The absorption and translocation patterns of terbutryn [2-(tert-butylamino)-4-(ethylamino)-6-(methylthio)-s-triazine] and propazine [2-chloro-4,6-bis(isopropylamino)-s-triazine] were determined in wheat (Triticum vulgare Vill. ‘Kaw’) and sorghum (Sorghum bicolor L. ‘RS 612’). Bioassay studies showed sorghum to be tolerant and wheat susceptible to terbutryn. Absorption and translocation of uniform 14C-labeled terbutryn from 1 to 24 hr after initial treatment showed the roots of sorghum and the foliage of wheat to be the major sites of radioactivity accumulation. Foliage was the major site for propazine accumulation with both plant species. Thin-layer chromatography of extracts from terbutryn-treated plants showed that sorghum contained a higher percentage of metabolic breakdown products in the foliage than did the root systems, and wheat contained a high percentage of intact terbutryn in the foliage and roots. High temperature (32 C) enhanced translocation of terbutryn and propazine in both sorghum and wheat. The susceptibility of wheat and sorghum to terbutryn appears to be correlated with a combination of the factors of accumulation within the foliage of the plant and the ability to degrade the terbutryn molecule.

Tall morningglory [Ipomoea purpurea (L.) Roth] seeds were germinated at various temperatures and dry weight conversion measured at 24, 48, 72, 96, and 120 hr. Germination and dry weight conversion were slower at the lower temperatures although both occurred. Tall morningglory could germinate and become established over a wide range of temperatures. Some herbicides were effective in reducing germination, and dry weight conversion was reduced most with the dithiocarbamates followed in sequence by the amides, benzoic acids, uracils, dinitroanilines, phthalamic acids, triazines, and ureas.

Placing hydrilla (Hydrilla verticillata Royle) in 2.7 and 5.4 μM solutions of carbon-14-labeled endothali [7-ox = abicyclo(2,2,1)heptane-2,3-dicarboxylic acid] under controlled conditions resulted in a sigmoid-shaped uptake curve for both herbicide concentrations. Apical sections of hydrilla, which included the apical bud, absorbed greater amounts of endothall-14C than sections excised from the center of the plant below the apical bud. Low concentrations of copper as copper sulfate pentahydrate solutions of 0.4 and 2.0 μM in combination with endothall-14C increased the amount of radioactivity found in hydrilla, but copper concentrations of 4.0, 8.0, and 16.0 μM inhibited endothall-14C uptake. The greatest uptake by hydrilla in 5.4 and 2.7 μM solutions of endothall-14C exposed to temperatures of 10, 20, and 30 C occurred in the 20 and 30 C solutions, respectively. Endothall-14C uptake was studied under light intensities of 0, 540, 5400, and 21,500 lux. Uptake of radioactivity from 2.7 and 5.4 μM solutions of endothall-14C was greatest at 540 and 21,500 lux, respectively.

Twenty herbicides were tested for activity in a paper disc agar bioassay. The growth of Chlorella pyrenoidosa Chick was inhibited by dinoseb (2-sec-butyl-4,6-dinitrophenol), diquat [6,7-dihydropyrido(1,2-a:2′,1′-c)pyrazinediium ion], paraquat (1,1′-dimetnyl-4,4′-bipyridinium ion), 3′,4′-dichloro-2-methylvaleranilide, propachlor (2-chloro-N-isopropylacetanilide), and linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea]. The growth of Bacillus subtilis Cohn was inhibited by dinoseb, diquat, paraquat, and 3′,4′-dichloro-2-methylvaleranilide. This assay using C. pyrenoidosa or B. subtilis offers a convenient means for the testing of herbicides.

