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.

Experiments were initiated to determine the amount of time required for postemergence herbicides to render yellow nutsedge physiologically noncompetitive. The rate of net CO2 assimilation (A N) was chosen as the response variable to describe competitiveness. Specifically, the time required after herbicide treatment for A N to drop to 50% of that of the untreated control (A N50) was determined. A N50 values for halosulfuron, imazapic, glyphosate, and MSMA were 1.6, 2.1, 3.2, and 3.3 d, respectively. An A N50 value was not calculated for bentazon because A N rapidly decreased below 50% but recovered to > 50% by 9 d after treatment (DAT). Stomatal conductance to water vapor (g s) declined similarly with A N over time for halosulfuron, imazapic, and glyphosate treatments. However, g s of MSMA-treated plants was near 95% of the untreated control, whereas A N declined to 35% 11 DAT. At 11 DAT, all aboveground biomass was removed, and plants were returned to the greenhouse, and regrowth was determined after an additional 14 d. Yellow nutsedge regrowth for halosulfuron, imazapic, glyphosate, and MSMA was below 5% of the untreated control and was not statistically different. However, regrowth from bentazon was 44% of the control. Therefore, bentazon was the least effective herbicide tested, whereas halosulfuron and imazapic were most effective for yellow nutsedge control.

Growth and competition of barnyardgrass [Echinochloa crus-galli (L.) Beauv. ♯ ECHCG] and redroot pigweed (Amaranthus retroflexus L. ♯ AMARE) were studied at different seed proportions, seed burial depths, and soil moisture levels. After 7 days, emergence from 1-, 2-, 4-, and 8-cm depths was 96, 90, 83, and 27% for barnyardgrass and 84, 73, 62, and 0% for redroot pigweed, respectively. Barnyardgrass was more competitive than redroot pigweed. Intraspecific competition of barnyardgrass was greater than interspecific competition from redroot pigweed. Increasing planting depth from 1 to 4 cm and increasing soil moisture from 30 to 50% (low) to 100% (high) of field capacity reduced the competitive ability of redroot pigweed.

Single and repeat applications of herbicides or herbicide combinations were made over-the-top of young cotton (Gossypium hirsutum L.). DMSA (disodium methanearsonate) and MSMA (monodosium methanearsonate) applied 4 or 8 weeks after emergence had less effect on cotton yield, boll components, and fiber properties than did applications made 12 weeks after emergence. Most single, over-the-top applications of DSMA, fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea], or DSMA with fluometuron 4 weeks after emergence did not affect cotton yield, boll components, or fiber properties. One or two applications of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] or prometryn [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine] alone, or with DSMA, reduced cotton yields. Applications of 1.1 and 2.2 kg/ha of fluometuron over-the-top of cotton 2 to 8 weeks after emergence did not affect cotton yields, boll components, or fiber properties.

Tomato and pepper differ in their whole-plant tolerance to sulfonylurea (SU) herbicides rimsulfuron and halosulfuron despite both being members of the Solanaceae family. This study examined whether tomato's tolerance to SU herbicides rimsulfuron and halosulfuron was due to insensitivity of the target enzyme acetolactate synthase (ALS). Rimsulfuron and halosulfuron inhibited ALS from both tomato and pepper leaves. Enzyme inhibition and kinetic analyses showed that extractable ALS from tomato was more sensitive to rimsulfuron and halosulfuron than ALS from pepper. ALS from both species were inhibited with a mixed inhibition pattern. Thus, results indicate that enzyme insensitivity is not the reason why tomato is more tolerant than pepper to these herbicides. Tomato tolerance to rimsulfuron at the whole-plant level was reduced in the presence of terbufos, a known inhibitor of cytochrome P450 enzymes. Rimsulfuron applied at 0.018 and 0.035 kg ha−1 with 1.1 kg ha−1 of terbufos reduced tomato shoot weight 69 and 66%, respectively, compared with a 4 and 29% reduction when rimsulfuron was applied alone. The reduction of tomato tolerance to rimsulfuron by terbufos suggests that the sensitivity differences between these species may reflect their differences in SU herbicide metabolism.

Effects of sub-acute levels of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) on bluegill sunfish (Lepomis macrochirus Rafinesque) were assessed in a pond environment. Eight 0.1-A earthen ponds were each stocked with 300 bluegill fingerlings and treated once with diuron wettable powder at 0, 0.5, 1.5, and 3.0 ppmw, two ponds per treatment level. Dissolved oxygen was reduced severely in some pond waters 2 days following treatment and the low level persisted for 3 to 4 days. Gill lamellae were ruptured and hemorrhagic in 20% of the fish from the 3.0 ppmw ponds at 3 days post-treatment. Fish in a cage succumbed during this period in a 3.0 ppmw pond. No further bluegill mortality was observed in treated ponds 3 days after treatment. Hematocrit measurements of treated and control fish could not be correlated with treatment level. Best growth was exhibited by control fish and their progeny. Diuron residues were not detectable in treated pond waters after 28 days. Residues of diuron in treated-pond vegetation were detectable up to 95 days following treatment, whereas residues in mud were measured by gas chromatography 122 days after treatment. Invertebrate populations increased in all ponds with time, indicating little or no effect of the herbicide on their numbers. Good control of filamentous algae and vascular aquatic vegetation was demonstrated in the treated ponds.

In laboratory experiments, the effects of the herbicides HOE-39866 [ammonium (3-amino-3-carboxypropyl)-methylphosphinate] and SC-0224 (trimethylsulfonium carboxymethylaminomethylphosphonate) on the incorporation of NaH14CO3, [14C]-leucine, [14C]-uracil, and [14C]-acetate into enzymatically isolated soybean [Glycine max (L.) Merr. ‘Essex’] cells were evaluated to assess the activity of these herbicides on CO2 fixation, protein, ribonucleic acid (RNA), and lipid syntheses. At low concentrations neither compound exhibited rapid or distinct inhibitions of any process as might be expected in the case of inhibition of a primary target site. Photosynthesis was the process least affected. At equimolar concentrations, protein and RNA syntheses were more sensitive to HOE-39866 than to SC-0224 while the reverse occurred in lipid synthesis. Protein synthesis appears to be a possible target site that may be involved in the herbicidal action of these two compounds.

Absorption and translocation of 14C-dicamba (3,6-dichloro-o-anisic acid) in seven salt formulations were determined 60 h after application to leaves of soybean [Glycine max (L.) Merr. ‘Williams’] grown in nutrient solution. The dimethylamine (DMA) formulation was consistently absorbed and retained in the plant in amounts equal to or greater (46% of recovered 14C) than other formulations (which averaged 19% of recovered 14C) when applied without surfactant. Absorption and subsequent retention of the DMA formulation in the plant was least affected of all formulations by the addition of a surfactant. With a surfactant, absorption of the DMA, monoethanolamine (MEA), and inorganic salt formulations was similar (>75% of recovered 14C). Addition of seven surfactants to the K-salt of dicamba increased both the amount of 14C absorbed by 35 to 56% and the amount recovered in the plant. All surfactants except one enhanced absorption of the K-salt of dicamba to a similar degree. Dicamba exhibited predominantly symplastic translocation with the majority of 14C being recovered in the new second trifoliolate leaves and nutrient solution. As much as 66% of the radioactivity absorbed through the leaves was exuded by roots into the nutrient solution 60 h after leaf treatment.