Because soil-residual PRE herbicides reduce and delay annual weed emergence and decrease later weed growth, susceptible weeds surviving or recovering from herbicide treatment reduce crop yields less than do untreated weeds. Recently, corn yields were shown to be reduced differently by untreated weeds emerging in and between crop rows. However, equations have not been reported before that relate corn yield to in-row and between-row weed cover of mixed weed populations recovering from PRE soil-residual herbicides. Published data from PRE herbicide screening research for 3 site-yr in Missouri were reanalyzed to characterize this relation. In-row and between-row weed cover of mixed weed populations, chiefly giant foxtail and common waterhemp, were measured from photographs at midsummer. In 2 of 3 site-yr and with the 3 site-yr average, corn yields were a nonlinear function of both in-row and between-row weed cover recovering from various PRE soil-residual herbicide treatments. In 1 of 3 site-yr, corn yields were a nonlinear function of only between-row total weed cover. Subdividing weed cover into in-row and between-row subpopulations in equations accounted for more data variability in yield estimates than including either subpopulation alone. For all 3 site-yr after PRE herbicide treatment, corn yields were a nonlinear function of only between-row visually rated total weed control. Visual evaluation was less sensitive than photographic weed cover for measuring the contribution of in-row weeds to corn yield loss and characterizing the functional form of the equations.

Field and greenhouse studies were conducted in 2002 and 2003 to evaluate mechanically stimulated compensatory growth response of ivyleaf morningglory, common waterhemp, and giant ragweed. Compensatory growth was initiated by the physical removal of the apical shoot to break apical dominance. The amount of apical shoot removed had an effect on mechanically stimulated compensatory growth of common waterhemp and giant ragweed. With these species, the more of the apical shoot removed from the plant, the less compensatory growth occurred. Removal of the shoot from above the cotyledons resulted in giant ragweed that were 48% shorter and weighed 41% less than control plants at 6 wk after shoot removal. However, the amount of apical shoot removed had no effect on the growth of ivyleaf morningglory compared with control plants at the completion of the study. The influence of plant height at the time of shoot removal on compensatory growth was specific to each weed species. Ivyleaf morningglory exhibited less compensatory growth when the plants were 10 cm at the time of shoot removal compared with 20-, 30-, and 40-cm-tall plants. Removal of the shoot when common waterhemp plants were 30 or 40 cm in height reduced plant weight by 23 and 21%, respectively, compared with control plants. However, no reductions in plant weight were observed when common waterhemp were 10 or 20 cm tall at the time of shoot removal. Giant ragweed subjected to shoot removal was smaller in most growth parameters than control plants, regardless of plant height at the time of shoot removal.

Renewed interest in volatility of hormone-like compounds has occurred since government restrictions were placed on the sale of certain esters used for herbicidal purposes. After crop plants neighboring on fields sprayed with volatile herbicides were injured, attempts were made to find low volatile esters which could be used with greater safety. This was done by making long chain esters containing five or more carbon atoms. Since many of these are now being made, the problem is to find satisfactory test methods for determining the relative volatility as compared with known compounds and standard formulations.

The fate of the C14 label in ethyl N,N-di-n-propylthiolcarbamate (EPTC) was studied following root uptake by alfalfa plants for periods of 2 and 5 days. The uptake and movement of the C14 label in alfalfa was demonstrated by means of autoradiography and measurements of radioactivity with a Geiger-Müller detector. The amount of radioactivity accumulating in plants during the 5-day uptake period was approximately twice the amount accumulating in 2 days. The autoradiographs of plants receiving the 5-day uptake treatment showed an accumulation of C14 in the youngest tissue. Radioactive CO2 was liberated by the treated plants and their extracts contained a large number of C14 labeled compounds.

Preemergence herbicides were applied to lawn turf on a loam soil in April, 1963. Polychlorodicyclopentadiene isomers, N-2-mercaptoethyl)benzenesulfonamide (bensulide), calcium arsenate, 1,2,4,5,6,7,8,8a-octachloro-4,7-methano-3a,4,7,7a-tetrahydroindane (chlordane), dimethyl 2,3,5,6-tetrachloroterephthalate (DCPA) 0-(2, 4-dichlorophenyl)-0-methyl isopropylphosphoramidothioate (DMPA) and 2,6-di-tert-butyl-p-tolyl-methylcarbamate (terbutol) were included. Soil of the respective plots were sampled from 0 to 2- and 2 to 4-in depths in December. These soils samples were used for planting plugs of mature Merion Kentucky bluegrass. The cultures were grown for 18 days in the greenhouse. Twenty-three in of rain had fallen between the treatment and sampling dates. Yet root growth was seriously reduced in the soil from the 0 to 2-in depth that had received terbutol and bensulide. Several chemicals gave significant reductions in topgrowth. Preemergence herbicide residues had sufficient influence on Kentucky bluegrass type lawn turf to justify specific study of each chemical with regard to this factor before widespread use.

