Yellow rocket (Barbarea vulgaris R. Br.) was effectively controlled in established alfalfa (Medicago sativa L.) by September 15 applications of 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine), 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine), 3-tert-butyl-5-chloro-6-methyluracil (terbacil), and 2-sec-butylamino-4-ethylamino-6-methoxy-s-triazine (hereinafter referred to as GS 14254). White cockle (Lychnis alba Mill.) was more difficult to control, but simazine was the most effective herbicide. Herbicide applications in early October reduced reserve nonstructural carbohydrate accumulations in roots of yellow rocket by November 15 but not in white cockle. Alfalfa yields were not reduced by two consecutive autumn applications of the herbicides at rates that provided adequate control of yellow rocket and white cockle.

We collected tubers from greenhouse-grown yellow nutsedge (Cyperus esculentus L.) control plants and plants foliarly-treated with 3.36 kg/ha of disodium methanearsonate (DSMA) or monosodium methanearsonate (MSMA). Where sufficient tubers were produced, they were separated into two classes, large and small. Some of the tubers were analyzed for elemental arsenic, and others were stored at 2 C and planted at various intervals. Vitality of tubers was noted in terms of sprouting and vegetative growth. Tubers collected from treated plants contained significantly more arsenic (4 to 33 ppm) than control tubers (1 ppm). Tubers collected from treated plants and planted without separation sprouted in significantly reduced numbers compared to control tubers. Small tubers contained a significantly higher concentration of arsenic (23 to 33 ppm) than large tubers (4 to 12 ppm). The treatments reduced the vitality of small tubers but had little or no effect on vitality of large tubers.

British Agriculture has existed for at least a thousand years, and it would require a book to record the major developments in weed control. My concern today is with the events of the past 25 years during which weed control has become established as a science, and herbicides have been given a widespread introduction. I hope to set these events against a historical background as they relate to Great Britain, and thereafter, to draw out some thoughts on the impact that modern weed science is making and will make in the future on crop production and land use.

I would like to start with a premise, then discuss a bit of history as it applies to agriculture and food production, then relate food production to a country's total economy, and lastly, relate the profession of a weed scientist to a country's capacity to produce food.

I have enjoyed close and direct association with four different Land Grant Colleges. At the fourth, I served 20 years on the staff and became 50 years of age, giving me the privilege of retiring. If my comments appear critical of Land Grant Colleges as recently administered, these comments are intended to serve as constructive criticism. Contributions of the Land Grant Colleges are basic to our total United States welfare. Our society and our way of life continue to need these contributions. Perhaps the goals and objectives should be changed, but the contributions are still strongly needed.

The changes in the nucleic acid metabolism were studied in plants susceptible and resistant to 4-amino-3,5,6-trichloropicolinic acid (picloram). The total RNA and DNA content of the tissue correlated inversely with the herbicide resistance; the resistant plants were low in nucleic acids, whereas sensitive plants were high. The increase in the nucleic acids of the sensitive species 24 hr after picloram treatment appeared to be associated with lower levels of ribonuclease and deoxyribonuclease. The inability of the resistant species to make more RNA may be associated with high levels of nucleases in the tissue.

Root applications of (2,4-dichlorophenoxy)acetic acid (2,4-D) at concentrations of 2.5 × 10−8M or higher inhibited growth of emersed parrotfeather (Myriophyllum brasiliense Camb.). There was little acropetal movement after applications of 1.1 × 10−5M 2,4-D-1-14C to the roots of emersed parrotfeather. When the metabolic inhibitor dinitrophenol at concentrations of 10−3 or 10−4M was root-applied concomitantly with 10−8M 2,4-D-1-14C, there was an acropetal movement of radioactivity in the transpiration stream to the plant shoot. Basipetal movement occurred in the phloem after applications of 2.2 μg 2,4-D-1-14C to mature leaves in the shoot center of emersed parrotfeather.

Canada is a very large country with about 3,700,000 square miles of land surface but with only 100,000,000 acres of land in production and approximately 40,000,000 acres of virgin land capable of being used for crop production. Of the 100 million acres, about 80% of this is in the three western provinces of Manitoba, Saskatchewan, and Alberta. Saskatchewan alone has over 50% of this resource. Contrasted with this is the small area in the Maritimes of less than 2 million acres, some 6 to 7 million acres in Quebec, and 11 million acres in Ontario. Canada, therefore, has one major surplus resource and that is grain production in western Canada.

Ester derivatives of (2,4-dichlorophenoxy)acetic acid (2,4-D), 4-(2,4-dichlorophenoxy)butyric acid (2,4-DB), 4-(2,4-dichlorophenoxy)crotonic acid, and 4-(2,4-dichlorophenoxy-β-hydroxy)butyric acid each were applied to alfalfa (Medicago sativa L.). Analysis of alfalfa extracts by gas chromatography and mass spectroscopy indicated 2-carbon additions to the aliphatic side chain of the applied chlorophenoxy compounds.

