The following surfactants were prepared at various concentrations in distilled water, with and without 3% W/V technical or formulated 2,2-dichloropropionic acid (dalapon): anionic—Vatsol OT (sodium dioctylsulfosuccinate), sodium lauryl sulfate; nonionic—Dynawet (chemistry undisclosed), X-77 (alkylarylpolyoxyethylene glycols, free fatty acids and isopropanol), Tween 20 (polyoxyethylene sorbitan monolaurate), Tween 80 (polyoxyethylene sorbitan monooleate), T-1947 (polyoxyethylene polyoxypropylene polyols). Contact angles on paraffin coated plexiglas and corn leaf surfaces correlated well with surface tension measurements. With solutions having surface tensions of 31 dynes/cm or less, leaf wetting was complete. Although surfactants differed considerably in their influence on surface tension and wetting, all markedly enhanced herbicidal activity, increasingly with rate. The superiority of Vatsol OT as a surface tension reducer and wetting agent was confirmed. Vatsol OT alone was toxic to corn at 0.5% concentration and higher; T-1947 and sodium lauryl sulfate produced early injury symptoms at 5.0% but caused no lasting effect; all other surfactants were nontoxic at all concentrations used. Minimum surface tensions and contact angles occurred at 0.1–0.5% concentration for all surfactants. However, maximum herbicidal activity was observed at ten times these levels or greater. Thus above 0.1–0.5% surfactant concentration herbicidal enhancement was not correlated with surface tension lowering, contact angle, observed wettability or initial toxicity of the surfactants. This confirms the view that herbicide-surfactant-plant surface interactions, more specific than mere increased wetting, are a part of total surfactant action.

Downy brome (Bromus tectorum L.), and rattail fescue (Festuca myuros L.) were controlled by 2-methoxy-3,6-dichlorobenzoic acid (dicamba) and 2,4-bis(isoproplyamino)-6-methylmercapto-s-triazine (prometryne). Both herbicides gave 70–100% control when applied soon after the first postharvest irrigation. Dicamba was somewhat less effective when applied before this irrigation. Neither herbicide reduced seed yields when applied before or immediately after the first postharvest irrigation, but both herbicides caused some significant seed yield reductions when treatments were delayed until after considerable crop regrowth had occurred.

Root moisture extraction profiles varied from 20 square feet for Kochia scoparia (L.) Schrad, (kochia to 44 square feet for Xanthium pennsylvanicum Wallr. (cocklebur). Weeds within the extremes with increasing root moisture extraction profiles were Eragrostis pectinacea (Michx) Ness (tufted lovegrass), Solanum rostratum Dunal. (buffalobur), Digitaria sanguinalis (L.) Scop. (large crabgrass), Tribulus terrestris L. (puncturevine), Salsola kali L., var. tenuifolia Tausch (Russian thistle), Amaranthus palmeri S. Wats. (Palmer amaranth) and sorghum.

The preemergence herbicide N, N-dimethyl-2, 2-diphenylacetamide (diphenamid) alone and in combination with the contact herbicides 1,1′-dimethyl-4, 4′-bipyridinium salt (paraquat) and 3, 4-dichloropropionanilide (propanil) was studied over three years. Application at planting and crop emergence (delayed preemergence) were compared. Weed control and crop tolerance were equally effective at either stage in tomatoes. Delayed preemergence applications of contact materials alone were erratic as herbicides but were more effective in peppers than in tomatoes. At emergence, combinations were more effective. Selectivity of propanil lessened when the cotyledons of tomato expanded fully.

Herbicidal rates (5 to 9 lb/A) of 2-chloroallyl diethyldithiocarbamate (CDEC) retarded emergence of head lettuce (Lactuca sativa L.) reduced both pre- and postthinning plant populations, caused injury symptoms in young plants, affected the subsequent rate of growth, date of maturity, weight of marketable heads, and yield. Decreased yields were attributed to a reduction in plant population, poor head solidity, and small head development. Reductions in yield were in proportion to dosage and of economic importance.

Watering with 1 surface cm or more following spray treatment with dicamba (2-methoxy-3,6-dichlorobenzoic acid) and picloram (4-amino-3,5,6-trichloropicolinic acid) markedly increased inhibition of shoot growth from rhizome sections of quackgrass (Agropyron repens (L.) Beauv.) and bromegrass (Bromus inermis Leyss). Shoots were most sensitive to the herbicides at early stages of development. Bromegrass and quackgrass were about equally susceptible to the two herbicides. Uptake through roots or rhizomes was more effective than foliar uptake. Kentucky bluegrass in established sod was not injured by dosages of the two herbicides that killed or controlled quackgrass. Young stands of Kentucky bluegrass were more sensitive.

Effective chemical control of alligatorweed (Alternanthera philoxeroides (Mart.) Griseb.) has been prevented by rapid regeneration of plants from inactive axillary buds following treatment with herbicides. Destruction of phloem, cambium, and associated parenchyma occurred above and within the nodes of plants treated with 2 lb/A dichlobenil (2,6-dichlorobenzonitrile) or dicamba (2-methoxy-3,6-dichlorobenzoic acid). Application of dichlobenil and dicamba in combination increased the extent of tissue destruction. Herbicidal activity was noted within the axillary buds only when vascular strands between bud and stem were well differentiated.

