It has long been recognized that one of the inherent problems in spray application, particularly with airplanes, is that of droplet size control. It is not generally known which droplet sizes or ranges of droplet sizes are the most effective biologically for the various types of treatments. It is known, however, that excessively large droplets result in a serious waste of material, and that very small droplets present a serious drift problem. For these reasons, spray droplet size and the range of sizes in a given spray have become important criterions in evaluating a spray distribution pattern.

The possibility of using 2,4-D as a soil sterilant was investigated by Crafts in 1949. He concluded that 2,4-D may be useful under very dry conditions. In 1954, Shafer reported several years work using soil applications of 2,4-D for control of perennial weeds. Since that time many research workers have evaluated 2,4-D and other phenoxy herbicides for the control of bindweed and other perennial weeds. Results of these trials varied from excellent to poor.

During 1962, barnyardgrass (Echinochloa crusgalli (L.) Beauv.) seedlings were infested by the larvae of Hyperodes humilis Gyll. The larvae attacked the growing points and the youngest tissues in the crown as well as meristematic tissues of intercalary growth. These infestations produced considerable decreases of barnyardgrass growth and yields, suggesting the possibility of effective biological control of barnyardgrass.

The dimethylamine salt and isopropyl and isooctyl ester formulations of 2,4-dichlorophenoxyacetic acid (2,4-D) were applied at 0, ½, 1, 2, and 4 lb/A 21, 14, and 7 days before harvesting Bison hard red winter wheat. Treatment effects on yield, chemical composition, or milling and baking properties of the grain were either nil or of no practical significance. When treated with ½ or 1 lb/A, rates generally recommended for farm use, 2,4-D residues in the grain ranged from 0.04 to 0.27 ppm. As rates of the three formulations of 2,4-D were increased from ½ to 4 lb/A, increasing amounts of 2,4-D residues occurred in the grain and reached a maximum of 1.8 ppm when the isopropyl ester of 2,4-D was applied at 4 lb/A 14 days before harvest. Grain from plots treated 21 days before harvest had less 2,4-D residue than grain from plots treated 14 and 7 days before harvest.

At the Third British Weed Control Conference in 1956 I had the pleasure to discuss weed control research and development in Sweden (3). Some of the statements I made at that time will be used as a background to this paper. It was emphasized that there has been continuous change in weed control methods since World War I depending on the introduction of chemical weed killers but also on improved methods for cultivating and using the lands. Use of chemicals have brought with it changes in the weed flora meaning that certain weeds which were not serious in earlier days have now become a menace to the farmers. This brings with it a need for new chemicals with other weed killing properties. But it also brings with it a need for new cultivating methods and a better crop sequence. Cultivated plants are influenced by the chemicals. The effect on the cultivated plants depends on the stage of development of these plants. In uneven fields the harmful effect can be serious as there are always some plants that are sensitive at the time of spraying. The effect of the chemicals may depend on the purity of the acids. In MCPA, for example, the percentage of the 4–isomer, i.e. the 2–methyl–4–chlorophenoxyacetic acid, is important. It should be 95 per cent or slightly above as shown by åberg (1). The after effect of chemicals in the soils may be longer and more severe under northern conditions than under southern. For the choice of crops this must be considered. Thus there is no doubt that today, more than at any earlier period, weed control is a crop production problem. It can not be treated without considering crop production problems. Sometimes there is a feeling over in our part of the world that since the end of World War II chemicals and their properties have been emphasized too much in weed control discussions. Chemicals are, no doubt, important, but they can never get the place they are entitled to, unless our research work in weed control pays attention also to biology and ecology of those plants that we treat; cultivated plants as well as weeds. I believe we are in Europe thinking more about this particular end of the weed control work than you need to do over here. We usually have small farms with a number of different crops on each one of them. Thus we must learn to apply our chemical weed killers or use our cultivated methods in different ways for each one of these crops. For economical reasons and with regard to the supply of food and feed we need high yields per hectare. Every measure on a farm must be chosen with this in mind. Our problems, progress and organization of weed control must then be seen against the background I have now tried to give you.

