Derivative of 2,4-dichlorophenoxyacetic acid (2,4-D), type of bottom sorbent, and application concentration affected the rate and quantity of 2,4-D released into water from attapulgite granules. All three factors were temperature dependent. Temperature, granule size, and solution pH affected the rate during short exposure periods, but not the total quantity of release of herbicide during 256 hours. Generally, decrease in temperature was associated with a decrease in rate of release of 2,4-D. Decrease in granule size slightly increased the rate of release. Increased acidity reduced the rate of release of 2,4-D acid. Types of attapulgite granules were not significantly different.

Rates of subaqueous release of eleven granular herbicides were measured at concentrations of 10, 15, and 20 μg ai/ml. Compounds tested were 2,4-D and its butoxyethanol ester (BE), propylene glycol butyl ether ester (PGBE), and isooctyl ester (IOE) derivatives, tris-(2,4-dichlorophenoxyethyl)phosphite, the IOE of 2,4,5-trichlorophenoxyacetic acid, the BE, PGBE, and potassium salt of 2-(2,4,5-trichlorophenoxy)propionic acid (silvex), the sodium salt of 2,3,6-trichlorobenzoic acid, and 2,3,6-trichlorophenylacetic acid (fenac). The rate of release of herbicides from granules varied from complete release of silvex potassium salt in 4 hours to less than 10 per cent release of 2,4-D IOE in 256 hours.

Mixtures of CDAA + atrazine or propazine applied pre-emergence gave excellent grass and non-grass weed control and no sorghum injury. Such mixtures offer promise of more consistent weed control than either component alone and less soil residue than a higher rate of atrazine or propazine alone. CDAA + trichlorobenzyl chloride preemergence was a less effective mixture but gave better grass weed control and poorer non-grass control than propazine or atrazine pre- or postemergence. Atrazine or propazine postemergence following CDAA preemergence gave excellent results. The best time to spray sorghum with atrazine or propazine between planting and the 11-leaf stage was when the weeds were in the very early postemergence stage. Sorghum was tolerant at all times of application. Atrazine over all trials averaged superior to propazine as an herbicide for grain sorghum.

An effective technique was developed for partitioning the environment of intact submersed aquatic plants. The technique facilitates absorption and translocation studies by permitting application of radioactive herbicides to selected portions of the plants. Root and shoot treatments of Potamogeton pectinatus L. for 24 to 96 hours with C14-labeled 2,3,6-trichlorophenylacetic acid (fenac) showed no leakage across the partitioned system. Little or no basipetal translocation of the herbicide was observed. Limited acropetal translocation occurred and this was reduced by removal of tubers prior to herbicide application. Accumulation of activity in nodal regions of the stem was noted.

Volatilities of 2-chloro-4,6-bis(ethylamino)-s-triazine [simazine], 2-chloro-4-ethylamino-6-isopropylamino-s-triazine [atrazine], 2-chloro-4,6-bis(isopropylamino)-s-triazine [propazine], 2-methoxy-4,6-bis(isopropylamino)-s-triazine [prometone], 2-ethylamino-4-isopropylamino-6-methylmercapto-s-triazine [ametryne], 2,4-bis-(isopropylamino)-6-methylmercapto-s-triazine [prometryne], and 2-chloro-4-diethylamino-6-ethylamino-s-triazine [trietazine] were studied at different temperatures. In descending order at 25 C the relative volatilities of the herbicides from nickel-plated planchets were prometone ≅ trietazine > atrazine ≅ ametryne ≅ prometryne > propazine ≅ simazine. Prometone losses from five soils appeared to be directly related to per cent sand and inversely related to per cent clay and organic matter. Atrazine and simazine losses from the same soils appeared to be less influenced by soil properties than prometone. All seven s-triazines were examined at one temperature on wet and dry Tifton loamy sand. Moisture level affected both the amount of compound lost and the relative order of loss among compounds. Conversion of atrazine and prometone to their corresponding hydroxy analogues was a practical method for preventing vapor losses from planchets.

