The concept of controlled release of herbicides has created in some workers expectations beyond possibility. In this theoretical paper, we examine the results to be expected based on a simplistic model. The purpose of the development is that it serve as a guide to experimentation and as a stimulant to such experimentation by revealing the possible advantages which may occur.

Field and greenhouse studies were conducted to determine the influence of soil organic matter on herbicidal activity using four Pocomoke soils with organic matter contents of 4.8, 7.0, 11.9, and 17.0%. In field experiments, control of giant green foxtail [Setaria viridis var. major (Gaud.) Posp.] was greater than 75% from all treatments of 2-chloro-2′,6′-diethyl-N-(methoxymethyl) acetanilide (alachlor), 2-chloro-N-isopropylacetanilide (propachlor), and N,N-diallyl-2-chloroacetamide (CDAA) with no statistical differences between chemicals, rates, or organic matter levels. Control was statistically lower from all 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) treatments except 2.6 kg/ha at 7% organic matter and 4.4 kg/ha at 7 and 17% organic matter. Under greenhouse conditions, giant foxtail (Setaria faberi Hermm.) was used to establish GR50 values on soils or soil mixtures containing 0.8, 1.9, 3.9, 6.4, 11.0, and 18.7% organic matter for the herbicides used in the field study and for 2-chloro-N-(1-methyl-2-propynyl)acetanilide (prynachlor). Generally as organic matter levels increased, the GR50 values for herbicides increased; the rate of GR50 increase varied with herbicides. A ranking of herbicides from most toxic to least toxic is: propachlor>alachlor>prynachlor>CDAA. Atrazine GR50 values varied from a low similar to propachlor at 0.8% organic matter to 20 times greater than propachlor at 17% organic matter.

Studies were conducted to determine the effect on photosynthesis, the absorption, and the metabolism of simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] in two biotypes of common groundsel (Senecio vulgaris L.). Simazine inhibited photosynthesis in the susceptible (S) plants, but resistant (R) plants were unaffected. When the herbicide was removed from the S biotype after 24 hr, photosynthesis resumed. Both biotypes absorbed the herbicide equally well and were unable to metabolize simazine during 96 hr. The greatest concentration of 14C activity (80 to 90%) was located in the chloroform-soluble fraction of the foliage of each biotype and was identified as simazine. Small amounts of radioactivity (10 to 15%) occurred in the water-soluble fraction, but there was no differential increase in water-soluble simazine metabolites. A different mechanism of resistance than previously reported for triazine-resistant plants may be operative in one groundsel biotype.

Dalapon (2,2-dichloropropionic acid), injurious to Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) and grand fir (Abies grandis (Dougl.) Lindl.) when used alone for weed control, was used with safety and even with beneficial effects when combined with atrazine [2-chloro-4-(ethylamine)-6-(isopropylamino)-s-triazine] and 2,4-D, [(2,4-dichlorophenoxy) acetic acid] at rates of up to 3.36 and 4.48 kg/ha, respectively. Harmful effects of dalapon were masked at rates up to three times those used for adequate control of grasses. This suggests a type of selectivity previously unreported. Interpretation of herbicide effects and interactions was made possible with an analytical model that separated effects of vegetation from those of herbicides on a causal basis. This technique included two-dimensional adjustment of the base of reference for a four-dimensional response-surface equation. This surface fit observed data as well as a single multiple-regression equation, which included all variables. This approach, however, estimated herbicide parameters with appropriate consideration of environmental data and permitted interpretation with respect to cause.

Competition studies were conducted with soybeans Glycine max. (L.) Merr. ‘Clark 63’ and Venice mallow (Hibiscus trionum L.). One Venice mallow per 7.5 cm of soybean row reduced soybean seed yield 632 kg/ha after 85 days competition. Thirty to 40-cm weed bands in and between soybean rows reduced yields 270 to 651 kg/ha with 35 to 40 days of competition. A natural stand of 215 Venice mallow plants per square meter reduced soybean yield 454 kg/ha after 30 days of competition, and competition up to 110 days reduced yield as much as 1490 kg/ha. Weed competition affected the number of pods per soybean plant more than any other seed-yield component, and soybean height was reduced. Soybean yields were reduced more when soil moisture was abundant early in the growing season and limited in late summer than when moisture was limited early in the growing season and above average until soybeans matured.

The Beatitudes could well be extended to bless those who continue to pursue learning aggressively throughout their life, for surely such individuals shall be confronted with challenge and their days shall be full of wonderment and accomplishment and self-satisfaction. As I reflect on this business of learning, it is apparent that a great deal of it takes place at the subconscious level. Throughout all of my undergraduate and graduate student days and ever since through affiliation with knowledgeable associates, the concept of professionalism seems to have been taking shape for me as an individual. Perhaps it is well at this juncture in the life of WSSA to consider what professionalism means for the discipline of weed science.

