The most effective and dependable method of controlling wild cane [Sorghum bicolor (L.) Moench] in corn (Zea mays L.) was with a combination of cultivation plus herbicides. Timely cultivations were equally or more effective than preplant herbicides in controlling wild cane, but neither method was adequate by itself. The best herbicide in this study for the control of wild cane in corn was S-ethyl dipropylthiocarbamate (EPTC) alone or in combination with (2,4-dichlorophenoxy)acetic acid (2,4-D) or 2-chloro-4,6-bis-(ethylamino)-s-triazine (simazine). Residual effects of simazine at 4 lb/A in the soil reduced the yield of the following oats (Avena sativa L.) crop 1 out of 3 years.

Wheat (Triticum aestivum L., var. Selkirk) was most susceptible at the late tiller stage to 4-amino-3,5,6-trichloropicolinic acid (picloram) as determined from weekly applications in the field and the degree of injury increased with rate of picloram. Wheat injury from picloram was manifested by lower kernel yield, greater protein content in the kernels, and reduction in plant height. A reduction in the length of the stem occurred while the length of the flag leaf sheath was not affected. Picloram increased kernel size in 1966 but reduced it in 1965. Picloram did not influence germination of kernels from treated plants. The addition of (2,4-dichlorophenoxy)acetic acid (2,4-D) to picloram tended to increase wheat injury at the 2 to 4-leaf stage.

An implanted soil mass technique was modified to study the effect of soil-incorporated herbicides on root growth. The technique was used to study the effects of α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) and 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin) on root growth of cotton (Gossypium hirsutum L., var. Auburn 56) and the effects of trifluralin and S-propyl dipropylthiocarbamate (vernolate) on soybeans (Glycine max (L.) Merr., var. Bragg). Vernolate had no effect, but there was only 57% as much soybean root tissue in the soil receiving 1 ppm of trifluralin as there was in the untreated check 2 months after initiating the treatments. Trifluralin and nitralin at 1 ppm reduced cotton roots to 75% and 50%, respectively, of that of the untreated check. The effects of trifluralin and low soil pH were additive, but there was no interaction between them.

Rates of dissipation, control of troublesome aquatic weeds, and toxicity to fish by the disodium and dipotassium salts of 7-oxabicyclo(2,2,1)-heptane-2,3-dicarboxylic acid (endothall) in farm reservoirs and in growth pools were studied from 1964 to 1967. In 4 out of 14 reservoir applications, initial concentrations of 0.3 to 1.4 ppm dissipated to near the limit of detection in 8 to 20 days. In the other 10, the dissipation ranged from 23 to an increase of 160% in 12 days. The average dissipation was 71%. In growth pools, initial concentrations of 0.5 to 4.0 ppm of endothal dissipated to 0.26 to 2.5 ppm in 12 days.

A recirculating sprayer was developed for applying herbicides in row crops to weeds taller than the crop. Herbicide solutions are applied through solid stream nozzles above and at right angles to the rows, so that a trap collects herbicide spray not deposited on weeds. Trapped solution is returned to the original spray tank by gravity flow. Good to excellent control of pigweed (Amaranthus spp.), cocklebur (Xanthium spp.), and sesbania (Sesbania spp.) was obtained with (2,4-dichlorophenoxy)acetic acid (2,4-D) while monosodium methanearsonate (MSMA) effectively controlled johnsongrass (Sorghum halepense (L.) Pers.). The better treatments increased the harvested yields of soybeans (Glycine max (L.) Merr., var. Lee) 6 to 8 bu/A when weed infestations were severe at time of treatment. Use of the sprayer permits treatment with herbicides normally considered too toxic to crops, and reduces costs through recovery of most of the herbicide solution that is not intercepted by weeds.