Experiments were conducted in 200-gal concrete tanks to evaluate a large fresh-water snail, Marisa cornuarietis, as a biological aquatic weed control agent. Adult Marisa snails were collected from a canal near Miami, Florida, where a colony had recently become established. These snails are of South American origin and appear identical to those being used in Puerto Rico for biological control of schistosomiasis. The snails controlled Ceratophyllum demersum, Najas guadalupensis, and Potamogeton illinoensis completely and Pistia stratiotes and Alternanthera philoxeroides partially. Eichhornia crassipes was not completely eaten, but its growth and flowering were greatly retarded by the root-pruning action of the snails. Marisa preferred submersed weeds to floating or emersed weeds, but the floating weed Salvinia rotundifolia was eaten nearly as readily as submersed weeds. Little damage was done by Marisa to 4- and 5-week-old rice plants, but younger rice was killed when the snails had no other source of food. A common snail-eating bird, Cassidix mexicanus, was found to be a predator of Marisa in Florida. Except for its possible deletarious effects in rice-growing areas, Marisa was regarded as very promising for control of aquatic weeds at least in confined bodies of water.

The persistence of soil-surface applied ethyl N,N-di-n-propylthiolcarbamate [EPTC] was studied at air velocities of ⅓ to 4 mph in special air-flow equipment. Persistence was inversely related to velocity though the effect was quantitatively changed by soil composition and the materials used in formulating the EPTC spray.

Complete control of established plants of absinth wormwood (Artemisia absinthium) was obtained with a single application of borax derivatives at 650 lb/A or less. Of several phenoxy-acetic, benzoic, and borax compounds which were tested, the most effective, economical treatment was 2,4-dichlorophenoxyacetic acid (2,4-D). Competition from perennial grasses was beneficial. Fall tillage prevented the establishment of absinth seedlings, and intensive tillage during the summerfallow year eradicated established plants.

Preemergence herbicides for the control of crabgrass, (Digitaria ischaemum (Schreb.) Muhl. and D. sanguinalis (L.) Scop.) were applied on bluegrass sod at three different rates for three years to determine residual effects on the stand and vigor of perennial ryegrass, red fescue, tall fescue, and Merion and common Kentucky bluegrass seedlings. With few exceptions, the herbicides retarded stand and vigor of these turfgrasses seeded in turf killed with methyl bromide. Chlordane was least and a commercial arsenic complex plus 7% N most toxic to young seedlings. Seedlings of Merion Kentucky bluegrass were most resistant to herbicide injury. No appreciable decrease in original turf density was noted except for the arsenic complex material which severely injured bluegrass turf at the two heavier rates.

Germination of the same turfgrasses seeded in flats of sterilized soil in the greenhouse 1 day, 41 days, and 93 days after the application of preemergence crabgrass herbicides, showed the most reduction in emergence from treatments with DMPA [O-(2,4-dichlorophenyl) O-methyl isopropylphosphoramidoate], trifluralin (2,6-dinitro-N,N-di-n-propyl-alpha-alpha-alpha-trifluro-p-toluidine), DCPA (2,3,5,6-tetrachloroterephthalic acid), and dipropalin (N,N-di-n-propyl-2,6-dinitro-p-toluidine). Lead arsenate was least injurious to germinating seedlings. Tall and red fescue were more tolerant to herbicides than the other grasses studied.

When applied in enough water to wet tubes of dry Pullman silty clay loam top soil to a depth of 22 inches, dimethylamine salts of 2,3,6-trichlorobenzoic acid (2,3,6-TBA) and polychlorobenzoic acid (PBA) were leached to about 20 inches; an amine salt of 2,4-dichlorophenoxyacetic acid (2,4-D) and the sodium salt of 2,3,6-trichlorophenylacetic acid (fenac) leached to 15 inches; esters of fenac, 3-phenyl-1,1-dimethylurea (fenuron), 3-(p-chlorophenyl)-1,1-dimethylurea (monuron) and amine salts of 2-(2,4,5-trichlorophenoxyl)propionic acid (silvex) and 2,4,5-trichlorophenoxy-acetic acid (2,4,5-T) leached to approximately 9 inches. Esters of silvex, 2,4,5-T, and 2,4-D remained in the top 3 inches of soil. The leaching with additional water was in the same general order as just given.

