The adsorption of nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether) and oxyfluorfen [2-cholor-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene] from aqueous solution by muck soil, and by kaolinite and bentonite saturated with hydrogen or calcium ions, was studied using 14C-labeled herbicides. Both compounds were readily adsorbed from solution by muck soil and Ca- and H-Al-bentonite but only slightly by Ca- and H-Al-kaolinite. Very little of the adsorbed compounds was desorbed after four extractions with distilled water. A bioactivity study using sorghum seedlings (Sorghum bicolor L. ‘RS610′) was conducted with the herbicides in a silica sand medium amended with 1% (w/w) of the various adsorbents. The herbicides were strongly inactivated by muck soil but there was very little inactivation by the clays. There was essentially no movement of either herbicide through 5-cm columns of a silt loam soil and a fine sand soil.

Field and laboratory experiments were conducted over a 3-yr period to evaluate the persistence of several dinitroaniline herbicides. Incorporation of these herbicides was delayed for 1, 3, and 7 days after application. Herbicidal activity was assessed by a sorghum bioassay, and by GLC analysis of soil samples. Herbicides least affected by a 2-day delay in incorporation were oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide, nitralin 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline, butralin 4-(1,1-dimethylethyl)-N-(1-methylpropyl)-2,6-dinitrobenzenamine, dinitramine (N4, N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine), fluchloralin N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)aniline, and penoxalin N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine. Of the herbicides evaluated, trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-P-toluidine) and profluralin N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine, were the least persistent after a 1-day incorporation delay. Losses of nitralin, butralin, dinitramine, fluchloralin, penoxalin, trifluralin, profluralin, benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine), and isopropalin (2,6-dinitro-N, N-dipropylcumidine) increased dramatically when incorporation was delayed 3 or more days. Persistence on the soil fur-face under field conditions was demonstrated the most by oryzalin. After incorporation, dinitramine was least persistent. The effects of temperature in UV light and dark on loss of dinitroaniline herbicides were demonstrated in the laboratory by applying the herbicide to TLC plates of soil. While herbicide losses did occur in 24 h of UV light, differences in herbicide losses were not significantly different between butralin, penoxalin, profluralin, trifluralin, isopropalin, oryzalin, nitralin, fluchloralin, and benefin. Dinitramine was most affected by the UV light. Butralin, oryzalin, nitralin, isopropalin, and dinitramine were least affected by 45 C in the dark with losses of 2 to 10% in 24 h. Profluralin, benefin, and trifluralin were found most volatile with losses of 35%, 25%, and 18%, in 24 h respectively. With increasing moisture levels, no significant increased losses were detected for butralin, nitralin, oryzalin, penoxalin, and isopropalin at the greater moisture contents. There was a moderate increase in the loss of dinitramine with increased soil moisture. AT 33% initial soil moisture, fluchloralin, benefin, and trifluralin were rapidly lost (75 to 94% in 24 h at 30 C). The trifluoro-methyl group was a common structural component where moisture affected the compound's loss. Application of the intermediate to very volatile dinitroanilines to moist soil surfaces without soil incorporation as soon as possible is not feasible unless higher rates of herbicide are applied.

A typical scotoactive stomatal behavior was noticed in Carissa spinarum L.; Gymnosporia emarginata Laws; Maba buxifolia Cl.; Flacourtia sepiaria Roxb.; Dodonaea viscosa L. and Randia malabarica Lamk. This stomatal behavior was reversed artificially by foliar application of paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) at 100 ppmw or 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] at 2000 ppmw. The size of the stomatal aperture, stomatal conductance and the rates of transpiration were enhanced significantly by the herbicide treatment. The physiological basis for the induction of desiccation and death of plant organs is thought to be the excessive stimulation of stomatal aperture, stomatal conductance and consequently high rates of transpiration observed here. The data suggest that herbicide-induced desiccation is the consequence of inhibition of scotoactive behavior and increased water loss with attendant desiccation and death of leaves.