The phytotoxicity of terbacil (3-tert-butyl-5-chloro-6-methyluracil) is not closely correlated with the amount applied, the amount in available soil solution, or the concentration in available soil solution since soil type has a pronounced effect on the levels necessary for phytotoxicity. About 19 times more terbacil was needed in a Chalmers silty clay loam (24% organic matter) than in a Bloomfield fine sand (0.3% organic matter) to cause a 30% control of sorghum (Sorghum biclor (L.) Moench ‘R.S. 610’). However, the Bloomfield fine sand required twice as great a concentration of terbacil in the soil solution as the Chalmers silty clay loam (0.314 μg/ml versus 0.157 μg/ml). The total adsorption of terbacil in the latter soil decreased 4.5 fold when the water: soil ratio was increased from 0.6:1 (approximately field capacity) to 32:1, but the ratio of the concentration adsorbed: concentration in the soil solution did not vary appreciably.

Several herbicides and growth substances were applied singly and in combination at varying concentrations to soybean [Glycine max (L.) Merr. ‘Lee’]. This was an attempt to compare the growth inhibition obtained with that previously measured in the single-celled organism Chlorella pyrenoidosa Chick, and to investigate the plant pathways and sites by which inhibition occurs. Inhibition induced by paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), and 2,4-D [(2,4-dichlorophenoxy)acetic acid] satisfactorily supported the hypothesis inherent in a kinetic analysis of such results, whereas, that induced by atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] and chloramben (3-amino-2,5-dichlorobenzoic acid) did not. A probit analysis of the atrazine and chloramben results indicated variability in the type of toxicity. Soybean was considerably more susceptible to 2,4-D than Chlorella pyrenoidosa but there was little difference in the type of growth inhibition response produced. Both were equally susceptible to atrazine. High concentrations of the growth regulator IAA (indoleacetic acid) were antagonistic to the growth inhibition induced by 2,4-D, while competitive inhibition occurred at the low concentration of IAA. The 2,4-D had only a slight effect on the inhibitory effect of paraquat and antagonistically interfered with that induced by atrazine.

The effects of seven s-triazines on the opening of the hypocotyl hook of cotton (Gossypium hirsutum L. ‘DPL Smooth Leaf’) and the germination of lettuce seed (Lactuca sativa L. ‘Grand Rapids’) were investigated. The s-triazines used were ametryne [2-(ethylamino)-4-(isopropylamino)-6-(methylthio)-s-triazine], atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], cyprazine [2-chloro-4-(cyclopropylamino)-6-(isopropylamino)-s-triazine], prometone [2,4-bis (isopropylamino)-6-methoxy-s-triazine], prometryne [2,4-bis (isopropylamino)-6-(methylthio)-s-triazine], propazine [2-chloro-4,6-bis(isopropylamino)-s-triazine], and simazine [2-chloro-4,6-bis(ethylamino)-s-triazine]. All triazines except cyprazine stimulated germination of lettuce seed given 4 min of dim red light but none were stimulatory in the dark. Maximum stimulation occurred with 1 X 10-8 to 1 X 10-12 M s-triazine. All triazines except atrazine and cyprazine stimulated the opening of cotton hypocotyl hooks given 2 hr of dim red light of the s-triazines tested. Prometryne and ametryne were the most stimulatory to hook opening in the light and the most inhibitory in the dark. Their effects paralleled those of kinetin.

Enhanced foliar injury was obtained with sprays containing the herbicide linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] and the insecticide carbaryl (napthyl-N-methylcarbamate) in tolerant carrot (Daucus carota L. ‘Chantenay’). Synergism occurred when the compounds were applied as tank mixes or applied at 1 day intervals. The photosynthetic rate of parsnip (Pastinacea sativa L. ‘Hollow Crown’) leaf discs exposed to both chemicals was greatly reduced when compared to tissues receiving linuron or carbaryl alone. Carbaryl enhanced the penetration of 14C-linuron into intact carrot leaves and parsnip leaf discs. The rate of linuron metabolism was also decreased in the presence of carbaryl. Both of these factors may contribute to the enhanced toxicity obtained with this combination of pesticides.