Concentrations of 2,2-dichloropropionic acid (dalapon), trichloroacetic acid (TCA), and (2,4-dichlorophenoxy) acetic acid (2,4-D) were determined in irrigation water following bank applications for weed control. Maximum concentrations of dalapon in the water varied from 23 to 365 ppb from application rates of 6.7 to 20 lb/A. The highest levels of TCA ranged from 31 to 128 ppb following applications of 3.8 to 5.9 lb/A. Applications of 1.9 to 3 lb/A of 2,4-D produced maximum concentrations of 25 to 61 ppb. Reduction of herbicide levels appeared to be due to dilution as the water flowed downstream. Rates of reduction in herbicide levels showed that negligible concentrations would remain after the water traveled a distance of 20 to 25 miles. The low concentrations of herbicides observed in the irrigation water likely would not be hazardous to crops or animals.

Two overhead applications of monosodium methanearsonate (MSMA) at either 4 + 4 or 4 + 2.5 lb/A were required for effective postemergence control of rhizome johnsongrass (Sorghum halepense (L.) Pers.) in ratoon sugarcane (hybrids of the genus Saccharum). Two applications of MSMA in the spring controlled 95% of the johnsongrass, whereas two applications of 2,2-dichloropropionic acid (dalapon) at 4.5 lb/A, the standard treatment, controlled only 70%. In heavily infested fields, sugarcane treated with MSMA also outyielded sugarcane treated with dalapon. Sugarcane tolerated MSMA applied before June; the yield of weed-free sugarcane treated with MSMA was not significantly less than that of the untreated control. However, most MSMA treatments, particularly those applied in late spring, caused temporary leaf chlorosis and stunting. Sugarcane sprayed with MSMA before June generally contained no more arsenic in the juice and bagasse at harvest than untreated sugarcane. Application of MSMA in June or August increased the arsenic content, and resulted in concentrations up to 0.45 ppm in juice, and up to 1.68 ppm in bagasse.

The maximum concentrations of 3-amino-s-triazole (amitrole) found in two flowing-water canals (1.13 and 0.65 cu m/sec) following treatment of a single ditchbank of each canal with 4.5 and 3.4 kg/ha of amitrole-ammonium thiocyanate (amitrole-T) were 31 and 43 ppb. Conjunctive treatment of both banks of another canal, prior to entry of water, resulted in a maximum of 98 ppb of amitrole upon turning 1.42 cu m/sec of water into the canal. Two hours after passage of the main body of amitrole-bearing water at the last sampling station on each canal, amitrole levels were down to approximately 1 ppb or less. The dissipation of amitrole in canals, for distances up to about 14.5 km, was a linear function of amitrole concentration and downstream flow. The rate of dissipation was fastest on a canal in which the herbicide was placed directly into the water (slope of 3.8), modest for a single bank treatment (slope of 2.7), and slowest where opposite banks of a canal were treated (slope of 1.8).

Five species of Nymphaeaceae, representing four genera, were collected from various sites in New Jersey and their tissues analyzed for 12 elements. Three species were separated into leaf blades and petioles before the mineral analyses were made. Variations in the concentrations of many elements were noted between these two structures. Except for the petioles of these three species, the N content of the plants appeared to be sufficiently high so that no extra N would be required to prepare composts from them.

Experiments were conducted on poison ivy (Rhus radicans L.) to determine the effect of auxin on the formation of sprouts. Stump sprouting occurred where poison ivy propagules were decapitated. The influence of the shoot could be replaced by applying indoleacetic acid (hereinafter referred to as IAA) in lanolin paste to the cut surface of the stump. When the paste was removed after inhibiting stump sprouting for a month, sprouts formed within 35 days. This evidence supports the apical dominance theory of stump sprouting. When IAA-2-14C in lanolin was applied to the cut surface of the root stump, autoradiographs showed that 14C activity was concentrated where the majority of stump sprouts would develop, and chromatography of an extract indicated the presence of an auxin oxidation product of IAA. Dialyzed enzyme preparations from poison ivy stumps oxidized IAA in a Warburg apparatus which demonstrated that an IAA oxidizing system was present.

Root application of N,N-dimethyl-2,2-diphenylacetamide (diphenamid) caused reduction of root and shoot growth of oats (Avena sativa L., var. Jaycee) seedlings. Shoot application did not affect plant growth, but studies with labeled diphenamid showed that diphenamid will enter also through the shoot. In ivyleaf morningglory (Ipomoea hederacea L.), a considerable amount of label was translocated from the roots to the shoots, but not in oats seedlings. The difference in tolerance between these two species (oats susceptible, morningglory resistant) may lie in the ability of morningglory to translocate diphenamid out of the roots into the shoots faster than oats. The inhibitory effect of diphenamid was restricted to the site of uptake. Reduction in shoot growth of treated plants was the result of the limited root system and it was not a direct effect of diphenamid. Diphenamid was 10 times as toxic to oats as its metabolites. Oats seedlings inhibited by diphenamid for up to 5 days, and then placed in water recovered from the diphenamid caused inhibition. The resumed root growth appeared to be normal. The amount of uptake of 14C-labeled sucrose by excised roots treated with 10−5 M diphenamid was equal to that in untreated roots; however, more sugar was incorporated into the untreated roots than the treated roots. It appears that diphenamid is a reversible metabolic inhibitor; it inhibits cell division in the root tip perhaps by limiting utilization of substrates in the cells.

