Foliar applications of (2,4-dichlorophenoxy)acetic acid (2,4-D) to both field- and greenhouse-grown honeyvine milkweed (Ampelamus albidus (Nutt.) Britt.) caused 22% and 36% reduction in starch in roots at 2 and 3 days after treatment, respectively. No changes in soluble sugars occurred during the period, but protein had increased by 35% and 80% on the two respective dates. No increase in α-amylase was measured. Leakage of nucleotides and α-amylase from root sections began 2 days after treatment. A 20 to 30-fold increase in cellulase activity occurred in roots of treated plants starting 2 days after treatment.

Competition studies in field trials were conducted between common purslane (Portulaca oleracea L.) and table beets (Beta vulgaris L., var. Detroit Red) and between common purslane and snap beans (Phaseolus vulgaris L., var. Eastern Butter). Common purslane control was most critical during the first 2 weeks after beet and bean emergence. Common purslane control for longer than 2 weeks did not increase beet or bean yields. The longer common purslane was allowed to compete after beet or bean emergence, the more yields were decreased. Common purslane was a stronger competitor in beets than in beans. The faster and taller-growing bean plants provided more competition than did beets. Cultivation between rows until lay-by increased both beet and bean yields.

In leaching studies utilizing slotted columns of soil and redroot pigweed (Amaranthus retroflexus L.) bioassay, 2,4-bis(isopropylamino)-6-methylmercapto-s-triazine (prometryne was leached to a greater depth in the coarse-textured sandy soils than in the fine-textured clay soils. There was little correlation between the depths of leaching and the amount of water used to leach the herbicide. Prometryne formulated as an emulsifiable concentrate was leached to a greater depth than the wettable powder and the granules. The 14C-pro-metryne was much more strongly adsorbed to a clay soil than to loam and silt loam soils. Volatility studies, using cotton (Gossypium hirsutum L.) plants to assay for vapor injury, showed the vapor loss of prometryne was greater from a metal surface than from a soil surface. Injury from prometryne vapors was greater with silt loam and sandy loam soils than clay soils. Cotton plants exposed 1 week after emergence were more severely injured by prometryne vapors than cotton plants exposed at emergence or 2 and 3 weeks after emergence. The vapor injury from prometryne formulated as a wettable powder or an emulsifiable concentrate was greater from granules. Prometryne vapor injury was increased as soil moisture and temperature was increased. Vapor injury to leaves of cotton was characterized by interveinal chlorosis while injury from root uptake was characterized by veinal chlorosis.

Concentrations of α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) causing 50% growth reduction (hereinafter referred to as GR50) were determined in nutrient culture and 64 simulated soils using foxtail millet (Setaria italica (L.) Beau.) as an indicator species. The relative order of effectiveness of soil components in reducing trifluralin phytotoxicity was steamed organic matter ≫ organic matter ≫ steamed montomorillonite ≥ steamed kaolinite ≃ kaolinite ≃ montmorillonite. Steaming the organic matter more than doubled the anion exchange capacity. Anion exchange capacity was a better parameter than cation exchange capacity for assessing the potential of an adsorbent to reduce phytotoxicity. Surface area, cation exchange capacity, and adsorption of trifluralin from solution were less reliable indices. The effectiveness of organic matter in reducing phytotoxicity may be due to the exchange capacity and high surface area. Montomorillonite apparently interacted synergistically with other adsorbents to reduce phytotoxicity. Trifluralin did not adsorb on the internal surfaces of montmorillonite as judged by surface area comparisons and X-ray diffraction determinations. Increasing moisture content appeared to block the active sites of trifluralin adsorption. This may be concluded from greater vapor movement and decreased adsorption from a xylene solvent system for moist compared to air dry soils.

The phenolic content of purple nutsedge (Cyperus rotundus L.) and yellow nutsedge (Cyperus esculentus L.) was determined. The major phenolic components were p-coumaric, ferulic, p-hydroxybenzoic, syringic, vanillic, salicylic, proto-catechuic, and caffeic acids, and eugenol. High concentrations of eugenol and salicylic acid inhibited the sprouting of nutsedge tubers. The lack of activity at lower concentrations argues against a major role for these compounds in maintaining nutsedge tuber dormancy. Exogenous abscisic acid inhibited nutsedge tuber sprouting and may be a natural dormancy factor in nutsedge.

Sericea lespedeza (Lespedeza cuneata (Dumont) G. Don, var. Serala) was planted in three field experiments at three seeding rates with four rates of S-propyl dipropylthiocarbamate (vernolate). Grass and broadleaf weed populations were reduced, but sericea was unaffected by vernolate incorporated preplant. Use of a herbicide permitted a reduction in seeding rate with no decrease in sericea stand or forage yield. This treatment permitted harvesting a cutting of hay the establishment year with only a minor effect on production the next year. The beneficial effect of vernolate on sericea yield continued the second year, mainly because sericea plants were better established and more vigorous. Sericea seeding rate did not affect weed competition or forage yield. A seeding rate of 11 kg/ha with 3.4 kg/ha vernolate was the most practical treatment.

