The phytotoxicity of 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron) to corn (Zea mays L.) and soybean (Glycine max (L.) Merr.) seedlings and 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) to soybean seedlings increased with increasing temperature from 20 to 30 C. The phytotoxicity of α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) did not change significantly between 20 and 30 C. Corn and soybean plants grown at 30 C translocated more 14C from 14C-atrazine and soybeans more 14C from 14C-linuron to the shoots during the 4-hr root uptake treatment period than plants grown at 20 C. There was less accumulation of 14C from 14C-atrazine in soybean roots and 14C-linuron and 14C-trifluralin in the roots of corn and soybean plants grown at 30 C compared to those grown at 20 C. Comparison of data at 30 C and 20 C during the 4-hr root uptake treatment period showed enhanced root to shoot movement of 14C from 14C-atrazine in corn and from 14C-linuron in soybean at the higher uptake treatment temperature indicating a possible relationship between increased herbicide transport to the shoot at high temperature and increased phytotoxicity.

The effects of time, concentration, pH, temperature, and metabolic inhibitors on 4-amino-3,5,6-trichloropicolinic acid (picloram) uptake from nutrient solution by oats (Avena sativa L. ‘Markton’) and soybeans (Glycine max L. ‘Lee’) were studied. Oats and soybeans had similar absorption patterns of rapid initial uptake. However, total accumulation patterns markedly differed in that accumulation was concentration-dependent for oats but not for soybeans. Initial uptake by oats and soybean roots increased as solution concentration increased. Picloram was redistributed in oats and soybeans and some egress from roots to solution occurred. Picloram uptake by both plant species was markedly diminished with an increase in pH from 3.5 to 4.5, but pH had little effect from 4.5 to 9.5. Less picloram was taken up by oats and soybean roots from solution maintained at 4 C than at 26 C. Translocation to tops followed a similar trend. Increasing concentrations of three metabolic inhibitors, 2,4-dinitrophenol (DNP), sodium azide, and sodium arsenite, reduced root uptake of picloram in both species. All inhibitors (except DNP for oats) at 10−6 to 10−5 molar concentrations stimulated translocation of picloram to oats and soybean tops while higher concentrations depressed translocation.

The uptake of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) was studied in sudangrass [Sorghum sudanense (Piper) Stapf, var. Piper], grain sorghum [Sorghum bicolor (L.) Moench], and corn (Zea mays L.) to find whether differences in atrazine uptake exist among these species. The uptake of atrazine followed closely the growth patterns of corn, sorghum, and sudangrass during the first 5 weeks of growth. Concentration of 14C from ring-labeled 14C-atrazine in the soil reached a peak in corn, sorghum, and sudangrass plants after 2 weeks of growth and then declined. The 14C concentrations were two to three times greater in sorghum and sudangrass than in corn throughout the 5-week period. Atrazine uptake per gram of plant growth by these crops was directly proportional to the concentration of atrazine in the soil and the proportionality factors were in the order: sudangrass < sorghum ≫ corn. Total uptake and the total growth were in order: corn ≫ sorghum = sudangrass. In a study where relative humidity was a variable, the amount of atrazine absorbed per ml of water was inversely related to total water usage.

Dissipation of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) in sprinkler-irrigated fields was faster in a silty clay loam soil of eastern Nebraska than in loam soils of central or western Nebraska. Atrazine dissipated faster under fallow than under corn (Zea mays L.) culture in western Nebraska, but there was no difference in atrazine loss whether in corn or fallow in central or eastern Nebraska. In central and western Nebraska, atrazine persisted in the soil for longer than 1 year. In eastern Nebraska under sprinkler irrigation, most of the atrazine had dissipated before the following growing season. Sprinkler irrigation markedly reduced atrazine longevity in soils studied.

