. The CWC still meets as a working planning committee to review current work, up-date recommendations and coordinate testing for the forthcoming year.

A portable electric sprayer is described which can be used for greenhouse and small field experiments. It has the flexibility of larger conventional sprayers and precision of laboratory sprayers. The unit is compact, lightweight, and easy to construct.

The effects of seven preemergence herbicides on turfgrass quality, clipping yield, root growth, thatch accumulation, and carbohydrate reserves of three turfgrasses were measured. Nearly all herbicides caused some effect on one or more of the turfgrasses at some point during the 8-yr experiment, especially during mid-summer stress periods. The most consistently injurious herbicide was bandane (polychlorodicyclopentadiene) which caused a marked reduction in turfgrass quality, poor rooting, and increased susceptibility to stripe smut (Ustilago striiformis West. Niesel.). Clipping yields were reduced only in red fescue (Festuca rubra L. ‘Pennlawn’) by bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(20mercaptoethyl)-benzenesulfonamide], siduron [1-(2-methylcyclohexyl)-3-phenylurea], and terbutol (2,6-di-tert-butyl-p-tolyl methylcarbamate). Except for bandane, only siduron and terbutol caused significant reductions in root growth, and only in ‘Kenblue’-type Kentucky bluegrass (Poa pratensis L.). Thatch accumulation was reduced in ‘Merion’ Kentucky bluegrass treated with benefin (N-butyl-N-ethyl-α,α,α,-trifluoro-2,6-dinitro-p-toluidine) in ‘Kenblue’-type Kentucky bluegrass treated with bandane, benefin, bensulide, and terbutol; and in ‘Pennlawn’ red fescue treated with bandane, calcium arsenate, and terbutol. Carbohydrate reserves were not significantly different among treatments.

Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] at a concentration of 10−8M stimulated the elongation of the embryonic axis of red kidney beans (Phaseolus vulgaris L. ‘Charlevoix’). This stimulation of elongation was accompanied by a light-independent increase in protein synthesis as measured by radioactive amino acid incorporation.

Dormancy of spurred anoda [Anoda cristata (L.) Schlecht] seeds was not broken 60 days after harvest by stratification, presoaking in tap water, or by treatment with thiourea, potassium nitrate, or kinetin. Dormancy was broken by scarification or treatment with concentrated sulfuric acid. A high percentage of seedling emergence was obtained when scarified seeds were planted in soil at depths of 7.5 cm or less. Emergence decreased as planting depth increased. No seedlings emerged at depths of 12.5 cm or greater. Even at depths of 15.0 cm germination occurred, but no seedlings emerged.

Autotrophic growth, photosynthesis, and respiration of Chlorella sorokiniana Shihira and Krauss were inhibited by the cupric ion, but photosynthesis was more sensitive than respiration. The percent inhibition was determined by the ratio of cells to cupric ions present. Photosynthesis and respiration were inhibited within 2 and 5 min, respectively, after adding 1.0 mM cupric ions. Chlorella cells which had been incubated for a short time in concentrations of the cupric ion that completely inhibited photosynthesis were not able to grow when cultured in a fresh medium without cupric ions, indicating high concentrations of the ion may have destroyed the photosynthetic apparatus and deprived the cells of their ability for autotrophic growth. Dark preincubation of the cells, as well as high bicarbonate concentrations in the assay medium, decreased inhibition. Treatment with cupric ions reduced the cellular chlorophyll and sulfhydryl content, but anaerobiosis, a condition that increased toxicity, had little effect on the sulfhydryl content. Electron transport in photosystems I and II in intact Chlorella cells was inhibited, but the specific sites of inhibition in the photosynthetic electron transport chain could not be determined using intact cells.

The effects of drop-size, dosage, and spray volume on the toxicity of aqueous sprays of paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) were measured using sunflower (Helianthus annuus L. ‘Peredovik’). Small drops (100 μ) were more phytotoxic than large ones (350 μ), and concentrated solutions (5.5 L/ha) were more phytotoxic than dilute solutions (2.2 L/ha) at the same dosage rate.

