Vapors of 11 dinitroaniline herbicides from soil were trapped in a Florisil column under controlled laboratory conditions for a 3-hr period. No vapor losses of nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline] and oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) were detected at the highest temperature, 50 C, from moist Lakeland sand with an air flow of 50 ml/min; whereas, under the same conditions vapor losses approached 25% for benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine), profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine] and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine). Vapor losses for the remaining herbicides studied were moderate with values ranging between 2 and 13%. Volatility of all herbicides increased with increasing temperatures of 30, 40, and 50 C. Vapor losses for each herbicide from Hagerstown clay loam, Littleton silt loam and Lakeland sand were statistically different for five of the 11 herbicides.

Six herbicides including DNP (2,4-dinitrophenol) were tested for their effects upon nitrate metabolism in green leaves. It was found that these herbicides which are not classified as “photosynthetic inhibitors” permitted nitrite to accumulate within green leaves in darkness but not in light. It is postulated that these herbicides have an uncoupling effect, similar to that of DNP, which indirectly affects the process of nitrate reduction. A new technique which demonstrates this effect is presented and discussed.

Translocation of 14C-labeled and toxicity of nonradiolabeled bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4)3H-one 2,2-dioxide] was determined for common cocklebur (Xanthium pensylvanicum Wallr.) and soybeans [Glycine max (L.) Merr.]. Significantly greater 14C-movement and herbicide toxicity occurred in common cocklebur growing in wet soil at field capacity than in dry soil near the wilting point. In common cocklebur there was a trend toward greater bentazon toxicity and 14C-translocation at high temperature (35 C) and high relative humidity (RH) (96%) than at low temperature (25 C) and low RH (35%). ‘Lee 68’ soybeans were injured less than 10% by bentazon under any environmental condition of this study. Translocation of 14C was primarily acropetal in both common cocklebur and soybeans. Herbicide movement was affected by leaf maturity with the greatest movement of 14C resulting from 14C-bentazon applied to the most mature common cocklebur leaf near the base of the shoot and to soybeans at the youngest fully expanded leaf near the apex of the shoot. Bentazon was more toxic and 14C translocation was greater in the soybean cultivar ‘Hurrelbrink’ than ‘Hill’ or Hill X Hurrelbrink cross.

Laboratory studies were conducted to measure the relative volatility of triallate [S-(2,3,3-trichloroallyl) diisopropylthiocarbamate] from soils and to determine the effect of surfactants on triallate mobility. Significant volatilization occurred from continuously moist soils under constant air exposure but triallate did not volatilize more rapidly than herbicides which do not respond to incorporation. Volatilization rates from Ray silt soil fell in the order of propachlor (2-chloro-N-isopropylacetanilide) > triallate > alachlor [2-chloro-2′, 6′-diethyl-N-(methoxymethyl)acetanilide] and from Drummer silty clay loam were propachlor > alachlor > triallate. In suspension studies soils reversibly adsorbed 93 to 98% of the triallate in aqueous solution. With soil at field moisture capacity, the concentration of triallate in soil solution was 13 ppbw without surfactant and 14 ppbw with 3 parts emulsifier blend to 1 part of triallate (w/w). With this level of emulsifier 92% of triallate applied to the soil surface remained in the upper 3 cm of soil following a 15.2-cm simulated rainfall. Without surfactant 99% remained in the upper 3 cm of soil. Lower triallate mobility in moist soils observed in this study coupled with the strong dependence of triallate bioactivity as reported by others strongly suggests that deactivation by dry surface soils rather than volatility is primarily responsible for the triallate response to incorporation.

The absorption, translocation, and metabolism of 14C-profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine] and 14C-dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine) in sorghum [Sorghum bicolor (L.) Moench ‘RS6–12′], barnyardgrass [Echinochloa crus-galli (L.) Beauv.], soybean [Glycine max (L.) Merr. ‘Dare’], and Palmer amaranth (Amaranthus palmeri S. Wats.) were determined after treatment with 14C-labeled herbicides in nutrient solution for 24 hr at 16 or 38 C. 14C-profluralin accumulated in roots to a greater extent at 16 C, while metabolism was greatest at 38 C. Very little 14C-profluralin was translocated to the tops of plants. Conversely, 14C-dinitramine accumulated in the tops of plants to a greater extent at 38 C. Metabolism was not greatly affected by temperature. These effects may relate to excess toxicity of profluralin at 16 C and dinitramine at 38 C in species which normally exhibit resistance to the herbicides.

