The relative susceptibility of 40 plant species to postemergence applications of 2-sec-butyl-4,6-dinitrophenol (dinoseb) in isoparaffinic oil was determined. Peanuts (Arachis hypogaea L. ‘Holland Virginia 56R’), with an I50 of greater than 2.24 kg/ha, were the most tolerant, and johnsongrass (Sorghum halepense (L.) Pers.) seedlings, with an I50 of 0.011 kg/ha, were the most susceptible. This is greater than a 200-fold difference in susceptibility, due primarily to internal tolerance, because penetration differences were reduced with the isoparaffinic oil carrier. Legumes generally were the most tolerant, and grasses ranged from tolerant to the most susceptible. Several species, primarily grasses, showed greater than 25% inhibition of shoot fresh weight from the isoparaffinic oil carrier alone.

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.

Excellent protection from 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) injury at twice the dose needed for weed control was obtained by dipping the roots of strawberry plants (Fragaria grandiflora Ehrh.) in a 10% slurry of activated carbon before transplanting. Protection was greater when the roots were dipped in the slurry of activated carbon than when activated carbon was applied in the transplant water. Protection was obtained from three different activated carbons. Protection from injury to varying degrees was observed when several other herbicides were used.

Several herbicides were tested in the greenhouse on ivyleaf morningglory (Ipomoea hederacea (L.) Jacq.), green foxtail (Setaria viridis (L.) Beauv.), purple nutsedge (Cyperus rotundus L.), and quackgrass (Agropyron repens (L.) Beauv.) to determine the degree of enhancement in activity that could be obtained with an isoparaffinic oil carrier applied at 140 L/ha. The enhancement varied with the herbicide and with the species, ranging from 16-fold enhancement with 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) and 2-sec-butyl-4,6-dinitrophenol (dinoseb) on ivyleaf morningglory to no enhancement of atrazine activity on purple nutsedge and quackgrass or (2,4-dichlorophenoxy)acetic acid (2,4-D) activity on quackgrass and ivyleaf morningglory. An oil adjuvant was less effective in enhancing dinoseb and 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron) activity than was the isoparaffinic oil carrier. Also, the isoparaffinic oil carrier emulsified in water was less effective than the undiluted oil in enhancing dinoseb activity on green foxtail, even though equal volumes of the isoparaffinic oil were applied.

The herbicides 3-tert-butyl-5-chloro-6-methyluracil (terbacil) and isopropyl m-chlorocarbanilate (chlorpropham) showed greatly enhanced activity on giant foxtail (Setaria faberii Herrm.) and ivyleaf morningglory (Ipomoea hederacea (L.) Jacq.) when applied in an isoparaffinic oil rather than water. The activity of terbacil was enhanced but to a lesser extent when crop oil was added to a water carrier at a concentration of 10%. In field trials, similar enhancement of terbacil and chlorpropham activity was obtained on several weeds. Onions (Allium cepa L., var. Spartan Gem) in the “loop stage” were moderately tolerant and carrots (Daucus carota L., var. Royal Chantenay) were highly tolerant to chlorpropham at 4 lb/A applied in the isoparaffinic oil. Peppermint (Mentha peperita L.) and spearmint (Mentha spicata L.) were tolerant to terbacil applied in the oil at rates sufficient to give good weed control. The oil alone had no injurious effects on onions, carrots, peppermint, or spearmint. This enhancement in activity in greenhouse and field studies appeared to be due to increased penetration as shown by washing, speed of killing plants, and tracer studies. Tracer studies showed that within 2 hr after application, the isoparaffinic oil increased the penetration of chlorpropham more than eightfold in ivyleaf morningglory and more than fourfold in giant foxtail compared to a water carrier. This increase in penetration was even more striking with terbacil. After 4 hr, penetration was increased over 16 times in ivyleaf morningglory and over 18 times in giant foxtail, when applied in the oil rather than acetone. Chlorpropham and terbacil were translocated to the shoot apex of ivyleaf morningglory only when they were applied in the oil.

Comparative phytotoxicity 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 several plant species indicated trifluralin was more toxic than nitralin to the shoots while nitralin was more toxic than trifluralin to the roots. An E0 concentration, defined as that concentration required to prevent seedling emergence, was established for trifluralin on nearly all species assayed. Nitralin did not prevent emergence of any species. Trifluralin was more toxic than nitralin to the shoots of sorghum (Sorghum bicolor (L.) Moench, var. RS-610) and cucumber (Cucumis sativus L., var. Wis. SMR-15 and Pioneer) via shoot exposure. Nitralin was more toxic than trifluralin to the roots via root exposure. A comparison of the phytotoxicity through vapor activity showed trifluralin was much more toxic than nitralin.