Doveweed is a summer annual that is difficult to control in turfgrass. Photosystem II inhibitors have the potential to control doveweed, but research is limited on the efficacy of these herbicides. The objectives of this research were to evaluate (1) the differential tolerance levels of doveweed to atrazine and simazine, (2) the influence of application placement and rate on herbicide efficacy, and (3) uptake and metabolism of these herbicides in doveweed. In greenhouse experiments, the time required to injure doveweed 50% was three to five times faster for atrazine than simazine. Simazine soil or foliar + soil application reduced doveweed biomass 77% from the nontreated, but foliar-only treatments reduced biomass 51%. Application placements for atrazine equally reduced shoot biomass 96% from the nontreated. In a dose–response experiment, atrazine and simazine required ≤ 1.8 kg ha−1 and ≥ 5.1 kg ha−1 to injure doveweed 50% from 8 to 16 d after treatment (DAT), respectively. Doveweed required 79% less atrazine to reduce biomass 50% from the nontreated compared with simazine. In laboratory experiments, doveweed had similar root absorption levels of 14C-atrazine and 14C-simazine. Metabolism of both herbicides linearly increased from 1 to 7 DAT, but parent herbicide levels averaged 39 and 25% of the extracted radioactivity from 14C-atrazine and 14C-simazine, respectively. Doveweed metabolized 14C-simazine to three major metabolites, including hydroxysimazine, that each ranged from 24 to 29% of the extracted radioactivity. Hydroxyatrazine was the only major metabolite (> 10% of total 14C extracted) of 14C-atrazine. Overall, doveweed has slower metabolism of atrazine compared with simazine and is the basis for differential tolerance levels to these herbicides.

Palmer amaranth is a highly invasive weed species causing huge economic losses in agricultural cropping systems under a broad range of environmental conditions. Sensitivity of this species to ozone (O3) air pollution and to soil water deficit, relative to native species or competing crops, may affect its competitiveness and invasive potential. In recent years, both high tropospheric O3 and soil water deficiency have become common in the San Joaquin Valley of California. Responses to these environmental parameters may help predict the invasiveness of this species and have implications for landscape hydrology. We assessed the impact of O3 and soil water deficit on Palmer amaranth. Five- to seven-leaf–stage potted plants were placed in continuous stirred tank reactor chambers and maintained for 30 to 35 d under 12-h mean daylight O3 exposures (0700–1900 hours) of 4, 59, or 114 ppb O3. Within the chambers the plants were either well-watered (WW) or exposed to regulated deficit irrigation (RDI) and grown for about 7 wk. Dry weights of the leaves, stems, roots, and leaf area were determined. Day- and nighttime stomatal conductances (gs) were measured at 1.5-h intervals. Nocturnal gs was about 16 to 29% of daytime gs; this suggests that the species could have substantial nighttime water loss, uncoupled from carbon gain in the weed, and could affect water availability for crops and reduce irrigation efficiency. Nocturnal gs was lower in the RDI than in the WW, but daytime gs was not affected by O3 or irrigation regime. Neither O3 nor irrigation regime affected root or shoot parameters. As O3 and drought are two key stressors in the San Joaquin Valley, to which potential competing species have been found to be sensitive, Palmer amaranth may proliferate and become more invasive in the future, potentially altering landscape hydrology and reducing irrigation efficiency.

Biennial wormwood has become an important weed problem in the northern Great Plains, but little is known about its biology. Biennial wormwood seeds were collected from Fargo, ND, and Fergus Falls, MN, for field experiments in 1999 and 2000 to determine the influence of transplanting date on growth, biomass, and seed production. Seeds were seeded in a greenhouse every 2 wk, and seedling rosettes were transplanted to the field 2 wk after emergence from April 30 until September 15 to simulate season-long emergence. Weekly destructive subsampling started 2 wk after transplanting and ended on September 29 in both years. All seedlings that grew for at least 5 wk after transplanting produced flowers by mid- to late August of the same year. Late-transplanted seedlings with less than 5 wk of growth did not flower or survive the winter. Biennial wormwood biomass allocation patterns resemble those of an annual species, with about 15% of the total dry weight allocated to roots, 20% to stems, 25% to leaves, and 40% to flowers. Transplant date had a substantial influence on biomass partitioning. Seedlings transplanted early in the growing season produced more biomass and seed than late-season transplants. Biennial wormwood seedlings transplanted on April 30 produced over 435,000 seeds per plant, whereas seedlings transplanted on August 15 produced 500 to 3,000 seeds. Biennial wormwood was photoperiod sensitive and flowered when the day length was about 14 h or less, between August 18 and 25, in both years.