Relative vaporization losses of five C14 ring-labeled 2-chloro-4,6-alkylamino-s-triazines were studied at 25 and 60 C. Herbicide solutions in 95% ethanol were deposited on metal planchets, dried and counted at intervals. The herbicides, ranked in order of decreasing volatility, were: trietazine (2-chloro-4-diethylamino-6-ethylamino-s-triazine), ipazine (2-chloro-4-diethylamino-6-isopropylamino-s-triazine), atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine), propazine (2-chloro-4,6-bis(isopropylamino)-s-triazine) and simazine (2-chloro-4,6-bis(ethylamino)-s-triazine). Prometone (2-methoxy-4,6-bis (isopropylamino)-s-triazine) and the 2-hydroxy analogues of simazine and propazine, dissolved in water at pH 2–3 (HC1) before plating, showed no detectible loss in 25 hours at 60 C. Foliar penetration and acute toxicity following drop application of the five 2-chloro-triazines and prometone to corn, soybean, tomato, cotton, oat and sorghum appeared to be correlated with their water solubilities. A surfactant tended to enhance activity. Important differences were noted among species, although apparently not related to inherent herbicidal tolerance or susceptibility. Tomato was most sensitive to acute toxicity; soybean cotyledons were least permeable. Basipetal translocation was negligible under all conditions (e.g. 6 herbicides, 6 species, 2 solvents, with or without a surfactant). The 2-hydroxy analogues tended to translocate downward but appeared restricted by acute, acid (pH 2–3) destruction of the transport mechanism. Acropetal (apoplastic) movement of all compounds occurred readily with transpiration, reflecting the vasculature of the species. All 2-chlorotriazines and prometone (but not the two 2-hydroxy compounds) showed pronounced accumulation of C14 in the lysigenous glands of cotton. Root uptake and distribution of C14 within the plant body occurred generally for all compounds and species.

Ford soybean yields and weed yields were studied under combinations of tillage treatments, 3-amino-2,5-dichlorobenzoic acid (amiben) applications, hand weedings, and row spacings on irrigated and non-irrigated locations in Nebraska during 1961 and 1962. Soybean yields increased and weed yields decreased with tillage, amiben applications, hand weedings, and narrow-row spacing of soybeans. Combinations of these weed control treatments gave more dependable results than any one alone. Each 86 lb/A of weeds present produced an average soybean yield reduction of 1 bu/A. Advantages of growing soybeans with amiben applications in 10-inch rows as compared to 40-inch rows are: (a) an average soybean yield increase of 39%, (b) elimination or reduction of tillage (c) a 50 to 75% reduction in amiben application rate, and (d) little or no soybean injury from the lower rates of amiben required in the 10-inch rows.

Movement of 2-methoxy-3,6-dichlorobenzoic acid (dicamba) and N,N-dimethyl-2,2-diphenylacetamide (diphenamid) in Hagerstown silty clay was greater with either 5 or 10 surface inches of water when the water was applied in 0.25-inch increments rather than 1-inch. Upward movement of these herbicides occurred under sub-irrigation and when surface-applied water was allowed to evaporate freely from the soil surface. Dicamba always moved more readily than diphenamid. The results indicate that weather patterns may be important in addition to total rainfall in determining the movement of herbicides in soil.

The postemergence herbicidal activity and specificity of 16 s-triazines on 8 test species were determined at 3 application rates and the influence of various substitutions discussed.

Volunteer wheat and downy brome (Bromus tectorum L.) were consistently controlled by aerial applications of granular 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) without supplemental tillage. Injury to winter wheat seeded in the fall 13 and 14 months after application of atrazine has occurred. Plots aerially treated with 2 lb/A atrazine produced yields comparable to the check but plots treated with 4 lb/A atrazine produced no wheat. Use of persistent herbicides for chemical fallow must be restricted until further knowledge is obtained.

The adsorption of herbicides from aqueous solution by muck (organic soil), bentonite, an anion exchanger, and a cation exchanger was studied. The nature of the adsorbent, pH, and temperature all influenced adsorption, and different herbicides responded differently to changes in these factors. Lowering of the pH resulted in increased adsorption by bentonite of all of the herbicides studied, except 6,7-dihydrodipyrido (1,2-a: 2’, 1′-c) pyrazidiinium salt (diquat) which was completely adsorbed at both a high and a low pH. The influence of pH was greatest for 4,6-dinitro-o-sec-butylphenol (DNBP) and 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine). The DNBP was adsorbed by an anion exchanger, but not by a cation exchanger, while isopropyl N-(3-chlorophenyl)carbamate (CIPC), 3-(p-chlorophenyl)-1,1-dimethylurea (monuron), and atrazine were adsorbed by both. Diquat was completely adsorbed by the cation exchanger and only slightly by the anion exchanger. All were adsorbed by muck but to varying extents as follows: diquat > CIPC > DNBP > monuron > atrazine. No relationship was found between water solubility and adsorption. Adsorption by bentonite (pH 8.5) was much greater at 0C than at 50C, but adsorption by muck was the same at both temperatures.

