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.

In the last few years the possibility of growing small fruits and several vegetable crops without any soil disturbance has been demonstrated. On many soil types crop yield has been unaffected and has sometimes shown a slight increase compared with traditional cultivation. Advantages of non-cultivation include the possibility of increasing crop uniformity and yield by using closer row spacings and completely new methods of crop production, the avoidance of injury to surface-feeding roots, decreased risk of frost and easier mechanical harvesting of some crops. In small-fruit plantations the weed problem has greatly diminished after about 3 years, because of non-disturbance of seeds lying below the germinating zone and the absence of a “seed-bed”. While the surface crust that sometimes forms where the soil is not disturbed may affect plant growth in certain circumstances, no evidence was obtained in recent experiments in Britain that a crust was detrimental to the growth of established plants. However, water infiltration on bare non-cultivated soil was sometimes retarded and increased run-off occurred on sloping sites. Due to the wide diversity of soil types, climatic conditions and crop response it is impossible to generalize about the effect of eliminating cultivation. Nevertheless, as some of the advantages are considerable while the disadvantages can often be overcome it seems likely that non-cultivation practice will extend to many horticultural crops in the future.

Four concentrations of 3-(p-chlorophenyl)-1,1-dimethylurea (monuron), 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), 1-n-butyl-3-(3,4-dichlorophenyl)-1-methylurea (neburon) and 3-phenyl-1,1-dimethylurea (fenuron), adsorbed on photometrically uniform filter paper, were irradiated with ultraviolet light 253.7 millimicrons) or sunlight. Marked changes in the absorption spectra after irradiation indicated photodecomposition of the four herbicides was different with the two light sources.

Weed Science—a new scientific discipline, has evolved and caused a revolution in agricultural technology. Weeds and their control are basically ecological and economic problems. The losses caused by weeds and the cost of their control, now estimated to exceed $4½ billion annually, are motivating forces in the revolution.

The technological revolution in Weed Science is characterized by the rapid and extensive acceptance and use of chemical weed control methods, expanded scope and diversity of weed research, advances in Weed Science technology, needs and challenges for advances in future technology, impact of chemical weed control on farm management practices, and its effect on the objectives and direction of agricultural research and educational programs.

Chemical methods of weed control greatly reduce energy requirements on farms. Herbicides reduce the manpower, machine hours, and machine horsepower requirements in crop production. Thus, herbicides provide a new dimension for improving farming efficiency and lowering production costs.

In 1962, chemical methods of weed control were used on more than 70 million acres of agricultural land at a cost of more than $272 million, as compared to approximately 53 million acres treated in 1959 at a cost of $128 million, a 33 percent increase in the acreage treated in 1962. The acreage treated in 1962 was equivalent to about 25 percent of the national crop acreage. These use data do not include chemical weed control on industrial sites and other non-agricultural lands.

Chemical weed control is having a far-reaching impact on all phases of crop production. New chemical methods of weed control will affect choice of crop and variety; seedbed preparation; method of seeding; seeding rates; row spacing; plant spacing in the row; plant populations; fertilizer practices including type, time of application, and placement; cultivation; irrigation practices; harvesting; seed-cleaning operations; erosion control; fallow practices for weed control; disease and insect control practices; pasture renovation; pasture and range management; clearing new lands for crops or pasture; forest management; utilization of farm water resources for irrigation and recreation; and maintenance of drainage ditches, ditchbanks, irrigation canals, and farm roadsides.

Agriculture is on the horizon of a second-generation breakthrough in production efficiency because of the revolution in Weed Science. Already the accomplishments made possible by this revolution have established the necessity for a new research cycle in crop production that can result in new plateaus of crop yields, crop quality, and production and harvesting efficiency.

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.

I am honored to meet here today with this distinguished group of scientists, engineers, educators and businessmen. I have looked forward to this conference as an opportunity particularly to discuss the problem of chemicals in our environment, a matter which concerns us all deeply … and to describe some of the steps we are taking in the Department in this regard. I also want to discuss our activities as they apply to the broader context of the responsibilities of science and education today in agriculture.

Selected, representative research on surfactants, herbicide penetration, and plant cuticles was reviewed briefly. New evidence was presented that surfactants influence the activity of herbicides in oil sprays as spectacularly as in aqueous sprays. Most of the experimental facts about surfactants were integrated in a blanketing theory for entry of herbicides by separate hydrophilic and lipophilic pathways.

Recrystallized 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine), 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine), and 2-methylmercapto-4-ethylamino-6-isopropylamino-s-triazine (ametryne) were adsorbed on filter paper, and exposed to ultraviolet light (253.7 millimicrons) or sunlight. All underwent photodecomposition, which was different under ultraviolet light and sunlight.

The nature and mode of action of surfactants is reviewed. Surfactants are useful additives for formulated herbicides because they contribute to wetting, spreading, emulsification, and solubilization of the herbicide. The use of extra surfactant to increase herbicidal activity is a desirable practice. The factors in selecting a suitable agent are discussed in terms of surfactant properties.

