Directed applications of low rates of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), disodium methanearsonate (DSMA), monosodium methanearsonate (MSMA), 1,1′-dimethyl-4,4′-bipyridinium salts (paraquat), and 2,4-bis(isopropylamino)-6-(methylthio)-s-triazine (prometryne) controlled annual weeds in irrigated cotton (Gossypium hirsutum L.). Although the first applications of most herbicides caused temporary, localized foliage chlorosis or burning, cotton yields, fiber properties, and boll components were not affected. Early applications of DSMA followed by diuron selectively controlled annual weeds. When a herbicide was applied before planting, fewer postemergence applications were needed for weed control.

The most effective and dependable method of controlling wild cane [Sorghum bicolor (L.) Moench] in corn (Zea mays L.) was with a combination of cultivation plus herbicides. Timely cultivations were equally or more effective than preplant herbicides in controlling wild cane, but neither method was adequate by itself. The best herbicide in this study for the control of wild cane in corn was S-ethyl dipropylthiocarbamate (EPTC) alone or in combination with (2,4-dichlorophenoxy)acetic acid (2,4-D) or 2-chloro-4,6-bis-(ethylamino)-s-triazine (simazine). Residual effects of simazine at 4 lb/A in the soil reduced the yield of the following oats (Avena sativa L.) crop 1 out of 3 years.

Corn (Zea mays L.) in the two to three-leaf stage grown 18 to 21 days in a growth chamber under cold, wet conditions was injured by postemergence application of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) plus emulsifiable phytobland oil. Injury was most severe when these plants were kept under cold, wet conditions for 48 hr after the herbicidal spray was applied, followed by exposure to high light intensity and high temperature. Under these growth chamber conditions, approximately 50% of the atrazine-treated plants died. Since wet foliage before and after application increased foliar penetration and low temperature decreased the rate of detoxication to peptide conjugates, atrazine accumulated under cold, wet conditions. This accumulation of foliarly-absorbed atrazine and the “weakened” conditions of the plants grown under the stress conditions is believed to be responsible for the injury to corn. Hydroxylation and the dihydroxybenzoxazin-3-one content in the roots were reduced at low temperature, but it is unlikely that this contributed to the death of the corn.

Rhizomes develop from the crowns of yellow nutsedge (Cyperus esculentus L.) shoots and the tips transform into shoots or tubers. Transformation of primary rhizomes developed by the original shoot of a plant is a valid index of plant response to treatment when compared with the transformation of all rhizomes (primary, secondary, tertiary, and others), developed by a plant under treatment.

Failure to control common groundsel (Senecio vulgaris L.) was observed in 1968 in a nursery where 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) or 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) had been used once or twice annually since 1958. Seedlings from seed collected at that location were not controlled by pre-emergence applications of simazine or atrazine at rates up to 17.92 kg/ha. Seedlings from a seed source where triazine herbicides had not been in continuous use were completely controlled by 1.12 or 2.24 kg/ha of either chemical, and partially controlled by 0.28 to 0.56 kg/ha. Postemergence applications of atrazine at 1.12, 2.24, or 4.48 kg/ha did not affect common groundsel from the nursery source, but killed small seedlings from the other source. Preemergence applications of four other herbicides were equally effective against seedlings from both sources.

Grain sorghum (Sorghum bicolor (L.) Moench, var. RS-610) grown under field conditions during 1965 to 1967 on three soils in the High Plains of west Texas, was treated at different stages of plant growth with 2-chloro-4-(ethylamino)-6-(isopropylamino)s-triazine (atrazine). Maximum injury was caused by supplemental sprinkler irrigation. Tolerance of grain sorghum to atrazine increased as height of sorghum plants increased. Treatments on 1 and 3-inch sorghum reduced grain yields significantly, but plants treated when 6 inches or more in height produced yields similar to hand-weeded plots, except on Brownfield loamy sand where yields were reduced even at ½ lb/A. Similar trends were observed in 1966 with a forage sorghum (Lindsey 101F). However, yield reductions occurred only when atrazine was applied at 2 and 4 lb/A to sorghum plants I inch tall. Results show that atrazine can be used effectively and safely for weed control in sorghum grown on fine sandy loam or heavier soils in the southern High Plains, providing the crop is at least 6 inches tall when treated.