Subirrigated pot-plant systems were developed for greenhouse simulations of field methods being tested for herbicidal control of saltcedar (Tamarix pentandra Pall.). The methods included: over-the-top spraying; soil injection; soil layering, with whole plants transplanted onto the herbicide layer; and soil layering by severing the roots and concomitantly injecting herbicide. Existing foliar application techniques were improved for greenhouse testing of herbicides and results from preliminary tests were apparently similar to literature reports of limited efficacy in the field. Preliminary results from these greenhouse techniques showed that root zone applications, either by soil layering or soil injection, were very effective; stem or foliar applications were less effective.

The effect of alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] and gibberellic acid (GA3) on increase in length of corn (Zea mays L.) epicotyl segments and the interactions between alachlor (0, 5 × 10-6, 5 × 10-4, 4.4 × 10-4, and 5 × 10 M) and GA3 (0, 1 × 10-6, 2.8 × 10-4, and 1 × 10-4 M) were investigated. Alachlor significantly inhibited growth of these segments while GA3 usually increased growth. GA3 in combination with alachlor caused a significant increase in growth compared to alachlor alone resulting in growth comparable to that occurring in untreated tissues. The magnitude of GA3 induced growth in the presence of alachlor depended upon the concentrations of the herbicide and GA3 employed. Alachlor was, however, able to inhibit the GA3 induced growth. The maximum degree of growth inhibition resulted from exposure of the segments to alachlor with or without GA3 from the start of incubation. This inhibition decreased as the exposure to alachlor was delayed. Alachlor started inhibiting growth in the presence of GA3 after the first 9 hr of incubation and after the first 21 hr of incubation in the absence of GA3.

Various levels of intraspecific competition influenced johnsongrass [Sorghum halepense (L.) Pers.] reproduction. Increases in density, from one to eight plants per 20-cm pot, delayed for formation of rhizomes and panicles and reduced the final dry weight accumulation in these reproductive structures under greenhouse conditions. Tillering was delayed by medium density (4 plants per pot) and inhibited by the highest density (8 plants per pot). At all densities, the dry weight accumulation in reproductive structures was associated with a decrease in dry weight of the shoot material. Most of the reproductive effort was in the formation of rhizomes rather than panicles. Crowding of johnsongrass plants delayed the formation of the reproductive structures and reduced their final dry weight.

The selectivity of {2-[4-(2′,4′-dichlorophenoxy) phenoxy] methyl propionate}, (hereinafter referred to as dichlofop methyl), among wheat (Triticum aestivum L. ‘Neepawa’), barley (Hordeum vulgare L. ‘Bonanza’), wild oat (Avena fatua L.), and green foxtail (Setaria viridis (L.) Beauv.) was investigated. On an ED50 basis, barley, wild oat, and green foxtail were 2, 190, and 1,090 times more sensitive, respectively, to foliar-applied dichlofop methyl at the two-leaf stage than was wheat. Selectivity decreased with increasing maturity of the plant material with the ratio of selectivity between barley and wild oat decreasing from 55 at the two-leaf stage to three at the four-leaf-plus-one-tiller stage. Greater spray retention and more rapid penetration of dichlofop methyl partially explained the susceptibility of green foxtail, but did not explain selectivity between wheat, wild oat, and barley. Root uptake of 14C-dichlofop methyl by the four species was proportional to the amount of solution absorbed during the treatment period and to the concentration of dichlofop methyl in the treatment solution but was not related to species sensitivity to this herbicide.