The effects of soil organic matter, clay, extractable Al, cation exchange capacity, and pH on the adsorption of picloram (4-amino-3,5,6-trichloropicolinic acid) from aqueous and surfactant solutions were investigated. Linear adsorption isotherms for the soils were obtained with the Freundlich equation. Of the five soil properties investigated, Freundlich K values correlated with extractable Al and clay content. Picloram adsorption from aqueous solutions and from the non-ionic and anionic surfactant solutions was greater on the soils at pH 5 than at pH 7. The anionic surfactant competed with picloram for adsorption sites on the soils at pH 5. Picloram adsorption from solutions containing 0.1 and 1% cationic surfactant was greater than that from aqeuous and anionic and nonionic surfactant solutions. Picloram adsorption from the 10% cationic surfactant solution was similar on soils with pH 5 and 7 and increased with decreased organic matter content.

Control of spurred anoda [Anoda cristata (L.) Schlecht.] in the greenhouse was less than 75% after 28 days with preplant incorporated herbicides except dinitramine [N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine] which gave 88 to 94% control. In greenhouse and field studies with cotton (Gossypium hirsutum L. ‘Coker 210′) preemergence applications of norflurazon [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone] controlled 93 to 100% of the spurred anoda 4 weeks after application. Control with postemergence applications of fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-toly)urea] was 46.0 to 92.5%; 90.7 to 100% with prometryn [2,4-bis(isopropylamino)-6-(methylthio-s-triazine]; and 100% with methazole, [2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione]. Preemergence applications of norflurazon plus fluometuron, prometryn, or methazole applied postemergence controlled 93, 97, and 100% of spurred anoda, respectively. Fluometuron plus the same three postemergence treatments controlled 63, 95, and 88% of spurred anoda, respectively. Results of our tests suggest that the best control of spurred anoda can be obtained in cotton by a combination of norflurazon applied preemergence at 1.68 kg/ha followed by two postemergence applications of either fluometuron at a rate of 2.24 kg/ha, prometryn at a rate of 1.68 kg/ha, or methazole at a rate of 1.68 kg/ha.

Field and greenhouse studies of 2,4-D [(2,4-dichlorophenoxy)acetic acid] and glyphosate [N-(phosphonomethyl) glycine] absorption, translocation, and metabolism were initiated to explain field observations which indicated susceptibility of common milkweed (Asclepias syriaca L.) but not hemp dogbane (Apocynum cannabinum L.) to glyphosate and the reverse response to 2,4-D. Glyphosate was absorbed less than 2,4-D in both species with absorption of both herbicides being greater in common milkweed. Greater herbicide absorption by common milkweed was attributed to less epicuticular wax, less cuticle, lower contact angle of the herbicide spray, and the presence of stomata and trichomes on the adaxial leaf surface. No major translocation differences of the herbicides were noted between species. Translocation of glyphosate was more rapid than that of 2,4-D. More glyphosate than 2,4-D accumulated in areas of high meristematic and metabolic activity. Rapid 2,4-D metabolism occurred in common milkweed leaves above treated leaves. There was no detectable 2,4-D metabolism in hemp dogbane roots after 20 days, while 60% of the 2,4-D in common milkweed roots was metabolized. Limited absorption of glyphosate but not 2,4-D by hemp dogbane and metabolism of 2,4-D but not glyphosate by common milkweed were considered the primary factors involved in explaining observed susceptibility differences.

Bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4) 3H-one 2, 2-dioxide] was applied postemergence to common cocklebur (Xanthium pensylvanicum Wallr.) and velvetleaf (Abutilon theophrasti Medic.) at various times of the day in growth chamber and field studies and to soybeans [Glycine max (L.) Merr.] in field studies. Soybeans were tolerant of bentazon regardless of time of day when treated. Results with common cocklebur and velvetleaf suggest that the time of day when bentazon is applied can be of practical importance. Poor control might occur following application in late evening, night, or early morning.

The effect of light on the response of green beans (Phaseolus vulgaris L. ‘Tendercrop’) and soybeans [Glycine max (L.) Merr. ‘Merit’] to fluorodifen (p-nitrophenyl α,α,α-trifluoro-2-nitro-p-tolyl ether) was evaluated with respect to light quantity, quality and time of exposure. Herbicide-induced injury was intensified with exposure of plants to reduced levels of light. Comparisons of light quality indicated that this herbicide interaction with light was greatest at longer wavelengths of visible light (yellow and red). The most critical time for light exposure to result in increased herbicide injury was at the time of emergence of seedlings.

Spurred anoda [Anoda cristata (L.) Schlect.] seed germination averaged 0.5 to 3.0% for seeds buried in the field for up to 20 months under natural conditions. These same seeds averaged over 76% germination after scarification with concentrated sulfuric acid, indicating hard seed coat involvement in seed dormancy. Germination was unaffected by light variables but increased as temperature increased. Germination of scarified seed increased from 50% to 85% as temperature was increased from 18 C to 30 C. Spurred anoda developed more slowly than did cotton (Gossypium hirsutum L. ‘Coker 310′) for the first 45 days. After that spurred anoda grew more rapidly until by 60 days after emergence, the weed was larger than cotton as measured by shoot height and total leaf surface area. This difference in development between cotton and spurred anoda indicates postemergence directed sprays of herbicides might be useful as a control tool.