Canada thistle [Cirsium arvense (L.) Scop.] infestations were treated with 3-(p-chlorophenyl)-1,1-dimethylurea (monuron) at 10 rates ranging from 5 to 160 lb/A. Depths to which monuron leached were determined annually by bioassays with flax, peas and wheat. Toxicity at all rates continued for 3 years. The low sand, high clay, and high organic matter contents of this soil combined with cool or dry climatic conditions inhibited leaching and prolonged the toxicity of monuron.

P32 was injected into the soil at specific locations to allow determination of the phosphorus uptake pattern of Phaseolus vulgaris (snap bean), Amaranthus retroflexus (pigweed), and Setaria viridis (green foxtail). All species absorbed phosphorus primarily from the top 6 inches of soil. Bean absorbed phosphorus from a zone of relatively small volume. Pigweed roots showed the greatest amount of lateral spread and foxtail roots the deepest soil penetration.

One, two, three, or four plants of each of the above-mentioned species were grown 6 inches from a test bean plant to evaluate the effects of associated plants on the phosphorus uptake of the test bean. The effects observed were quite different for the three species studied.

Metabolic incorporation of adenine-2-14C by Saccharomyces cerevisiae was examined for alterations produced by 3-amino-1,2,4-triazole (amitrole) and histidine. The radioactivity recovered from cells after a 4-hour incubation was found predominantly in ethanol-insoluble components (nucleic acids and proteins) of untreated cultures. Amitrole inhibited incorporation of 14C into insoluble components. Carbon-labeled imidazoleglycerol phosphate, a precursor of histidine, and labeled imidazoleglycerol accumulated in the ethanol-soluble fraction of amitrole treated cells. Imidazoleglycerol accumulated in the external medium. Histidine prevented 14C incorporation into the hot trichloroacetic acid-insoluble residue (protein), prevented amitrole-induced imidazoleglycerol and imidazoleglycerol phosphate accumulation, and circumvented amitrole inhibition of 14C incorporation into the hot trichloroacetic acid-soluble (nucleic acids) fraction.

Effects of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,3,6-trichlorobenzoic acid (2,3,6-TBA) on plant numbers and on the reproductive bulbs were studied by counting plants and digging and examining the bulbs in soil cores.

Foliar application of both herbicides resulted in necrosis, reduction in size, growth abnormalities (hardshell bulbs only), changes in the makeup of bulb population, and eventually a large decline in bulb numbers. Soft offset bulbs were damaged less than central bulbs by both herbicides. Soft offset bulbs increased in proportion to total bulb population following 2,3,6-TBA treatment. Both herbicides caused abnormal growth of developing hardshell bulbs and reduced viability. At the 2-lb rate, 2,3,6-TBA reduced hardshell bulb production more than 2,4-D; at 4 lb/A, 2,3,6-TBA prevented hardshell bulb production. Dormant hardshell bulbs of previous seasons' production were not affected by either herbicide. Plant populations declined more rapidly and to a lower level than bulb populations under adverse conditions of environment and herbicide treatments. The slower decline in bulb numbers resulted from dormancy in the hardshell bulbs.

In greenhouse tests, temperature, humidity, drought stress, and concentration of surfactant influenced the foliar activity of spray mixtures containing a dodecyl ether of polyethylene glycol (Surfactant WK) and 3-(3,4-dichlorophenyl)-1,1-dimethyl urea (diuron) or 3-(3,4-dichlorophenyl)-1-methoxy-1-methyl urea (linuron). In comparisons with other commonly used surfactants, Surfactant WK gave a superior performance when used in conjunction with diuron, linuron, and 5-bromo-3-sec-butyl-6-methyl uracil (bromacil). Increased water solubility of these herbicides in the presence of surfactant is only one factor among many involved in the enhanced activity of such combinations. Surfactant WK facilitated the deposition of high concentrations of linuron on leaf surfaces of Johnsongrass. Once a gradient was established, subsequent rapid movement of the herbicide into the leaf was noted.

A 4-year study was made at Huntley, Montana. When the seed coats were ruptured, 100% germination of sago pondweed (Potomogeton pectinatus L.) seeds occurred. Tubers grow in soil to a depth of 18 inches. Formation of tubers was greatest in August. Single plants of sago pondweed, grown from a tuber and a seed, in 6 months developed over 36,000 tubers and 63,000 seeds, respectively. Tubers survived winter temperatures well when buried in the soil. When dipped in paraffin tubers survived up to four years in storage.

Doses required to reduce fresh weights of seedling oats 50 percent (ED50) in 32 soils were determined for isopropyl N-(3-chlorophenyl)carbamate [CIPC], 3-(3,4-dichlorophenyl)-1,1-dimethylurea [diuron], and 2-chloro-4,6-bis(ethylamino)-s-triazine [simazine]. Physical and chemical properties of soils and the extent of adsorption of the three herbicides on the soils were also determined and evaluated by correlation and multiple regression analysis for usefulness in predicting dose requirements.