Cotton (Gossypium hirsutum L.) was grown at two locations in Alabama during 1966 to 1969 with specific densities of sicklepod (Cassia obtusifolia L.) and tall morningglory (Ipomoea purpurea L. Roth). Competition from sicklepod and tall morningglory caused cotton yield reductions at densities as low as eight weeds per 7.31 m of row. Tall morningglory was usually more competitive than sicklepod in cotton. Both species were more competitive on Lucedale sandy clay loam than on Norfolk sandy loam. Sicklepod at eight weeds per 7.31 m of row reduced yields from 10 to 23% on the Norfolk soil and approximately 40% on the Lucedale soil. At the highest density, 48 sicklepod plants per 7.31 m of row, yields were reduced 45 to 65% on the Norfolk soil and approximately 80% on the Lucedale soil. Tall morningglory at a density of eight weeds per 7.31 m of row reduced cotton yields 10 to 40% on the Norfolk soil and 50 to 75% on the Lucedale soil. Vegetative growth, boll, and seed size were not affected as much as cotton yields by competition. Percentage lint and lint fiber properties were unaffected by competition.

The differential response of three selections of johnsongrass (Sorghum halepense (L.) Pers.) to different temperatures and dark periods was studied in two experiments conducted in growth chambers. The three selections of johnsongrass were obtained from locations representing different climates. At 20 C all three selections grew equally with respect to most parameters of growth studied; however, at 35 C the selection from the southern climate produced more total fresh weight than the other two selections. Rhizome production and the number of stems also were greater in the southern selection at 35 C. An 8-hr dark period prevented flowering in all three selections and significantly reduced rhizome production in two selections compared to the 12-hr dark period. Flowering occurred most rapidly in the selection from a northern climate and most slowly in the selection from a southern climate. The results are discussed in relation to the possible plant adaptive changes and the possibility of weed control through dark period interruption.

Competitive effects of cocklebur (Xanthium pensylvanicum Wallr.) and redroot pigweed (Amaranthus retroflexus L.) on cotton (Gossypium hirsutum L.) were evaluated in four experiments at two locations in Alabama during the period 1966 to 1968. Cocklebur was more competitive with cotton than was pigweed on Norfolk sandy loam soil. A density of eight cocklebur plants per 7.31 m of row reduced cotton yields 20 to 40%. Higher densities of cocklebur resulted in greater yield reductions. Forty-eight cocklebur plants per 7.31 m of row caused cotton yields to be reduced more than 80%. Pigweed at a density of 48 weeds per 7.31 m of row reduced cotton yields less than 50% on the Norfolk soil. On Lucedale sandy clay loam, cocklebur and pigweed were equally competitive and both species were more competitive than on Norfolk soil. A density of eight cocklebur or pigweed plants per 7.31 m of row resulted in 60 to 70% cotton yield reductions. The highest density of pigweed studied, 48 plants per 7.31 m of row, reduced cotton yields 90% on the Lucedale soil. Vegetative growth, boll, and seed size were not affected as much as cotton yields by either weed species. Percentage lint and fiber properties were unaffected by plant competition.

Two new varieties of foxtails, Setaria viridis var. robusta alba Schreiber and Setaria viridis var. robusta-purpurea Schreiber are described. As their names imply, they differ from each other only in the color of their bristles but differ from Setaria viridis (L.) Beauv. and Setaria viridis var. major (Gaud.) Posp. in their robust growth habit, morphology, and physiological responses. A key distinguishes these from other species of similar habit and habitat.

Toxicity of soil-applied 2-(tert-butylamino)-4-(ethylamino)-6-(methylthio)-s-triazine (terbutryn) to cucumbers (Cucumis sativus L. ‘Gemni’) and oats (Avena sativus L. ‘Nodaway’) was increased 2.2 times when the light intensity was raised from 11,000 to 22,000 lumens/m2 and 1.5 times when the moisture level was raised from low (25 to 50% field capacity) to high (75 to 100% field capacity). When the temperature was raised from the low level (19 C day, 14 C night) to the high level (29 C day, 24 C night) toxicity of terbutryn to oats was increased 1.6 times and toxicity to cucumber was increased 1.3 times. Analysis of interactions of the three variables on toxicity of terbutryn showed that environmental conditions favoring rapid growth resulted in an increase in phytotoxicity.

Gamma radiation of 3 megarads (Mrad) achieved complete sterilization in Newe Ya'ar clay soil, without affecting subsequent growth of oats (Avena sativa L., var. Mulga) in the irradiated soil. N,N-dimethyl-2,2-diphenylacetamide (diphenamid) in aqueous solution or mixed within Newe Ya'ar soil was detoxified by irradiation with 3 Mrad.