The phytotoxicity of soil-applied terbutryn [2-(tert-butylamino)-4-(ethylamino)-6-(methylthio)-s-triazine] to wheat (Triticum aestivum Vill.) was significantly affected by soil moisture and soil temperature. Distribution coefficients (Kd) provided a better indication of the phytotoxicity of terbutryn to wheat than any single measured parameter contributing to herbicide adsorption by the soil. Soil temperatures and soil moisture levels suitable for good plant growth tended to enhance the phytotoxicity of terbutryn. No phytotoxic levels of terbutryn to wheat were detected in Teller sandy loam after 20 weeks of incubation at above 10C and 14% soil moisture by weight. However, phytotoxicity to wheat was observed in air-dry terbutryntreated soil after an incubation period of 20 weeks, regardless of incubation temperature. Significant quantities of terbutryn may remain in the field under dry soil conditions.

In field studies, bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4)3H-one 2,2-dioxide] was applied as postemergence sprays over the top of weeds and soybeans [Glycine max (L.) Merr.]. Bentazon at 0.84 to 1.68 kg/ha applied as an early postemergence treatment controlled wild mustard [Brassica kaber (DC.) L.C. Wheeler var. pinnatifida (Stokes) L.C. Wheeler], common ragweed (Ambrosia artemisiifolia L.), velvetleaf (Abutilon theophrasti Medic.), Pennsylvania smartweed, (Polygonum pensylvanicum L.), common cocklebur (Xanthium pensylvanicum Wallr.), and wild common sunflower (Helianthus annuus L.). Pigweeds (Amaranthus sp.) were controlled by applications in the three true-leaf stage but became more resistant at later stages. Control of common lambsquarters (Chenopodium album L.) was erratic. The optimum time for controlling weeds with bentazon was around the first trifoliolate stage of soybeans. Rainfall within several hours after treatment reduced weed control. Eight yield studies, two of which included eight cultivars, were conducted on weed-free soybeans. In none were yields reduced significantly by bentazon at 3.36 kg/ha (the highest rate studied). Eight yield studies were conducted on soybeans infested with common cocklebur or velvetleaf. Weed control was generally excellent with 0.84 kg/ha of bentazon. Where infestations were sufficient to reduce yields, bentazon treatments increased the yields to levels generally comparable with those of the handweeded checks. One exception was an application of bentazon to soybeans growing in a low area that was periodically flooded by heavy rains. In that experiment the benefit of controlling common cocklebur was offset by bentazon injury to the soybeans, and yields from the treated plots were about the same as those of the weedy check.

Purple nutsedge (Cyperus rotundus L.) plants were treated in the greenhouse and field with glyphosate [N-(phosphonomethyl)glycine]. Fresh weight of leaves, sprouts per original tuber, and sprouts per new tuber were reduced by 4 kg/ha glyphosate in the greenhouse. In the field, glyphosate at 2 and 4 kg/ha was compared to several herbicides for nutsedge control in repeated applications over an 8-month period. After several applications, glyphosate reduced the number of plants per unit area. After rotovation (working the soil thoroughly to a depth of 15 cm) and reapplication, glyphosate and MSMA (monosodium methanearsonate) plots had fewer plants and tubers per unit area than controls.

Isolated plant cells from leaf tissue of soybean [Glycine max (L.) Merr. ‘Harosoy’] and wild onion (Allium canadense L.) were used to study the effects of four surfactants on cell permeability as measured by loss of intracellular material and on photosynthetic 14CO2 fixation. Surfactant-induced alteration in cell permeability could not be related to surfactant-ionogenic class but could be related to reported phytotoxicity. Surfactants that altered cell permeability also inhibited photosynthetic 14CO2 fixation, indicating that surfactant effects were not restricted to the outer-cell membrane. Isolated cells from the monocotyledonous wild onion were more susceptible to surfactant-induced alterations in cell permeability than were cells from the dicotyledonous soybean. Efflux of intracellular material was modified by Ca++ and Mg++ to a greater extent for soybean than for wild onion. Integrity of the isolated cells, before and after surfactant treatment, was verified by microscopic observation.

Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one] (0, 0.56, 1.12, 1.68 kg/ha) applied the soybean (Glycine max (L.) Merr.) cultivars ‘Bragg,’ ‘Hampton,’ ‘Bienville,’ ‘Coker 318,’ ‘Coker 102,’ and ‘Hardee’ induced significant changes in total fatty acid concentration of soybean oil. Minor changes in soybean oil quality were induced by metribuzin but percent protein was not influenced.

Waterhyacinth [Eichornia crassipes (Mart.) Solms.] was partially controlled with 10.6 nm laser radiation. Radiation levels of < 1 J/cm2 for individually irradiated plants and 69 J/cm2 for group-irradiated plants significantly inhibited growth. Photosynthesis in treated plant-leaf tissue was inhibited about 50% by an exposure level of 4 J/cm2. 14C-labeled compounds fixed by plant-leaf tissue following laser treatment were found to be normally distributed.

The response of several hundred soybean [Glycine max (L.) Merr.] cultivars to postemergence application of four herbicides was evaluated in the field, greenhouse, and growth chamber in 1970, 1971, and 1972. Postemergence application of 3.4 kg/ha of bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4)3H-one 2,2-dioxide] did not significantly reduce yields of the seven commercially important soybean cultivars evaluated. All entries in the regional breeding trials, Uniform Test I to IV, were relatively tolerant of postemergence applications of the herbicides at rates about double those required for weed control. The observed order of phytotoxicity was 3.4 kg/ha of bentazon < 3.4 kg/ha of chloroxuron [3-[p-(p-chlorophenoxy)phenyl]-1,1-dimethylurea] < 0.3 kg/ha of bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) = 0.4 kg/ha of 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid]. Of the 338 named U.S. and Canadian cultivars in the U.S. Department of Agriculture soybean germplasm collection, all but one were tolerant to a postemergence application of 3.4 kg/ha bentazon. One U.S. cultivar, ‘Hurrelbrink,’ and ten plant introductions from Japan were highly sensitive to bentazon. These 11 cultivars were also highly sensitive to bromoxynil and 2,4-DB and somewhat sensitive to chloroxuron.

The selective action of chloroxuron [3-(p-(p-chlorophenoxy)phenyl)-1,1-dimethylurea] on tolerant soybean [Glycine max (L.) Merr. ‘Kent’] and susceptible tall morningglory [Ipomea purpurea (L.) Roth] was studied using root and foliar applications. In root uptake studies with carbonyl-14C-chloroxuron, soybean roots contained greater than 90% of the total absorbed radioactivity; whereas tall morningglory roots contained approximately 60% of the total absorbed radioactivity. Leaves of 1, 2, and 3-wk old soybean plants contained 0.8, 3.7, and 3.5% of the total radioactivity, respectively; whereas leaves of tall morningglory plants of corresponding age contained 29.1, 33.0, and 37.4% of the total radioactivity. Metabolism from root uptake of both species was similar; and metabolites were identified as approximately 85% chloroxuron, 13% 3-(p-(p-chlorophenoxy)phenyl-1-methylurea (Compound II), and 2.5% 3-(p-(p-chlorophenoxy)phenylurea (Compound III) in 3-wk old plants. In a nutrient solution containing 5.6 × 10−6M chloroxuron, soybean plants with roots intact were tolerant; whereas plants with roots detached were susceptible indicating the importance of differential translocation for selective action from root uptake. Following foliar spray and washing of 2-wk old plants, tall morningglory foliage absorbed about two times more radioactivity than soybean foliage. Further, 18 hr after foliar application, chloroplasts isolated from tall morningglory contained twice as much 14C-chloroxuron as soybean chloroplasts. Metabolite concentrations recovered from foliar treatment of both species were similar; and metabolites were identified as 88.1 to 92.2% chloroxuron, 6.4 to 8.6 % Compound II and 0.5 to 1.7% Compound III.

Three methods of applying linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] with trifluralin (α,α,α-triflu-oro-2,6-dinitro-N,N-dipropyl-p-toluidine) were compared for control of annual weeds in furrow-irrigated cotton (Gossypium hirsutum L. ‘Deltapine 16′). The linuron-trifluralin combinations controlled annual weeds effectively until harvest. There was no difference in cotton yield, boll components, or fiber properties among the three methods of applying combinations of linuron and trifluralin.