Under the erractic rainfall distribution of the Southern Great Plains, average pigweed (Amaranthus sp.) control in five studies with seven herbicides was enhanced by incorporation in 1 or 3 inches of soil with a power rototiller. Compared to no incorporation, 9-inch incorporation improved pigweed control with two herbicides, had no effect on weed control with two others, and decreased weed control with another three. Soil incorporation at 1 or 3 inches did not increase weed control with three compounds if 0.4 inch of rainfall occurred within 2 weeks after application. Incorporation into 1 or 3 inches of soil improved weed control with four herbicides even when rainfall occurred within 2 days after application. In four of the trials, neither herbicides nor incorporation depth affected cotton stand or vigor. Under the soil moisture conditions prevailing in the one trial where yield data were obtained, cotton (Gossypium hirsutum L.) stand and lint yield decreased lineally with depth of soil incorporation. Herbicides did not affect cotton stand or yield.

We characterized soil and vegetation assemblages, many of which are infested with medusahead (Taeniatherum asperum (Sim.) Nevski), on the margin of the Great Basin. Interpretations of these assemblages provide an index of the validity of the basic environmental unit of this ecosystem which can be manipulated through weed control and revegetation techniques. Vertisol (churning clay soils) sites with sparse native plant communities are more susceptible to medusahead invasion than more complex low sagebrush (Artemisia arbuscula Nutt.) or low sagebrush-woodland communities on related clay soils. If the more complex communities are degraded to a low seral state, medusahead can invade and occupy the site. Wet meadows and burned coniferous forest sites at high elevations were the only sites where medusahead occurred on soils with textures other than clay. Big sagebrush (Artemisia tridentata Nutt.) communities on medium to coarse textured soils were very resistant to medusahead invasion. The restriction of medusahead to certain sites controls the mechanism of invasion and interacts with the breeding system of the species to influence its evolution.

Nitralin (4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline) controlled grasses and 3-[p-(p-chlorophenoxy)phenyl]-1,1-dimethylurea (chloroxuron) controlled broadleaf weeds in soybeans (Glycine max (L.) Merr.) as well singly as when combined. In 1 year out of 2, nitralin and chloroxuron in combination caused more plant injury than either herbicide alone. The combination of nitralin (0.56 or 0.84 kg/ha) with chloroxuron (1.68 kg/ha) reduced seed yields 37% from the value obtained with chloroxuron alone (1.68 kg/ha).

Wheat (Triticum aestivum L., var. Selkirk) was most susceptible at the late tiller stage to 4-amino-3,5,6-trichloropicolinic acid (picloram) as determined from weekly applications in the field and the degree of injury increased with rate of picloram. Wheat injury from picloram was manifested by lower kernel yield, greater protein content in the kernels, and reduction in plant height. A reduction in the length of the stem occurred while the length of the flag leaf sheath was not affected. Picloram increased kernel size in 1966 but reduced it in 1965. Picloram did not influence germination of kernels from treated plants. The addition of (2,4-dichlorophenoxy)acetic acid (2,4-D) to picloram tended to increase wheat injury at the 2 to 4-leaf stage.

The degradation kinetics of propylene glycol butyl ether (hereafter referred to as PGBE) ester of 2-(2,4,5-trichlorophenoxy) propionic acid (silvex) and the persistence of silvex in water and sediment were studied under impounded conditions. PGBE ester of silvex was applied to the surface of three ponds at the rate of 9 kg/ha/A. Water and sediment samples were collected at 4, 12, 24, and 48 hr after treatment and were extracted for PGBE ester of silvex immediately after collection. The concentrations of PGBE ester of silvex and silvex present in the water and sediment samples were determined by gas chromatography. Physico-chemical and mineralogical characteristics of the sediment samples collected prior to treatment were determined. The hydrolysis of PGBE ester of silvex to silvex obeyed first order reaction kinetics, the specific reaction rate constants for the three ponds being 0.09 hr−1, 0.10 hr−1, and 0.14 hr−1. Fifty percent hydrolysis of PGBE ester of silvex occurred in 5 to 8 hr, 90% hydrolysis occurred in 16 to 24 hr, and 99% hydrolysis occurred in 33 to 49 hr. The concentration of silvex in water initially increased, but decreased to zero by the end of 3 weeks. Adsorption of both the PGBE ester of silvex and silvex appeared to occur on the sediment; essentially complete disappearance of both occurred by the fifth week following treatment. Under laboratory conditions, silvex adsorption by the sediments conformed to the Freundlich adsorption equation.

An implanted soil mass technique was modified to study the effect of soil-incorporated herbicides on root growth. The technique was used to study the effects 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 root growth of cotton (Gossypium hirsutum L., var. Auburn 56) and the effects of trifluralin and S-propyl dipropylthiocarbamate (vernolate) on soybeans (Glycine max (L.) Merr., var. Bragg). Vernolate had no effect, but there was only 57% as much soybean root tissue in the soil receiving 1 ppm of trifluralin as there was in the untreated check 2 months after initiating the treatments. Trifluralin and nitralin at 1 ppm reduced cotton roots to 75% and 50%, respectively, of that of the untreated check. The effects of trifluralin and low soil pH were additive, but there was no interaction between them.

