The phytotoxicity from preemergence applications of the herbicides 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine), 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), isopropyl N-(3-chlorophenyl) carbamate (CIPC), 2-chloroallyl diethyldithiocarbamate (CDEC) and 2-chloro-N,N-diallylacetamide (CDAA) was measured at 17 field locations in the coastal plain of North Carolina over three years. Site selections were made with specific regard for soil organic matter, which varied from 0.7 to 48.8 percent. Phytotoxicity responses determined at four to five weeks after treatment were the amounts of herbicide required to cause a 50 percent reduction in (1) soybean dry shoot weight, (2) cotton dry shoot weight and (3) number of weedy annual grasses. Fourteen factors were measured at each location to characterize soil, climatic and biotic factors, and correlated with plant responses obtained. For simazine, diuron and CIPC the factors measured accounted for 60 percent of the plant response variation. The highest simple correlation was usually between soil organic matter and plant response. Phytotoxicity of the aromatic herbicides was inversely correlated with soil organic matter level. CDAA and CDEC usually gave reliable and repeatable performance at constant rates on soils containing between 3 and 40 percent soil organic matter. Below 3 percent soil organic matter, extreme variation in CDAA and CDEC toxicity was encountered.

Effects of simazine (2-chloro-4,6-bis(ethylamino)-s-triazine) and atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) were observed when applied in connection with 3-amino-1,2,4-triazole (amitrole) to citrus trees. The amitrole had no significant effect. In heavy soil, atrazine toxicity to citrus trees was found during the summer following applications after a period of severe hot dry wind. The leaves became bronzed and dried, growth was checked, dry matter, chlorophyll, and catalase activity of leaves reduced, and their peroxidase activity increased when compared with controls from unsprayed plots; ascorbic acid content of leaves also was affected. Simazine, on the contrary, enhanced growth of trees, total and protein nitrogen and chlorophyll in leaves, did not affect peroxidase, catalase or ascorbic acid, and only slightly depressed dry matter content. In a light soil, probably due to less residual triazines, no toxic effects were observed and untreated controls evinced less growth, lower chlorophyll and nitrogen content of leaves, and higher peroxidase activity than all triazine treatments.

Among 12 of the more effective surfactants selected from a preliminary experiment, there were few differences in their ability to increase atrazine toxicity to large crabgrass [Digitaria sanguinalis (L.) Scop.] and sorghum (Sorghum vulgare Pers.), or in toxicity to large crabgrass and sorghum when used alone. Surfactants per se showed some toxicity to large crabgrass and sorghum. As large crabgrass increased in size, it became less susceptible to injury from atrazine plus dodecyl ether of polyethylene glycol (Surfactant WK). Early spraying with atrazine plus Surfactant WK reduced the top-growth yield of six grass species.

In field studies, atrazine alone and surfactants plus atrazine applied at the 1-in weed height gave very good early weed control. Field plots treated at the 4-in weed height generally produced more weed top-growth and less sorghum than plots treated at the 1-in height. Only the preemergence atrazine treatments gave weed yields that were equal to treatments that included handweeding. Sorghum injury from the surfactants was evidenced by reduced stover yields.

Atrazine plus surfactant toxicity to emerged large crabgrass, grown in growth chambers, increased with higher relative humidities. This was not true for sorghum. The 1% surfactant mixtures generally had a lower surface tension than the 0.1% concentrations although the differences were not great. Surface tension was not the main factor governing the phytotoxicity of foliar-applied atrazine solutions. Translocation of atrazine from sorghum and large crabgrass leaves dipped in a C14-ring-labeled atrazine solution was very slight or nonexistent.

The herbicide 3-amino-2,5-dichlorobenzoic acid (amiben) was converted to N-(3-carboxy-2,5-dichlorophenyl)-glucosylamine, N-glucosyl amiben, in roots of plants treated with amiben. Identification of N-glucosyl amiben was accomplished by means of thin-layer and gas chromatography and confirmed by infrared spectroscopy. The postulated metabolite was synthesized and found to be identical with the product of amiben metabolism in plants.

Cotton seedlings emerged normally following applications of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) before or after furrowing for the preplanting irrigation, but 7 to 10 days after emergence stands were sometimes reduced when diuron was applied before furrowing. Stand reductions were most severe when cottonseed were planted at or above the layer of diuron-treated soil. Cotton varieties differed in tolerance to diuron. Preplanting applications controlled annual weeds until mid-season and treated cotton produced normal yields, except where stands were reduced. Fiber properties and boll components of treated cotton were not altered. Content of diuron was highest in young cotton plants. No diuron was found in cottonseed at harvest using an analytical procedure having a sensitivity of 0.1 ppm.

