Several herbicides were evaluated for control of western false hellebore (Veratrum californicum Durand). The dimethylamine salt and propylene glycol butyl ether esters of (2,4-dichlorophenoxy)acetic acid (2,4-D), potassium salt of 2-[(4-chloro-o-tolyl)oxy]propionic acid (mecoprop), and the butoxy ethanol ester of 2-(2,4,5-trichlorophenoxy)propionic acid (silvex) controlled 95 to 99% of the plants when applied at 2 lb/A followed by 2 lb/A of the dimethylamine salt of 2,4-D the second year. Optimum control was achieved when plants were treated after the last leaf had expanded and before flower bud initiation.

Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triaazine] diffused at a rate of 15.2 × 10−8 sq cm/sec at 25 C which was faster than the diffusion rate of 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) and 2-chloro-4,6-bis(isopropylamino)-s-triazine (propazine) in the same soils. Diffusion rates were highly correlated with total surface area of the soil. Increasing soil moisture content, soil pH, and soil temperature resulted in greater diffusion rates. A relative indication of herbicide mobility may be obtained from some of the physical and chemical properties of the soils and herbicides involved; however, rate of diffusion appears to be governed by a combination of soil and herbicide properties.

Chenopodium humile L. did not germinate under laboratory conditions while the pericarp was intact. Scarification, leaching, ethanol, gibberellic acid, and thiourea stimulated germination. Germination was enhanced by moderate temperature (30 C), and long days. Factors which stimulated germination shortened the time between planting and maturation under short-day conditions but did not promote flowering which was absent under long-day growing conditions. Water stress did not affect germination but hastened maturation.

In laboratory studies, ethylene and an ethylene-releasing agent, 2-chloroethylphosphonic acid (hereinafter referred to as CEPA), stimulated germination of aged, pretreated but still dormant witchweed (Striga lutea Lour.) seed. Ethylene gas at 10−1 μl/L produced maximal (89 to 98%) seed germination. Witchweed seed also germinated when incubated directly in Eustis loamy sand treated with CEPA. A half-maximal response was obtained with 10 mg of CEPA per kg of soil. Vapors produced by apple (Pyrus malus L. Mill) slices, by an alkaline solution of CEPA, and by soil treated with CEPA also stimulated germination. Vapors from soil contained an inhibitor of the ethylene-induced seed germination. Exposure of the soil vapors to 20% potassium hydroxide removed the inhibitor. Germination studies with 10% carbon dioxide, carbon dioxide-free air, and ethylene indicated that carbon dioxide inhibited the ethylene-induced germination of witchweed seed.

Mixtures of 5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone (pyrazon) plus 2,2-dichloropropionic acid (dalapon) were applied to sugarbeets (Beta vulgaris L.) at three growth stages 1 year and six growth stages another year. The growth of tops and roots was retarded most when sugarbeets were treated in the two-leaf stage of growth. The weight of tops and roots was reduced 43 and 50%, respectively, 6 weeks following an application of a mixture of 3 lb/A each of pyrazon and dalapon. However, when these sugarbeets were sampled 2 weeks later, the tops and roots weighed only 4 and 12% less, respectively, than the untreated controls. Furthermore, the early suppression in the growth of sugarbeets for 3 to 8 weeks following herbicide treatment had no effect on final yield of roots, pounds of sucrose, or sucrose content at harvest.

The comparative performances of several herbicides incorporated 2.5 cm deep and unincorporated in furrow-irrigated soil were studied in four field experiments. Among eight herbicides evaluated, a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) was the most effective herbicide and controlled redroot pigweed (Amaranthus retroflexus L.), Palmer amaranth (Amaranthus palmeri S. Wats.), common purslane (Portulaca oleracea L.), and barnyardgrass (Echinochloa crusgalli (L.) Beauv.) when incorporated, without reduction of yield in carrots (Daucus carota L., var. saliva, cv. Long Imperator). Trifluralin and O,O-diisopropyl phosphorodithioate S ester with N-(2-mercaptoethyl)benzenesulfonamide (bensulide) gave consistently good results in all years although soil temperatures and evaporative losses of water were variable. Bioassays indicated and gas-liquid chromatographic (hereinafter referred to as GLC) assays confirmed that rainfall moved bensulide and trifluralin 2.5 cm downward in soil, and that dimethyl tetrachloroterephthalate (DCPA) was not moved below the original depth of incorporation in soil. GLC assays were most sensitive but generally agreed with bioassays of trifluralin-treated soils. Under high temperatures, infrequent rainfall, and furrow irrigation, the half-life of DCPA and trifluralin activities was 3 weeks, with no biological activity after 7 months. The half-life of bensulide activity was 6 months, with no biological activity after 22 months.