Vapor losses of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-p-toluidine), and nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline] were studied under controlled laboratory conditions using a Florisil vapor trap. No nitralin vapor losses were detected at 50 C from a Lakeland loamy sand at field capacity with an air flow rate of 0.04 m3/hr for 3 hr; whereas, 24.5% and 12.5% of trifluralin and benefin, respectively, were lost as vapors. Volatility of trifluralin and benefin increased with increasing temperatures of 30, 40, and 50 C and increasing soil moisture from air dryness to field capacity. Vapor losses from granular benefin were similar to the spray applications at 30 and 40 C. Volatilization of granular trifluralin was reduced when compared to the spray application at 40 C and 30 C but was similar for both formulations for benefin. No significant losses from photodecomposition were noted for trifluralin, benefin, or nitralin when comparing radiated and unradiated soil surface treated samples.

Johnsongrass [Sorghum halepense (L.) Pers.] control in corn (Zea mays L.) was studied from 1970 to 1972 using consecutive annual applications of alachlor (2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide) at 3.4 kg/ha, butylate (S-ethyi diisobutylthiocarbamate) at 4.5, 9.0, and 13.4 kg/ha, and EPTC (S-ethyl dipropylthiocarbamate) at 3.4, 6.7, and 13.4 kg/ha. In 1970, control was less than 60% for all herbicides, and there was no significant rate response. In 1971 butylate and EPTC at all rates provided 79 to 93% control. Alachlor gave 49% control. In 1972 control was similar to 1971. Control with one cultivation was additive to these herbicidal effects. Seed treatment with 0.5% 1,8-naphthalic anhydride adequately protected the corn from herbicide injury. Corn yields were closely correlated with johnsongrass control.

Dinoseb (2-sec-butyl-4,6-dinitrophenol) and MBR 8251 [1,1 1-trifluoro-4′-(phenylsulfonyl)-methanesulfono-o-toluidide] inhibited enzymic synthesis of glycerides in vitro. The physiological significance of this inhibition was confirmed in intact wheat [Triticum aestivum L., ‘Mediterranean’ (C.I. 5303)] seedlings; dinoseb and MBR 8251 inhibition of glyceride synthesis in vivo was evidenced by a buildup in free fatty acids and a decrease in neutral and polar lipids. Glyceride synthesis and growth were reduced approximately equally by dinoseb and MBR 8251. However, polar (membrane) lipids were reduced more drastically than growth. It is suggested that dinoseb and MBR 8251 alter membrane structure and function through an inhibition of membrane lipid synthesis. DNP (dinitrophenol) was only slightly inhibitory in either the in vitro or in vivo system. Dinoseb was more effective than MBR 8251 in destruction of cell membrane permeability of intact roots immediately after treatment.

Diffusion of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) through Mexico silt loam soil was measured in diffusion cells under laboratory conditions. Radiolabeled herbicide was extracted from each sample and counted by liquid scintillation. Fick's Second Law with a constant diffusion coefficient adequately describes trifluralin diffusion regardless of concentration or diffusing time. Solution diffusion increases directly with bulk densities to 1.1 g/cm3 and then decreases. Vapor diffusion is decreased approximately 50% for every 10% decrease in air-filled porosity. Vapor diffusion contributes the major portion of total diffusion at bulk densities of less than 1.2 g/cm3. For bulk densities between 1.2 and 1.4 g/cm3, the magnitudes of vapor and solution diffusion are similar.

In the range of 4.4 to 49 C, there is an exponential relationship between temperature and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) diffusion coefficients. Diffusion is low in air-dry soil for all temperatures. It increases to a maximum value when the soil has between 8 and 15% w/w soil moisture content and then decreases steadily as moisture content increases. When the air-filled fraction of soil void space is reduced below approximately 40% v/v by either compression or addition of moisture, diffusion begins to decrease. An equation was developed to predict trifluralin diffusion coefficients from a factorial experiment with seven soil moisture contents, five soil temperatures, and two bulk densities. Diffusion coefficients range from 3.8 X 10-11 cm2/sec to 2.8 X 10-6 cm2/sec. Fifteen terms are required in the prediction model to describe accurately the response surface of trifluralin diffusion coefficients. With the equation it is possible to predict trifluralin diffusion coefficients for any combination of measured soil parameters as long as they are represented by the range of the variables used in the experiment.