Foliar applications of (2,4-dichlorophenoxy)acetic acid (2,4-D) to both field- and greenhouse-grown honeyvine milkweed (Ampelamus albidus (Nutt.) Britt.) caused 22% and 36% reduction in starch in roots at 2 and 3 days after treatment, respectively. No changes in soluble sugars occurred during the period, but protein had increased by 35% and 80% on the two respective dates. No increase in α-amylase was measured. Leakage of nucleotides and α-amylase from root sections began 2 days after treatment. A 20 to 30-fold increase in cellulase activity occurred in roots of treated plants starting 2 days after treatment.

The future of weed science, and indeed of all of modern agricultural science and technology, is in jeopardy today because the public does not clearly understand their importance. As a result, decisions may be made and actions taken that can, and will if continued, most certainly destroy our complex and highly productive agricultural systems where one worker annually provides food for more than 46 people. We can improve prospects for the future by effective action.

Effects of 22 herbicides on the ATP content of excised soybean [Glycine max (L.) Merr., var. Lee] hypocotyls were determined and compared with interferences reported previously on RNA and protein syntheses. Herbicides that reduced ATP levels and inhibited RNA and protein syntheses were 2-sec-butyl-4,6-dinitrophenol (dinoseb), 4-hydroxy-3,5-diiodobenzonitrile (ioxynil), 3′,4′-dichloropropionanilide (propanil), isopropyl m-chlorocarbanilate (chlorpropham), 2,3,5-trichloro-4-pyridinol (pyriclor), 2-chloro-N-isopropylacetanilide (propachlor), (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T), and (2,3,6-trichlorophenyl)acetic acid (fenac). No herbicide was found which reduced tissue ATP levels, but did not inhibit RNA and protein syntheses. The correlations established between tissue ATP levels and inhibition of RNA and protein syntheses suggested that interference with the production of energy, required to drive the biosynthetic reactions, could be the mechanism through which these herbicides expressed their effects.

Seed dormancy of common milkweed (Asclepias syriaca L.) is broken by a few days of moist low-temperature after-ripening. The duration of low-temperature after-ripening of the seeds is temperature dependent. Seedling emergence is best when the seeds are planted 1 to 2 cm deep and extremely limited when planted 6 cm deep. Seedlings have the capacity to produce new shoots if clipped in the 1 to 1¾-leaf pair stage and multiple shoots if clipped in the 2 to 2½-leaf pair stage. All seedlings reaching the 4 to 4½-leaf pair stage before clipping produced new shoots.

I am grateful for the opportunity to share with you some thoughts on the benefits of agricultural chemicals. I want to invite you to help examine some important aspects of this complex subject.

In a 2-year study, five densities of kochia (Kochia scoparia (L.) Schrad.) competed with sugarbeets (Beta vulgaris L.) for the entire growing season. The yield of sugarbeet roots and pounds of sucrose per acre decreased as the intensity of competition from kochia plants increased. One kochia plant per 25 ft of row reduced the average yield of roots by 2.6 T/A and sucrose by 960 lb/A. A density of one kochia plant, or more, per 2 ft of row in the first year, or one kochia plant per 1 ft of row in the second year, significantly reduced the sucrose content of the roots. Individual kochia plants significantly reduced the weight of sugarbeet tops and roots within a radius of 31 inches from the center of the sugarbeet row.

I have chosen to begin with the proposition that more energy is expended for the weeding of man's crops than for any other single human task. Because it is one of man's principal occupations, the burden is intricately woven into the fabric of his family and community life and to lift it from the tangled skeins of his existence so that we may examine it, or judge it, is well nigh impossible. In the writings of Aristotle, there are these words which seem appropriate to the task ahead, “The search for Truth is in one way hard and in another easy, for it is evident that no one can master it fully nor miss it wholly.”

The herbicide S-ethyl hexahydro-1H-azepine-1-carbothioate [molinate] at 0, 3, and 6 lb/A was applied to drill-seeded rice [Oryza sativa L.] into the irrigation water at 8, 13, and 20 days after rice and weed emergence; the plots remained flooded for 2, 7, or 12 days. Three lb/A applied when weeds had 1 to 6 leaves and rice had 2 to 8 leaves controlled barnyardgrass [Echinochloa crusgalli (L.) Beauv.] and broadleaf signalgrass [Brachiaria platyphylla (Griseb.) Nash] and did not injure rice when the water remained for 7 or 12 days. Weed control and yield of rice were reduced when the irrigation water was held for only 2 days. When the weeds were tillering, molinate controlled barnyardgrass better than it controlled broadleaf signalgrass. Molinate at 0, 3, and 6 lb/A was applied to drill-seeded rice into the irrigation water 1 week after rice and weed emergence; 7 days later the water was either left on the plots or was drained for 5, 10, 20, or 29 days. Three lb/A usually prevented reinfestations of barnyardgrass when plots were drained for 5, 10, or 20 days. Barnyardgrass reinfested rice drained for 29 days and reduced yields.