We evaluated the effectiveness of aqueous sprays and granules of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), 1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea (fluometuron), isopropyl m-chlorocarbanilate (chlorpropham), α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin), and 2-chloro-2′, 6′-diethyl-N-(methoxymethyl) acetanilide (alachlor) incorporated shallow for weed control in cotton (Gossypium hirsutum L., var. Stoneville 7A). In general, liquid formulation provided better weed control than did granular formulation. Applications of alachlor resulted in good weed control, but in a dry season the liquid spray form of the herbicide at high rates reduced the yield of cotton.

Added surfactant (Atlox 210) at 1% (v/v) and high relative humidity enhanced the penetration of both 4-amino-3,5,6-trichloropicolinic acid (picloram) and (2,4-dichlorophenoxy)acetic acid (2,4-D) into detached leaves of aspen poplar (Populus tremuloides Michx.). The influence of added surfactant was greater for picloram and the dimethylamine of 2,4-D than for the ethyl or butoxyethanol ester of 2,4-D. Penetration of picloram and the dimethylamine of 2,4-D occurred more readily from the abaxial than from adaxial surfaces of leaves. The ethyl ester of 2,4-D penetrated equally readily from both leaf surfaces. Penetration of picloram and the dimethylamine of 2,4-D from the adaxial surface of leaves occurred readily in young leaves in early June. There was an increase in penetration in early July followed by a decrease in August and September to a level equal to or less than that in June. Penetration from the abaxial surface of leaves was nearly equal in June and July, but there was a gradual decrease in August and September. An increase in temperature from 10 to 25.5 or to 40.5 C resulted in a sharp increase in penetration of both picloram and 2,4-D under both low and high relative humidity. Autoradiographic evidence showed that movement of picloram within the leaf also was much more extensive at the higher temperatures. Partial removal of cuticular waxes from the adaxial surface of leaves with chloroform resulted in up to four-fold increases in penetration of picloram and 2,4-D. Differences in penetration rate of picloram between leaves of aspen poplar and balsam poplar (Populus balsamifera L.) did not account for reported differences in susceptibility between these two species.

Various combinations of crops, herbicides, and tillage were evaluated for field bindweed (Convolvulus arvensis L.) control in western South Dakota. Four crop rotations (continuous wheat (Triticum aestivum L.), wheat-fallow, wheat-sorghum (Sorghum vulgare Pers.), and wheat-sorghum-fallow) were modified by the application of (2,4-dichlorophenoxy)acetic acid (2,4-D) and/or the use of post-harvest tillage. Intensive cultivation and 2,4-D treatment were used to aid in the control of field bindweed in forage crops grown on a long-term basis and in conjunction with small grain rotations. Treatment with 2,4-D in a grain crop and with non-selective herbicides after harvest were tested. Crops were planted the succeeding 2 or 3 years and observed for effect of chemical residue. The established plants could be essentially eliminated while utilizing adapted crop rotations. The use of 2,4-D alone or in combination with cultivation made it possible to reduce the stand of field bindweed (20.7 to 22.2 shoots/sq yd) 90% or more in 3 years in all rotations. A ¾-lb/A rate of 2,4-D in June prevented seed production, killed susceptible plants, and weakened the remaining plants, but a follow-up treatment of 2,4-D in the fall, post-harvest cultivation, or post-harvest treatment with herbicides such as 2,3,6-trichlorobenzoic acid (2,3,6-TBA), 3,6-dichloro-o-anisic acid (dicamba), or 4-amino-3,5,6-trichloropicolinic acid (picloram) was necessary to kill them.

