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William M. Stall and Thomas A. Bewick

Twelve sweet corn (Zea mays L. var. rugosa Bonaf.) cultivars were tested for response to nicosulfuron at rates of 0, 18, 36, and 72 g a.i./ha. Weight of marketable ears indicated that five cultivars were intolerant to the herbicide. Three of the cultivars that were intolerant contained the shrunken-2 endosperm mutant (sh) and two contained the sugary enhancer endosperm mutant (se). Cultivars that were most tolerant of nicosulfuron contained the sh, gene. Incorporation of terbufos insecticide before planting led to decreased marketable yield when nicosulfuron was applied at 36 g·ha in all cultivars tested. Chlorpyrifos insecticide incorporated before planting did not affect tolerance to nicosulfuron. Neither soil-applied insecticide affected yield when nicosulfuron was not applied. Chemical names used: 2-[[[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]amino]sulfony]-N,N-dimethyl-3-pyridinecarboxamide (nicosulfuron); S-[[(1,1-dimethylethyl)thio]methyl] O,O-diethylphosphorodithioate (terbufos); O,O-diethyl O-(3,5,6-trichloro-2-pyridyl)phosphorothioate (chlorpyrifos).

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Jennifer A. Gargiulo, Russell T. Nagata and Thomas A. Bewick

An-assay was developed to determine the level of resistance to the herbicide glyphosate in trangenic seedlings of lettuce. Results of the seedling assay were correlated to results of a similar assay using callus lines of the identical transgenic plants. Transgenic plants were found to be a 32-fold increase in tolerance to glyphosate when compared to wild type plants. This was similar to the response of these transgenic lines in the callus line assay.

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Eric B. Bish, Thomas A. Bewick and Donn G. Shilling

Laboratory experiments were conducted to evaluate the relationship between leaf area, leaf number, dry weight, and mg extract of Lycopersicon hirsutum (LA 1777) leaf washes and germination or root growth of common purslane (Portulaca oleracea) seeds. Additional experiments were conducted to determine the relationship between L. hirsutum (accessions 1777 and 1625) leaf washes and germination or root growth of common purslane seeds. Activity of separated sesquiterpenes from trichomes were compared to crude leaf washes. Results from the leaf washes of the L. hirsutum accessions (1777 and 1625) indicated that there was no significant difference between hexane leaf washes, methanol leaf washes, or crude leaf extracts when common purslane was used as the assay species. The accession 1777 was greater than 800 x more inhibitory to germination and greater than 300x more inhibitory to root growth of purslane seeds than accession 1625.

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Thomas A. Bewick, Larry K. Binning and Nelson E. Balke

Absorption of “C-labeled glyphosate by whole carrot (Daucus carota L.) plants infected or not infected by swamp dodder (Cuscuta gronovii Willd ex R & S) increased from 14% 1 day after treatment to 56% 14 days after treatment. Absorption of 14C-labeled glyphosate did not increase from 14 to 45 days after treatment. 14Carbon-labeled glyphosate appeared in the carrot root 1 day after application and its concentration increased with time in both infected and noninfected plants until 14 days after treatment. From 14 to 45 days after treatment, the concentration of 14C-labeled glyphosate in the roots decreased. At 1 day after treatment, dodder tissue contained as much 14C-labeled glyphosate as any physiological sink in the carrot. At 45 days after treatment, dodder tissue contained more 14C-labeled glyphosate than all other physiological sinks, except the petiole of the treated leaf. Swamp dodder stems had absorbed 14C-labeled glyphosate directly from a solution within 1 day after treatment. Chemical name used: N-(phosphonomethyl)glycine (glyphosphate).

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Monica Ozores-Hampton, Thomas A. Bewick, Peter Stoffella, Daniel J. Cantliffe and Thomas A. Obreza

The influence of compost (derived from MSW and biosolids) maturity on seed germination of several weed species was evaluated. A bioassay was developed by extracting 20 g of compost of different maturities with various volumes of water, then measuring germination percentage of ivyleaf morningglory (Ipomoea hederacea) seeds placed on extract-saturated filter paper in a petri dish. A 20 g (dry weight) compost: 50 mL of water generated an extract that produced the widest percentage seed germination variation in response to composts of different maturity. Ivyleaf morningglory, barnyardgrass (Echinochloa crus-galli L.), purslane (Potulaca oleracea L.), and corn (Zea mays L) were selected as plant indicators to determine the compost maturity stage with maximum germination inhibition. Compost 8-week-old decreased percent germination, root growth, and germination index (combines germination rate and root growth), and increased mean days to germination (MDG) of each plant indicator. Immature 8 week-old compost extract effect on MDG and germination percent of 15 weed species was evaluated. Extract from 8-week-old compost inhibited germination in most weed species, except yellow nutsedge (Cyperus esculentus). Compost extracts derided from immature (3-day, 4-, and 8-week-old) compost resulted in delayed and reduced germination percent of important economic weed species.