Seven herbicides were applied for selective weed control on three different seedling stands of five cool-season grasses. The herbicides were evaluated for their influence on weed control, grass establishment, and first crop grass seed production. These experiments indicate that 3,5-dibromo-4-hydroxybenzonitrile (bromoxynil) was outstanding in selective control of broadleaf weeds in seedling grass stands. Two other herbicides, 3,6-dichloro-o-anisic acid (dicamba) and 6,7-dihydrodipyrido[1,2-a:2′,1′-c]pyrazinediium ion (diquat) were valuable under most conditions. The remaining herbicides—(2,4-dichlorophenoxy)acetic acid (2,4-D), 2-sec-butyl-4,6-dinitrophenol (dinoseb), 2,3,6-trichlorobenzoic acid (2,3,6-TBA), and 1-butyl-3-(3,4-dichlorophenyl)-1-methylurea (neburon)—were satisfactory for selective weed control under some conditions, but their effects were not uniform for the different species and plantings.

Growth and percentage survival was measured for slash pine (Pinus elliottii Engelm.), shortleaf pine (P. echinata Mill.), Virginia pine (P. virginiana Mill.), and loblolly pine (P. taeda L.) seedlings treated with: (a) 0.07 to 4.48 kg/ha 2,6-dichlorobenzonitrile (dichlobenil), (b) 0.28 to 8.96 kg/ha 1,1-dimethyl-3-(a,a,a-trifluoro-m-tolyl)urea (fluometuron), or (c) 1.12 to 8.96 kg/ha S-propyl butylethylthiocarbamate (pebulate). Herbicide toxicity to pine seedlings was in order of dichlobenil > fluometuron > pebulate. Acceptance of mild growth reduction would permit pebulate utilization in seed bed nurseries.

Available literature indicates that relatively few agricultural leaders and farmers became interested in weeds as a problem before 1200 A.D. or even 1500 A.D. For many centuries, weed control was mostly incidental to tillage for seedbed preparation and growing of crops and to growing and cutting or pasturing of thickly planted crops. Occasional references in literature previous to 1900 mentioned use of mechanical devices and a few inorganic herbicides specifically for weed control.

State weed laws directed at control of plant diseases were enacted during 1721 to 1766, but weed and seed laws involving weeds directly were not enacted until 100 to 200 years later. Only a few extension-type publications on weeds were issued in the United States and Canada between 1860 and 1900. There was a rapid increase in such publications after 1900. Research with inorganic chemicals as herbicides was begun in the 1890's in Europe and in a few states and provinces, and was increased at a rapid pace until the early 1940's. New developments in mechanical and biological control of weeds increased steadily during the same period. However, weed control remained a relatively minor phase of agronomy, botany, horticulture, agricultural engineering, and plant physiology until the early 1950's.

About 10 years after the discovery of (2,4-dichlorophenoxy)acetic acid (2,4-D) in 1942–1944, the much increased interest of scientists, federal and state governments, industrial companies, and the general public had begun to bear fruit. The word “weed” or “weeds” began to appear in the titles of college courses and extension specialists. Weed conferences had been organized in six regions of the United States and Canada and in 10 states.

The first meeting of the Weed Science Society of America was held in 1956 and Weed Science was adopted as its official journal. The number of herbicides in general use in the United States and Canada increased from 15 in 1940 to 25 in 1950, and to 100 in 1969. The total support for weed research in 1962 in the United States was six times that in 1950. The number of full-time research and extension workers or their equivalents in part-time workers had increased 20-fold and 13-fold, respectively, over the number in 1940.

The rate of advancement in the art and science of weed control has increased so rapidly that the progress in each of the recent brief periods 1941 to 1968, 1901 to 1940, and 1800 to 1900 is considered greater than that in all previous periods, beginning about 6000 B.C.

Canada thistle (Cirsium arvense (L.) Scop.) on roadsides was controlled by 4-amino-3,5,6-trichloropicolinic acid (picloram), (2,4-dichlorophenoxy)acetic acid (2,4-D), and (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T), alone and in combination at various rates. There was no synergistic or additive effect, as determined by Canada thistle response, due to the addition of 2,4-D or 2,4,5-T to picloram. Control with ¾ lb/A picloram was not significantly less than that obtained with higher rates 1½ and 2 lb/A. Picloram reduced Canada thistle stands 80 to 100% and 2,4-D generally reduced the plant population 50% or less during the year of application and the year after. Late summer appeared to be an opportune time for spraying Canada thistle with ¾ to 1 lb/A picloram.