Five thiocarbamate herbicides, butylate (S-ethyl diisobutylthiocarbamate), EPTC (S-ethyl dipropylthiocarbamate), molinate (S-ethyl-hexahydro-1H-azepine-1-carbothioate), pebulate (S-propyl butylethyl-thiocarbamate), and vernolate (S-propyl dipropylthiocarbamate) were used in the greenhouse at doses of 0.5 to 5 kg/ha incorporated 6 cm deep in a silt loam. Purple nutsedge (Cyperus rotundus L.) tubers were planted 5 cm deep. Three and 9 weeks after treatments were applied, nutsedge plants were harvested. EPTC also was used at doses of 0.25 to 10 kg/ha and plants were harvested every 2 days up to 20 days and every 3 weeks up to 24 weeks. The most effective reduction in the number of sprouts above ground was given by butylate, EPTC, and vernolate followed by pebulate and molinate. Persistence was directly related to level of initial activity. No effect was observed on the number of tubers which sprouted. However, all the thiocarbamates stimulated the number of sprouts produced per nondormant tuber. These sprouts were abnormal and did not reach the soil surface. Treated tubers produced approximately twice as many sprouts as controls. The number of rhizomes produced from the basal bulb was reduced with all the thiocarbamates used, even 24 weeks after treatment for the higher doses.

Sublethal concentrations of isopropyl N-(3-chlorophenyl)- carbamate (CIPC) labeled with 14C in the ring or side chain were applied to all leaves present or to the roots of redroot pigweed (Amaranthus retroflexus L.), pale smartweed (Polygonum lapathiofolium L.), and parsnip (Pastinaca sativa L.). These species were selected because of their different susceptibilities to CIPC. The herbicide did not move out of the treated leaves in pigweed and smartweed and only slightly in parsnip in 21 days. In root treatment (3 days), the herbicide moved to all plant parts and the extent of movement was essentially the same in all species. Water soluble metabolites, which differed in Rf values were extracted from all three species. The metabolites apparently were not the result of cleavage of the CIPC molecule, but were more likely conjugates of CIPC with natural plant component(s). Very little 14CO2 was released by any of the species in 3 days. These data indicate that differences in movement and metabolism are not sufficient to account for the different susceptibilities of these three plant species.

Prometryn [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine] and dinoseb (2-sec-butyl-4,6-dinitrophenol) were applied in a non-phytotoxic undiluted oil carrier to sorghum (Sorghum bicolor L. ‘RS 610’), bean (Phaseolus vulgaris L. ‘Cascade’), and cucumber (Cucumis sativas ‘Wis. SMR-18’) simultaneously or separately, where prometryn treatment was followed by dinoseb at varying intervals of time. The simultaneous application of the two herbicides resulted in an additive response on all three plants, except that a slight antagonism was observed at one rate on both bean and cucumber. A synergistic response was observed when dinoseb treatment was delayed for at least 1 day on bean and cucumber and 2 days on sorghum. 14C-prometryn (14C) movement in bean leaves was not altered by simultaneous dinoseb application.

The concentration of N,N-dimethyl-2,2-diphenylacetamide (diphenamid) required to cause 50% growth inhibition (I50) of the shoots or roots in soil, or the roots in a bioassay, was determined for several species. of the plants tested, grasses were the most sensitive, while Solanaceae were among the most tolerant to diphenamid. Based on shoot inhibition, the sensitivity difference between the sensitive foxtail millet (Setaria italica L.) and the tolerant pepper (Capsicum frutescens L.) was 150 fold. Highly significant correlations among the I50 values indicate that any of the three methods would be satisfactory for measuring the sensitivity of species to diphenamid.

Dimethyl tetrachloroterephthalate (DCPA) caused swelling of a localized region of the hypocotyls of cucumber (Cucumis sativus L., var. Wis. SMR-15), tomato (Lycopersicon esculentum Mill., var. Heinz 1370), and jimsonweed (Datura stramonium L.). DCPA caused stem swelling in jimsonweed by affecting dividing and/or differentiating cells in the vascular cambium. As swelling proceeded, xylem tissue was increased over the controls and xylem cells were disorganized and no longer continuous. Swelling was induced at the site of DCPA application, and was reduced when DCPA concentration per unit of stem was lowered, even though the same amount per plant was applied. Uptake of 14C-DCPA from the treated stem region was slow, but the treated area had the highest specific activity.