An application was developed to project UHF electromagnetic fields into soils containing seeds. The unconfined field (2450±20 Mhz) was effective in killing seeds in the soil. At a fixed energy level the toxicity of the field to wheat (Triticum aestivum L.) and radish (Raphanus sativus L.) was constant or slightly increased as the time of exposure was decreased. Thus, the energy requirement for a given level of toxicity can be met by substituting increased power levels for time of exposure in the range of 100 and 1200 watts.

Greenhouse studies were conducted to evaluate the activity of fluometuron [1,1-dimethyl-3-(α-α-α-trifluoro-m-tolyl)urea] and disulfoton [o,o-diethyl s-(ethylthio ethyl) phosphorodithioate] alone and in combination on the height of seedling cotton (Gossypium hirsutum L.) in 10 light-textured soils from the lower alluvial floodplain of the Mississippi River. An antogonistic interaction was demonstrated between the two pesticides in six of the soils studied. The phytotoxic effects of high rates of fluometuron applied preemergence were decreased by granular application of disulfoton. This interaction was repeated in four of the soils and was modified but not eliminated by partial sterilization of the soils, by autoclaving, or by fumigation before treatment. Correlation analyses detected no significant association between the antagonistic interaction and any measurable soil property in the 10 soils. Three field studies failed to demonstrate this interaction. Neither the greenhouse nor the field studies revealed any deleterious interaction between these two chemicals.

Absorption of the butyl ether esters of (2,4,5-trichlorophenoxy)-acetic acid (2,4,5-T) by honey mesquite [Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell] foliage was more rapid when 0.56 kg/ha was applied in 15 L/ha paraffin oil than when diesel oil, water, or emulsions of the oils in water were used as carriers. However, carrier had little effect on 2,4,5-T translocation to stems or roots. The percentage of greenhouse-grown honey mesquite plants killed was reduced when 2,4,5-T was applied in diesel oil as compared to other carriers studied.

Crystallization of methyl m-hydroxycarbanilate m-methyl-carbanilate (phenmedipham) occurred from aqueous emulsions of the commercial formulation when dilutions exceeded one part of the formulation to 30 parts water. Dilutions greater than 1 to 30 accelerated crystallization and increased the quantity of phenmedipham that crystallized out. Mechanical agitation increased the rate of crystallization during the first 12 hr after initial mixing. Low water temperature increased the rate of crystallization and total amount of phenmedipham that crystallized out. Phenmedipham crystallization was not altered by water hardness or pH over the range 4.0 to 8.0. Simulated refilling of a partially empty spray tank before adding formulated phenmedipham produced considerable crystallization, whereas adding formulated phenmedipham before adding water minimized crystallization. The solvent used in the commercial formulation to dissolve phenmedipham is partially soluble in water. The partitioning of this solvent into the aqueous phase of the emulsion explains crystallization of phenmedipham.

Buds of locally collected yellow nutsedge (Cyperus esculentus L.) tubers are formed only at the six most apical nodes with a 1/3 phyllotaxy. The oldest bud is largest. Bud size grades to the small apical bud. Veins of the rhizome are continuous through the tuber to each bud, root, and leaf. Buds break dormancy in acropetal order, starting with the oldest bud. If the tubers and buds remain undisturbed, usually only two buds break dormancy and grow into shoots.

We hear the expression “cost-benefit” a great deal nowadays; and when we do, we should always ask “cost to whom? Benefit to whom?” We should also remember that cost-benefit analysis requires that account be taken not only of financial gains and losses but also of all advantages and disadvantages of any kind. Consideration only of income and expenditure is investment appraisal, and many of the so-called “cost-benefit” studies of herbicide usage which have been published come into this category. Such studies are useful, but they should not be considered in isolation from investment appraisal of herbicide discovery, development, and production for the manufacturer; and both must be integrated into a total view of cost-benefit of weed control for the whole community, a broad and long-term view which takes account not only of economic values but also of social values. To make decisions and to formulate policies which will set herbicides in an optimum way in the social and economic context of an entire community and which will produce the most favourable cost-benefit for that whole community demands study and analysis of the total system. In the short time allocated to me I can do no more than skim over this wide field and indicate a number of relevant topics, and I plead guilty in advance to the charge of being superficial and of suggesting things that should be done without describing in detail how they could be done. My remarks will apply to the developed countries because the herbicide needs of the under-developed countries are a separate subject.

Metabolism of the herbicide 2-(α-naphthoxy)-N,N-diethyl propionamide (R-7465) by tomato plants (Lycopersicon esculentum Mill. ‘Mechanical Harvester’) was investigated. Ring-labeled R-7465-14C was taken up rapidly by the roots and distributed throughout the leaves within 8 hr. R-7465 was converted primarily into water soluble metabolites. The principal metabolite was identified as a hexose conjugate of 2-(α-naphthoxy-4-hydroxy)-N,N-diethyl propionamide. This metabolite represented 47% of the soluble radioactivity in the plant. A different hexose conjugate of 2-(α-naphthoxy-4-hydroxy)-N,N-diethyl propionamide together with a hexose conjugate of 2-(α-naphthoxy-4-hydroxy)-N-ethyl propionamide accounted for another 22% of the radioactivity. Nonmetabolized R-7465 was found to represent only 5% of the total soluble radioactivity. Other identified metabolites included 2-(α-napthoxy)-N-ethyl propionamide, 2-(α-naphthoxy-5-hydroxy)-N,N-diethyl propionamide, and 1,4-naphthoquinone. None of these metabolites individually represented more than 3% of the soluble radioactivity in the plants. Ring hydroxylation and N-dealkylation appeared to be the initial steps in detoxification of R-7465 followed by conjugation with sugars.