Root and shoot extracts of 3-week-old sudangrass [Sorghum sudanense (Piper) Stapf, var. Piper], grain sorghum [Sorghum bicolor (L.) Moench], and corn (Zea mays L.) plants degraded 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) in order: shoot > root and corn ≫ sorghum = sudangrass. In 3-week-old detopped plants, the rate of atrazine exudation was 14 times greater in sudangrass and sorghum than in corn when grown in Keith sandy loam containing 0.5 ppmw 14C-atrazine. Extraction and analysis of plant shoots revealed that 7 to 8% of the 14C was present as atrazine in sudangrass and sorghum whereas no atrazine was found in corn. In 14C tracer studies, thin-layer chromatography showed that sudangrass and sorghum metabolized atrazine by a pathway which differed from the pathway in corn. Sudangrass and sorghum metabolized atrazine primarily to 2-chloro-4-amino-6-(isopropylamino)-s-triazine and 2-chloro-4-amino-6-(ethylamino)-s-triazine which are only partially detoxified compounds. Corn metabolized atrazine to 2-hydroxy-4-(ethylamino)-6-(isopropylamino)-s-triazine (hydroxyatrazine) which is non-phytotoxic.

Studies were made of isozyme patterns of three enzymes and of total soluble proteins from seedlings of three crop species which were grown in association with different weed species. The gel electrofocusing separation technique was used. Marked qualitative and quantitative changes were observed in peroxidase of cabbage (Brassica oleracea L.) seedlings when grown in association with jimsonweed (Datura stramonium L.), velvetleaf (Abutilon theophrasti Medic.), wild mustard (Brassica kaber DC.), and green foxtail (Setaria viridis (L.) Beauv.). No differences were observed when lettuce (Lactuca sativa L.) and tomato (Lycopersicum esculentum Mill.) were grown in association with the above weed species. No differences were found in total soluble proteins or the isozyme patterns of esterase and acid phosphatase.

A mixture of dimethyl sulfoxide (DMSO), glycerol, phytobland oil, and water (50:25:15:10, v/v) proved to be outstandingly effective as a carrier for water-soluble formulations of 4-amino-3,5,6-trichloropicolinic acid (picloram), (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T), and mixtures thereof. The carrier was selected after numerous experiments in which these and other adjuvants, used individually, gave at least some degree of herbicidal enhancement on velvet mesquite seedlings [Prosopis juliflora var. velutina (Woot.) Sarg.]. Maximum synergism between the carrier complex and herbicide occurred with the triethylamine salt of 2,4,5-T; relatively little influence on the butoxyethanol ester was observed. Picloram and 3,6-dichloro-o-anisic acid (dicamba) were intermediate in activity between the two phenoxy formulations.

A soil sampler was constructed for moisture and pesticide residue determinations that will retrieve soils with rocky and heavy clay layers. The sampler consisted of a commercially constructed worm-gear driven auger mounted in a 3.7-m-tall vertical frame. Depth, speed, accuracy, and ease of sample retrieval were substantially increased, compared to manual sampling.

Nonradioactive and 14C-organic arsenical herbicides were applied to foliage of young cotton (Gossypium hirsutum L., var. Acala SJ-1) at various temperatures. An application of 3.36 kg/ha of monosodium methanearsonate (MSMA), with and without 0.5% surfactant, severely injured plants exposed at 13 C. Similar injury resulted when plants were exposed and treated at 20 C with MSMA containing 0.5% surfactant. Applications of MSMA did not injure plants exposed at 31 C. Disodium methanearsonate (DSMA) was less injurious to cotton than MSMA. Only slight to moderate injury resulted when plants were exposed and treated at 13 C with 3.36 kg/ha of DSMA containing 0.5% surfactant. Applications at higher temperatures did not injure cotton. Cotyledons absorbed 14C-methanearsonic acid (MAA) and 14C-MSMA more readily than 14C-DSMA. Contact injury from these herbicides was slight at 13 C but was pronounced at 20 and 29 C. Generally, translocation of herbicides into developing true leaves was slight. The exception resulted from applications of 14C-MSMA to plants at 13 C when contact injury was negligible.