Root sections of Canada thistles (Cirsium arvense (L.) Scop.) from 10 locations in Montana, Idaho, Washington, and Wyoming were planted at Bozeman, Montana. Leaf margins varied from deeply ruffled and lobed with numerous spines, to entire margins essentially without spines. Flowers varied in color from shades of purple to pale blue and white. Seed size ranged from 300,000 to 673,000 seeds per pound. The earliest eco-type emerged about 2 weeks before the latest and shoot and flower development and height of plants were varied.

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.

Amitrole (3-amino-1,2,4-triazole) and 5-chlorobenzo-1,2,3-triazole were the only compounds tested that inhibited wheat root elongation and growth of carrot explants, produced chlorosis, and depressed catalase activity. Ten other heterocyclic compounds were more effective in inhibiting growth in wheat roots or carrot explants. Overall biological activity was reduced when substituents other than the amino group on the number three position were substituted on the triazole nucleus.

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.

Seed dormancy in velvetleaf (Abutilon theophrasti Medic.) was due primarily to an impermeable seed coat. Embryo dormancy was not a factor in the occurrence or maintenance of seed dormancy. The presence of germination inhibitors was indicated, but their role in seed dormancy appeared limited. The termination of dormancy under field conditions was considered to result from naturally occurring fractures in the seed coat. The point of fracture was always in the region of the chalazal slit and was considered to follow intense drying under natural conditions. Drying seed in laboratory experiments produced the same fractures in seed coats.

Seven different types of nozzles were compared as to uniformity of spray application, spray drift, and tendency to clog. The wide angle whirl chamber nozzles applied the spray more uniformly than other nozzles. Increasing nozzle height to 1.5 times the recommended height increased uniformity of spray application with most nozzles. Lowering the nozzle height to half the recommended height seriously reduced uniformity of spray application with almost all nozzles except the wide angle whirl chamber nozzles which provided a uniform spray at all 3 heights. The whirl chamber nozzles were least easily clogged of the nozzles studied. Wettable powders normally applied in 30 gallons or more per acre have been satisfactorily applied at rates of less than ¼ of this amount. Spray drift was reduced to a no crop hazard level, with effective coverage, at rates of application as low as 7 gallons per acre.

In short-term studies, diquat (6,7-dihydrodipyrido(1,2-a:2’,1′-c) pyrazidiinium salt) and paraquat (1,1′-dimethyl-4,4′-dipyridinium salt) caused a stimulation in respiration and an inhibition in photosynthesis of duckweed (Lemna minor L.). Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) and monuron [3-(p-chlorophenyl)-1,1-dimethylurea] caused inhibition of the Hill reaction at rates lower (10-6M) than diquat and paraquat (10-5M), and diquat was considerably more effective than paraquat. The effect of a combination of monuron and diquat on O2 production was additive. Inhibition of the Hill reaction by these dipyridyliums was directly related to their redox potentials. Auto-radiographs of chromatograms and electrochromatograms as well as CO2 studies indicated that neither diquat nor paraquat was degraded in alligatorweed [Alternanthera philoxeriodes (Mart.) Griseb.] and garden, or snap beans (Phaseolus vulgaris L. var. Black Valentine).

Selections of wild oats (Avena fatua. L.) had varying degrees of resistance to isopropyl N-phenylcarbamate (IPC). Strains with gray glabrous lemmas and non-dormant seed tended to be more resistant to IPC than those with brown pubescent lemmas and dormant seed.

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 rates of decarboxylation of 2,4-dichlorophenoxyacetic acid (2,4-D), 2-chloro-4-fluorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) in excised leaves of blackjack oak (Quercus marilandica Muenchh,) were determined by collecting the C14O2 evolved from carboxyl-labeled herbicides. 2,4,5-T was decarboxylated only in trace amounts. 2,4-D was decarboxylated to a maximum of about 1 per cent and 2-chloro-4-fluorophenoxyacetic acid of about 7 per cent, of the amounts taken up by the leaf. Decarboxylation rates for 2,4-D in June were highest in persimmon (Diospryos virginiana L.) and blackjack oak, and were very low in winged elm (Ulmus alata Michx.), sweet gum (Liquidambar styraciflua L.), and green ash (Fraxinus pennsylvanica Marsh.). The rates of decarboxylation of 2,4-D apparently were not correlated with susceptibility to 2,4-D.

As the seeds of leafy spurge (Euphorbia esula L.) increase in age after fertilization, their color changes from yellow to yellow with brown tips, to brown ends with a narrow yellow band, to brown with an orange band, and to a reddish-brown seed, followed in order by brown, gray-brown, gray, and finally, mottled. The last four are viable; the others are not. Mowing of leafy spurge to prevent viable seed production must be done before seeds have turned brown. Brown seeds appeared 10 to 13 days after fertilization depending upon seasonal conditions.