Burley tobacco (Nicotiana tabacum L. ‘Kentucky 14′) was grown as a no-tillage crop in 1974 and 1975 by planting tobacco directly into an existing stand of orchardgrass (Dactylis glomerata L.) or rye (Secale cereale L.). Paraquat (1,1′-dimethyl-4,4′bipyridium ion) and glyphosate [N-(phosphonomethyl)glycine] were used to kill existing vegetation. Benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine), oryzalin (3,5-dinitro-N4,N4-dipropylsulfaniiamide), metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)one], and chlorbromuron [3-(4-bromo-3-chlorophenyl), 1-methoxy-1-methylurea] were used to control annual grasses and broadleaf weeds.

Glyphosate was generally more effective than paraquat in killing existing vegetation. There was some injury to the tobacco associated with the glyphosate and paraquat treatments, but this was generally confined to those plants which came into contact with the treated herbage. Metribuzin caused severe damage to the tobacco and was discontinued after the first year. Chlorbromuron caused little injury if kept on the surface but injured the tobacco if incorporated by cultivation as in conventional tillage. Benefin and oryzalin caused little or no injury to the tobacco. All four herbicides gave adequate control of annual grasses and broadleaf weeds.

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.

Most herbicides are applied preemergence onto bare soil or during the early stage of plant development. Therefore, the major part of the active ingredient either reaches the soil surface immediately or later with decaying plant material. The further fate of the herbicide depends largely on the physicochemical behavior of the respective compound, the amount and method of application, and a number of soil, plant, and climatic factors influencing the persistence and bio availability of organic compounds in a given soil (5, 7). Especially in the upper 2-cm soil layer, drastic changes in temperature and moisture content during a growing season have a great influence on the degradation and adsorption of herbicides in soil (10, 31).

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.

Directed applications of low rates of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), disodium methanearsonate (DSMA), monosodium methanearsonate (MSMA), 1,1′-dimethyl-4,4′-bipyridinium salts (paraquat), and 2,4-bis(isopropylamino)-6-(methylthio)-s-triazine (prometryne) controlled annual weeds in irrigated cotton (Gossypium hirsutum L.). Although the first applications of most herbicides caused temporary, localized foliage chlorosis or burning, cotton yields, fiber properties, and boll components were not affected. Early applications of DSMA followed by diuron selectively controlled annual weeds. When a herbicide was applied before planting, fewer postemergence applications were needed for weed control.

Resistance to propanil by a barnyardgrass (BYG) biotype has been reported, and its occurrence is becoming widespread in U.S. rice-producing regions. Interactions between propanil and the herbicides anilofos, molinate, pendimethalin, piperophos, quinclorac, and thiobencarb and the insecticide carbaryl were evaluated in laboratory studies for improved control of propanil-resistant barnyardgrass (R-BYG). Chlorophyll fluorescence measurements of BYG leaf segments were used to ascertain electron transport inhibition and to assess the synergy/antagonism of propanil (100 μM) with the various additives (50 μM). Synergistic effects on photosynthetic inhibition were found with anilofos, carbaryl, pendimethalin, and piperophos in combination with propanil. Such synergistic actions of chemicals with propanil may lead to chemical combinations useful for R-BYG control.

A hammer mill removed most of the lemmas, paleas, and pericarps from cheat florets. Typically, the cuticular layer of the testa was the only remaining intact layer, and damage to the embryos and endosperm was severe. A roller mill disrupted tissue organization of lemmas, paleas, and outer layers of the caryopses primarily at the cuts. Large gaps between the aleurone layer and testa, between testa and pericarp, and between the scutellum and endosperm were created. In the field, germination of mill-damaged florets was reduced, and florets exhibited progressive degradation the longer they were buried. Nematodes and fungi penetrated the cuticular layer of mill-damaged seed. Attaching a hammer mill or a roller mill to a grain combine to treat cheat seed before it is returned to the field could provide a novel method of cheat control.

Demand for organic food products has consistently increased for more than 20 yr. The largest obstacle to organic soybean production in the southeastern United States is weed management. Current organic soybean production relies on mechanical weed control, including multiple postplant rotary hoe uses. Although postplant rotary hoe use is effective at the weed germination stage, its efficacy is severely compromised by delays due to weather. Preplant rotary hoeing is also a practice that has been utilized for weed control but the effectiveness of this practice to reduce the need for multiple postplant rotary hoeing for organic soybean production in the southeastern United States has not been investigated. Preplant rotary hoe treatments included a weekly rotary hoeing 4 wk before planting, 2 wk before planting, and none. Postplant rotary hoe treatments consisted of zero, one, two, three, and four postplant rotary hoe uses. Weed control was increased with preplant rotary hoeing at Plymouth in 2006 and 2007 but this effect disappeared with the first postplant rotary hoeing. Multiple postplant rotary hoe uses decreased soybean plant populations, decreased soybean canopy height, lowered soybean pod position, and decreased soybean yield. Plant mapping revealed that the percentage of total nodes and pods below 30 cm was increased by increased frequency of postplant rotary hoe use.

The chloro-substituted benzoic acid compounds discussed here were included with a number of other chemicals tested in 1955, 1956, and 1957 as soil sterilizing herbicides at Hays, Kansas. The experiments were designed to yield information on the effectiveness of various treatments for field bindweed (Convolvulus arvensis) control. Results of the bindweed control studies have been briefly summarized by Phillips (9).

Studies were conducted to determine whether photosynthesis-inhibiting herbicides atrazine or bifenox, and shade affect the number, weight, senescence, and N fixation activity of nodules on the roots of the perennial legume crownvetch. Atrazine and bifenox were applied at rates of 2.24 kg ai/ha to shaded and unshaded plots. The shade was varied during the growing season to simulate changing irradiance levels beneath a corn canopy. Atrazine and bifenox treatments reduced nodule number to 13 and 42% of the untreated control, respectively, in 1980, and 18 and 35% in 1981. Shade treatments reduced nodule number to a low of 40% of the control in 1980 and 50% in 1981. Combined effects of herbicides and shade on nodule numbers were more than additive. Nodule fresh weights were reduced an average of 37% by herbicide treatments and 39% by shade treatments. Sloughed nodule numbers decreased in the herbicide and shaded treatments, suggesting that the reduction in nodule numbers was due to fewer nodules being produced. Nodule numbers were reduced a greater percentage by herbicides and shade than was herbage dry matter production. Specific nodule activity (SNA) did not differ in nodules from the atrazine, bifenox, or shade treatments on the six sampling dates in 1980 or on two of three sampling dates in 1981.

Norflurazon adsorption and dissipation under field and laboratory conditions, and distribution within the soil profile were determined in three soils representative of cotton-growing regions of the southeastern U.S. Norflurazon adsorption was greater in soil from 0 to 8 cm in a Lexington silt loam (Tennessee) and a Beulah silt loam (Mississippi) than in a Dothan loamy sand (Georgia). Adsorption was directly related to organic matter. Norflurazon degradation under controlled conditions in soil from 0 to 8 cm from each state was not different among locations, with half-lives ranging from 63 to 167 d. Degradation at 30 C in soil from the 30- to 45- and 60- to 90-cm depths was not different among locations, and was slower at the 60- to 90-cm depth than in surface soil. Norflurazon dissipation was more rapid under field conditions than under laboratory conditions, with half-lives ranging from 7 to 79 d in the 0- to 8-cm soil horizon. Dry field conditions slowed norflurazon dissipation. Norflurazon was not detected below 15 cm in the profile in any soil, and concentrations in the 8- to 15-cm soil zone were < 36 ppbw 112 d after treatment.

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.

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.

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.

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.