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.

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.

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.

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.

The plant characteristics which makes ‘Hybelle’ cabbage (Brassica oleracea var. capitata L.) relatively tolerant while ‘Rio Verde’ is susceptible to the toxic action of 2,4-dichlorophenyl-p-nitrophenyl ether (nitrofen) were investigated. No differences between ‘Hybelle’ and ‘Rio Verde’ were found in growth rates, light or dark germination, or stomata density. Little xylem or phloem translocation of nitrofen-14C occurred. Disruption and removal of the cuticle of ‘Hybelle’ increased its susceptibility to nitrofen while ‘Rio Verde’ with more than normal wax deposition was tolerant. Plants with less cuticle were more susceptible, regardless of cultivar. ‘Hybelle’ had more wax per unit surface than ‘Rio Verde’ and wax deposition increased with leaf age. Both cultivars were equally tolerant to nitrofen when 6 weeks old. ‘Rio Verde’ leaves absorbed nitrofen-14C twice as fast as ‘Hybelle’ leaves. The results show that the mechanism of intraspecific selectivity of cabbage to nitrofen is dependent on the amount of cuticular wax on the leaves at the time of nitrofen application.

Gas chromatographic analysis of benzene extracts was used to study the effects of temperature and relative humidity on the degradation and volatilization of 2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide (alachlor) in the soil. The relative humidity of a closed system had little effect on alachlor retention in air dry Sawyer fine sandy loam at 22 C, but had a pronounced effect when soil temperature was 38 C or higher. At 0% relative humidity (38 C or 46 C) alachlor was degraded to 2-chloro-2′,6′-diethylacetanilide. Decomposition, which also occurred in 5 N aqueous HCl, was attributed to acidic soil water film surfaces. As relative humidity within the system increased, the rate of degradation decreased, apparently because condensation of water vapor increased the thickness of the soil water film and decreased the surface acidity. At 38 C, minimum loss was noted at 31% relative humidity, and at 46 C, minimum loss was found at 79% relative humidity. The increased loss of alachlor at relative humidities above these critical points was attributed to volatility and not to chemical degradation.

Tolerance of corn (Zea mays L. ‘B’), cotton (Gossypium hirsutum L. ‘coker 413’), soybean (Glycine max Merr. ‘Hardee’), turnip (Brassica rapa L. ‘Tendergreen’), sorghum (Sorghum bicolor (L.) Moench. ‘Georgia 615’), purple nutsedge (Cyperus rotundus L.), yellow nutsedge (C. esculentus L.), and johnsongrass (Sorghum halepense (L.) Pers.) to 2,6-dichlorobenzonitrile (dichlobenil) at 0, 0.14, 0.28, 0.56, 1.12, and 2.24 kg/ha in four Georgia soils was determined. Equivalent rates of dichlobenil generally were more toxic in Davidson clay loam which had the highest clay content. Crop tolerance was corn > sorghum > cotton > turnip. Purple and yellow nutsedge tolerance to dichlobenil was intermediate to that of the crops tested. Johnsongrass response was equivalent to that shown by sorghum.

A bioassay for photosynthetic and respiratory inhibitors was devised. The chlorophyll production of Chlorella pyrenoidosa Sorokin, high temperature strain 7-11-05, served as the basis of the bioassay which required 18 to 36 hr to complete. The sensitivity to nine photosynthetic and two respiratory inhibitors ranged from 0.013 to 0.4 ppm. The bioassay was successfully employed to assay leachates from soil columns and to monitor a field residue of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine).

Nitrofen (2,4-dichlorophenyl p-nitrophenyl ether) injured meristematic tissues and reduced germination and growth of cabbage (Brassica oleracea var. capitata L.) in the dark. Cabbage was more susceptible to nitrofen when the plants were grown under a low water potential or when they were maintained in the dark after spraying. This toxicity was overcome by exogenous sucrose and light was not required for nitrofen activity. Nitrofen promoted membrane permeability of red beet (Beta vulgaris L.) root sections and this was enhanced by dimethylsulfoxide (DMSO). Sucrose or Carbowax 1500 prevented this increase in permeability. Nitrofen inhibited non-cyclic photophosphorylation and electron transport in isolated spinach (Spinacia oleracea L.) chloroplasts and increased oxygen uptake of cabbage leaf sections. These effects appeared dependent upon permeability. Nitrofen induced stomatal closure, decreased transpiration, and increased leaf temperature. The leaf sustains thermal injury under high temperatures or high light intensities.