In at least three metabolic processes in wheat (Triticum aestivum L. var. ‘Arthur’) shoots inhibitory activity can be related to the chemical structure of substituted pyridazinones. Inhibitory activities include: inhibition of the Hill reaction and photosynthetic CO2 fixation; inhibition of carotenoid biosynthesis accompanied by photodestruction of chlorophyll; and interference with the formation of chloroplast membrane polar lipids. The parent compound, pyrazon [5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone], inhibits the Hill reaction and photosynthetic CO2 fixation. Trifluoromethyl substitution of the phenyl ring of pyrazon, mono-methyl substitution of the amine, or substitutions at both positions result in inhibition of carotenoid biosynthesis. However, both substitutions are required for maximum effect. Substitutions onto the molecular structure of pyrazon are also related to alterations in the formation of membrane polar lipids. Dimethyl substitution of the amine of pyrazon is related to a decrease in linolenic acid accompanied by an increase in linoleic acid without a shift in the relative proportion of saturated to unsaturated fatty acids of the membrane lipids. The trifluoromethyl substitution of the phenyl ring and mono-methyl substitution of the amine are related to a shift toward a higher proportion of saturated fatty acids of chloroplast membrane lipids. Results obtained with diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] and with dark-grown wheat tissue indicated that activity of the pyridazinones on the formation of membrane lipids was probably not related to inhibition of the Hill reaction.

The movement and persistence of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] and its degradation product, 3,4-DCA (3,4-dichloraniline) were studied in an orchard soil which had received diuron annually at the rate of 4.5 kg/ha for 7 yr. Accumulation of residues was not observed at significant levels although carry-over of the herbicide occurred between years. The bulk of the herbicide residue was confined to the upper 15 cm of soil. The degradation rate of diuron generally followed first-order kinetics and the residual levels of diuron in the soil were highly phytotoxic to oat (Avena sativa L.) plants during the 3 yr after the last application. The levels of 3,4-DCA were low in all soil samples (< 21 ppb) and its relative distribution in the soil profile was similar to that of diuron.

The effects of prometryn [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine], diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], fluometuron [1,1-dimethyl-3-(a,a,a-trifluoro-m-tolyl)urea], and MSMA (monosodium methanearsonate) on Chlorella pyrenoidosa Chick ‘Strain 252′, Trichoderma viride Pers. ex Fr., and Aspergillus terreus Thom were investigated. Minimum herbicide concentrations necessary to decrease C. pyrenoidosa growth after exposure for 35 generations were 10-8M diuron, 10-7M prometryn, and 10-6M fluometuron. MSMA had no effect. C. pyrenoidosa photosynthesis was essentially stopped by a 2-hr exposure to 5 × 10-6M prometryn or diuron and by 5 × 10-5M fluometuron. Prometryn (5 × 10-5M) or diuron (5 × 10-7M) increased respiration by 70 and 44%, respectively after an 80-min treatment. Maximum fluometuron inhibition of respiration was ca 25% and MSMA had little or no effect. Herbicide concentrations of 0, 10-6, 10-5, and 10-4M were used to measure their effects on colony diameter growth, gain in mycelial dry weight, sporulation, and respiration of the two fungi. No concentration of any of the herbicides had any major effect on any of these parameters except sporulation. T. viride sporulation was increased approximately 20, 30, 35, and 50% by 10-6M concentrations of prometryn, diuron, fluometuron, and MSMA, respectively. Sporulation of A. terreus was also somewhat increased by these herbicides.

A brief history of chemical weed control in Europe from ancient Greek and Roman times to 1850 is given. The use of the various chemicals recorded is discussed and their possible efficacy commented upon.

Light after treatment was found to be required for the herbicidal activity of nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether) and oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene] following postemergence applications of both herbicides to greenbean (Phaseolus vulgaris L. ‘Spartan Arrow’). The effect of photosynthate and/or light before treatment was investigated. A 24-hr dark period prior to postemergence treatment of the bean seedlings had no effect on herbicidal activity when light followed treatment. The effect of plant pigments on the activity of both herbicides was studied using mutants of corn (Zea mays L.) and soybean [Glycine max (L.) Merr.]. A white mutant of corn was much more resistant to the herbicides than a greenish-yellow mutant or the normal plant. A yellow mutant of soybean was equally as susceptible as the normal type. Studies with radiolabeled foliar applications of both herbicides showed no significant difference in translocation in the light or dark.