An antagonistic interaction between S-ethyl dipropylthiocarbamate (EPTC) and (2,4-dichlorophenoxy)acetic acid (2,4-D) was observed on sorghum (Sorghum vulgare Pers.) and corn (Zea mays L.) after 21 days growth in soil incorporated treatments. Increasing the 2,4-D concentration increased the antagonism to EPTC. The antagonistic interaction was also observed on sorghum grown in solution culture. The antagonistic interaction occurred when the site of uptake was restricted to either the root or shoot zone of sorghum. Uptake studies with 14C-EPTC indicated that 2,4-D does not interfere with uptake or subsequent movement of 14C radioactivity within sorghum plants. Respiration of sorghum treated with the combination EPTC-2,4-D appeared to be normal. Respiration of EPTC-treated plants was inhibited.

Root sections of Canada thistle (Cirsium arvense (L.) Scop.) ecotypes from different states were field planted at Bozeman, Montana. Canada thistle survival from repeated applications of (2,4-dichlorophenoxy)acetic acid (2,4-D), and 3-amino-1,2,4-triazole (amitrole) was markedly different. Ecotypes varied less markedly to cultivation although they differed significantly. Resistance of ecotypes to cultivation seemed related to adaptation to site while resistance to herbicides apparently was related to inherent physiological differences as well as to differences in adaptation.

Uptake and movement of various herbicides and auxins by bean (Phaseolus vulgaris L.) petiole sections were studied. Isopropyl m-chlorocarbanilate (chlorpropham) was the most mobile of the compunds studied, followed in order of decreasing mobility by: indole-3-acetic acid (IAA), 3-amino-s-triazole (amitrole), (2,4-dichlorophenoxy)acetic acid (2,4-D), 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron), and 3-amino-2,5-dichlorobenzoic acid (amiben). Amiben immobilization may have been due to glucoside formation in the tissues. IAA was rapidly transported through basipetally but not acropetally oriented tissue. Tissue orientation had little effect on the movement of the other compounds. Mobility of the compounds studied, in general, appears to be a function of the amount of uncomplexed parent chemical. Retention is likely the result of conjugation with products in the cells or of physical binding in the cells.

In a stationary sprayer in a laboratory, wear was not detected in nozzles delivering α,α,α-trifluro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) in 4.3 to 6.9 gpa (assuming 4 mph at 30 psi) after 60 hr of use. In contrast, there was 1.7 to 2.0% increase in discharge volume during the first 5 to 10 hr from nozzles delivering 12.9 to 26.6 gpa. Wear was attributed to the greater amount of liquid discharged through the larger nozzles. Average wear in stainless steel nozzles was 1.7% as compared with 2.5 and 2.6% in brass and aluminum nozzles, respectively, delivering 4.3 to 26.0 gpa over a 60-hr period, while volume decreased 4.1% in nylon nozzles. Although trifluralin concentrations in the field were lower when the herbicide was applied in 2.7 or 5.4 gal of carrier/A, as compared to nozzles discharging 8.0 to 31.0 gpa, control of smooth pigweed (Amaranthus hybridus L.) was 95% or higher with all carrier rates 6 months following application.

Aqueous sprays of 4-ammo-3,5,6-trichloropicolinic acid (picloram) (1 lb aehg) were applied to individual plants in stands of burroweed (Haplopappus tenuisectus (Greene) Blake) and creosotebush (Larrea tridentata (DC.) Coville) August 27 to 31, 1965, to prepare the areas for seeding to fourwing saltbush (A triplex canescens (Pursh) Nutt.). By July 1967, 99% of the burroweed was dead, but 90% of the creosotebush was still alive. Samples of the surface ½ inch of soil, taken February 1, 1966, were planted to fourwing saltbush. Emergence and growth of fourwing saltbush were seriously reduced on soil taken from under the sprayed burroweed crowns. Growth of fourwing saltbush seedlings was retarded on soils from beneath sprayed creosotebushes, but emergence was not reduced significantly. The surface soil under sprayed burroweed crowns contained 0.11 ppm picloram 2 years after treatment, but the picloram test was negative on soils from the creosotebush area.

The selective action of α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) for the control of green foxtail (Setaria viridis (L.) Beauv.) in wheat (Triticum aestivum L.) was studied. Seedlings of both species, especially in the early stage of growth, were particularly susceptible to herbicide applied in the region of the coleoptile node. Selective control with trifluralin was possible, however, because of the morphological differences between the seedlings of the two species. Thus, the sensitive coleoptilar node area of green foxtail was located at a depth of less than 1 cm from the soil surface regardless of planting depth. The coleoptile node of wheat remained closely associated with the caryopsis. When a protective band of untreated soil was used to separate the caryopses from a 5-cm band of surface soil containing 1.12 ppmw of trifluralin, the shoot growth of wheat was normal. Much lower rates of trifluralin effectively controlled green foxtail, as surface or subsurface placement of a 1.3-cm layer of soil containing 1.12 ppmw of chemical above the foxtail caryopses completely inhibited shoot development. In addition to the differences in morphological development between the two species, the fact that green foxtail was considerably more susceptible to trifluralin than wheat was considered as an important factor contributing to the selective control.