There were no apparent herbicide-insecticide or herbicide-fungicide interactions when two pesticides were used on peanuts (Arachis hypogaea L.) in the greenhouse. In field studies, O,O-diethyl s-(2-(ethylthio)-ethyl)-phosphorodithioate (disulfoton), O,O-diethyl s-((ethylthio)-methyl)-phosphorodithioate (phorate), 1,2-dibromo-3-chloropropane (dibromochloropropane), and pentachloronitrobenzene (PCNB) had little influence on phytotoxicity of the herbicides 3-amino-2,5-dichlorobenzoic acid (chloramben) and α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) to peanuts. There was no phytotoxic effect or yield reduction as a result of application of chloramben or trifluralin combined with the use of fungicide-treated seed in the field. However, in the greenhouse, top growth of the fungicide-treated checks was greater than that of the herbicide-fungicide seed treatments. Dibromochloropropane nematocide alone was injurious to peanut seedlings grown in the greenhouse, but the application of a herbicide did not increase the injury.

Vapor losses of 2,6-dichlorobenzonitrile (dichlobenil) were studied under controlled laboratory conditions by trapping vapors directly in a magnesia silica absorbant. Vapor losses increased with increasing temperature. Herbicide loss from a spray formulation in 3 hr amounted to 10% at 30 C and 18% at 40 C. Volatility increased as the soil moisture level increased from air dryness to field capacity. However, as the moisture level was increased to saturation, vapor losses remained similar to losses at field capacity. Volatility from a granular formulation was reduced when compared to the spray application. Volatility decreased as the cation exchange capacity of the soils increased.

Comparative phytotoxicity of α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) and 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin) on several plant species indicated trifluralin was more toxic than nitralin to the shoots while nitralin was more toxic than trifluralin to the roots. An E0 concentration, defined as that concentration required to prevent seedling emergence, was established for trifluralin on nearly all species assayed. Nitralin did not prevent emergence of any species. Trifluralin was more toxic than nitralin to the shoots of sorghum (Sorghum bicolor (L.) Moench, var. RS-610) and cucumber (Cucumis sativus L., var. Wis. SMR-15 and Pioneer) via shoot exposure. Nitralin was more toxic than trifluralin to the roots via root exposure. A comparison of the phytotoxicity through vapor activity showed trifluralin was much more toxic than nitralin.

When localized treatments of α,α,α-trifluoro-2,6-di-nitro-N,N-dipropyl-p-toluidine (trifluralin) and 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin) were applied to the shoot zone of sorghum (Sorghum bicolor (L.) Moench, var. RS-610) and cucumber (Cucumis sativus L., var. Wis. SMR-15) before seedling emergence, the most susceptible sites were the sorghum coleoptilar node and the cucumber hypocotyl hook. The longer before emergence that the sorghum shoot was exposed to the herbicides, the greater was the injury. However, if herbicide concentration was sufficient, the growing point just above the sorghum coleoptilar node was inhibited by both herbicides when applied after seedling emergence. Maximum uptake of 14C-trifluralin and 14C-nitralin occurred through the coleoptilar node and hypocotyI hook of sorghum and cucumber, respectively. Rate of entry, uptake, and translocation of 14C-trifluralin was greater than that of 14C-nitralin in sorghum and cucumber shoots.

The selectivity of 2,4-dichlorophenyl p-nitrophenyl ether (nitrofen) among rape (Brassica campestris L., var. Echo) and two weed species, redroot pigweed (Amaranthus retroflexus L.) and green foxtail (Setaria viridis (L.) Beauv.), was determined quantitatively by a replicated dosage-response experiment. On an ED50 basis, green foxtail and redroot pigweed were, respectively, 5.8 and 63.3 times more susceptible than rape. Selectivity was divided into three parameters; viz., differential spray retention, differential penetration, and differential effects within the plant. Differences in retention were measured with the use of a water-soluble dye, while differences in penetration were determined with 14C-labelled nitrofen. Spray retention on green foxtail was 66% of that on the rape and 64% as much nitrofen penetrated redroot pigweed as penetrated rape. Under the conditions of these tests it was estimated that green foxtail and redroot pigweed were, respectively, 9 and 99 times more susceptible to nitrofen than was rape.

The phytophagous insects associated with silverleaf nightshade (Solanum elaeagnifolium Cav.) were surveyed in southern California, Arizona, New Mexico, and southwestern Texas. In California, this introduced weed was largely free of deleterious insect injury. Its insect associates mostly were sap or foliage-feeding species that attack a wide range of plants, a few were species restricted to Solanaceae, and several were species economically important as crop pests. The insect fauna became increasingly complex in species diversity and plant parts attacked as the survey progressed eastward from California towards southwestern Texas and the presumed native habitats of this weed in adjacent Mexico. The feasibility of biological control of silverleaf nightshade and the value of faunistic surveys in ascertaining the indigenous or alien status of plants are good.

The germination and growth of six pigweeds (Amaranthus spp.) were studied in the germinator and greenhouse. Treatments with sulfuric acid, acetone, sodium hypochlorate, and potassium nitrate variously influenced species germination. Seedlings emerged more rapidly at 100 F than at other soil temperatures. Variation in seedling characteristics was noted. Some species were more susceptible to 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin) and 2,4-bis (isopropylamino)-6-(methylthio)-s-triazine (prometryne) than others in the greenhouse. In the field little variation in susceptibility to several preplant and preemergence herbicides was found; but there were differences when postemergence herbicides were used.