Cotton plants were treated with 2,4-D-2-C-14 (2,4-dichlorophenoxyacetic acid) applied with pentachlorophenol and arsenic acid. Seed kernels and regrowth leaves were extracted and various components of the extracts were applied to leaf surfaces and injected into the stems of cotton seedlings. Results indicated that 2,4-D itself and/or a metabolite of 2,4-D, were responsible for the persistence of the 2,4-D stimulus in cotton.

Over-the-top applications of metriflufen {2-[4-(4-trifluoromethylphenoxy)phenoxy] propanoic acid} at 0.6 to 2.2 kg/ha were highly toxic to johnsongrass [Sorghum halepense (L.) Pers.], but caused little visual injury to soybeans [Glycine max (L.) Merr. ‘Hill’]. Directed applications of metriflufen at 0.8 to 3.4 kg/ha provided equal and, in a few comparisons, better control of johnsongrass than did some rates of the herbicide applied over-the-top. Application of metriflufen at 0.8 and 1.7 kg/ha in directed sprays resulted in higher soybean yields than did comparable treatments applied over-the-top; yields of directed vs. over-the-top applications of metriflufen at 3.4 kg/ha resulted in statistically equal soybean yields. The research suggested that metriflufen entered johnsongrass plants through shoots and leaves and also through roots. Johnsongrass control was excellent following applications of metriflufen at 1.7 and 2.2 kg/ha without soybean injury and with greatly increased soybean yields. Results following over-the-top applications of metriflufen at 1.1 kg/ha to ‘Hill’, ‘Tracy’, ‘Lee 68’, ‘Bragg’, and ‘Forrest’ soybeans at three different stages of morphological development did not demonstrate any appreciable differences in the response of the cultivars to the herbicide.

Bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] was evaluated for Canada thistle [Cirsium arvense (L.) Scop. # CIRAR] control and birdsfoot trefoil (Lotus corniculatus L. ‘Norcen’) tolerance. Bentazon applied in split applications controlled more Canada thistle than a single application of equal rate in both greenhouse and field studies. Bentazon applied four times reduced the level of total nonstructural carbohydrates (TNC) in the roots of both greenhouse- and field-grown Canada thistle and increased birdsfoot trefoil injury more than bentazon applied in a single application of equal rate. All bentazon treatments caused unacceptable injury when birdsfoot trefoil was grown for seed.

Extracts from the roots and shoots of tobacco (Nicotiana tabacum L. ‘Kentucky 14′) seedlings treated with 14C-pebulate (S-propyl-1-14C butylethylthiocarbamate) were separated into various organic and aqueous phases to determine the distribution of 14C. In the roots the organic acid-carbohydrate fraction became the most highly labeled fraction with time while in the shoots the fraction containing the sterol esters and oligoglycerides was the most highly labeled early in the treatment period but gradually lost radioactivity at later time intervals. Pebulate was not recovered in detectable amounts in either the leaves or roots.

The combination of salts at the approximate ratio found in saline irrigation water, (NaCl 41.9 mM, CaCl2 20.9 mM, and MgCl2.6H2O 10.5 mM), with either 1 mM EPTC (S-ethyl dipropylthiocarbamate) or 0.1 mM CDEC (2-chloroallyl diethyldithiocarbamate) induced a greater reduction of root length, shoot length, and fresh weight of tomato (Lycopersicon esculentum Mill. ‘VF-315’) relative to either factor alone. The osmotic pressure of this salt solution is 0.40 MPa (mega Pascal), which is equivalent to 4.0 bar or ca. 4.0 atm. Similar results were found in lettuce (Lactuca sativa L. ‘Great Lakes–659’) using salts at 0.30 MPa (NaCl 31.4 mM, CaCl2 15.7 mM, and MgCl2.6H2O 7.3 mM) combined with either 0.75 mM EPTC or 0.2 mM CDEC. In tomato, the inhibition was additive for each parameter measured. In lettuce, however, the effect on fresh weight and shoot length was synergistic and the effect on root length was additive. Calcium chloride was the single salt component of the mixture, which when combined with either EPTC or CDEC, induced a significant reduction of root length, shoot length, and fresh weight in tomato relative to either factor alone. No additional reduction in growth was found in lettuce when each individual salt was combined with either EPTC or CDEC.