Imopea purpurea (L.) Roth and /. hederacea (L.) Jacq. significantly and equally reduced soybean yields and plant height, and increased lodging and the difficulty of harvesting. Damage to soybeans increased as the population of morningglories increased. Control of morningglories was needed for 6 to 8 weeks from the date of soybean planting. Morningglories germinated throughout the season and emerged from a depth of 6 inches below the soil surface.

Most of the 3-amino-2,5-dichlorobenzoic acid (amiben) absorbed by treated plants was converted to N-glucosyl amiben in the roots. Only small amounts of amiben and N-glucosyl amiben occurred in stems and leaves. The N-glucoside was not metabolized further and remained in vegetative tissue of soybeans for at least 50 days. Soybeans which were depleted of carbohydrate reserves by starvation in the dark absorbed less amiben and produced less N-glucosyl amiben than did plants treated under normal illumination. A similar trend was noted for tomato plants treated in a comparable manner.

The tolerances of wheat and wild buckwheat (Polygonum convolvulus) to various rates of 2-methoxy-3,6-dichlorobenzoic acid (dicamba) were determined under field conditions and supplemented by studies with wheat in the growth chamber. Wheat height and yield were inversely proportional to rate, but response to various rates was dependent on stage of growth at application. Greatest reductions in wheat height and yield resulted from treatment at the late tiller and boot stages, respectively. The weight per 100 wheat seeds was increased from treatment at the boot and flower stages but was decreased at the early tiller stage.

The ratio of peduncle length: length of the flag leaf-sheath was decreased most from 24 oz/A applied preemergence and 12 oz/A applied at the late tiller stage.

Growth rate of wheat was decreased for a 2-week period after treatment. Excellent kill of wild buckwheat was observed from all rates applied through the 12- to 15-leaf stage of growth.

Addition of organic matter reduced the effectiveness of 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) to oats in Regina heavy clay soil. At high moisture levels, changes in the relative amounts of clay in the soil did not affect the toxicity of simazine. Toxicity of simazine decreased as the soil moisture level was reduced.

A substantial movement of sugar from alfalfa (Medicago sativa L.) to dodder (Cuscuta sp.) was noted in all experiments, while autoradiograms indicated little or no movement from the parasite to the host. Even when metabolic activities in the host were limited, dodder continued to withdraw sugars from the host.

Seeds of Striga asiatica (L.) Kuntze were induced to germinate with a stimulant from host exudates in the presence of a water-soluble germination inhibitor extracted from Striga seeds. Germination obtained was dependent upon the relative concentrations of stimulant and inhibitor present in the germination medium. The inhibitor had no effect on radical elongation of Striga seeds that germinated in its presence.

Plots infested with quackgrass (Agropyron repens (L.) Beauv.) were treated with 2-chloro-4-ethylamino-6-isopropyl-s-triazine (atrazine) at several rates at various times and subjected to a number of cultural and cropping treatments. Depletion of carbohydrate reserves in the rhizomes increased with time after treatment. Recovery of the quackgrass occurred after 2 lb/A but usually not after 4 lb/A applications. Applications of nitrogen increased the rate of carbohydrate depletion. Two applications of atrazine at reduced rates were equal or superior to a single heavy rate. Tillage after treatment and crop competition improved the control of quackgrass obtained.

Carrot (Daucus carota L. var. Imperator) seeds were planted in soil treated with amiben-C14 at 3 and 6 lb/A. Plants were harvested after 69, 103, and 191 days, autoradiographed or analyzed for the radioactivity in the 80 percent ethanol soluble fraction and in the insoluble fraction. The highest concentration of radioactivity was on or near the surface of the roots, but some radioactivity was present throughout the leaves and roots. The concentration of radioactivity decreased with time both in the soluble fraction and insoluble fraction of the root; in contrast it decreased in the insoluble fraction and increased in the soluble fraction of the leaves.

Disks of carrot root were placed in an aerated solution of amiben-C14. After 6 days, only 18.7 percent of the amiben remained unaltered. About 4 percent of the radioactivity was released as C14O2; 64.3 percent was present in an unknown compound which may contain a sugar moiety; the remaining 11.8 percent was distributed among four additional unknown compounds.