Prior to germination, seed of some plant species either adsorb or absorb some herbicides applied to the soil. Equations were developed describing the concentration of the herbicide expected in the seed both when diffusion of the herbicide in the soil is the limiting factor and when diffusion of the herbicide within the seed is the limiting factor. Expected concentrations of the herbicide in the seed were presented for combinations of three seed radii (seed were assumed to be spheres) five diffusion times, and five diffusion coefficients. The calculated concentrations of the herbicide in the seed in ppm increased as seed size or radii decreased. This theoretical result was consistent with experimental data and potentially explains why some large-seeded plant species are difficult to control with the use of herbicides. The equation developed for a perfect “sink” predicted within experimental error the concentration of isopropyl m-chlorocarbanilate (chlorpropham) absorbed by soybean (Glycine max (L.) Merr.) seed from aqueous solutions of chlorpropham.

The dissipation and detoxification of 3,6-dichloro-o-anisic acid (dicamba), 4-amino-3,5,6-trichloropicolinic acid (picloram), and 2,3,6-trichlorobenzoic acid (2,3,6-TBA) was followed for 6 years at three locations across Nebraska. Herbicide persistence was determined by growing field bioassays of field beans (Phaseolus vulgaris L.) and soybeans [Glycine max (L.) Merr.]. Picloram showed the greatest soil persistence, 2,3,6-TBA was intermediate, and dicamba showed the least persistence across Nebraska. The residual phytotoxicity of picloram in soil was not necessarily dependent upon rainfall but was greatest in the fine textured soil with higher organic matter content.

Competition studies in field trials were conducted between common purslane (Portulaca oleracea L.) and table beets (Beta vulgaris L., var. Detroit Red) and between common purslane and snap beans (Phaseolus vulgaris L., var. Eastern Butter). Common purslane control was most critical during the first 2 weeks after beet and bean emergence. Common purslane control for longer than 2 weeks did not increase beet or bean yields. The longer common purslane was allowed to compete after beet or bean emergence, the more yields were decreased. Common purslane was a stronger competitor in beets than in beans. The faster and taller-growing bean plants provided more competition than did beets. Cultivation between rows until lay-by increased both beet and bean yields.

Responses of weeds and sugarbeets (Beta vulgaris L.) to postemergence treatments of methyl m-hydroxycarbanilate m-methylcarbanilate (phenmedipham) and two analogues were evaluated in six field studies. Phenmedipham at 1.7 kg/ha controlled foxtail millet (Setaria italica (L.) Beauv.) and kochia (Kochia scoparia (L.) Schrad.) better than 2.2 kg/ha of methyl m-hydroxycarbanilate carbanilate and ethyl m-hydroxycarbanilate carbanilate. Pigweed (Amaranthus spp.) was controlled better by the analogues at 1.1 kg/ha than by phenmedipham. The foliar growth of sugarbeets was generally suppressed more by the analogues than by phenmedipham, but injury was not considered detrimental at 1.1 kg/ha. Yield of sugarbeet roots and sugar was reduced by 7% or less by phenmedipham at rates of 1.1 to 4.5 kg/ha, but these yield reductions were associated primarily with the failure of phenmedipham to completely control all weeds for 5 to 9 weeks after treatment.

Four 14C-labeled herbicide solutions were used to determine uptake and translocation patterns in mugwort (Artemisia vulgaris L.) roots. The 14C-(2,3,6-trichlorophenyl)acetic acid (14C-fenac) was bound in the roots and rhizomes and structures initiated on the rhizomes were heavily labeled. Little movement of 14C-isomers of fenac or 14C-fenac occurred from point of application on leaves. Rhizomes devoid of roots did not offer an appreciable avenue for entry of 2-chloro-4,6-bis-(ethylamino)-s-triazine (14C-simazine) into mugwort. Little movement of 3-amino-s-triazole (14C-amitrole) occurred from primary to secondary plants. Uptake of 14C-fenac was not increased appreciably by pretreatment of the plant root-rhizome system with (2,4-dichlorophenoxy)acetic acid (2,4-D), 2,4-dinitrophenol (DNP), or simazine.

In leaching studies utilizing slotted columns of soil and redroot pigweed (Amaranthus retroflexus L.) bioassay, 2,4-bis(isopropylamino)-6-methylmercapto-s-triazine (prometryne was leached to a greater depth in the coarse-textured sandy soils than in the fine-textured clay soils. There was little correlation between the depths of leaching and the amount of water used to leach the herbicide. Prometryne formulated as an emulsifiable concentrate was leached to a greater depth than the wettable powder and the granules. The 14C-pro-metryne was much more strongly adsorbed to a clay soil than to loam and silt loam soils. Volatility studies, using cotton (Gossypium hirsutum L.) plants to assay for vapor injury, showed the vapor loss of prometryne was greater from a metal surface than from a soil surface. Injury from prometryne vapors was greater with silt loam and sandy loam soils than clay soils. Cotton plants exposed 1 week after emergence were more severely injured by prometryne vapors than cotton plants exposed at emergence or 2 and 3 weeks after emergence. The vapor injury from prometryne formulated as a wettable powder or an emulsifiable concentrate was greater from granules. Prometryne vapor injury was increased as soil moisture and temperature was increased. Vapor injury to leaves of cotton was characterized by interveinal chlorosis while injury from root uptake was characterized by veinal chlorosis.