I am pleased to be with you today at this 13th meeting of the Weed Science Society of America. As the president of this organization, Dr. Upchurch, has noted, this event is an excellent mechanism for an exchange of ideas between the various disciplines in the field of weed science. It also allows today for me an opportunity to express to you the view of the Environmental Protection Agency with respect to agriculture in general and pesticide herbicide questions in particular, by a discussion of the new Environmental Pesticide Control Act.

Trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) required more thorough soil incorporation with a disk, probably to prevent loss by volatility, than did 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin). Mechanical incorporation of nitralin could be delayed for 96 hr after application, whereas trifluralin needed to be incorporated within 24 hr to control weeds. Gas chromatographic analyses of soil showed that trifluralin decreased rapidly during the first 24 hr that incorporation was delayed. Application of trifluralin with undiluted crop oil on dry soil did not prolong the persistence prior to incorporation compared to applications with water.

Ten commercial soybean [Glycine max (L.) Merr.] cultivars were evaluated for reaction to over-the-top applications of two rates of 3′,4′-dichloropropionanilide (propanil) at the growth stage when three nodes on the main stem had completely unrolled leaves. Propanil, a herbicide commonly applied to rice [Oryza sativa L.] for control of grass weeds, was applied at 0.56 and 3.36 kg/ha; the higher rate is commonly used for control of weeds in rice. ‘Davis’, ‘Hood’, and ‘York’ soybean cultivars were damaged more by propanil than ‘Hill’, ‘Lee’, ‘Lee 68’, ‘Pickett’, ‘Semmes’, ‘Bragg’, or ‘Dare’ when damage was measured by reductions in seed yield and stand and by leaf injury.

Five fallow treatments in an alternate winter wheat (Triticum aestivum L.) fallow rotation experiment were compared over a 6-yr period at North Platte, Nebraska. During the 14-month fallow period from winter wheat harvest until winter wheat planting, plots receiving no tillage (weeds were controlled by herbicides) had the least weed growth, most soil water stored, and highest amount of surface mulch maintained. Also, the plots receiving only herbicides had the highest grain yields of all treatments. However, an average of 3.8 herbicide applications were needed to control grass weeds missed by 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) during the last 5.5 months of the fallow period. Greatest weed growth during the fallow period was on plots that received only tillage and occurred during the first 3 months after harvest.

The incidence of puncturevine (Tribulus terrestris L.) carpels and viable seed recovered from soil samples varied inversely and linearly with depths to 24 cm. Soil type and texture and method of tillage influenced the gradients of carpel distribution and their rate and degree of vertical migration. Evidence for enforced, induced, and innate dormancy in puncturevine seed is presented. Most seed germinated from depths of less than 4 cm in cultivated, sandy loam and clayloam soils. The intra-carpel pattern of seed germination was such that seed located nearest the stylar end of two, three, and four-seeded carpels tended to germinate first, with the other seed tending to follow in order of their position in the carpel from the stylar to the receptaclar end. However, all possible combinations of intra-carpel germination patterns occurred under field conditions.

Exposure of pea plants (Pisum sativum L. ‘Little Marvel’) to vapors of S-(2,3-dichloroallyl)diisopropylthiocarbamate (diallate) increased the subsequent foliar uptake of 14C-labeled herbicides. Increased amounts of 14C-activity were found in the tissues of diallate-treated plants as compared to the controls when herbicides were applied to the leaves as aqueous solutions or embedded in agar blocks. The herbicides were (2,4-dichlorophenoxy)acetic acid-1-14C (2,4-D), uniformly ring-14C 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine),trichloroacetic acid-2-14C (TCA), and ethylene-14C 6,7-dihydrodipyrido[1,2-a:2′,1′-c]pyrazinediium ion (diquat). The increased movement of herbicides into diallate-treated peas was primarily attributed to a reduction of epicuticular lipids on leaves of the treated plants.

The effect of soil temperature, soil moisture content, and soil bulk density on the diffusion of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], propachlor (2-chloro-N-isopropylacetanilide), and diazinon [O,O-diethyl O-(2-isopropyl-6-methyl-4-pyrimidinyl) phosphorothioate] in Ida silt loam soil was studied in the laboratory. Diffusion coefficients of 1.90, 1.36, and 0.63 mm2/day at 27 C for propachlor, atrazine, and diazinon, respectively, show in a relative way the expected movement of these chemicals in Ida silt loam soil. The greatest amount of movement occurred with high temperatures and high moisture contents. Soil moisture had more effect on atrazine movement than on propachlor movement, and very little effect on diazinon movement. Movement for all chemicals decreased with an increase in bulk density.