The glandular trichomes on velvetleaf (Abutilon theophrasti Medic. # ABUTH) stems and petioles exude liquid globules which are phytotoxic in petri plate bioassays. Because the exudate is easily removed with water, it was hypothesized that it may be washed from velvetleaf stems and petioles into the surrounding soil environment where it may exert allelopathic influences. Field and greenhouse studies attempted to separate the influence of exudates from other mechanisms of interference by removing exudates from some velvetleaf plants and not from others. Velvetleaf trichome exudates did not increase interference by velvetleaf in either field or greenhouse studies. A velvetleaf accession from Rosemount, MN, produced 1.4 times more exudate/stem dry weight than another accession from Stoneville, MS. However, the MS exudate was about 1.4 times more toxic in petri plate assays when compared to the MN exudate. Although greenhouse-grown plants had approximately 3.3 times more exudate/stem dry weight than field-grown plants, the field exudate was 1.6 times more toxic. The activity of velvetleaf exudates was also assayed in autoclaved and nonautoclaved soil. Although active in autoclaved soil, extract activity was lost at all but the highest dosage when the soil was not autoclaved. Microorganisms appear to rapidly detoxify the velvetleaf toxin(s) and may reduce or eliminate its impact in the field.

Weed germination studies often quantify only radicle emergence to indicate germinated seeds. Four categories were used to investigate root and shoot emergence from germinating seeds including: root (seeds with radicles emerged); shoot (seeds with plumules or cotyledons emerged); complete (both roots and plumules emerged); and total (any emergence: roots, shoots, or both). Medusahead and yellow starthistle germination tests illustrated that emergence was equal in the root and total categories. Shoot and complete categories had identical counts, but those counts were often different from the total and root categories. Emergence of medusahead shoots at 8 C was 3 d later than roots, but at 18 C roots and shoots emerged nearly simultaneously. Yellow starthistle roots were not affected by picloram, but emergence of cotyledons (shoot category) was reduced by 80 %. Yellow starthistle seeds stored for 74 and 90 mo produced more radicles than cotyledons after 28 d at 28 C. Medusahead and yellow starthistle root emergence in the laboratory sometimes exceeded seedling emergence from a greenhouse soil mixture. The presence of both roots and shoots (complete category) was the most accurate criterion for documenting yellow starthistle and medusahead seed response to laboratory test conditions.

Laboratory and field experiments were conducted to determine the effects of light, temperature, oxygen, and seed burial depth on seed germination and seed production of Eriochloa villosa without the interference of a crop. Eriochloa villosa seed germination did not respond to light, although it is possible that experimental conditions were not appropriate for this response to develop. Seeds germinated above 10 C and below 45 C, with germination above 85% occurring for temperatures between 20 and 40 C. Seed germination rate and total germination increased as the oxygen concentration increased to the ambient level. Eriochloa villosa seed emerged from 15 cm deep, with maximum emergence from 1 to 4 cm. In the field, emergence was dependent on tillage that affected the vertical distribution of seeds in the soil. Seeds emerged in the reduced-tillage field from between 0.5 and 9 cm deep in soil, with maximum emergence from 2 cm. A delay in planting greatly reduced the growth and seed production of E. villosa. Seed production under noncompetitive conditions was reduced by at least 75% when planting was delayed 6 to 8 wk. However, plants that emerged after July 7 still produced approximately 3,000 seeds when grown under conditions without intraspecific and interspecific competition.

Applications of a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) at 1/2 and 1 lb/A and ethyl N,N-dipropylthiocarbamate (EPTC) at 1 1\2 and 3 lb/A were incorporated preplant with five different tillage implements to determine the influence of incorporation on weed control effectiveness in safflower (Carthamus tinctorius L.). Weed yields were lowest in plots incorporated with the tandem disc and rotary incorporator. Oats (Avena sativa L.) were overseeded 1 year later on the entire safflower plot area. Stand loss occurred on plots receiving the high rate of both herbicides and incorporated with the disc or rotary incorporator.

