Slow advances were made in weed technology over 10,000 yr as agriculture progressed from hand weeding to the use of hand tools, animal power, cultural practices, mechanical power, biological controls, and most recently to chemical control.

President Hay, distinguished officers of the Society, and learned colleagues. Let me express my deep appreciation for the honor you confer on me.

It was my good fortune to begin a career in weed control at the point of transition between the modern chemical era and what I have chosen to call the cultural-mechanical era of weed control, which just preceded it. It was, therefore, my privilege to have known and worked with some of the handful of scientists who laid the foundation of weed science. Some are yet with us, but most have passed on to a greater glory.

Field studies were conducted in 1977 and 1978 to compare the efficacy of the starch xanthate and activated-sludge polymer controlled-release herbicide formulations with the emulsifiable-concentrate formulations. As incorporation was delayed from immediately to never incorporated, starch xanthate and sludge polymer thiocarbamate herbicide formulations had activity equal to that of the emulsifiable concentrates at our initial and final rating dates. Trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine)-starch xanthate in 1977 had increased activity over that of the emulsifiable concentrate as incorporation was delayed, as indicated by initial and final visual rating. Starch xanthate did not greatly increase the residual activity of alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide], metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], or several thiocarbamate herbicides. Starch xanthate formulations of EPTC (S-ethyl dipropylthiocarbamate) and vernolate (S-propyl dipropylthiocarbamate) provided significantly less protection to corn than did addition of the protectant R-29148 [3-(dichloroacetyl)-2,2,5-trimethyloxazolidine]. The sludge polymer formulation had no controlled-release properties.

The plant pathogenic fungus Albugo tragopogi (Pers.) S. F. Gray (“white rust”), isolated from a local population of common ragweed (Ambrosia artemisiifolia L.) and inoculated into ragweed seedlings at the two-leaf stage, reduced pollen production by 99%, seed production by 98%, and top weight by 79% of plants that developed systemic disease symptoms while growing in a controlled environment. However, only 14% of the inoculated plants developed systemic symptoms. A convenient method of inoculating leaves of seedling plants with zoospores of a fungus is described.

The patterns of buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2 imidazolidinone} uptake, translocation, and metabolism, and their potential contribution to crop selectivity, were studied in tolerant alfalfa (Medicago sativa L. ‘Vernal’) and susceptible quackgrass [Agropyron repens (L.) Beauv.]. 14C-Buthidazole was absorbed from a 5-μl droplet by leaves of both alfalfa and quackgrass plants, but did not move basipetally to the roots or nontreated leaves in 14 days. 14C-Buthidazole was absorbed very rapidly from Hoagland's solution by the roots of both species and translocated apoplastically to the leaves. Absorption and translocation of buthidazole did not differ between species, indicating that these processes did not contribute to crop selectivity. The herbicide and five metabolites were present in alfalfa leaf extracts 6 days after treatment. One unidentified metabolite accounted for 40% of the detected radioactivity 6 days after root application. Unmetabolized 14C-buthidazole accounted for 87% of the total radioactivity in quackgrass after 6 days. Metabolites having different chromatographic properties were recovered from the two species. Differential rate and type of metabolism appeared to contribute to buthidazole selectivity between the species.

The effects of oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene] were studied on electron transport and phosphorylation in isolated spinach (Spinacia oleracea L.) chloroplasts and on the response of green bean (Phaseolus vulgaris L. ‘Spartan Arrow’) to applications of oxyfluorfen alone or in combination with other herbicides. Coupled non-cyclic electron transfer and phosphorylation through photosystems I and II (H2 O å methyl viologen) were inhibited about 30% and 55%, respectively, by 10−4 M oxyfluorfen. Photosystem II-linked phosphorylation with dimethylbenzoquinone (2,5-dimethyl-p-benzoquinone) as the electron acceptor (H2 O å DMQ) was completely inhibited by 10−4 M oxyfluorfen. Photosystem II electron transport with dimethylbenzoquinone as the electron acceptor was inhibited 60% by 10−4 M oxyfluorfen, whereas photosystem I electron transport with 2,6-dichlorophenol indophenol as electron donor (DCIPH2 å MV) was not susceptible to oxyfluorfen inhibition. Photosystem I-linked phosphorylation and the accompanying electron transport supported by durohydroquinone electron donation (DQH2 å MV) were inhibited about 50% by 10−4 M oxyfluorfen, whereas cyclic phosphorylation was not inhibited at that concentration. Increased conductivity of a solution that contained leaf discs taken from green beans treated with various combinations of foliar-applied herbicides was a measure of membrane damage caused by the herbicides, and revealed that oxyfluorfen has a different site of action than do photosynthesis inhibitor and bipyridilium herbicides. Oxyfluorfen plus dinoseb (2-sec-butyl-4,6-dinitrophenol) injury to green beans was additive, but the two herbicides did not have the same site of action. Oxyfluorfen did not appear to inhibit electron transport in chloroplasts at herbicidal rates, nor was it dependent on electron transport for activation.

The influence of acetamide herbicide applications on efficacy of CGA-43089 [α-(cyanomethoximino)-benzacetonitrile] in grain sorghum [Sorghum bicolor (L.) Moench] was studied under field conditions. Acetamide herbicides applied preplant and incorporated on a Haynie very fine sandy loam caused more grain sorghum injury in 1979 than in 1978. Reductions in plant population, plant height and yield, along with delay in maturity, were severe for acetochlor [2-chloro-N-(ethoxymethyl)-6′-ethyl-O-acetotoluidide], metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], and alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide]; moderate for diethatyl [N-(chloroacetyl)-N-(2,6-diethylphenyl)glycine], xylachlor [2-chloro-N-(2,3-dimethylphenyl)-N-(1-methylethyl)acetamide], and butam [2,2-dimethyl-N-(1-methylethyl)-N-(phenylmethyl)propanamide]; and did not occur for propachlor (2-chloro-N-isopropylacetanilide) treatments. Acetamide herbicides caused less grain sorghum injury on a Reading silt loam than on a Haynie very fine sandy loam in 1979. CGA-43089 applied as a seed treatment protected grain sorghum grown on soils treated with metolachlor, alachlor, diethatyl, or xylachlor. Metolachlor-triazine combinations at five locations in Kansas reduced yields at two locations. CGA-43089 provided protection from metolachlor injury at those two locations.

The effects of soil temperature, moisture, and herbicide concentration on the rate of degradation of dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine) were measured in clay loam and sandy loam in the laboratory. In sandy loam, the rate of degradation increased with increasing temperature. In clay loam, the rate of degradation increased from 10 to 30 C and decreased at 40 C. Soil moisture content influenced the rate of degradation in the following order: 22>11>>2.2% (air-dry) for clay loam and 12.0 = 6.0>>0.5% (air-dry) for sandy loam. First-order half-lives ranged from 3.2 at 30 C to 47 weeks at 10 C in clay loam, and 2.3 at 40 C to 31 weeks at 10 C in sandy loam. Applications in 2 yr did not cause buildup of dinitramine in the field. A mathematical model was used in an attempt to correlate laboratory and field data.

A field experiment of 2 yr duration at two locations was conducted to determine the effectiveness of glyphosate [N-(phosphonomethyl)glycine] and vernolate (S-propyl dipropylthiocarbamate) as single or combination treatments for quackgrass [Agropyron repens (L.) Beauv.] control in a soybean [Glycine max (L.) Merr.]-corn [Zea mays (L.)] rotation. Vernolate applied preplant incorporated at 3.36 kg/ha gave 30 to 58% and 28 to 34% quackgrass control at the end of the first and second growing seasons, respectively. Spring applications of glyphosate at 1.12 and 1.68 kg/ha before plowing gave 53 to 90% quackgrass control at the end of the second growing season. Glyphosate at 1.12 and 1.68 kg/ha followed by vernolate preplant incorporated at 3.36 kg/ha gave 85 to 99% quackgrass control at the end of the second growing season. Although vernolate did not provide effective long term quackgrass control, it did effectively augment quackgrass control when applied as a sequential treatment to glyphosate applied at 0.56 or 1.12 kg/ha.

The allelopathic potential of germinating seed of velvetleaf (Abutilon theophrasti Medic.) was established in a laboratory study with germinating seed of turnip (Brassica rapa L. ‘Purple Top’). Two-day-old velvetleaf seedlings inhibited radicle growth of germinating turnip by 17% at 24 h after both were placed in the same petri plate. Alcoholic and aqueous extracts of velvetleaf seed, however, seriously inhibited germination of turnip seed. The extract of velvetleaf seed was fractionated by ion-exchange chromatography into acid, basic, and neutral fractions. Most of the allelopathic activity was located in the acid fraction, which includes the plant phenolics. The basic fraction (amino acids) inhibited radicle growth of turnip by 18% after 48 h. The amino acid profile of velvetleaf seed extracts is presented and discussed, because this fraction has previously been implicated as the allelopathic fraction.

Atrazine [2-chloro-4-(ethylamino)-6-isopropylamino)-s-triazine] carryover under reduced or no-till row crop production systems was measured by planting oats (Avena sativa L.) the following year as a field bioassay during 1970 through 1976 at Lincoln and North Platte, Nebraska. Oat yields indicate that soil persistence of normal-use rates of atrazine into the subsequent year is only a minor residue problem under reduced tillage cropping systems. Atrazine carryover in soil was less of a problem under these reduced tillage systems as compared with prior experiments with conventional tillage systems across Nebraska.

Greenhouse-grown honey mesquite [Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell] plants were treated with the propylene glycol butyl ether esters of 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], the triethylamine salt or the ethylene glycol butyl ether esters of triclopyr {[(3,5,6-trichloro-2-pyridinyl) oxy]acetic acicd}, the potassium salt of picloram (4-amino-3,5,6-trichloropicolinic acid), or the monoethanol amine salt of 3,6-dichloropicolinic acid applied at the rate of 1.1 kg/ha to soil, foliage, or soil plus foliage. All herbicides were effective as foliar sprays in killing the stems of honey mesquite. When applied to the soil, picloram and 3,6-dichloropicolinic acid killed all above ground stems, and the ester and amine formulation of triclopyr killed 70 and 91% of the stem tissue, respectively, but 2,4,5-T was ineffective. Accumulation of herbicides in leaves 10 days after foliar spray was 28, 167, and 266 μg/g fresh wt for triclopyr, 3,6-dichloropicolinic acid, and picloram, respectively. Upward transport of picloram and 3,6-dichloropicolinic acid (2.7 to 5.9 μg/g) was also more extensive than that of 2,4,5-T or triclopyr after soil treatment. Higher concentrations of 3,6-dichloropicolinic acid than 2,4,5-T, triclopyr, or picloram usually was found in honey mesquite stems and roots 3, 10, or 30 days after application to soil or foliage. This may be one reason that 3,6-dichloropicolinic acid is highly effective in controlling honey mesquite.

When discs of red beet (Beta vulgaris L.) root were immersed in various concentrations of glyphosate [N-(phosphonomethyl)glycine] either in phosphate (pH 6.8) or citrate (pH 6.2) buffer, no efflux of betacyanin occurred even after 1 week. This suggests that glyphosate had little or no effect on membrane permeability. When beet discs were immersed in distilled water containing glyphosate, the betacyanin efflux increased with time and concentration. Measurement of pH indicated that the solutions were strongly acidic at first, but tended to approach a pH of 6.0 over 8 h, after which time betacyanin efflux slowed down or stopped. The tissue was able to buffer the solutions sufficiently to prevent further efflux. When tissue discs were immersed in a series of citrate buffer ranging from pH 3 to 6.2, efflux occurred at pH 3 and slightly at pH 6.2. Efflux was not altered significantly with the addition of glyphosate.

Research was conducted on the leachability and dissipation of sodium azide applied to soil as a solution or as granules with various coatings. The sodium azide leached readily from all formulations, leaving sections of the soil profile with insufficient concentrations to stimulate germination of dormant wild oat (Avena fatua L.) seed. Sodium azide-impregnated clay granules coated with 5% (w/w) polyethylene glycol increased germination of wild oat seed two-fold over uncoated granules at a rate of 5.6 kg sodium azide/ha in field experiments. The polyethylene glycol coating reduced the rate of sodium azide dissipation from the soil in growth chamber experiments. Formulation of sodium azide has potential for increasing wild oat germination stimulation under field conditions.

Detached leaves of Drummond's goldenweed [Isocoma drummondii (T. & G.) Greene] absorbed the potassium salt of 2,4-D [(2,4-dichlorophenoxy)acetic acid] from aqueous solutions more slowly than did sunflower (Helianthus annuus L.), and both species absorbed less of the potassium salt of picloram (4-amino-3,5,6-trichloropicolinic acid) than 2,4-D. However, there was no difference in absorption of the herbicides by Drummond's goldenweed leaves after 6 h of exposure to solutions containing 0.5% (v/v) surfactant. Attached Drummond's goldenweed leaves absorbed about 50% of available 2,4-D (diethylamine) and 25% of available picloram (potassium salt) within 5 days after spraying in the field during July or November. Herbicide accumulation in Drummond's goldenweed taproots after spray applications was generally slow, regardless of season, but translocation to taproots was substantially greater after application in November than after treatment in March or July. Accumulation of picloram in taproots was faster and more extensive than accumulation of 2,4-D. However, based on mortality at 6 months after treatment, both herbicides were translocated in quantities adequate for control. The greater effectiveness of picloram, despite its low foliar uptake, than 2,4-D is attributed to its greater mobility and root uptake in Drummond's goldenweed after broadcast sprays.

Fall panicum (Panicum dichotomiflorum Michx.) seed were found to be dormant at harvest. This dormancy was overcome by an after-ripening period of 17 to 22 weeks, alternating germination temperatures (10 C for 16 h and 30 C for 8 h), stratification, and mechanical or chemical scarification. Soaking seed in gibberellic acid (GA3) or thiourea for 1 day, or washing seed in running tap water for up to 96 h before seed were placed in a germinator, had no effect on dormancy. In the greenhouse, fall panicum emergence was greatest (82%) when seed were placed on the growth media surface. The maximum number of seedlings (39%) emerged in the field when seed were placed 1.3 cm below the soil surface, although some emerged from as deep as 5.1 cm.

Scanning electron micrographs that depict the surface and internal structure of several starch-encapsulated granular formulations of EPTC (S-ethyl dipropylthiocarbamate) and butylate (S-ethyl diisobutylthiocarbamate) relate well with herbicidal release rates previously reported. Fast-release formulations appear to have a porous surface with little distinctive internal structure. Diffusion would be expected to be more rapid as fewer diffusion barriers are present. Slow-release formulations have a smooth, hard surface with irregular surface pores and a honeycombed internal structure. The slower release characteristics are associated with stronger oxidants used for crosslinking xanthate in the entrapment of herbicides. The scanning electron microscope would be an excellent quality control technique in the preparation of starch-encapsulated herbicides.

We describe a small, light-weight, battery-powered timer that emits an audible signal at 1-s intervals. This audible timer is used to monitor ground speed when applying chemicals to plots, thereby eliminating the need for manual manipulation of a stop watch.

We studied the effectiveness of glyphosate [N-(phosphono-methyl)glycine] for the control of Orobanche spp. in the field when applied to the crop foliage prior to the emergence of the parasite. The best Orobanche control in October-sown carrots (Daucus carota L.) parasitized by Orobanche crenata Forsk. and O. aegyptiaca Pers. and in December-sown broad bean (Vicia faba L.) and peas (Pisum sativum L.) parasitized by O. crenata was obtained by spraying twice, 2 weeks apart, in late January and in February, respectively. Carrot root yield remained unaffected by glyphosate at rates up to 200 g/ha. In heavily infested fields, carrots were irreversibly damaged by early Orobanche parasitism. The highest yields of pods of broad beans occurred after two or three applications of 150 g/ha glyphosate. Peas were seriously damaged by 150 g/ha. Two or three sprays of 50 g/ha glyphosate resulted in the highest green-kernel yield of pea where the soil was not heavily infested. Glyphosate effectively reduced O. cernua Loeffl. emergence in non-irrigated tomatoes (Lycopersicum esculentum Mill.), but was very phytotoxic to the crop. Glyphosate was highly effective in controlling Orobanche spp.; however, marginal selectivity may be sufficient in some crops and not in glyphosate-susceptible ones.

R-25788 (N,N-diallyl-2,2-dichloroacetamide) and H-31866 [N-allyl-N-(3,3-dichloroallyl)dichloroacetamide] were more effective than CDAA (N,N-diallyl-2-chloroacetamide) in preventing yield reductions to corn (Zea mays L. ‘NB-611’) from alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] or metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] in the greenhouse. A CGA-43089 [α-(cyanomethoximino)-benzacetonitrile] seed treatment (1.25 g/kg) was more effective than a R-25788 tank mix in preventing yield reductions to grain sorghum [Sorghum bicolor (L.) Moench ‘G-623 GBR’] from alachlor or metolachlor in the greenhouse. Absorption of 14C-alachlor by sorghum seedlings grown in petri dishes, and absorption, translocation, and metabolism of 14C-metolachlor by sorghum seedlings grown in soil, were not affected by CGA-43089 seed treatment. Forage sorghum [Sorghum bicolor (L.) Moench ‘Rox Orange’] was used to simulate shatter cane [Sorghum bicolor (L.) Moench] in field plots. In the absence of Rox Orange, alachlor and metolachlor reduced sorghum grain yields. This yield reduction was prevented by a CGA-43089 seed treatment, but not by a R-25788 tank mix with herbicides. In plots seeded with 10,000 Rox Orange seed/57 m2, grain yields of sorghum increased as alachlor or metolachlor plus CGA-43089 rates increased. There was no grain yield response to any herbicide treatment in plots seeded with 50,000 Rox Orange seed/57 m2.