Seedlings of corn (Zea mays L., var. GT-112 RfRf and GT-112, resistant and susceptible, respectively) to 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) were grown 48 hr in sterile Hoagland's solution containing 14C-ethyl-labeled atrazine. More incorporation of the 14C-ethyl side-chain into free amino acids was found in the roots and shoots of GT-112 RfRf than GT-112, based on radioactivity. More radioactivity was found in roots of susceptible plants than in resistant plants; however, the trend was reversed in the shoots.

The rate of uptake and translocation of N,N-dimethyl-2,2-diphenylacetamide (diphenamid-14C) varied among different species. Apoplastic translocation of diphenamid occurred rapidly in tomato (Lycopersicon esculentum Mill.) seedlings, intermediate in bermudagrass (Cynodon dactylon L. ‘328’) and slowly in winged euonymus [Euonymus alatus (Thunb.) Seib. ‘compacta’]. Diphenamid-14C was dealkylated to give N-methyl-2,2-diphenylacetamide (MDA) in both winged euonymus and tomato plants. After 8 days, approximately 60% of the benzene-extractable labeled compounds from both plants was MDA and 39% was diphenamid. However, less of the radioactive material in winged euonymus was extracted.

Dicamba (3,6-dichloro-o-anisic acid), 1,1′-dimethyl-4,4′-dipyridinium ion (paraquat), and (2,4,5-trichlorophenoxy)-acetic acid (2,4,5-T) were applied as foliar sprays to 4-year-old sweetgum (Liquidambar styraciflua L.), green ash (Fraxinus pennsylvanica Marsh.), water oak (Quercus nigra L.), and loblolly pine (Pinus taeda L.). For the three hardwood species the amount of herbicide absorbed and translocated, as measured 4 days after application, was correlated closely with tops killed 1 year later. Applications in May were more effective than those made later in the growing season. Loblolly pine was defoliated by all herbicides but recovered the second season after spraying.

Greenhouse and field experiments were conducted to compare the response of cucumber (Cucumis sativus L. ‘Ashley’), muskmelon (Cucumis melo L. ‘Delicious 51’), watermelon (Citrillus vulgaris L. ‘Charleston Grey’), and three winter squashes (Cucurbita moschata Duch. ex Poir. ‘Butternut’, Cucurbita pepo L. ‘Table Queen’, and Cucurbita maxima Duch. ‘Boston Marrow’) to 3-amino-2,5-dichlorobenzoic acid (chloramben) and six of its analogs (ammonium salt, amide, mixed salts, methyl ester, hydroxy propyl ester, and butoxy ethyl ester). There were little differences among the analogs except the amide was generally nontoxic to all test crops and weeds. Great differences in growth were noted among species. When chloramben was incorporated in the soil, cucumber and watermelon were very susceptible to all analogs except the amide. Muskmelon was tolerant of all analogs. Squashes exhibited variable susceptibility with ‘Butternut’ the least tolerant, ‘Table Queen’ intermediate, and ‘Boston Marrow’ quite tolerant of the analogs. Separation of exposure of the germinating and emerging seedling on the basis of root or shoot showed cucumber to be most susceptible to root exposure but also susceptible to shoot exposure. Muskmelon and ‘Boston Marrow’ squash were susceptible to root exposure but not to shoot exposure. Muskmelon was not susceptible to either hypocotyl or cotyledon exposure, but cucumber was susceptible to both these treatments. All three species were severely injured by postemergence sprays of chloramben.

The addition of 0.5 and 5.0 ppmw of 7-oxabicyclo [2.2.1] = heptane-2,3-dicarboxylic acid (endothall) to solutions of copper sulfate pentahydrate (CSP) at 1.0 ppmw of copper applied to the roots of emersed parrotfeather (Myriophyllum brasiliense (Camb.) increased the copper content of the roots of these plants. Growth of parrotfeather was inhibited by root applications of 0.5 and 5.0 ppmw of endothall, but CSP did not increase its phytotoxicity. However, a synergistic effect, as determined by dry weight, was calculated after treatment of hydrilla (Hydrilla verticillata Casp.) with a combination of 5.0 ppmw of endothall plus CSP at 1.0 ppmw of copper. An increase in copper uptake and a reduction in phosphorus levels was associated with those plants treated with the combination.

In experiments conducted at the International Rice Research Institute, Philippines, all commonly marketed formulations and derivatives of either [(4-chloro-o-tolyl)oxy]acetic acid (MCPA) or (2,4-dichlorophenoxy) acetic acid (2,4,D) performed in about the same way and were equally safe for use in controlling barnyardgrass [Echinochloa crusgalli (L.) Beauv.] and other annual weeds in transplanted rice (Oryza sativa L.). Eleven-day-old rice seedlings were more susceptible to amine salts of 2,4-D or MCPA than 21-day-old seedlings. Granular formulations of some chemicals were relatively less toxic than liquid formulations. The toxic effect of spraying the potassium salt of MCPA was less prolonged on the indica variety, IR22, than it was on the japonica variety, Chianung 242, which had delayed flowering and maturity.