The movement of chemicals in the soil caused by water percolation was treated in a manner analogous to the development of materials through chromatographic columns. A “slotted tube test” was developed, which simulated a miniature field plot, utilizing a chromatographic soil column and the growth of either seeds or an indicator organism in agar as the detector. It was found that the median effective dose was higher for the more strongly sorptive soils. When correlations were made between soil compositions and the corresponding median effective doses for nonionic organic molecules, virtually all of the variations in required dosages were accounted for by percent organic matter and water content. The “active fraction” of organic matter, that fraction concerned with sorption equilibria, appeared to be of the same nature in soils of various compositions from various sources. This provided a technique for calculating the percent “active” organic matter of soil.

Differences in the competitive effects of three major species of foxtail on soybeans were due primarily to differences in the mature plant yields of the species. Giant foxtail (Setaria Faberi) grew more vigorously and caused greater soybean yield reductions than did either yellow foxtail (Setaria lutescens) or green foxtail (Setaria viridis). The competitive effects of velvetleaf (Abutilon theophrasti) per cwt. of mature weeds were approximately double those of yellow and green foxtail, but produced about the same yield reduction.

The photosynthetic capacities of three species of dodder, largeseed dodder (Cuscuta indecora, Choisy), field dodder (Cuscuta campestris, Yuncker), and small-seeded dodder (Cuscuta approximata, Bab.) were studied by radioactive carbon dioxide uptake in light and darkness, and by manometric methods. Both methods showed that all three species were able to carry on a small amount of photosynthesis. The photosynthetic capacity was highest in the seedling, and decreased as the dodder became parasitic.

In nutrient solution, 2,3,6-trichlorobenzoic acid (2,3,6-TBA) was less toxic to oats than either 2-methoxy-3,6-dichlorobenzoic acid (dicamba) or 3-amino-2,5-dichlorobenzoic acid (amiben). The latter two herbicides were similar in phytotoxicity.

In soil, dicamba was the most phytotoxic in each of four soils used, while 2,3,6-TBA and amiben were similar in toxicity in all soils except the organic soil, in which amiben was less phytotoxic than 2,3,6-TBA. In the sandy soils the same amount of herbicide was required to reduce the growth of oats by 50% as was required in nutrient solution, but considerably higher amounts were required in the organic soil. This reduction in phytotoxicity was attributed to adsorption of the herbicides in an unavailable form by the organic matter of the soils, amiben being adsorbed to a greater extent than 2,3,6-TBA or dicamba. Practically no adsorption occurred on the clay colloids of the various soils.

In persistence studies, amiben was more subject to apparent microbial decomposition than 2,3,6-TBA or dicamba. Decomposition was more rapid in the organic soil than in the clay or sandy soils. In leaching studies, the three herbicides were readily washed out of columns of the various soils. Differences in movement of herbicide in these soils could be related to the rate of water movement through the soil.

The most successful herbicides for control of downy brome (Bromus tectorum L.) in grassland were: 3-amino-1,2,4-triazole (amitrole), 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine), 2-chloro-4,6-bis(isopropylamino)-s-triazine (propazine), and 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine). More consistent downy brome control was obtained with atrazine than the other s-triazines. Amitrole improved postemergence control of the s-triazines in the tillering stage. Intermediate wheatgrass (Agropyron intermedium (Host.) Beauv.), crested wheatgrass (Agropyron cristatum L. Gaertn.), western wheatgrass (Agropyron smithii Rydb.), blue grama (Bouteloua gracilis (H. B. K.) Lag.), and sedge (Carex spp.) appeared to be more sensitive to most s-triazines than needle-and-thread (Stipa comata Trin. & Rupr.) and sand dropseed (Sporobolus cryptandrus Torr.). Sand dropseed was extremely tolerant.

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.

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.

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.

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.

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.

Enhancement of 3(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) toxicity to oat plants was not dependent on type—anionic, cationic, or nonionic—of surfactant. However, specific surfactant and concentration were important. Concentrations of surfactant above 0.1% were required for consistent phytotoxic effects. Concentration of diuron in solution at time of application was not an important factor in phytotoxicity. Lowering the temperature from 72 to 60 F slowed the expression of toxicity and increased the chances of plant recovery.