The relationships between the actual amount of spring-applied trifluralin detected in soil at seeding, initial injury to flax, and crop growth and yield were investigated in southern Manitoba over three growing seasons. As the amount of trifluralin in the soil increased, flax density and dry matter production decreased, such that at a soil concentration equivalent to 1 kg ai ha−1 trifluralin, the two were reduced by 40 and 49%, respectively. Recovery from early-season injury was characterized by enhanced crop growth rates (CGRs) and net assimilation rates (NARs) of surviving plants during the remainder of the growing season. Maximum recovery occurred in plots where trifluralin levels in the soil were between 0.8 and 1 kg ha−1 at seeding. During the interval between stem elongation and bud initiation, CGRs and NARs of flax in the trifluralin-treated plots exceeded those of flax in the untreated plots by up to 1.5 and 1.2 times, respectively. Additionally, the number of branches per plant increased linearly as trifluralin amounts in the soil increased. Flax seed yield was decreased by trifluralin as described by the equation: flax seed (% of untreated control) = 104.9 - 13.3[trifluralin detected (kg ha−1) at seeding]. Based on this equation, trifluralin levels in the soil of up to 0.7 kg ai ha−1 caused less than a 5% reduction in flax yield under weed-free conditions.

The influence of calcium arsenate (48% w/w tricalcium arsenate) rate, physical form, time of application, and phosphorus (P) rate on the growth of annual bluegrass (Poa annua L.) and Bray P1 extractable arsenic (As) were investigated. Both powder and granular formulations reduced clipping yields and enhanced extractable As levels. Higher initial soil As activity and significantly better control were obtained in one study when the powder formulation was used. Similar levels of control were achieved whether the As was applied prior to germination or to the mature turf. Soil P-levels did not influence the effectiveness of either As formulation.

International challenges in any field of science occur only from time to time. On occasions where the development of mankind is seriously endangered due to constraints of one kind or another, the ground for the germination of such challenges may be particularly fertile.

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.

Greenhouse benches and pots were specially designed to facilitate herbicide research on plants. Four 0.8-cm risers were added to the bottom of polyethylene pots to improve drainage after subirrigation or surface watering. A rule die was made to punch out paper discs needed to cover the holes in the bottom of the pots to prevent soil loss during watering or drainage. Flat, level greenhouse tables with a 3-cm hinged side around the edges, were covered with 2-mm polyethylene sheeting to facilitate water retention when the side was in the up position during subirrigation and subsequent drainage of water when the side was down. Much time was saved and the soil was watered more uniformly by this system. Economics dictated discarding pots after herbicide experiments rather than incurring the expense of washing them and risking contamination of subsequent experiments.

Farming elements other than the crop, when integrated into the system, are supplementary, with multifold uses that include weed and pest management. Elements such as fish and poultry birds are integrated with transplanted wetland rice (Oryza sativa L.) for ensuring farmers’ livelihoods and the nutritional security and sustainability of the system. Integrated animal components such as poultry birds and fish also supplement the system with weed control. The role and efficacy of these animal components as tools for managing weedy rice (Oryza sativa L.) were explored, as weedy rice infestation is increasing. This threat of weedy rice is due to scarcity of water resulting from poor water management and improper field leveling. Grass carp (Ctenopharyngodon idella val.) produced the highest reduction of weedy rice biomass, 28% within 24 h under laboratory conditions. Polyculture of C. idella, mrigal (Cirrhinus mrigala Ham.), and silver carp (Hypophthalmichthys molitrix val.) reduced the biomass of weedy rice by 21% within 24 h. In laboratory studies, poultry manure at the highest concentration of 5% reduced the weedy rice seed germination 100% compared with rice seed germination at 91%. This conformed with microplot experiments in which poultry manure at 15.6 g d−1 resulted in a weed control index (WCI) of 8% in both years. However, poultry manure at 15.6 g d−1 in combination with herbicide application resulted in the highest control indices of weedy rice: 52% in 2017 and 2018. Integrating fish and poultry with PRE application of oxyfluorfen (0.25 kg ha−1) resulted in the highest WCI and grain yield in field experiments.