The abilities of herbicides to either produce superoxide radical or react with this radical were examined. The effect of the herbicides on the superoxide-induced reduction of p-nitro blue tetrazolium chloride was used as an index. Paraquat (1,1-dimethyl-4,4′-bipyridinium ion) enhanced and diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] inhibited the reduction of p-nitro blue tetrazolium chloride. Paraquat was reduced photochemically (riboflavin/methionine) or enzymatically (xanthine/xanthine oxidase) and produced superoxide radical upon reoxidation. Diuron and monuron [3-(p-chlorophenyl)-1,1-dimethylurea] interacted with photochemically produced superoxide radical, but not with enzymatically produced superoxide radical. The product of the monuron/superoxide interaction was a demethylated, dechlorinated, water-soluble compound containing phenolic hydroxyl group(s), and was not toxic to oats (Avena sativa L.). The enzyme superoxide dismutase prevented the formation of this product.

We investigated the toxicity of MSMA (monosodium methanearsonate), fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea], and propanil (3′,4′-dichloropropionanilide) to soybeans [Glycine max (L.) Merr. ‘Hill’]. Over-the-top treatments were applied to soybeans at four stages of growth using MSMA at 0.1, 0.2, and 0.4 kg/ha, propanil at 0.2, 0.4, and 0.9 kg/ha, and fluometuron at 0.05, 0.1, and 0.2 kg/ha. Each herbicide caused 10 to 30% soybean injury at the lowest rate, and 40 to 70% injury at the highest rate. Soybeans treated earliest in the growing season usually recovered from injury better than soybeans treated later in the season. Soybean yields were reduced 50 to 70% by MSMA at 0.4 kg/ha and 25 to 35% by propanil at 0.9 kg/ha. Yield losses increased with stage of soybean maturity at time of treatment. Fluometuron at 0.2 kg/ha significantly reduced yield only when applied to soybeans with 7 or 10 trifoliolates or in midbloom.

Phytotoxicity of herbicides in water was measured before and after exposure to gamma radiation from a 60Co irradiator. Chromatographic methods and bioassays were used to measure alterations that occurred during 60Co exposure. Phytotoxicity of picloram (4-amino-3,5,6-trichloropicolinic acid and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) solutions was reduced even with the lowest dose of 60Co, 1.7-megarad (Mrad). Alterations in phytotoxicity of atrazine (2-chloro-4-ethylamino-6-esopropylamino-s-triazine) and dicamba (3,6-dichloro-o-anisic acid) solution occurred only at 5 Mrad, which was the highest dose used. The phytotoxicity of atrazine solutons increased with the 5-Mrad irradiation. Thin layer chromatography (TLC) data showed that all herbicides were altered by 60Co irradiation. Several products resulted when trifluralin was irradiated.

Postemergence herbicide treatments that were most effective for controlling horsenettle (Solarium carolinense L.) were glyphosate [N-(phosphonomethyl)glycine], dicamba (3,6-dichloro-o-anisic acid), silvex [2-(2,4,5-trichlorophenoxy)-propionic acid], and picloram (4-amino-3,5,6-trichloropicolinic acid). All exhibited good to excellent long term control of the horsenettle plant when applied annually for at least 2 yr. Picloram and glyphosate both provided better control of horsenettle when applied at a postbloom or fruiting stage of growth. Dicamba and picloram also were very effective in controlling horsenettle when used as a subsurface layer (SSL) treatment. However, all of these treatments caused visual injury to peanuts (Arachis hypogaea L.). Applications of 2,4-DB [4-(2,4-dichorophenoxy)butyric acid] were effective in causing an 80 to 90% fruiting inhibition of horsenettle plants when applied at a prebloom stage of growth, with no damage to the peanuts. Applications of several dinitroaniline herbicides as SSL treatments exhibited some control of horsenettle with little crop injury. Postemergence treatments which effectively controlled seedling horsenettle plants grown in the greenhouse were glyphosate and dinoseb (2-sec-butyl-4,6-dinitrophenol).

The initial dormancy in mature seeds of 12 out of 14 species of grass weeds studied was significantly overcome by pretreatment of the dry seeds at 50 C in stoppered vials. The time required for maximum effect varied depending upon species and lots within species. The procedure, termed accelerated after-ripening, can produce seeds in various stages of dormancy simply by varying the duration of the pretreatment. One of the first stages that becomes apparent is an increased response to light.

Benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) applied as a preplant incorporated treatment followed by application at the ground-cracking stage (GC) of a mixture of alachlor [(2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] plus naptalam (N-1-naphthylphthalamic acid) and dinoseb (2-sec-butyl-4,6-dinitro-phenol) significantly increased the yield of peanuts (Arachis hypogaea L. ‘Florunner’). Delaying treatment with the GC mixture for 10 days did not significantly depress peanut yields when averaged over all soils, although exceptions occurred within soil series. Substantial and consistent yield reductions occurred when the herbicide sequences terminated with five repeated applications of dinoseb, especially on the Ruston soil. Late planted peanuts often were more susceptible to intensive herbicide treatments than the early plantings. Beginning intensive sequential treatments with vernolate (S-propyl dipropylthiocarbamate) reduced yields more than when benefin initiated the sequence. Average yields of Florunner peanuts were increased significantly by the insecticide disulfoton (O,O-diethyl S[2-(ethylthio)ethyl]phosphorodithioate) on the Greenville and Ruston soil series, but not on the Dothan soil. The disulfotan x herbicide interaction was not significant. Herbicides interacted more frequently with planting date, treatment time, soil series, and year than did disulfoton.

The degradation and leaching of methazole [2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione] and metabolites in Elmwood sandy loam soil over time in response to average spring environmental conditions was studied by using soil columns placed on a rainfall simulator in an environmental growth chamber. Methazole was degraded to 3-(3,4-dichlorophenyl)-1-methylurea (DCPMU) and 3-(3,4-dichlorophenyl) urea (DCPU) over a 6-week period following methazole application, during which the soil columns received simulated rainfall of 1.27 cm every fourth day. Methazole level decreased to 27% of the original amount while DCPMU and DCPU levels increased to 53% and 1%, respectively. Of the total radioactivity remaining in the soil columns after 44 days and after 14 cm rainfall, approximately 80% remained above a depth of 6.35 mm.

Seed cotton (Gossypium hirsutum L.) yields were not reduced when competing with prickly sida (Sida spinosa L.) for 7 weeks or less after cotton emergence and maintained weed-free for the remainder of the season. Cotton yields were not affected when pure prickly sida stands were controlled for 5 to 6 weeks after cotton emergence and then allowed to grow uncontrolled for the remainder of the season. In the more severe weed competition treatments, cotton plant height and main stem diameter were reduced; however, yield of seed cotton was the most sensitive indicator of prickly sida competition. Maturity of cotton, as measured by percent of total yield obtained at first picking, indicated a delay in maturity in 1 of 3 yr in treatments where competing prickly sida was present for 8 weeks or more. In density studies, where prickly sida emerged with cotton and was allowed to compete for the full growing season, 45 prickly sida plants/15 m of row caused reductions in yield of seed cotton in two of five experiments. In another series of three experiments as few as 32 prickly sida plants/15 m of row significantly reduced seed cotton yields in two of the three experiments. Trash content of machine-harvested cotton was increased at densities of 64 and 128 prickly sida plants/15 m of row in one experiment. Staple length and grade of cotton were not affected by any weed density studied. Micronaire measurements of cotton were reduced at prickly sida densities of 64 and 128 weeds/15 m of row during 1972.

The effects of intraspecific competition on the growth and development of purple nutsedge (Cyperus rotundus L.) were studied under greenhouse conditions. Increases in plant density increased the dry weight accumulation on a per pot basis but decreased the dry weight accumulation on a per plant basis. The partitioning of dry weight, whether on a per pot or per plant basis, indicated a shift in the method of reproduction as to density. Under low density conditions more dry weight was partitioned into inflorescences than into tubers. However, under high density conditions more dry weight was partitioned into tubers rather than inflorescences. Dry weight partitioned into rhizomes did not vary as to density. Dry weight partitioned into shoots and roots decreased with the concomitant increase in dry weight partitioned into reproductive structures. This shift to vegetative reproduction under stress conditions caused by competition provides further insight into the difficulties of controlling purple nutsedge.