Extent of adsorption was most closely correlated with ED50 values for diuron and simazine, but organic matter content was most closely correlated with ED50 values for CIPC. None of the soil properties nor the extent of adsorption provided consistent predictive value for all of the soils and herbicides studied.

The effect of temperature and relative humidity on root and foliar uptake of C14-labeled atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) in quackgrass (Agropyron repens (L.) Beauv.) was studied in a controlled environment growth chamber. Uptake and translocation of root-fed atrazine increased as temperature increased. Greater uptake and translocation of root-fed atrazine occurred under low relative humidity than under high relative humidity. Slightly greater uptake and translocation of foliar-applied atrazine occurred as temperature was increased from 60 to 80 F.

It was shown that less sprouting of blue oak (Quercus douglasii) and California black oak (Q. kelloggii) occurred when treated stumps were (a) cut 30 cm rather than 90 cm high, (b) treated at once after cutting rather than after 7 days, (c) treated with 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) amine rather than with 2,4-dichlorophenoxyacetic acid (2,4-D) amine, and (d) left uncovered rather than covered. The differences between treatments eventually disappeared because of the death of the sprouts, possibly due to the levels of herbicide used in making the treatments.

The downward movement of carboxyl C14-labeled 2,4-D and 2,4,5-T, 3-amino-1,2,4-triazole-5-C14, and C14-labeled urea in interior live oak (Q. wislizenii) stumps was studied. Rainfall, level of 2,4-D applied, and time interval all appeared to influence downward movement.

Lambsquarters (Chenopodium album L.), redroot pigweed (Amaranthus retroflexus L.), and white mustard (Brassica hirta L.) were highly susceptible to 2-methyl-4-chlorophenoxyacetic acid (MCPA) regardless of the pretreatment light exposure to which they were subjected. These broadleaved weeds were slightly more susceptible to MCPA applied after a prolonged period of darkness. Neither total carbohydrate, reducing sugar, protein, nor amino acid contents at the time of spraying were associated with the susceptibility of mustard plants to MCPA. Floral bud development on Canada thistle was greatly reduced by MCPA applied at any time of the day to plants 9 and 12 inches tall and was prevented on plants 3 and 6 inches tall. The susceptibility of broadleaved annual weeds and Canada thistle to MCPA was not affected by variations in temperature and humidity at time of spraying.

On three soils, 3-amino-2,5-dichlorobenzoic acid (amiben) at 1.5 and 15 ppmw did not inhibit the nitrifying microflora, but 150 and 1500 ppmw significantly reduced the nitrate nitrogen produced by the soil microflora. No breakdown of amiben in liquid media was detected during 70 days. Amiben had a net minus charge in solution, and traveled at about the same rate on paper strips in electrophoresis as the dye brilliant blue. The organic matter content of soil was the property most closely associated with adsorption of 14C-labeled amiben. Only kaolinite, of four clays studied, adsorbed amiben significantly. There was no volatilization of amiben from stainless steel planchets stored at temperatures of 15, 25 or 35 C and relative humidities of 0, 33, 66, or 100 per cent.

A natural product in corn, the 2-glucoside of 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one, is capable of inactivating triazine herbicides. Two essentially isogenic corn lines, Mississippi selection GT112 (susceptible to atrazine and simazine) and GT112 RfRf (resistant), contained the compound in both roots and shoots. The content of the roots was about equal for the two lines and decreased with age. In shoots of GT112 seedlings 13 to 28 days old, the 2-glucoside content reduced with time to half the original value. In shoots of GT112 RfRf, the 2-glucoside content doubled from 13 to 17 days, then decreased. Shoots of GT112 RfRf contained 1.6, 3.6, and 2.4 times more 2-glucoside at 13, 17, and 28 days, respectively, than GT112. However, 13-day-old homogenized shoots of GT112 converted 1.8 times more atrazine per μM of 2-glucoside than GT112 RfRf. Susceptibility of GT112 to triazine herbicides is not due to absence of the 2-glucoside or its inability to convert atrazine.

Dicamba (dimethylamine salt of 2-methoxy-3,6-dichlorobenzoic acid) followed slightly behind the forward penetration of added water in both loam and sandy loam soils. Dicamba persisted longer than 2,4-D butyl ester in autoclaved and not-autoclaved loam and sandy loam soils. Tartary buckwheat, Fagopyrum tataricum (L.) Gaertn. planted at intervals in the autoclaved soils showed no injury from the 2,4-D at 16 oz/A after 4 weeks but was completely killed by dicamba at 8 oz/A after 12 weeks of incubation. In the not-autoclaved soils there was no visible effect on the buckwheat plants from 2,4-D after 2 weeks but nearly all of the plants were killed by dicamba after 12 weeks of incubation. Oxygen consumption in the loam soil was greatly reduced by dicamba at concentrations of 10,000 ppm or higher. Similar concentrations of 2,4-D butyl ester had only a slight and sometimes no effect on oxygen uptake. These concentrations are well in excess of those suggested for selective weed control in grain crops.