The interactions between copper (Cu++) and cyanide (CN−) with 1,1′-dimethyl-4,4′-bipyridinium ion (paraquat) on phytotoxicity to Chlorella pyrenoidosa Chick, IAC 251, were determined by measuring chlorophyll absorbance at 434 and 670 mμ. Cu++ inhibited phytotoxicity and CN− accelerated paraquat activity with highly significant mutually antagonistic interactions occurring between Cu++ (2 ppm) and CN− (16 ppm) at paraquat levels to 2 ppm.

Pretreatment of bean (Phaseolus vulgaris L.) petiole sections with one of several metabolic inhibitors greatly stimulated the movement of 3-amino-2,5-dichlorobenzoic acid (amiben) and (2,4-dichlorophenoxy)acetic acid (2,4-D). However, the movement of 3-amino-s-triazole (amitrole), 3-(3,4-dichlorophenyl)-1-methylurea (linuron), and isopropyl m-chlorocarbanilate (chlorpropham) was stimulated only slightly or not at all. The basipetal movement of indole-3-acetic acid (IAA) was inhibited by concentrations of 2-sec-butyl-4,6-dinitrophenol (dinoseb) which stimulated respiration (5 × 10−7 M to 5 × 10−8M). Acropetal movement was stimulated by dinoseb concentrations greater than 10−5M. Translocation of root-applied amiben and 2,4-D to the stems and leaves of whole plants of bean, squash (Curcurbita pepo L.), and cucumber (Cucumis sativus L.) was stimulated by dinoseb root applications only at concentrations which were highly injurious to the plants. Amiben, 2,4-D, and their metabolites were extracted from dinosebtreated and untreated tissues. The stem exudate from cucumber plants fed amiben and 2,4-D via the roots contained primarily the parent compounds, which indicates that the parent compounds are the primary components translocated through the xylem.

Studies were conducted on and in the vicinity of the U. S. Cotton Research Station at Shafter, California, to evaluate the prevalence of the insect Bactra verutana Zeller (Olethreutidae) and its potential for injury to yellow nutsedge (Cyperus esculentus L.). Field surveys during August 1966, and August and October 1967 revealed many infested yellow nutsedge plants. Other field studies indicated that the insect may significantly suppress the growth of yellow nutsedge, providing that the insect infestation is early, sufficiently severe, and present on both parent and subsequently emerging vegetative plants. Greenhouse studies further revealed that severely infested plants may survive to produce numerous vegetative plants and tubers. While Bactra verutana Zeller damaged yellow nutsedge plants late in the season, the absence of early infestation limited its usefulness as a biological control agent.

In the greenhouse, five crops were grown in soil containing trichloroacetic acid (TCA) at 3 to 24 ppm. Based on seedling yields, corn (Zea mays L., var. Morden 88) and oats (Avena sativa L., var. Rodney) were relatively tolerant to TCA at all rates, barley (Hordeum vulgare L., var. Conquest) and rye (Secale cereale L., var. Antelope) were tolerant at lower rates, but wheat (Triticum aestivum L., var. Manitou) suffered injury at all rates. When TCA-2-14C was applied to the roots of wheat and oats seedlings in water or nutrient solution, wheat seedlings absorbed more TCA-2-14C than oats. Potassium cyanide (KCN) and 2,4-dichlorophenoxyacetic acid (2,4-D) decreased TCA-2-14C absorption by wheat more than that by oats. From 5 to 21 days after application, wheat retained two to four times as much TCA-2-14C as oats. Thus, half of the TCA-2-14C in shoots and roots of wheat disappeared in 11.3 and 11.4 days, respectively, compared with 7.9 and 3.5 days for oats. Based on this investigation, the difference in susceptibility of wheat and oats to TCA appeared to be governed by the metabolic processes involved in absorption and dissipation.