A mitochondrial fraction isolated from cotyledons of etiolated Cucumis sativus L. (Burpee's Improved Long Green) showed respiratory activity roughly comparable to that of other reported plant mitochondrial systems. Published procedures on extraction, centrifugation, and determination of cofactor requirements were modified for this system to obtain maximum activity as measured by Warburg manometry. Succinic dehydrogenase activity in the fraction was inhibited by known inhibitors such as sodium azide, DNP, and hydroxymalonic acid; α-ketoglutarate utilization was inhibited by sodium azide.

Dichlobenil (2,6-dichlorobenzonitrile) consistently increased respiration (up to 162% of the controls, using 1.45 × 10-4 M dichlobenil in a succinate substrate mixture); 2,5-diiodo-4-hydroxybenzonitrile (ioxynil) consistently reduced O2 uptake at 0.75 × 10-6 to 0.75 × 10-3 M concentrations. Picloram (4-amino-3,5,6-trichloropicolinic acid) performed in a manner generally similar to the five following substituted benzoic acids: 2,3,6-trichlorobenzoic acid (2,3,6-TBA); 3-amino-2,5-dichlorobenzoic acid (amiben); 3-nitro-2,5-dichlorobenzoic acid (dinoben); 2-methoxy-3,6-dichlorobenzoic acid (dicamba); and 2-methoxy-3,5,6-trichlorobenzoic acid (tricamba). Using succinate as substrate, stepwise inhibition occurred in the range of 10-5 to 10-3 M herbicide; however, the α-ketoglutarate system was much less sensitive to all compounds. For example, the effects of 10-3 M amiben and dicamba on α-ketoglutarate utilization were essentially negligible. Six other herbicides studied showed either no effect or varying degrees of inhibition, depending upon concentration and substrate employed. Dichlobenil uncoupled oxidative phosphorylation at a 1.45 × 10-4 M concentration.

Diuron, 3-(3,4-dichlorophenyl)-1,1-dimethylurea-C14, moved primarily in the apoplast with the transpiration stream, and did not move with the plant assimilates of red kidney bean, soybean, and barley plants. There did not appear to be a species difference in absorption, distribution, and accumulation. Uptake and distribution increased progressively as duration of treatments increased from 6 hours to 16 days. No phloem movement and distribution was observed in the 16-day treatment time. The addition of a surfactant did not alter the translocation pattern of diuron.

The evidence obtained from gross autoradiographs did not eliminate the possibility that very small amounts of diuron may get into the symplast. However, it did indicate that if diuron moved into the symplast, it was restricted and the movement of diuron out of the area of application by phloem was very limited.

The herbicide 3’,4′-dichloropropionanilide (propanil) effectively controlled barnyardgrass [Echinochloa crusgalli (L.) Beauv.], brachiaria [Brachiaria platyphylla (Griseb.) Nash], crab-grass [Digitaria spp.], sesbania [Sesbania exaltata (Raf.) Cory], curly indigo [Aeschynomene virginica (L.) B.S.P.], spikerush [Eleocharis spp.], and umbrellasedge [Cyperus spp.] in the 1- to 4-leaf stages without significant injury to commercial varieties of rice in the 1- to 2-leaf stages. It was ineffective for control of ducksalad [Heteranthera spp.], redstem [Ammannia coccinea Rottb.], morningglory [Ipomoea spp.], sprangletop [Leptochloa panicoides (Presl.) Hitchc.], and red rice [Oryza sativa L.]. Mixtures of propanil and a blended surfactant, containing petroleum sulfonate, free and combined fatty acids, and petroleum oil, and mixtures of propanil and isopropyl N-(3-chlorophenyl)carbamate (CIPC) and methyl 2,4-dichlorocarbanilate (swep), controlled barnyardgrass better than propanil alone. Propanil sometimes injured the rice, but it recovered in 5 to 10 days after treatment and yield and quality were unaffected.