Ten plant species were grown in competition with each other at different soil moisture levels in a greenhouse. Corn (Zea mays L.), barnyardgrass (Echinochloa crusgalli (L.) Beauv.), cocklebur (Xanthium pensylvanicum Wallr.), sorghum (Sorghum vulgare L., var. RS 626), and large crabgrass (Digitaria sanguinalis (L) Scop.) produced the most growth in wet soil. Dry soil greatly reduced growth of these species. Palmer amaranth (Amaranthus palmeri S. Wats.) produced an intermediate amount of growth under wet and medium soil moisture and much less in dry soil. Kochia (Kochia scoparia (L.) Schrad.), Russian thistle (Salsola kali L., var. tenuifolia Tausch), buffalobur (Solanum rostratum Dunal.), and tumble-grass (Schedonnardus paniculatus (Nutt.) Trel.) produced much less growth under wet conditions than the more competitive species, but growth was not reduced in dry soil. Russian thistle produced twice as much growth in dry as in wet soil.

The phytotoxicity of 3-[p-(p-chlorophenoxy)phenyl]-1,1-dimethylurea (chloroxuron) usually decreased as the stage of growth of five weed species at treatment increased. Giant foxtail (Setaria faberii Herrm.), velvetleaf (Abutilon theophrasti Medic.), and the cotyledonary stage of cocklebur (Xanthium pensylvanicum Wallr.) were most resistant to the herbicide. Ivyleaf morningglory (Ipomoea hederacea (L.) Jacq.) and jimsonweed (Datura stramonium L.) were more susceptible to chloroxuron. Soybean (Glycine max (L.) Merr.) seemed less susceptible at the cotyledonary stage than at later stages. Phytotoxicity on both weeds and soybeans was increased by increased temperature and relative humidity following chloroxuron application. The phytotoxicity of chloroxuron also was increased by simulated rainfall in greenhouse studies.

The influence of soil-applied phosphorus on the phytotoxicity of soil-applied 3-amino-s-triazole (amitrole) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) for corn (Zea mays L.), ryegrass (Lolium multiflorum L.), rye (Secale cereale L.), snapbeans (Phaseolus vulgaris L.), soybeans (Glycine max (L.) Mers.), sorghum (Sorghum vulgare Pers.), wheat (Triticum aestivum L.), cotton (Gossypium hirsutum L.), peanuts (Arachis hypogaea L.), and peas (Pisum sativum L.) was studied under greenhouse conditions. All species except cotton and peanuts indicated an amitrole-phosphorus interaction. Greater phytotoxicity was found for a given rate of amitrole as the soil phosphorus level was increased. A diuron-phosphorus interaction was observed for cotton and soybeans only.

Several herbicides were evaluated for control of spring parsley [Cymopterus watsonii (Coult. & Rose) Jones]. The propylene glycol butyl ether esters and dimethylamine salt of (2,4-dichlorophenoxy)acetic acid (2,4-D) applied at 2 lb/A were 99% effective. Ninety-nine percent control was achieved also with 0.5 lb/A of 4-amino-3,5,6-trichloropicolinic acid (picloram) and 2,4-D amine + picloram at 0.4 + 0.1 lb/A, 2,4-D amine + picloram at 0.33 + 0.17 lb/A, and (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) + picloram at 0.25 + 0.25 lb/A.

The uptake of herbicides by soybean (Glycine max (L.) Merr.) seed from 14C-labeled aqueous solutions of 3-amino-2,5-dichlorobenzoic acid (amiben), 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine), 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron), S-ethyl dipropylthiocarbamate (EPTC), and isopropyl m-chlorocarbanilate (chlorpropham) was determined by measuring reduction in the concentration of the herbicides in the soaking solution. There was a direct proportional relationship between uptake and concentration. Raising the temperature from 10 to 30 C increased uptake of herbicides. The greatest increase occurred from 10 to 20 C. After 48 hr at 30 C, 39% of the amiben, 61% of the atrazine, 65% of the EPTC, 83% of the linuron, and 92% of the chlorpropham in the original solution was absorbed by the seed. Uptake rates were similar in living and dead seed. Uptake was reversible with amiben but not with chlorpropham. Absorption of herbicides could not be associated with absorption of water except during the first few hours when the seed were rapidly imbibing water. Ratios of seed to solution herbicide concentrations all exceeded 1:1 after 48 hr and with chlorpropham, reached 68:1. The uptake of herbicides by seed was largely a physical process that required seed hydration, but herbicide uptake continued after water uptake ceased.