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Dorm G. Shilling, Joan A. Dusky, Mark A. Mossier and Thomas A. Bewick

Poor emergence of commercially grown lettuce has been observed when planted immediately after the removal of a celery crop. Greenhouse experiments were conducted to evaluate the possible allelopathic effects of celery residue on the emergence and growth of lettuce. The influence of amount and type of celery tissue, growth medium and fertility, incubation time in soil, and amendment of growth medium containing celery residue with activated charcoal was evaluated with respect to the allelopathic potential of celery. Celery root tissue was 1.8 and 1.6 times more toxic to lettuce seedling growth than was celery petiole or lamina tissue, respectively. Lettuce shoot growth was inhibited to a greater extent when grown in sand amended with celery residue rather than either amended vermiculite or potting soil. Incubation of celery root residue in soil for 4 weeks increased phytotoxicity at 1% (v/v) and decreased it at 4% (v/v). Increasing the fertility of pure sand with varying amounts of Hoagland's solution did not reverse the allelopathic effects of celery residue. The addition of activated carbon to the medium increased the growth of lettuce exposed to celery residues. Celery residues possess allelopathic potential to developing lettuce seedlings. Celery tissue type and concentration, soil type, incubation of celery root residue in soil, and addition of activated carbon to the growing medium influenced the magnitude of the observed phytotoxicity.

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Bielinski M. Santos, Joan A. Dusky, William M. Stall, Donn G. Shilling and Thomas A. Bewick

The effects of different populations densities of smooth pigweed and common purslane were determined in field trials conducted in organic soils. `South Bay' lettuce was planted in twin rows on 90-cm planting beds. Weed densities used were 0, 2, 4, 8, and 16 weeds per 6 m of row (5.4 m2). Phosphorus (P) was applied broadcast (1200 kg P/ha) and banded 2 inches below each lettuce row (600 kg P/ha). Lettuce fresh weights were collected 8 weeks after emergence. Data collected indicated that P regime and density had significant effects on lettuce yield and quality. For both weeds, yield decreased as density increased. In all cases, lettuce showed greater yields at a given density when grown with P banded than when P was applied broadcast. Critical density for smooth pigweed for P broadcast was between 2 and 4 plants per 5.4 m2, whereas this critical density occurred between 8 and 16 plants per 5.4 m2 when P was banded. Yield reductions of up to 24.4% and 20.1% occurred at the highest smooth pigweed density for broadcast and banded P, respectively. Two common purslane plants per 5.4 m2 were enough to reduce lettuce yields. Banding P helped lettuce to produce significantly more within each common purslane density. Yield reductions of 47.8% and 44.3% occurred at the highest common purslane density for broadcast and banded P, respectively. Apparently, banding P gives an additional advantage to the crop against smooth pigweed and common purslane.

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Bielinski M. Santos, Joan A. Dusky, William M. Stall, Donn G. Shilling and Thomas A. Bewick

The effects of different smooth pigweed and common purslane removal times and two phosphorus (P) fertility regimes were studied under field conditions. Head lettuce (cv. South Bay) in organic soils low in P fertility. Smooth pigweed and common purslane were grown at a density of 16 plants per 6 m of row (5.4 m2) and five removal times (0, 2, 4, 6, and 8 weeks) after lettuce emergence. Phosphorus (P) was applied broadcast (1200 kg P/ha) and banded 2 inches below each lettuce row (600 kg P/ha). Lettuce fresh weights were collected 8 weeks after emergence. When smooth pigweed was removed after 4 weeks, significant reductions (–17%) were observed for P banding. However, these reductions occurred after 2 weeks if P was broadcast. No significant differences were observed if removal was imposed later for P broadcast, whereas lettuce yields gradually decreased as removal time was delayed. These findings indicate that P banding can counteract the negative impact of smooth pigweed on lettuce and may allow farmers to delay weed control (if necessary) for another 2 weeks without significant yield reductions. Common purslane interference did not cause significant lettuce yield reductions as compared to the weed-free control for 6 weeks when P was banded, whereas this was true for P broadcast up to 4 weeks. Phosphorus fertility regime significantly influenced the period of weed interference of common purslane with lettuce, reducing its impact when P was banded.

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Thomas A. Bewick, William M. Stall, Stephen R. Kostewicz and Kenneth Smith

Cupric hydroxide, copper ammonium carbonate, basic copper sulfate, mancozeb, and a combination of cupric hydroxide and mancozeb were applied to American black nightshade (Solanum americanum Mill) before treatment with paraquat at 0.6 kg a.i./ha. Paraquat efficacy was reduced by all fungicides/bactericides, except a flowable formulation of basic copper sulfate, when compared to the herbicide only control. Compared to a surfactant only control, efficacy 1 week after paraquat application ranged from 86% with paraquat only to 42% with a combination of mancozeb and cupric hydroxide. Mancozeb and mancozeb in combination with cupric hydroxide resulted in greater shoot dry weight than the paraquat only control when measured 2 weeks after herbicide application. Chemical names used: 1,1'-dimethyl-4-4'-bipyridinium ion (paraquat); Mn, Zn ethylene bis diethyldithiocarbamate (mancozeb).

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Ernest R. Terry Jr., William M. Stall, Donn G. Shilling, Thomas A. Bewick and Steven R. Kostewicz

Studies were conducted to determine the critical period of smooth amaranth interference in watermelon (Citrullus lunatus L.) and muskmelon (Cucumis melo L. var. reticulatus). Best-fit linear or exponential regression models were used to predict the maximum period of competition and the minimum weed-free period for 10% yield loss. The maximum period of competition and minimum weed-free period was 0.50 and 2.97 weeks after watermelon emergence, respectively, and 1.0 and 3.9 weeks after muskmelon emergence, respectively. The critical periods of smooth amaranth interference for the crops were between those intervals. In both crops, late emerging smooth amaranth had little effect on total yield. Smooth amaranth introduced at crop emergence reduced total yield. The effect of competition on yield components, i.e., fruit number per hectare and fruit mass, varied by crop. Muskmelon fruit count was more sensitive to smooth amaranth competition than was watermelon fruit count. Conversely, mass per fruit of muskmelon was less sensitive to this competition than was mass per fruit of watermelon.