Differential selectivity was shown for 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine), 2-chloro-4, 6-bis(isopropylamino)-s-triazine (propazine), and S-ethyl diisobutylthiocarbamate (butylate) on giant foxtail (Setaria faberi Herrm.) yellow foxtail (Setaria glauca (L.) Beauv.), giant green foxtail (Setaria viridis var. major (Gaud.) Posp.), robust white foxtail (Setaria viridis var. robusta-alba Schreiber), and robust purple foxtail (Setaria viridis var. robusta-purpurea Schreiber). The differentials obtained could explain the reports of uncontrolled Setaria species and the apparent increase of the latter three varieties. The two new varieties of green foxtail, robust white and robust purple foxtails, were the most tolerant varieties or species to atrazine and propazine with giant green foxtail intermediate between the robust foxtails and green, giant, and yellow foxtail. The ED50 values for the robust foxtails were also higher than for the other varieties and species studied. Yellow foxtail was the most tolerant to butylate. The effective rate, measured as percent of control, was directly related to soil organic matter content.

Night applications of phenoxy herbicides on plains pricklypear (Opuntia polyacantha Haw.) resulted in more plants being killed than comparable day applications. Night applications gave rapid herbicidal responses that were negated by the second year if chemical concentrations were too high. With low herbicide concentrations (½ and 1 lb aehg) effectiveness increased with proportion of diesel oil in carrier. The ester forms of 2-(2,4,5-trichlorophenoxy)propionic acid (silvex) killed more plants than did the ester or amine forms of (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) in diesel oil:water (1:4, v/v) carriers.

The herbicide 3,6-dichloro-o-anisic acid (dicamba) is very mobile in Tartary buckwheat (Fagopyrum tataricum (L.) Gaertn.), a susceptible weedy species. After foliar or root application, the compound was translocated rapidly to meristematic tissues at the shoot apex and in leaf axils. Redistribution of dicamba in the shoot, to young tissues, continued for at least 20 days. Metabolism of dicamba occurred very slowly, both in intact plants and in detached leaves, and the only metabolite detected was conjugated with sugars. The nonphytotoxic metabolite was identified by paper and thin-layer chromatography as 5-hydroxy-3,6-dichloro-o-anisic acid. Decarboxylation of dicamba also occurred in the plants but extremely slowly. The rapid entry and translocation of dicamba, its continued mobility in treated plants, and its very low rate of detoxification are major contributing factors to the effectiveness of dicamba for controlling Tartary buckwheat.

Herbicide treatments of 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron), 2,4-bis(isopropylamino)-6-(methylthio-s-triazine (prometryne), or methyl ester of 3-amino-2,5-dichlorobenzoate (chloramben ester) were applied preemergence to soybean (Glycine max (L.) Merr. ‘Dare’ or ‘Bragg’) plots previously treated with S-propyl dipropylthiocarbamate (vernolate), α,α.α,-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin), or 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin). Sequential treatments of vernolate with linuron, prometryne, or chloramben ester controlled weeds more effectively in soybeans than did trifluralin or nitralin applied with the same preemergence treatments. Soybean injury was not severe enough to reduce seed yields in any year. Yields were greater in 1970 when soybeans were treated with vernolate than when treated with either trifluralin or nitralin. Soybean yields also were greater in 1970 when treated with chloramben ester than when treated with linuron or prometryne. In 1969 when soybeans were planted in a sandy loam, prometryne reduced stands more than did linuron or chloramben ester.

The absorption and translocation of foliarly applied 14C-labeled (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T-1-14C) in winged elms (Ulmus alata Michx.) as affected by season of application, air temperature, and soil moisture were determined by autoradiography of bark samples and liquid scintillation counting of leaf tissue. Treatments at 3-week intervals throughout the growing season showed highly variable trends in absorption and translocation within and between growing seasons. Seasonal variations in the absorption of 14C-2,4,5-T were similar to the variations in translocation. Translocation into the stem closely correlated with absorption into the leaves. Higher daily temperatures of 24 to 40 C appeared to enhance absorption and translocation. Variations in soil moisture showed little effect on absorption; whereas, a decrease in soil moisture reduced translocation from leaves to roots.