The maleic hydrazide-30 treated plants increased in protein hydrolysate significantly over the controls, without having any growth. Therefore, this suggests that the synthesis of protein and metabolism of amino acids is not directly related to growth in tea (Camellia sinensis). The inhibitory effects may be due to the lack of synthesis of growth hormones responsible for cell enlargement, or may have a direct effect on the cell wall, reducing the cell plasticity. Hydrolysis with 6N HCl causes a significant destruction of amino acids.

Sesbania (Sesbania exaltata (Raf.) Cory) in soybeans was effectively controlled with wax bars containing 2,4-dichlorophenoxyacetic acid (2,4-D). Bars, 22 in long, were attached horizontally 3 in apart to a tractor-mounted boom and the height was adjusted for it to travel 2 to 3 in above crop plants. Six-pound bars, containing 1 lb of 2,4-D gave better control than bars containing less 2,4-D. Bars made of wax with a melting point of 170 F provided more economical control than bars with waxes of lower melting points. Rate application of wax increased with the size of the weeds treated and with reduced tractor speed. Treatments controlled sesbania without visible injury to soybeans.

The adsorption and desorption of 2-chloro-4-ethylamino-6-isopropyl-amino-s-triazine (atrazine) as affected by pH, temperature, and cencentration of atrazine were studied on Drummer clay loam soil and a humic acid isolated from Leonardite. The adsorption of atrazine on the soil increased as pH decreased, but it was affected only slightly by temperature and cencentration of atrazine. Desorption of atrazine was greater with increasing temperature and pH. The adsorption of atrazine on the soil was reversible and desorption was nearly complete. Adsorption of atrazine on the humic acid increased as pH decreased and temperature increased, and there was very little desorption of atrazine from the humic acid.

The effect of ultraviolet (UV) light (240–260 mμ range) on 6, 7-dihydrodipyrido (1, 2-a:2’,1′-c)-pyrazidiinium salt (diquat) and 1,1′-dimethyl-4,4′-bipyridinium salt (paraquat) was studied. Both dipyridyls were very stable in dark but were altered rapidly in the presence of UV light. Radioassay data collected from planchets containing solidified diquat or paraquat indicated a loss of more than 50% of the C14 from both compounds after 48 hr and more than 75% after 96 hr. When radioactive aqueous solutions were placed under UV lights, little change in the radioactivity occurred during an 8-day period as determined by liquid scintillation. When the concentration of diquat or paraquat in these solutions was determined by chemical analysis, degradation of the original molecules was observed.

Information obtained by autoradiography of chromatograms, spotted with radioactive aqueous solutions exposed to UV light, indicated that two or possibly more C14-containing degradation products were formed from both diquat and paraquat. Co-chromatography indicated that one degradation product from paraquat was 1-methyl-4-carboxy-pyridinium ion.

A discussion is presented on some mechanisms whereby certain plant growth-regulating materials may exert their activity on plants. A discussion of photosynthesis is developed on the basis of two light reactions being involved in the photosynthetic process. Herbicides which may be active in photosynthesis are considered in relation to their site and mode of action. Current theories of nucleic acid metabolism and protein synthesis are presented and certain inhibitors of these processes are discussed and the possible involvement of plant growth-regulators is considered.

Opuntia laevis or O. polyacantha (prickly pear) plants exhibited little water loss, exceptional viability, low nutrient requirements for growth, slight photosynthetic activity, slow translocation, and low transpiration rate as compared with corn or soybean plants. The limited number of stomata, thick wax cuticle, and high water binding ability of cell mucilage in prickly pear are largely responsible for the aforementioned physiological characteristics. These studies show that prickly pear pads, which are modified stems, are not efficient organs for metabolic activities. Water extracts of prickly pear tissue applied to corn seeds were found to induce pronounced growth stimulation of corn seedlings.

The ultraviolet absorption spectra of aqueous dispersions of 2-chloroallyl diethyldithiocarbamate (CDEC) were altered by relatively short periods of exposure to far ultraviolet radiation. Evidence of molecular decomposition also was obtained from solvent partitioning characteristics, gas chromatography, and bioassays. Ultraviolet irradiation of soil surfaces treated with the herbicide decreased its persistence, but no evidence of decomposition was obtained.