A method is described that provides an accurate and useful assessment of herbicide performance in small plot experiments. This method is an extension of previous rating systems and provides an assessment of the control of individual species through an estimation of the percentage that each contributes to the total broadleaf or grass weed cover on the whole plot area. It permits data collection on individual weed species but is less time-consuming than counting individual plants and it takes into account the size and vigor of individual weed plants as well as their relative abundance. Further, the system allows tabulation of data from across the entire plot rather than from small areas within the plot. The data can be readily entered into various computerized retrieval systems.

The metabolism of Sandoz 6706 [4-chloro-5-(dimethylamino)-2-α,α,α-trifluoro-m-tolyl-3(2H)-pyridazinone] in soybean [Glycine max (L.) Merr. ‘Kent’] and in sicklepod (Cassia obtusifolia L.) was examined at 1, 2, 4, and 8 days after herbicide application to explain the relative susceptibility of soybean and sicklepod to the herbicide. The 14C-labeled Sandoz 6706 was applied via the plant roots in a liquid culture medium. The primary pathway of metabolism in both plant species involved N-demethylation to norflurazon [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone and the desmethyl Sandoz 9774 [5-amino-4-chloro-2-(α,α,α-trifluoro-m-tolyl-3(2H)-pyridazinone]. Soybean was more efficient in the N-demethylation of the herbicide to less toxic metabolites than was sicklepod. A second transformation pathway which resulted in the formation of polar products was present in the roots of both species.

Results from greenhouse and growth chamber studies indicated that alachlor [2-chloro-2′,6-diethyl-N-(methoxymethyl) acetanilide] injury to ‘Superior’ potatoes (Solanum tuberosum L.) was related to time of herbicide application and temperature. Injury to the ‘Superior’ cultivar was observed when alachlor was applied just before potato emergence. Necrosis of shoots near the soil surface, shoot dieback, stem swelling, leaf crinkle, and plant stunting were characteristic symptoms of alachlor injury. Cool temperatures appeared to intensify the injury. ‘Superior’ potatoes outgrew injury within 41 days after treatment. Herbicide placement studies in the growth chamber suggested that alachlor or its metabolites were absorbed by the shoots of emerging ‘Superior’ potatoes. Under growth chamber conditions the ‘Katahdin’ cultivar was injured by preemergence applications of alachlor when the herbicide was applied just before plant emergence. Injury symptoms were similar to those observed on the ‘Superior’ cultivar. ‘Pungo’ and ‘Norchip’ potatoes were tolerant to preemergence applications of the herbicide regardless of time of application.

Several experiments were conducted to determine the influence of temperature, relative humidity, leaf age, and additives on 14C-bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4)3H-one 2,2-dioxide] uptake and translocation by redroot pigweed (Amaranthus retroflexus L.), wild mustard [Brassica kaber (DC.) L.C. Wheeler var. pinnatifida (Stokes) L.C. Wheeler] and soybeans (Glycine max L. Merr. ‘Corsoy’). A water soluble linseed oil formulation enhanced absorption and translocation of the 14C-label by redroot pigweed more than did emulsifiable linseed oil, petroleum oil, or a surfactant. The oil additives reduced the 14C-label washed from the treated area of a leaf and increased absorption and translocation compared to bentazon applied alone. Low relative humidity and older leaves of redroot pigweed resulted in less 14C-bentazon absorption than with high relative humidity or younger leaves. The addition of emulsifiable linseed oil reduced the influence of low relative humidity and leaf age upon 14C-bentazon absorption. Comparative absorption and translocation of 14C-bentazon was wild mustard > redroot pigweed > soybeans. Uptake and translocation of 14C-bentazon by redroot pigweed was greater at 30 C than at 10 C.