Desorption studies were conducted using C14-labeled atrazine, monuron, 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine), 3-amino-2,5-dichlorobenzoic acid (amiben), and 2,4-dichlorophenoxyacetic acid (2,4-D). Repeated extractions with distilled water desorbed these herbicides from bentonite and muck and their desorption was more readily accomplished from bentonite than from muck.

Yield reductions from the heaviest stand of smooth pigweed (Amaranthus hybridus L.) averaged 39% for corn and 55% for soybeans. For corn the increase in pigweed dry matter about equalled the decrease in the dry matter from the crop; the total dry matter yield was relatively constant. Pigweed grew taller than soybeans, and the dry weight of crop plus pigweeds was 1⅓ times that of weed-free soybeans. As stand of pigweed was increased, there was a decrease in yield of grain, cobs and stalks or straw, diameter of cornstalks, height of crop, and soybean pods per plant. Yield reductions obtained emphasize the importance of both chemical and cultural measures for reducing competition between row crops and weeds.

Results of studies with microorganisms suggest that 5-bromo-3-isopropyl-6-methyluracil (isocil) does not interfere appreciably with pyrimidine metabolism. Instead the uracil herbicides studied appear to act in higher plants as inhibitors of photosynthesis. Strong inhibition of the Hill reaction of isolated chloroplasts by substituted uracils was noted (I50 of 2.7 × 10−6 M for isocil). Exogenously supplied carbohydrates partially nullified toxicity symptoms in intact barley plants growing in the presence of inhibitory concentrations of isocil.

Band applications of residual preemergence herbicides were equal to timely shallow cultivations for the control of annual weeds in corn, and were superior when wet weather delayed or interfered with early shallow cultivations. The average corn yield reduction of 7.4 bushels per acre from weed competition observed over a 13 year period, suggested that under average conditions the net cost of herbicide treatment would be less than the value of corn lost through failure to control weeds.

This investigation studied simazine (2-chloro-4,6-bis(ethylamino)-s-triazine), atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine), propazine (2-chloro-4,6-bis(isopropylamino)-s-triazine), and prometone (2-methoxy-4,6-bis(isopropylamino)-s-triazine). Preemergence applications of granular formulations of simazine on attaclay or calcium sulfate of simazine at 1 to 2 ppmw controlled Potamogeton, Najas, Ceratophyllum, Heteranthera and Zannichellia. Higher rates were required to control filamentous algae (Cladophora and Pithophora) and chara (Chara vulgaris). Early postemergence applications of wettable powder to submersed aquatics and filamentous algae were often effective. Atrazine gave similar results. Concentrations of 0.5 to 1.0 were effective in controlling Cladophora and Pithophora and three species of Potamogeton in pond applications. Spray applications, generally, were more effective than broadcasting granular atrazine. Propazine and prometone did not control submersed species in concentrations up to 3 ppmw.

Simazine had a relatively high margin of safety with respect to acute toxicity to fish. It was less toxic than propazine, prometone or atrazine. Granular forms were less toxic than wettable powder or emulsifiable concentrates. Laboratory tests on bottom organisms gave an acute LD50 toxic dosage of 28 ppmw. Field observations did not demonstrate a serious reduction in the production of bottom organisms. However, the control of aquatic vegetation brought about ecological changes affecting bottom dwelling and weed clinging organisms. These changes would affect certain fishes with special food habits.

Alligator juniper (Juniperus deppeana Steud.) is a weed tree of Arizona and New Mexico. It sprouts from stems, roots, or especially from buds on the crown, whenever the top is destroyed. Adequate mechanical control requires that the root crown be removed from the soil. Treatment of stumps with pelleted 3-phenyl-1,1-dimethylurea (fenuron) on the soil or polychlorobenzoic acid (PBA) sprayed on the stumps are promising means of preventing sprouting.