The response of tomato (Lycopersicon esculentum Mill. ‘Chico III’), jimsonweed (Datura stramonium L.), and velvetleaf (Abutilon theophrasti Medic.) to postemergence applications of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] applied after cloudy weather was determined by shading the plants artificially before field application of the herbicide. One day of 76% actual shade reduced the tolerance of tomato, jimsonweed, and velvetleaf to metribuzin, and 3 days of shade further reduced plant tolerance to the herbicide. The GR50 values showed that tomato was about 30 times more tolerant than jimsonweed and about 40 times more tolerant than velvetleaf to metribuzin. After 3 days of shade, 2 or 3 days of sunshine were required to return tomato to its full tolerance to metribuzin. After 3 days of cloudy weather, metribuzin applied at about 55% of the normal dose should control jimsonweed and velvetleaf. Weather conditions before postemergence applications of metribuzin will determine the appropriate timing of application and the herbicide dose.

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.

The herbicide 3-tert-butyl-5-chloro-6-methyluracil (terbacil) applied in an isoparaffinic oil caused, in susceptible ivyleaf morningglory (Ipomoea hederacea (L.) Jacq.), rapid and nearly complete inhibition of photosynthesis, from which it never recovered. Photosynthesis in peppermint (Mentha peperita L.), a tolerant species, was decreased only temporarily. Terbacil was readily absorbed by leaves of both species; however, there was little or no movement out of the treated peppermint leaves. Terbacil was translocated out of the treated leaves of ivyleaf morningglory to the untreated leaves and shoot apex. It was metabolized in both species but at a higher rate in peppermint. Therefore, it appears that foliarly-applied terbacil may be bound in peppermint leaves and this, together with the higher rate of metabolism, may contribute to the tolerance of peppermint. Terbacil was readily taken up and translocated to the foliage of both species when applied to the roots. Again, it was metabolized in both plants but at a higher rate in peppermint. However, the rate of metabolism alone did not appear to be sufficient to account for peppermint tolerance to root-applied terbacil.

Competition studies were conducted in Brazil during 1972 and 1973 between high populations (160 plants/0.1 m2 at 5 to 7 weeks after planting) of purple nutsedge (Cyperus rotundus L.) and the following vegetable crops: garlic (Allium sativum L. ‘Mineiro’), okra (Hibiscus esculentus L. ‘UFV 1152’), carrot (Daucus carota L. ‘Nantes’ and ‘Kuroda’), bush-type green bean (Phaseolus vulgaris L. ‘Topcrop’), cucumber (Cucumis sativus L. ‘Aldai’), transplanted cabbage (Brassica oleracea L. var. capitata ‘Louco’) and transplanted tomato (Lycopersicon esculentum Mill. ‘Santa Rita’). Purple nutsedge grew all year with irrigation, although growth was greater during the warm, wet season (October to March). Crop losses due to purple nutsedge competition during the entire cropping season were as follows: garlic 89%; okra 62%; two carrot cultivars, ‘Kuroda’ and ‘Nantes’ 39% and 50%, respectively; green bean 41%; cucumber 43%; cabbage 35%; and tomato 53%. Critical periods of purple nutsedge competition occurred between 3 and 13 weeks for garlic; 3 and 7 weeks for okra, cucumber and the carrot cultivar ‘Nantes’; 3 and 5 weeks for tomato and the carrot cultivar ‘Kuroda’; and at approximately 4 weeks for cabbage and green bean. Purple nutsedge competed for light in the slow-growing, non-competitive crops and for nutrients in all crops. Competition for water was reduced because the vegetables were irrigated regularly. The rate of leaf area development for a competitive crop, green bean, was similar to the rate for purple nutsedge, whereas the rate was much lower for the non-competitive okra.

A 2-yr field study was conducted to determine whether the addition of wetting agents to diclofop {2-[4-(2,4-dichlorophenoxy) phenoxy] propanoic acid} could enhance its postemergence control of grass weeds without altering its crop tolerance. In each year, 12 species were treated at two stages of growth with at least two concentrations of diclofop. Regardless of the treatment, selectivity was not altered on wheat (Triticum aestivum L.), soybeans [Glycine max (L.) Merr.], cucumber (Cucumis sativus L.), or sorghum [Sorghum bicolor (L.) Moench]. The addition of wetting agent to diclofop was of no value on highly susceptible grass weed species such as barnyardgrass [Echinochloa crus-galli (L.) Beauv.] or on the more resistant species such as large crabgrass [Digitaria sanguinalis (L.) Scop.]. Only on an intermediately susceptible species such as giant foxtail (Setaria faberi Herrm.) could any significant differences in control be attributed to a wetting agent. The stage of growth of the grass weed species at time of treatment and the diclofop concentration were more important than the presence of a nonionic wetting agent.

