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.

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.

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.

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.

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.

Livestock losses, mainly to cattle, from Astragalus miser Dougl. ex Hook. (timber milkvetch) have been reported since 1927. The species is found in the northwestern United States and also in Alberta and British Columbia. Recent taxonomic treatment distinguishes eight varieties. The most northern variety (A. miser var. serotinus (Gray) Barneby) and the most southern variety (A. miser var. oblongifolius (Rydb.) Cronq.) are the only two varieties known to cause livestock losses, but all varieties should be regarded as poisonous until it is known they are not. A. miser var. oblongifolius was controlled with 2 lb/A of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) or 2,4,5-trichlorophenoxypropionic acid (silvex). Removal of A. miser increased both cover and frequency of grass species.

Jimsonweed (Datura stromonium) was treated with carboxyl-labeled C14 2,4-dichlorophenoxyacetic acid (2,4-D*); auto-radiographs and extraction of radioactive materials were used to determine the movement and form of the herbicide. Activity rapidly decreased in the leafy tissue. There was an accumulation of activity in the stem, but very little accumulation in the roots. With the exception of the stem tissue where minor alteration of the herbicide occurred, 2,4-D* was the only radioactive material recovered from jimsonweed. A loss of radioactivity from the root systems indicated a possible detoxification mechanism for jimsonweed. Up to 25% of the 2,4-D* applied to jimsonweed was expelled from the roots in six weeks.

Naphthaleneacetic acid (NAA), 2,4-dichlorophenoxyacetic acid (2,4-D), and 2-chloro-4-ethylamino-6-isopropylamino s-triazine (atrazine) were applied to Chlorella pyrenoidosa in an attempt to characterize mathematically the growth inhibition responses obtained. (Chlorella was found to serve well as a test organism.) Inhibition results induced by NAA and 2,4-D satisfactorily supported the hypothesis inherent in the kinetic interpretation. Results with atrazine were most satisfactorily interpreted by a probit analysis which showed large differences in rate of toxicity between high and low concentrations. This difference is thought to be responsible for the poor fit to a straight line in the reciprocal plots of the kinetic analysis. It is assumed that growth inhibition by atrazine resulted from a blocking of the photosynthetic process.

Swainsona salsula is an unpalatable legume of Asiatic origin which spreads by seed and lateral roots and has become a problem in some poorly drained, marshy, or saline areas of several western states. Its growth characteristics indicate a high potential for establishment along stream banks, irrigation canals, wasteways, pastures, and meadows with high water tables and other poorly drained areas. Its aggressiveness results in its dominance on such areas. 2-(2,4,5-trichlorophenoxy)propionic acid (silvex), 2,4-dichlorophenoxyacetic acid, (2,4-D), or 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) applied at 2 lb/A for 2 or more years in succession controlled swainsonpea satisfactorily on cropped land. 2,3,6-trichlorobenzoic acid (2,3,6-TBA) was also effective.

Paraquat (1,1′-dimethyl-4,4′-dipyridylium cation) removed weedy annual grasses from seedings of rose clover (Trifolium hirtum All.) and subclover (T. subterraneum L.) with only temporary damage to the clovers when applied at early growth stages. Paraquat applied under weed-free conditions reduced herbage yields of Lana woollypod vetch (Vicia dasycarpa Ten.) and Wimmera ryegrass (Lolium rigidum Gaud.) at three dates of application; neither herbage nor seed yield of rose or subclover was reduced.

Direction and rate of translocation of sucrose* from urea* 2,4-D* (2,4-dichlorophenoxyacetic acid) and amitrole* (3-amino-l,2,4-triazole) were toward regions of active growth. In oak seedlings translocation was slower than in cotton seedlings. In oak seedlings growing leaves and shoots constitute active sinks toward which tracers move. Sucrose* from urea* translocates freely; 2,4-D* moves less freely because of accumulation enroute; amitrole* is intermediate between these. High humidity induces rapid and extensive uptake of tracers by oak seedlings; the increase over normal transport is mainly in the xylem.

A metabolite of swep [methyl N-(3,4-dichlorophenyl)-carbamate] was detected in the straw, hulls and bran layer of rice but not in the polished rice grain (endosperm) or bran oil, using microcoulometric gas chromatography (MCGC). This metabolite was identified as a swep-lignin complex which is quite stable and not extractable from plant tissues by common organic solvents. Upon extraction with HCl-dioxane, a portion of this complex is hydrolyzed to swep and soluble products of lignin. The swep was purified by adsorption chromatography and identified by infrared spectroscopy and microcoulometric gas chromatography retention times. The mechanism of swep-lignin complex formation is considered to be an example of a common detoxification mechanism by plants through immobilization.