Greenhouse and field studies were conducted to compare the phytotoxicity of HOE 23408 {methyl 2-[4-(2,4-dichlorophenoxy)phenoxy]-propanoate} to several crops and annual grass weeds, and to determine the herbicides's soil mobility and persistence. In general, the order of susceptibility of 13 seedling grassy weeds remained constant, whether the herbicide was applied preplant incorporated, pre-emergence, or postemergence. The herbicide was most phytotoxic when it was applied either preplant incorporated or early postemergence. Grain sorghum [Sorghum bicolor (L.) Moench ‘BR-54′] and oats (Avena sativa L. ‘Cimarron’) were moderately susceptible to HOE 23408, whereas barley (Hordeum vulgare L. ‘Will’) exhibited marginal tolerance. Wheat (Triticum aestivum L. ‘Triumph 64′) and cotton (Gossypium hirsutum L. ‘Westburn 70′) showed tolerance to HOE 23408 at rates up to 6 ppmw, and soybean [Glycine max (L.) Merr. ‘Bragg’] and peanut (Arachis hypogaea L. ‘Spanhoma’) demonstrated tolerance to concentrations as high as 24 ppmw. The soil mobility of HOE 23408 was similar to that of trifluralin (a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine). No soil phytotoxicity was found 8 weeks after herbicide application in the field or under laboratory incubation conditions of 5 or 10% soil moisture at 21 C. Dissipation was much slower at a temperature of 4.4 C, regardless of the soil moisture level.

Several dozen herbicide systems were evaluated over a 4-yr period for weed control in stubble no-till planted corn (Zea mays L.). Crop tolerance and corn yield data also were obtained. Paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) and glyphosate [N-(phosphonomethyl)glycine] afforded excellent desiccation of all emerged vegetation each year. The oil-soluble formulation of dinoseb (2-sec-butyl-4,6-dinitrophenol) also afforded complete contact control of emerged vegetation in 1975, the only year it was evaluated. A herbicide system consisting of an acetanilide plus a triazine afforded the most consistent residual weed control. The specific herbicides affording satisfactory control largely depended on the weed spectrum. Fall panicum (Panicum dichotomiflorum Michx.), large crabgrass [Digitaria sanguinalis (L.) Scop.], and yellow nutsedge (Cyperus esculentus L.) were the weeds most difficult to control with the herbicide systems used in these studies. Corn yields were influenced primarily by the degree of weed control achieved, and in several instances by secondary effects of stand reduction or injury.

Six species of Solanaceae including tomato (Lycopersicon esculentum Mill ‘Campbell 28′) were sprayed in the greenhouse at weekly intervals for 4 weeks starting when tomato plants had one true leaf. All species gained tolerance to metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one] with age but tomato and black nightshade (Solarium nigrum L.) were the most tolerant and gained tolerance fastest with age. Jimsonweed (Datura stramonium L.) and eggplant (Solanum melongena L. ‘Black Beauty’) were the most susceptible species and the ones that gained least tolerance with age. Potato (Solanum tuberosum L.) from true seeds and pepper (Capsicum annuum L. ‘Yolo wonder’) were intermediate in tolerance. In the field, tomato and nine weed species planted in separate plots and kept free from competition were sprayed at weekly intervals starting when tomato plants had one true leaf. Tomato, large crabgrass (Digitaria sanguinales (L.) Scop.), ivyleaf morningglory (Ipomoea hederaceae (L.) Jacq.) and yellow foxtail (Setaria glauca (L.) Beauv.) were the most resistant species to metribuzin and the ones that gained tolerance fastest with age. The most susceptible weeds were velvetleaf (Abutilon theophrasti Medic), common purslane (Portulaca oleracea L.), pale smartweed (Polygonum lapathifolium L.), redroot pigweed (Amaranthus retroflexus L.), common lambsquarters (Chenopodium album L.), and jimsonweed. Low amounts of sunlight during the 3 days before spraying greatly reduced the resistance of tomato to metribuzin.

Alachlor [2-chloro-2′,6′-diethyl-N(methoxymethyl)-acetanilide], propachlor (2-chloro-N-isopropylacetanilide) and prynachlor [2-chloro-N-(1-methyl-2-propynyl)acetanilide], inhibited gibberellic acid (GA3),-induced production of protease and α-amylase in deembryonated barley (Hordeum vulgare L, ‘Schuyler’) seed. Production of protease was more sensitive to these herbicides than α-amylase. The degree of inhibition of protease and α-amylase production caused by alachlor was equivalent to that caused by cycloheximide, puromycin and actinomycin-D, known protein and nucleic acid synthesis inhibitors. Higher GA3 concentrations reversed the inhibition of protease and α-amylase synthesis caused by alachlor but did not reduce the effect of alachlor on barley seed germination and growth. It is concluded that the inhibition of protease and α-amylase production by alachlor is perhaps only one of several effects on early seed germination and seedling development.