Diphenamid (N,N-dimethyl-2,2-diphenylacetamide) severely inhibited adventitious roots in the shoot zone of sorghum (Sorghum bicolor (L.) Moench., var. RS 610) and corn (Zea mays L., var. WF9 X B37) without decreasing foliage growth. Using diphenamid to inhibit shoot zone roots, the presence of adventitious roots was shown to increase foliage injury to corn, sorghum, or both when exposed to 3-(3,4-dichlorophenyl)-l,l-dimethylurea (diuron), 2-(ethylamino)-4-(isopropylamino)-6-(methylthio)-s-triazine (ametryne), or 3-tert-butyl-5-chloro-6-methyluracil (terbacil) in the shoot zone. Inhibition of adventitious roots was associated with a decrease in uptake of 14C-diuron and 14C-ametryne in both corn and sorghum. Inhibition of the adventitious roots did not alter the response of corn or sorghum, as measured by top growth, when treated with dimethyl tetrachloroterephthalate (DCPA), isopropyl-m-chlorocarbanilate (chlorpropham), S-ethyl dipropylthiocarbamate (EPTC), and α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin). The meristematic region of the sorghum shoot before emergence was more sensitive than other regions of the shoot to DCPA and chlorpropham. Injury from other application sites depended upon uptake from the treated area and movement to the meristematic region, where both herbicides appear to be acting.

A root bioassay was used to compare the adsorption of herbicides by activated carbon with that of muck soil, bentonite clay, a cation exchange resin, and an anion exchange resin. The effectiveness of different adsorbents was determined by comparing the concentrations of herbicide required to give 50% root inhibition of the test plant. Of eight herbicides tested, six were more strongly adsorbed by activated carbon than by any of the other adsorbents. The relative amount of adsorption by activated carbon as measured by the reduction in biological activity was as follows: isopropyl N-(3-chlorophenyl)-carbamate (CIPC) > α,α,α,trifluro-2,6-dinitro-N, N-dipropyl-p-toluidine (trifluralin) > 2,4-dichlorophenoxyacetic acid (2,4-D) > N,N-dimethyl-2,2-diphenylacetamide (diphenamid) > dimethyl 2,3,5,6-tetrachloroterephthalate (DCPA) > 4,6-dinitro-o-sec-butylphenol (DNBP) > 3-amino-2,5-dichlorobenzoic acid (amiben). The biological activity of 1,1'-dimethyl-4,4'-bipyridinium salt (paraquat), a cationic herbicide, was not reduced by activated carbon, but was reduced by bentonite clay and the cation exchange resin. DNBP was more strongly adsorbed by the anion exchange resin than by activated carbon. Desorption from activated carbon varied greatly for the herbicides tested. The most readily desorbed herbicide was 2,4-D while CIPC and DNBP showed little or no desorption.

The percentage composition of fat, protein, nitrogen-free extract (NFE), fiber, and ash was determined for 50 weed and crop species. Data on 16 additional species were compiled from the literature. Generally, within a family there was a tendency toward a certain type of storage material. Seeds of the Polygonaceae and Gramineae were low in fat, high in NFE and, with few exceptions, low in protein. Seeds of the Leguminosae family were the highest in protein and, with the exception of peanut (Arachis hypogaea L.) and soybean [Glycine max (L.) Merr] were low in fat and high in NFE. Seeds of the Compositae, Cruciferae, Cucurbitaceae, and Solanaceae were high in fat, moderately high in protein, and low in NFE. The data may be valuable in the interpretation of the mode of action or basis for selectivity of herbicides.

A bioassay for photosynthetic and respiratory inhibitors was devised. The chlorophyll production of Chlorella pyrenoidosa Sorokin, high temperature strain 7-11-05, served as the basis of the bioassay which required 18 to 36 hr to complete. The sensitivity to nine photosynthetic and two respiratory inhibitors ranged from 0.013 to 0.4 ppm. The bioassay was successfully employed to assay leachates from soil columns and to monitor a field residue of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine).