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.

Root colonization by soil microorganisms has been shown to increase the activity of glyphosate in resistant and susceptible biotypes of giant ragweed and a susceptible common lambsquarters biotype, but not in horseweed biotypes. The objective of this study was to investigate the colonization of roots in glyphosate-resistant and -susceptible giant ragweed and horseweed biotypes, and glyphosate-tolerant and -susceptible biotypes of common lambsquarters after a sublethal glyphosate application. The three weed species were grown separately in sterile and unsterile field soil and treated with glyphosate at two sublethal rates. Soil microbes were isolated from the roots onto sterile media 3 d after the glyphosate treatment. The susceptible biotypes of giant ragweed and horseweed grown in unsterile soil were colonized by more soil microbes at the higher rate of glyphosate, compared to the resistant biotype grown in unsterile soil. Oomycetes were isolated separately on a selective media and they were also more prevalent in the roots of the susceptible biotypes of each weed species grown in the unsterile soil when glyphosate was applied at the highest rate. Therefore, the ability of these three weed species to tolerate a glyphosate application may involve differences in the susceptibility to soil microbial colonization, especially oomycetes.

In order to germinate successfully, large crabgrass [Digitaria sanguinalis (L.) Scop.] seeds require a period of after-ripening. Some changes, either physical, biochemical or both, must occur in these seeds during this after-ripening process. This paper reports the differences in the activities of several enzymes between dormant (non-after-ripened) and nondormant (after-ripened) large crabgrass seeds at various periods of hydration. The total protein content of dormant seeds does not change during imbibition but increases greatly in nondormant seeds at 48 and 76 h of hydration. Initially, nondormant seeds exhibit high alpha-amylase activity and low peroxidase and acid phosphatase activities. Alpha-amylase activity remains unchanged relatively in both dormant and nondormant seeds up to 36 h of hydration, but increases greatly in nondormant seeds at 48 and 76 h of hydration. Peroxidase activity, which is initially low in nondormant seeds, increases substantially at 48 and 76 h of soaking. Acid phosphatase activity in dormant seeds does not change following hydration but is gradually elevated in nondormant seeds with duration of soaking. Lipase activity in dormant seeds remains fairly constant upon hydration. In nondormant seeds, however, the activity gradually decreases with duration of soaking, the decrease being 3 to 4 fold at 76 h of imbibition. Except for lipase, there is a positive correlation in the activities of alpha-amylase, peroxidase, and acid phosphatases with the increase of total protein content of nondormant seeds.

Strawberries are an important horticultural crop in Florida. Black medic is among the most problematic weeds within the production system. To better coordinate control measures, black medic growth and development while in competition with strawberry was studied. Twelve plants were randomly selected at each of four field sites in Hillsborough County, FL, in 2014. Plants were repeatedly measured over the growing season for stem length and number of primary branches, flower buds, flowers, and seed clusters. Growing degree days (GDD) were calculated (Tbase=0 C) starting from the hole-punch application of the plastic mulch (October 8, 2014, to October 10, 2014) from weather station data generated from the Florida Automated Weather Network. Strawberry height and width increased consistently across all sites, but black medic growth and development varied considerably. Strawberry suppressed black medic growth up to 1,805 cumulative GDD at three of four sites where black medic remained beneath the strawberry canopy. After 1,805 GDD, the black medic stems still remained below but experienced exponential growth for total stem length and, in turn, flower buds, inflorescence, and immature seed clusters. Ideal clopyralid spray timing based on susceptible plant size was 890 to 1,152 GDD. Optimal hand-weeding time frames would likely occur as the plant stems expand beyond the strawberry canopy (to improve visibility) and before flower production to prevent seed return to the seedbank. First seed production was observed at 1,200 GDD at the earliest site and between 1,966 to 2,365 GDD across all the other sites. Overall, consistent trends were observed across sites, but between-site variability was observed that could not be accounted for by differences in temperature.

This study provides a comparative analysis of the dormancy and germination mechanisms of the indehiscent fruits of hoary cress (Lepidium draba L.) and hairy whitetop (Lepidium appelianum Al-Shehbaz), two invasive weeds of the Brassicaceae. Germination assays comparing isolated seeds (manually removed from the fruits) and intact indehiscent fruits showed that the isolated seeds are nondormant and provided full germination for both species. In contrast to this, the species differed in the germination properties of their indehiscent fruits, in that L. appelianum fruits were nondormant, while the L. draba fruit coat (pericarp) conferred a coat-imposed dormancy. The pericarp of L. draba fresh fruit was water permeable, and neither mechanical scarification nor surface sterilization affected germination, supporting the concept that pericarp-mediated dormancy was not due to water impermeability or mechanical constraint. Washing of L. draba fruits with water, afterripening (dry storage), and treatment with gibberellin (GA) stimulated the germination of this species, all of which are indicative of physiological dormancy. Analyses of endogenous abscisic acid (ABA) and GA levels combined with treatment experiments with wash water from fresh and afterripened L. draba pericarps and with ABA dose–response quantification of germination revealed that ABA is a key component of a pericarp-mediated chemical dormancy in this species. Consistent with this, pericarp ABA levels decreased during afterripening and upon fruit washing, and isolated fresh or afterripened seeds did not differ in their ABA sensitivities. The possible roles of the ABA-mediated pericarp dormancy for the germination ecophysiology and weed management of these species are discussed.

Strip-intercropping of functionally diverse cover crop mixtures including cereal rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth) is one mechanism by which nitrogen (N) banding can be applied to an organic, strip-tilled system to increase crop competitiveness over weeds. We hypothesized that by targeting hairy vetch, a low C:N legume, to the tilled strip directly in row with future crop establishment, and cereal rye, a high C:N grass, to the untilled strip directly between future crop rows, that N would be preferentially available to the crop. We conducted a field study between 2011 to 2013 in southwest Michigan to examine the effects of rye–vetch mixture spatial arrangement (strip intercropping vs. full-width mixture) on (1) soil inorganic N; (2) weed biomass; and (3) sweet corn (Zea mays L.) biomass, yield, and competitiveness against weeds. We found that as the proportion of vetch biomass in the crop row (in-row, IR) increased, we also saw increasing levels of IR soil inorganic N and greater early sweet corn N uptake and growth relative to weeds. However, sweet corn yield and final biomass were more responsive to vetch biomass across the whole plot (WP) and did not respond to rye and vetch segregation into strips. Increasing vetch WP biomass increased sweet corn final biomass across both years, but only increased corn competitiveness against weeds in 1 out of 2 years and decreased sweet corn competitiveness in the other year. Strip-intercropping of cereal rye and hairy vetch has potential to increase soil N availability to the crop, thereby increasing early crop competitiveness, which may lower weed management costs.

Corn was grown in soils containing root residues of giant foxtail (Setaria faberii Herrm.), yellow foxtail (Setaria glauca (L.) Beauv.), and crabgrass (Digitaria sanguinalis (L.) Scop.). The effect of these residues on corn root growth was studied using a new technique which measures root response to soil properties with a single plant. Giant foxtail was the most inhibitory. Implications of these data are discussed in terms of the dominance and competitive ability of giant foxtail.

Lack of seedling vigor is a serious limitation to obtaining adequate stands of birdsfoot trefoil (Lotus corniculatus L.). Slow seedling growth makes establishment difficult because competition from weeds or companion crop plants often eliminates the young legume seedlings soon after they emerge. Gist and Mott found that birdsfoot trefoil grows much more slowly than alfalfa and red clover under identical light intensities. Seedlings not eliminated are greatly reduced in size and are susceptible to injury during the winter.

Sun (2) reported that pith cells in the hypocotyl of soybean (Glycine max (L.) Merr., variety Monroe) became meristematic and vascular strands developed in the pith after treatment with 2,4–dichlorophenoxyacetic acid (2,4–D). Later (3), he found a retardation in elongation of roots from treatment with 2,4–D. The pericycle produced a mass of dense meristematic tissue extending to the periphery of the root. Even non-conducting cells of the primary phloem of roots became meristematic.

Preplanting, soil-incorporated treatments of fenac (2,3,6-trichlorophenylacetic acid sodium salt) at 1, 2, 4, and 8 lb/A, 2,3,6-TBA (2,3,6-trichlorobenzoic acid dimethylamine salt) at 8, 12, and 16 lb/A, and 2,4-D 2,4-dichlorophenoxyacetic acid amine salt) at 12 lb/A applied in 1960 to six soil types infested with witchweed (Striga asiatica (L.) Kuntze) resulted in some control of witchweed as measured by visual observations and corn yield. Two or three additional postemergence applications of 2,4-D at 1 lb/A were required to prevent witchweed seed production for the growing season. Witchweed parasitism on corn was greatly reduced by a preplanting treatment of fenac at 2 lb/A plus 2,4-D as a postemergence treatment.

All rates of 2,3,6-TBA and fenac at 8 lb/A caused moderate to severe corn injury with the most severe injury occurring on soils with relatively high clay content in the subsoil. Soil residual studies and field observations indicated fenac and 2,3,6-TBA may be present in Coastal Plain soils for more than 18 months.

Three cultivars of wild rice (Zizania palustris L.) were grown with various densities of common waterplantain (Alisma triviale Pursh) established from seeds and from rootstocks during 1979 and 1980. Wild rice cultivars did not differ in their response to common waterplantain interference. Common waterplantain grown from seeds at densities up to 82/m2 did not significantly reduce wild rice yield. Common waterplantain established from rootstocks significantly reduced wild rice yield at densities as low as 3/m2. A density of 43/m2 reduced wild rice yield by 91%. The yield component most susceptible to interference from common waterplantain was panicles per plant. The number of seeds per panicle was reduced by densities as low as 11/m2 and seed weight was reduced by densities of 22/m2 or greater. Only a density of 43/m2 reduced the stand of wild rice. Common waterplantain established from rootstocks at a density of 17 plants/m2 did not reduce wild rice yield if removed by 7 weeks after planting. Interference from common waterplantain for 9 weeks or longer reduced wild rice yield by approximately 50%.

The development of 157 tanoak [Lithocarpus densiflorus (Hook. and Am.) Rehd.] and 130 Pacific madrone (Arbutus menziesii Pursh) sprout-clumps 1 to 6 yr after cutting or burning was studied on a range of sites in southwest Oregon. The width and area of sprout-clumps originating from trees ≥ 2-cm stem diameter at 1.4-m height of both species was related to the size of the parent stem and time since cutting (tanoak, r2 = 0.77 and 0.75; Pacific madrone, r2 = 0.84 and 0.83). The sprouting capacity of tanoak develops slowly, and 5 to 6 yr after cutting, sprout-clumps produced by small tanoak 40 to 50 yr old averaged only 37 cm in diameter. Prediction equations, along with stem-diameter distributions of these species in forest stands, can be used to estimate hardwood foliar cover up to 6 yr after cutting.

Benzoylprop ethyl [Ethyl N-benzoyl-N (3,4-dichlorophenyl)-2-amino-propionate] and WL 29761 [methyl-N-benzoyl-N-(3-chloro-4-fluorophenyl)-2-amino-propionate] were applied to wild oat (Avena fatua L.) in wheat (Triticum aestivum L. ‘Manitou’) to study the yield benefits occurring and the efficacy of the compounds on wild oat. Even though removal of the wild oat was at the later growth stages, benzoylprop ethyl and WL 29761 did produce significant yield increases at both rates tested. Efficacy on wild oat ranged from mediocre to virtually complete control. Crop tolerance was satisfactory throughout the study.

Cell suspension cultures of white clover (Trifolium repens L. ‘Regal Ladino’) were treated with 2,4-D [(2,4-dichlorophenoxy)acetic acid], 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid], 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], 2,4,5-TP [2-(2,4,5-trichlorophenoxy) propionic acid], and 2,4,5-TB [4-(2,4,5-trichlorophenoxy)butyric acid]. Cell population densities were monitored throughout the treatment period and herbicide remaining in the cells and culture medium was extracted and quantified at the termination of the treatment. Herbicide tolerance increased in cell populations which were conditioned by pretreatment with 2,4-DB and 2,4,5-T. However, 2,4-DB was rapidly degraded by all cell populations regardless of pretreatment. White clover cell suspension cultures treated with 2,4-D, 2,4-DB, 2,4,5-T, 2,4,5-TP and 2,4,5-TB metabolized the homologs, according to the following sequence: butyric acidåpropionic acidåacetic acid homologs. There was no difference in the rate of degradation of similar homologs of the 2,4-dichloro- and 2,4,5-trichloro- analogs.

Radicle length of barley (Hordeum vulgare L. ‘Larker’) seedlings was greatly reduced by the combination of the herbicide S-ethyl diisobutylthiocarbamate (butylate) applied in combination with the insecticide 2,2-dimethyl-2,3-dihydrobenzofuranyl-7-N-methylcarbamate (carbofuran). Corn (Zea mays L. ‘Michigan 400’) seedlings were not similarly affected. Carbofuran interacted with butylate to reduce synergistically the root and shoot growth of barley but not that of corn. The combination of these two carbamate pesticides synergistically increased respiration in barley. The basis for these interaction effects in barley appeared to be decreased metabolism of butylate and increased respiration in the presence of carbofuran. Although the same metabolism trend was apparent in tolerant corn, the butylate level was much lower since the absorption of butylate was reduced by the carbofuran seed treatment. The 14C from 14C-butylate preferentially accumulated in barley shoots and corn roots.

Leaching of dl-strigol at six rates between 0.3 and 4.5 kg/ha through columns of sandy loam soil was estimated using a witchweed [Striga asiatica (L.) Kuntze # STRLU] germination bioassay. After 21 days of leaching daily with 1.27 cm of simulated rainfall, about 86% of the applied chemical remained in the top 2.5 cm of the soil, about 6% in the zone between 2.5 and 7.5 cm, and less than 1% in the soil at depths between 7.5 and 30 cm. However, even with the lowest rate of the chemical application, sufficient dl-strigol was leached to a soil depth between 22.5 and 30 cm to cause most, if not all, of the witchweed seeds to germinate. These results suggest that dl-strigol has a potential for use as an effective tool for a witchweed control or eradication program. No significant degradation of the chemical occurred in moist soil during the 21-day period.

Retention, absorption, translocation, and metabolism of 2,4-D [(2,4-dichlorophenoxy)acetic acid] by common waterplantain (Alisma triviale Pursh. # ALSPA) at three growth stages were investigated to determine the basis for differential susceptibility of common waterplantain at different growth stages. Plants in the five-leaf and scape elongation stages retained more 2,4-D than plants in the early flowering stage. Absorption of 14C-2,4-D by the flower stalk was less than absorption by the treated leaves regardless of growth stage. The majority of the absorbed 14C translocated out of the treated plant part was recovered in the aerial portion of the plant younger than the treated leaves or in the corm, with greater movement of 14C into the corm at the older growth stages. Metabolism of 14C-2,4-D did not differ among the growth stages. The results suggest that the greater sensitivity of common waterplantain at the scape elongation stage to 2,4-D is due to greater translocation to the corm when compared to the five-leaf stage, and greater retention when compared to the early flowering stage.

Diffusion of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) through Mexico silt loam soil was measured in diffusion cells under laboratory conditions. Radiolabeled herbicide was extracted from each sample and counted by liquid scintillation. Fick's Second Law with a constant diffusion coefficient adequately describes trifluralin diffusion regardless of concentration or diffusing time. Solution diffusion increases directly with bulk densities to 1.1 g/cm3 and then decreases. Vapor diffusion is decreased approximately 50% for every 10% decrease in air-filled porosity. Vapor diffusion contributes the major portion of total diffusion at bulk densities of less than 1.2 g/cm3. For bulk densities between 1.2 and 1.4 g/cm3, the magnitudes of vapor and solution diffusion are similar.

Herbicides used in corn (Zea mays L.), sorghum [Sorghum bicolor (L.) Moench], and soybeans [Glycine max (L.) Merr.] were applied in the spring and their persistence into late summer was determined during 1974 to 1976. Composite soil samples from the top 5 cm of field plots were taken each August and bioassayed in the greenhouse. Bioassay species used were winter wheat [Triticum aestivum L.) and soybeans for herbicides used in corn and sorghum, and winter wheat and white mustard (Brassica hirta Moench) for herbicides used in soybeans. Soil persistence of triazine herbicides caused more injury to winter wheat, soybeans, and white mustard than any other class of herbicides tested. Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] showed the most soil persistence of the five triazines evaluated. At normal field application rates, herbicides other than the triazines showed little injury to the bioassay plants. Soil persistence of herbicides was further reduced when combinations of reduced rates of each herbicide were utilized. Herbicides used for spring applications in corn showed more soil persistence in August than did the herbicides for sorghum, while herbicides for soybeans generally were least persistent. Postemergence herbicide applications resulted in more injury in bioassay species than preplant incorporated or preemergence applications. Persistence of some herbicides will restrict certain options to the grower such as changing crops in case of crop failure, fall planting of winter wheat, double cropping, or certain crop rotations.