The Nebraska till-plant system of planting corn (Zea mays L.) moves weed seed away from the corn row. A reduction of weed seed in the row reduces the number of weeds emerging with the corn. In contrast, the conventional disking and plowing system of seedbed preparation does not remove weed seed from the row.

Field experiments were conducted during 1968 to 1970 to determine the influence of time of herbicide application on control of kudzu [Pueraria lobata (Willd.) Ohwi]. Picloram (4-amino-3,5,6-trichloropicolinic acid) effectively controlled kudzu when applications were made as early as May 22 and as late as October 28. Acceptable control was obtained with rates of picloram 0.34 kg/ha or higher. In contrast, (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) was most effective when applied during the first half of summer. Essentially no control of kudzu was obtained from 2,4,5-T applied 1 week before the first killing frost.

The I50 values obtained with preemergence applications of 2-sec-butyl-4,6-dinitrophenol (dinoseb) for shoot and root growth in soil, or root growth in a bioassay were determined for 68 plant varieties representing 66 species. The I50 values in soil indicate a difference of more than 240 fold between the most sensitive species, shepherdspurse (Capsella bursa-pastoris (L.) Medic.) and the most tolerant species, peanut (Arachis hypogaea L.). The correlations among the I50 values for shoot and root growth in soil and the root bioassay were significant. The I50 values between susceptibility of plants to soil-applied dinoseb and their seed size are correlated significantly. Large-seeded plant species and larger seeds within varieties, in general, were more tolerant to dinoseb than small-seeded species and smaller seeds within a given variety. However, there appeared to be other factors involved in susceptibility. For example, there were differences in response among families; the Leguminosae were the most tolerant, while the Solanaceae and Cruciferae were particularly susceptible.

Repeated, foliar applications of monosodium methanearsonate (MSMA) controlled established, space-planted purple nutsedge (Cyperus rotundus L.) while three other herbicides were less effective. Four to eight applications of 5.6 to 16.8 kg/ha of MSMA in 1 year destroyed most plants. There was little difference in final control from applications made at 2, 3, or 4-week intervals or from 187 to 1496 L/ha of spray solution. Clones of purple nutsedge responded similarly to herbicide treatments.

Water from several bodies of surface water and sections from several plants were collected from eastern North Carolina and bioassayed for stimulation of witchweed (Striga lutea Lour.) seed germination. Stimulatory activity was detected in water from 22 of 29 different ponds, streams, and lakes and in sections from 118 (57 families) of 163 plant species. Witchweed germination stimulants evidently occur widely in nature.

The dipeptidase activity of the cotyledons of the squash (Cucurbita maxima Duch. ‘Hubbard’) increases during germination. Several herbicides inhibited this increase in various degrees. Those herbicides inhibiting the development of dipeptidase activity 70% or more were (2,4-dichlorophenoxy)-acetic acid (2,4-D), 3,6-dichloro-o-anisic acid (dicamba), (2,3,6-trichlorophenyl)acetic acid (fenac), and N-1-naphthylphthalmic acid (naptalam). Those inhibiting dipeptidase activity by 63 to 34% were 4-amino-3,5,6-trichloropicolinic acid (picloram), 2,6-dichlorobenzonitrile (dichlobenil), 3,5-dibromo-4-hydroxybenzonitrile (bromoxynil), 3-amino-s-triazole (amitrole), 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine), 7-oxabicyclo[2.2.1] heptane-2,3-dicarboxylic acid (endothall), and 5-bromo-3-sec-butyl-6-methyluracil (bromacil). Those causing only slight inhibition, 24 to 16%, were N,N-dimethyl-2,2-diphenylacetamide (diphenamid), isopropyl m-chlorocarbanilate (chlorpropham), and α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin); 3-(p-chlorophenyl)-1,1-dimethylurea (monuron) was essentially the same as the control. However, 2,2-dichloropropionic acid (dalapon), O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)-benzenesulfonamide (bensulide), N,N-diallyl-2-chloroacetamide (CDAA), and 2-chloroallyl diethyldithiocarbamate (CDEC) were somewhat stimulatory. When compared with previously reported herbicide activity on the proteinase activity, those herbicides which inhibited dipeptidase activity did not necessarily affect proteinase activity to the same degree.

Movement of pesticides on soil thin-layer chromatographic (TLC) plates was detected by a bioassay employing a green alga, Chlorella sorokiniana Shihira and Krauss. After leaching the soil TLC plates with water, a Chlorella suspension in an enriched agar medium was aspirated onto the soil to give ca. 8 × 106 cells/cm2. Plates were incubated at 100% relative humidity at 30 C, with illumination of ca. 40 klux. Zones of pesticide movement were visible within 24 to 48 hr. Mobility in Hagerstown silty clay loam was assessed for two methylcarbamate insecticides and for nine phenylurea, 11 s-triazine, and 13 miscellaneous herbicides. Among analogous triazines, the mobility order was: -OCH3 > -Cl > -SCH3. Movement of 6,7-dihydrodipyrido[1,2-a:2′,1′-c]pyrazinediium ion (diquat) and 1,1′-dimethyl-4,4′-bipyridinium ion (paraquat), normally immobile in soils, was directly proportional to rate when applied in high doses.

Degradation of 1,1-dimethyl-3-(a,a,a-trifluoro-m-tolyl) urea (fluometuron) in a sandy loam soil was investigated in time-course and 14CO2 evolution studies. Degradation occurred only in nonautoclaved samples and was more rapid in glucose-amended soil, indicating that it is a function of microbial metabolism. Time-course studies showed that the pathway of degradation of fluometuron in soil is similar to that previously reported for other substituted ureas, involving a two-step demethylation, probably followed by hydrolysis of the urea linkage to form the aniline derivative. Further evidence for degradation was a small but significant recovery of 14CO2 from soil treated with fluometuron labeled in the trifluoromethyl group.

Sequential herbicide treatments of 3-[p-(p-chlorophenoxy)-phenyl]-1,1-dimethylurea (chloroxuron) with S-propyl dipropylthiocarbamate (vernolate) controlled weeds early in the season in soybeans (Glycine max (L.) Merr. ‘Dare’ or ‘Bragg’) better than when chloroxuron was applied in sequence with either α,α,α-trifluoro-2,6-dinitro-N,N dipropyl-p-toluidine (trifluralin) or 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin). The control of weeds late in the season was enhanced with split applications of 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron) or 2,4-bis(isopropylamino)-6-(methylthio)-s-triazine (prometryne) when applied to plots previously treated with chloroxuron as early postemergence and trifluralin, nitralin, or vernolate applied preplant. In 1969 nitralin injured soybeans, and reduced stands and seed yields significantly more than trifluralin or vernolate. In 1970 sequential treatments of prometryne with chloroxuron and vernolate were more phytotoxic to soybeans than were the same postemergence treatments when applied with nitralin and trifluralin.

Several herbicides were tested in the greenhouse on ivyleaf morningglory (Ipomoea hederacea (L.) Jacq.), green foxtail (Setaria viridis (L.) Beauv.), purple nutsedge (Cyperus rotundus L.), and quackgrass (Agropyron repens (L.) Beauv.) to determine the degree of enhancement in activity that could be obtained with an isoparaffinic oil carrier applied at 140 L/ha. The enhancement varied with the herbicide and with the species, ranging from 16-fold enhancement with 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) and 2-sec-butyl-4,6-dinitrophenol (dinoseb) on ivyleaf morningglory to no enhancement of atrazine activity on purple nutsedge and quackgrass or (2,4-dichlorophenoxy)acetic acid (2,4-D) activity on quackgrass and ivyleaf morningglory. An oil adjuvant was less effective in enhancing dinoseb and 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron) activity than was the isoparaffinic oil carrier. Also, the isoparaffinic oil carrier emulsified in water was less effective than the undiluted oil in enhancing dinoseb activity on green foxtail, even though equal volumes of the isoparaffinic oil were applied.

The relative susceptibility of 40 plant species to postemergence applications of 2-sec-butyl-4,6-dinitrophenol (dinoseb) in isoparaffinic oil was determined. Peanuts (Arachis hypogaea L. ‘Holland Virginia 56R’), with an I50 of greater than 2.24 kg/ha, were the most tolerant, and johnsongrass (Sorghum halepense (L.) Pers.) seedlings, with an I50 of 0.011 kg/ha, were the most susceptible. This is greater than a 200-fold difference in susceptibility, due primarily to internal tolerance, because penetration differences were reduced with the isoparaffinic oil carrier. Legumes generally were the most tolerant, and grasses ranged from tolerant to the most susceptible. Several species, primarily grasses, showed greater than 25% inhibition of shoot fresh weight from the isoparaffinic oil carrier alone.