Effects of 4-amino-3,5,6-trichloropicolinic acid (picloram) on mitochondrial volume changes and ATPase activity were studied with isolated barley (Hordeum vulgare L., var. Wong) and safflower (Carthamus tinctorius L., var. U. S. 10) mitochondria. Changes in mitochondrial volume and/or configuration of mitochondrial membranes were recorded in terms of changes in light scattering, which was expressed as absorbance. Picloram caused swelling of mitochondria previously contracted by ATP. Picloram-induced swelling was characterized by a later partial recovery of the mitochondria to a contracted state. Picloram did not affect succinate-induced contraction nor cause any additional swelling of the mitochondria in 0.3 M KCl medium. A high concentration (10−3 M) of picloram enhanced the activity of ATPase by 31%. This result was consistent with an increased rate of picloram-induced swelling in mitochondria contracted earlier by ATP. The action of picloram apparently differs from that of known mitochondrial swelling agents.

Laboratory and greenhouse studies were conducted to determine the response of four plant species to 4-amino-3,5,6-trichloropicolinic acid (picloram). Germination of soybean (Glycine max (L.) Merr., var. Lee) seeds was inhibited, step-wise, by 10−8 to 10−3 M concentrations of picloram. Safflower (Carthamus tinctorius L.) germination was inhibited at 10−3 M; however, radish (Raphanus sativus L.) and barley (Hordeum vulgare L.) were not affected by any concentration studied (10−6 to 10−3 M). Measurement of several parameters of growth such as fresh and dry weight, shoot height, number and dimensions of leaves, percent necrosis, hypocotyl or epicotyl length, and hypocotyl diameter revealed that picloram was both growth promotive and inhibitory to safflower, radish, and barley. Levels of picloram required for growth promotion or inhibition varied with the species, stage of plant growth, herbicide concentration, the specific tissue, and the parameter being measured. Typical malformations such as twisting of stems, death of growing points, and occurrence of callus growth (depending on the species and herbicide dosage) were observed in picloram-treated seedlings. Studies on water loss by evapotranspiration suggested that picloram caused a possible alteration of stomatal behavior and/or a disturbance of water metabolism in plants under appropriate conditions.

Seed of common ragweed (Ambrosia artemisiifolia L.) ecotypes were collected from 12 locations in North America and were planted at Ithaca, New York. Plants from seed collected in the northern latitudes flowered earlier and produced less vegetative growth. The difference in growth and development of the ecotypes was caused by the day length or latitude where they had originated. Seedlings emerging in early July produced approximately one-third as much fresh or dry weight and about one-third as many viable seeds as those emerging in the middle of May. The latter produced more than 32,000 seed per plant.

Leaching of N,N-dimethyl-2,2-diphenylacetamide (diphenamid) was measured with bioassays in three soils; a fine sand, a silt loam, and a muck. The movement of diphenamid was reduced as the clay or the organic matter content of these soils increased. Efficiency of organic matter for adsorption of diphenamid decreased as the organic matter content of soil mixtures increased. Clay (bentonite) was less efficient than organic matter in adsorbing diphenamid. Desorption of diphenamid from muck soil was very slow.

The concentration of N,N-dimethyl-2,2-diphenylacetamide (diphenamid) required to cause 50% growth inhibition (I50) of the shoots or roots in soil, or the roots in a bioassay, was determined for several species. of the plants tested, grasses were the most sensitive, while Solanaceae were among the most tolerant to diphenamid. Based on shoot inhibition, the sensitivity difference between the sensitive foxtail millet (Setaria italica L.) and the tolerant pepper (Capsicum frutescens L.) was 150 fold. Highly significant correlations among the I50 values indicate that any of the three methods would be satisfactory for measuring the sensitivity of species to diphenamid.

Foliar applications of 2-chloroethylphosphonic acid (CEPA) 7 days prior to spot applications of 14C-labelled 3,6-dichloro-o-anisic acid (dicamba) to leaves of wild garlic (Allium vineale L.) increased basipetal translocation of the dicamba as measured 7 days after dicamba treatment. High concentrations of CEPA were inhibitory. The ethylene released from CEPA degradation may have altered the metabolic “sink-source” relationships within the wild garlic plants allowing increased basipetal translocation of subsequent applications of dicamba when low concentrations of CEPA were applied.

Seeds of dyers woad (Isatis tinctoria L.) readily germinated at temperatures from 3 to 25 C. Dyers woad seeds in their fruits, from which they do not normally dehisce, had greatly depressed germination compared to that of threshed seeds. The presence of dyers woad fruits in the same Petri dish markedly depressed germination and/or root elongation of threshed dyers woad seeds and the seeds of some competing broadleaf and grass species. The depression was especially evident on seeds of other species of Cruciferae. Similar reductions in germination or root elongation were obtained when water used to soak dyers woad fruits was used to wet germination substrates.