Growth chamber studies showed crabgrass [Digitaria sanguinalis (L.) Scop.] to be more tolerant than witchgrass (Panicum capillare L.) to simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] and atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine]. Both grasses were more susceptible to simazine than to atrazine. The s-triazines were taken up by both weed species in equal quantities, but witchgrass translocated larger amounts of simazine and atrazine to the shoots. The greater sensitivity of witchgrass to simazine appeared to be due to the increased translocation of unchanged simazine to the shoots. Greater sensitivity of witchgrass to atrazine was attributed to increased translocation of atrazine to the shoots and less metabolism of the s-triazine to hydrophilic metabolites. It was concluded that the hydrophilic metabolites were the peptide conjugates formed by the enzyme glutathione-S-transferase.

Effects of 16 herbicides representing 14 herbicide classes on growth and extractable phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) were examined in light- and dark-grown soybean [Glycine max (L.) Merr. ‘Hill’] seedlings. High purity (96 to 100%) herbicides were supplied via aqueous culture at various concentrations: 0.5 mM amitrole (3-amino-s-triazole), 0.1 mM atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], 0.07 mM diclofop-methyl {methyl ester of 2-[4-(2,4-dichlorophenoxy)phenoxy] propanoicacid}, 0.5 mM DSMA (disodium methanearsonate), 0.2 mM fenuron (1,1-dimethyl-3-phenylurea), 0.05 mM fluridone {1-methyl-3-phenyl-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone}, 0.5 mM MH (1,2-dihydro-3,6-pyridazinedione), 0.5 mM metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one], 1.8 μM nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline], 0.5 mM norflurazon [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone], 0.05 mM paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), 0.15 mM perfluidone {1,1,1-trifluoro-N-[2-methyl-4-(phenylsulfonyl)phenyl] methanesulfonamide}, 0.2 mM propanil (3′,4′-dichloropropionanilide), 0.1 mM propham (isopropyl carbanilate), 0.5 mM TCA (trichloroacetic acid), and 0.05 mM 2,4-D [(2,4-dichlorophenoxy)acetic acid]. Dark-grown soybean seedlings (3-day-old) were transferred to control solutions (2 mM CaSO4) or to herbicide solutions (in 2 mM CaSO4) and grown at 25 C in continuous white light (200 μE•m-2•s-1) or continuous darkness until harvested 24 or 48 h after transfer. After 48 h, growth (fresh weight, dry weight, elongation) was inhibited by most of the chemicals. Other signs of toxicity (necrosis, secondary root stunting, and root tip swelling) were noted for some treatments. Roots were most affected, although hypocotyls were generally not changed. Hypocotyl elongation was stimulated by atrazine, fluridone, and norflurazon after 48 h light. Extractable PAL activity from soybean axes was decreased by atrazine, fenuron, metribuzin, norflurazon, propanil, propham, and 2,4-D. Amitrole and paraquat were the only herbicides that increased extractable PAL activity. Other compounds tested had no effect on the enzyme. None of the herbicides significantly affected in vitro PAL activity.

A mixture of microorganisms cultured under nonsterile conditions on propham (isopropyl carbanilate) herbicide as the sole carbon source was tested for its ability to degrade a number of chlorinated and nonchlorinated anilide compounds. In separate tests under pure-culture conditions, species of the microbial mixture reacted individually in a manner similar to the nonsterile whole. The microorganisms grew and respired rapidly on nonchlorinated anilides, but ring chlorination depressed respiration and inhibited growth. Studies on the dimethylphenylureas indicated that the two methyl groups were primarily responsible for the biological stability of these compounds. All other anilides were degraded by hydrolysis of the side chain followed by metabolic degradation of the ring. Appearance of aniline in the medium depended on the relative rates of production by side chain hydrolysis and disappearance by ring degradation. Acylanilides were hydrolyzed more rapidly than carbanilates and chlorinated rings were degraded much more slowly than unchlorinated rings. Chlorination affected rates of ring degradation and microbial respiration in the following order (most rapid to least rapid): 0 > 2,4 > 2,4,5 > 3 > 4 ≥ 3,4. It is proposed that this unexpected degradative sequence might be explained in terms of the degree of microbial toxicity in the system generated by the formation of chloroazobenzenes from chloroaniline intermediates.

Tank-mixed combinations of pyridate and 2,4-DB were synergistic with respect to sicklepod control and independent with respect to Florida beggarweed control and peanut tolerance in greenhouse studies. Leaf absorption of 14C-pyridate was generally enhanced by the addition of 2,4-DB. Translocation of 14C-pyridate out of the treated leaf did exceed 21% of the amount absorbed across all species, and 14C-pyridate was not affected by the addition of 2,4-DB. Sensitivity of peanut, Florida beggarweed, and sicklepod to pyridate was independent of both adsorption and translocation. Metabolic detoxification of pyridate into a benign metabolite was highest in the tolerant peanut, lowest in highly susceptible Florida beggarweed, and intermediate in slightly susceptible sicklepod. Absorption of 14C-2,4-DB by peanut was increased by approximately 10% with the addition of pyridate. No such increase was observed in either Florida beggarweed or sicklepod. Translocation of 14C-2,4-DB out of the treated leaf was not affected by the addition of pyridate in any of the three species evaluated.