Water samples were taken from Pickwick Reservoir from 1965 through 1968 and the nitrogen and phosphorus content determined. The nitrogen and phosphorus content over a period of 3 years was not related to the year-to-year plant growth. Physical and climatic data were obtained from 1961 through 1968, and it was found that available light was controlled by the amount of rainfall and ensuing reservoir elevation during the critical plant growth period in April and May. Available light was correlated with the 2 years of severe infestations.

Bean (Phaseolus vulgaris L., var. Tendercrop) plants treated during germination with 100 ppm 5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone (pyrazon) were indistinguishable from untreated plants until 5 days after seedling emergence. Chlorosis began at the leaf margins, progressed inward, and became more severe until the leaves became necrotic and died. Similar symptoms were observed on leaves of plants treated with 25 and 50 ppm, but they appeared 4 to 10 days later. The light-microscope study of leaf tissue revealed that chloroplast form and arrangement were altered by pyrazon treatment. Chloroplasts in leaves of treated plants became round and swollen rather than discoid, contained no starch, aggregated in clumps, and developed an affinity for safranin stain.

Rice (Oryza sativa L., var. Bluebonnet) bioassay was utilized to evaluate activity of several herbicide combinations at concentrations of each individual compound causing a 50% reduction in root length. Synergistic combinations were trichloroacetic acid (TCA) plus 1,1-dimethyl-3-phenylurea (fenuron); TCA plus 3-(p-chlorophenyl)-1,1-dimethylurea (monuron); TCA plus 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron); TCA plus 3-amino-s-triazole (amitrole); TCA plus 2,2-dichloropropionic acid (dalapon); and dalapon plus monuron. Additive results were obtained from combinations of TCA plus 1,2-dihydro-3,6-pyridazinedione (MH); dalapon plus fenuron; and dalapon plus diuron. MH and (2,4-dichlorophenoxy) acetic acid (2,4-D) exhibited antagonistic responses when combined with fenuron, monuron, diuron, dalapon, amitrole, and with each other. Antagonistic responses were obtained from combination of 2,4-D and TCA.

Preemergence applications of 3 lb/A of 1-(2-methylcyclohexyl)-3-phenylurea (siduron) plus 0.3 lb/A of 4-amino-3,5,6-trichloropicolinic acid (picloram) sufficiently suppressed competition from downy brome (Bromus tectorum L.) or medusahead (Taeniatherum asperum (Sim.) Nevski) and associated broadleaf species to allow the marginal establishment of intermediate wheatgrass (Agropyron intermedium (Host.) Beauv., var. Amur) seedlings. The technique was only successful on semi-arid range sites with above-average soil moisture and moderately dense stands of weed grasses. The range in tolerance of the three species to siduron is very similar, but downy brome is slightly more susceptible than medusahead or intermediate wheatgrass. There is a significant negative relation between plant moisture stress and root length of intermediate wheatgrass plants when root elongation is suppressed by low rates of siduron.

The influence of six Arkansas soils on the leaching characteristics of derivatives of 3-amino-2,5-dichlorobenzoic acid (amiben) and 3-nitro-2,5-dichlorobenzoic acid (hereinafter referred to as dinoben) in slotted soil columns was determined using large crabgrass [Digitaria sanguinalis (L.) Scop.] bioassay. The ammonium and aluminum salts of amiben and the sodium salt of dinoben were easily leached and leaching was not noticeably affected by soil type. The ammonium salt of amiben was not adsorbed, while the methyl ester of amiben was adsorbed by these soils. Adsorption was related to the clay and organic matter content of the soil. Methyl and butoxyethyl ester derivatives of amiben and dinoben resisted leaching in these soils and the amide of amiben was intermediate in leaching. The adsorption and leaching behavior of the ester derivatives of these compounds were complicated by their rapid hydrolysis in these soils. The hydrolyzed product behaved identically to the salt derivatives of the compounds in leaching, adsorption, and chromatographic properties. Hydrolysis of the methyl ester was inhibited by soil sterilization, dry soil, and temperatures below 20 C. In non-sterile, warm, moist soil, the half-life of the methyl ester of amiben was 28 hr. Four species of Bacillus were capable of hydrolyzing the methyl ester of amiben in pure culture studies.

A small laboratory sprayer was designed to spray small quantities of chemicals on test plants. The sprayer apparatus consisted of a spray nozzle assembly, air line, and syringe to inject the test solution into the spray nozzle assembly. In operation, the sprayer provides good coverage of test plants and can be used to treat a large number of subjects rapidly.