Effective control of Artemisia vulgaris L. (mugwort) was obtained with 2,3,6-trichlorophenylacetic acid (fenac) and 4-amino-3,5,6-trichloropicolinic acid (picloram). Dimethylamine salt of 2-methoxy-3,6-dichlorobenzoic acid (dicamba) gave control when applied in April when mugwort shoots were small. Dicamba was less effective later in the season even after clipping to obtain small new shoots. The amount of fenac necessary for effective control was reduced by mixing with dicamba, the butoxyethanol ester of 2,4-dichlorophenoxyacetic acid (2,4-D) or oleyl-1,3-propylenediamine salt of 2,4-D. Late in the season, fenac was more effective when applied after mowing than when applied to large mugwort. Soil incorporated ethyl N,N-dipropylthiolcarbamate and propyl dipropylthiolcarbamate reduced mugwort stands and rhizome weight; however, regrowth occurred in the same season.

These herbicides for vegetables in three desert areas managed under furrow irrigation exhibited extreme variability between locations in herbicide response and crop toxicity. Some treatments provided a reasonable compromise between weed control and crop injury at any one location, none met this requirement at each location. Soil-type, soil moisture at time of herbicide application, and interaction of crops and environment probably contributed to the observed variability.

Experiments of two types were conducted. (1) Weeds were allowed to grow for different periods after planting sugar beets; they were then removed and the beets hand-weeded until harvest. (2) Sugar beets were hand-weeded for different periods after planting; then no further weeding was done. Weed competition reduced beet yields up to 94%. Weeds that emerged soon after beet planting reduced yields the most, but they exerted little yield-reducing competition until later than 12 weeks after planting the beets (9 weeks after beet emergence). Full-season weed control resulted when beets were hand-weeded for 10 to 12 weeks after planting. Weeds that emerged later were controlled by crop competition.

A Streptomyces, apparently S. viridochromogenes, was isolated from Louisiana crop areas where seven chlorinated herbicides had been used in weed control. It liberated no chloride when grown in a liquid medium containing 100 ppm of any of these seven herbicides. With a cucumber root bioassay, detoxification of 2,4-dichlorophenoxyacetic acid (2,4-D), 2-(2,4,5-trichlorophenoxy)propionic acid (silvex), 2,3,6-trichlorophenylacetic acid (fenac), 2,2-dichloropropionic acid (dalapon) was observed, but little detoxification was shown with 2-chloro-N,N-diallylacetamide (CDAA), isopropyl N-(3-chlorophenyl)carbamate (CIPC), and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). Manometric studies with 2,4-D, 2,4,5-T, and silvex showed the streptomycete was capable of adapting to the compounds after a short period, but not to 2,4-dichlorophenol, a proposed intermediate of 2,4-D metabolism. The organism did not alter the ring structure of the aromatic herbicides, and 2,4-D and 2,4-dichlorophenol showed identical absorption curves with the spectrophotometer used.

C14 ring-labeled atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) was applied in nutrient solutions. Soybeans absorbed more atrazine per g of fresh weight than corn or cotton. The amount of atrazine absorbed by the plants increased with increases in atrazine concentration, in water absorption, and in length of absorption. Less atrazine was absorbed in the second than in the first 24-period wtih occasional indications of loss of atrazine back into the solution. C14O2 evolution was not established for any plant although many different environmental conditions were tried. Degradation to C14O2 is not a significant process for these plants under these conditions.

Three thiocarbamate herbicides, S-ethyl dipropylthiocarbamate, S-propyl dipropylthiocarbamate, and S-propyl butylethylthiocarbamate, applied at a depth of 1.5 inches in Tifton loamy sand were much more toxic to yellow nutsedge (Cyperus esculentus L.), sicklepod (Cassia tora L.), and Texas millet (Panicum texanum Buckl.) than when applied at 0.75 inches. The optimum depth of application may vary with different soils. Optimum subsurface placement was more effective than either soil incorporation or preemergence surface application.