Anatomical studies determined the effect of 0.8, 1.7, and 3.4 kg/ha of penoxalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine]; AC-92390 (N-sec-butyl-3-4-dimethyl-2,6-dinitrobenzenamine); oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide); and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) on the cell structure of snap bean (Phaseolus vulgaris L. ‘Tenderette’) and soybean [Glycine max (L.) Merr. ‘Corsoy’]. Cellular abnormalities in the swollen and brittle area of the stem of treated plants included thinnerwalled cells, elongated xylem elements, hypertrophy and hyperplasia of cells, and anomalous rings of vascular tissue in the cortical region. Injury caused by the four herbicides was similar in snap bean and soybean.

The objectives of this study were to determine the inheritance of aryloxyphenoxypropionate (APP) resistance in the wild oat population UM33 and to determine the genetic relationship between resistance in UM33 and another population, UM1, which has a different cross-resistance pattern. Reciprocal crosses were made between UM33 and a susceptible population UM5, and between UM33 and UM1. Initial screenings of F1 and F2 Is populations derived from crosses between UM33 and UM5 were conducted over a range of fenoxaprop-P rates to determine a discriminatory dosage. F2 populations and F2-derived F3 families were then screened at this dosage (1200 g ai ha−1) to determine segregation patterns. Results from reciprocal UM33 x UM5 F1 dose-response experiments, and F2 and F2-derived F3 segregation experiments indicated that UM33 resistance to fenoxaprop-P was governed by a single, partially dominant nuclear gene system. To determine if resistance in UM1 and UM33 results from alterations at the same gene locus, 584 F2 plants derived from reciprocal UM33 x UM1 crosses were screened with 150 g ha−1 fenoxaprop-P. This dosage was sufficient to kill susceptible plants (UM5), but was not sufficient to kill plants with a resistance allele from either parent. None of the treated F2 plants exhibited injury or death, indicating that UM1 and UM33 resistance genes did not segregate independently. From this it was concluded that resistance in both populations is encoded at the same gene locus.

The effects of prometryn [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine], diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], fluometuron [1,1-dimethyl-3-(a,a,a-trifluoro-m-tolyl)urea], and MSMA (monosodium methanearsonate) on Chlorella pyrenoidosa Chick ‘Strain 252′, Trichoderma viride Pers. ex Fr., and Aspergillus terreus Thom were investigated. Minimum herbicide concentrations necessary to decrease C. pyrenoidosa growth after exposure for 35 generations were 10-8M diuron, 10-7M prometryn, and 10-6M fluometuron. MSMA had no effect. C. pyrenoidosa photosynthesis was essentially stopped by a 2-hr exposure to 5 × 10-6M prometryn or diuron and by 5 × 10-5M fluometuron. Prometryn (5 × 10-5M) or diuron (5 × 10-7M) increased respiration by 70 and 44%, respectively after an 80-min treatment. Maximum fluometuron inhibition of respiration was ca 25% and MSMA had little or no effect. Herbicide concentrations of 0, 10-6, 10-5, and 10-4M were used to measure their effects on colony diameter growth, gain in mycelial dry weight, sporulation, and respiration of the two fungi. No concentration of any of the herbicides had any major effect on any of these parameters except sporulation. T. viride sporulation was increased approximately 20, 30, 35, and 50% by 10-6M concentrations of prometryn, diuron, fluometuron, and MSMA, respectively. Sporulation of A. terreus was also somewhat increased by these herbicides.

Studies were conducted to determine the effect of in-row eastern black nightshade establishment and removal timings in plasticulture tomato on tomato yield loss and nightshade berry production and seed viability. Eastern black nightshade was transplanted at 1, 2, 3, 4, 5, 6, and 12 wk after tomato planting (WAP) and remained until tomato harvest, or was established at tomato planting and removed at 2, 3, 4, 5, 6, 8, and 12 WAP to determine the critical weed-free periods. Eastern black nightshade seed viability increased with berry size and with length of establishment or removal time. The critical weed-free period to avoid viable nightshade seed production was 3–6 WAP. Tomato yield decreased with early weed establishment or with delayed time of weed removal. The critical weed-free period to avoid greater than 20% tomato yield loss for the sum weight of extra large and jumbo grades was 28 to 50 d after tomato transplanting.