In two experiments beans were kept weed-free for various periods early in the season, and in a third, weeds were allowed to grow with beans for various periods before being removed. Weeds which emerged soon after planting caused extensive reductions in bean yields, but the actual yield-reducing competition occurred considerably later in the season. For 5 to 7 weeks after planting, the grower must control weeds by chemical or other means; for the remainder of the season, bean competition provides weed control.

Sorghum grain yield losses in Northwest and Central Texas caused by uncontrolled weed growth varied from 8 to 41%. Under high moisture conditions, sorghum competed best with weeds when planted thickly in narrow rows. With less moisture, seeding in wide rows resulted in more effective competition. If rains produced weed germination immediately after planting, competition with the sorghum was more severe than when weeds germinated 1 or 2 months after sorghum planting. Several mechanical weed control methods were very successful.

Experiments were conducted at Lincoln, North Platte, and Alliance, Nebraska, during 1961 and 1962 to determine the effect of tillage, atrazine, hand-weeding, and row spacings on RS 501 sorghum and weed yields. Combinations of tillage, narrow row spacings, and preemergence 2-chloro-4-ethylamino-6-isoproplyamino-s-triazine (atrazine) treatments gave more dependable weed control than any one alone. Sorghum yields increased and weed yields decreased with tillage and atrazine treatments. Preemergence atrazine applications as low as 1 lb/A gave higher sorghum yields and lower weed yields than postemergence atrazine applications of 2 to 4 lb/A. Preemergence atrazine applications should be reduced on lighter soils because atrazine gives more effective weed control and increased sorghum injury on such soils. There was a 1 bu/A decrease in sorghum yield for each 50 lb/A of weeds present.

In one study, twelve treatments consisting of 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine), 2-chloro-4,6-bis-(ethylamino)-6-isoproplyamino-s-triazine (simazine), 3-(p-chlorophenyl)-1,1-dimethylurea (monuron) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) applied alternately in a program pre- and postemergence to the weeds were evaluated on ten sugar cane plantations. Averaged data indicated that combinations including atrazine outperformed simazine in every instance and diuron was better than monuron on all plantations but one. Diuron was most effective on grasses, e.g., Digitaria spp. whereas atrazine was outstanding against Commelina diffusa Burm. In a second study on the same plantations, the initial treatment of 5 lb/A of atrazine followed by 3 lb/A of diuron gave outstanding weed control on five plantations. Using 3 lb/A of each material applied simultaneously had merit at times but some plantations required only a single application of either material. Net days of weed control obtained by diuron were inversely dependent on the amount of chemical adsorbed by the soil in both studies and total days control appeared to be dependent on ample rainfall in the second.

Five strains of Johnsongrass [Sorghum halepense (L.) Pers.] in selected and random plantings received repeated foliar applications of 2,2-dichloropropionic acid (dalapon). For three characters studied, the residual variance was less with selected plantings than with random plantings. Johnsongrass strains differed in their response to dalapon.

When crop plants were competing with well-established quackgrass (Agropyron repens) for the same nutrient supply, chlorosis and stunting of crop plants occurred. Apparently this was due to the greater ability of quackgrass to withdraw available nutrients, especially nitrogen, and to a lesser extent phosphorus and potassium, from the nutrient solution. No evidence was obtained for a phytotoxic substance from living quackgrass roots or rhizomes that could inhibit germination or growth of alfalfa and oats. Quackgrass residues in large amounts caused chlorosis and stunting in alfalfa and oats when added to soil. The evidence obtained linked this behavior to the high C:N ratio with consequent temporary deficiency of available nitrogen. Water extracts of quackgrass leaves or rhizomes were not phytotoxic unless subjected to high temperatures during or subsequent to extraction. If soils contained decomposing quackgrass or crop plant residues, extremely phytotoxic extracts of such soils were obtained, but only when soils were saturated and decomposition was anaerobic.

Bioassay methods are described for determining the concentration of 4-amino-3,5,6-trichloropicolinic acid in solutions and in soil. These methods are suitable for determining the concentration of the herbicide in the presence of other herbicides. These test methods can detect considerably less than one microgram of herbicide.

A system involving resting cells of Euglena gracilis provides a rapid and convenient test system for screening potential herbicides which act as inhibitors of chlorophyll synthesis. The system appears to distinguish between inhibitors of chloroplast formation, such as 3-amino-1,2,4-triazole, and inhibitors of chlorophyll formation per se, such as ethionine.