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J.P. Syvertsen and M. Salyani

The effects of three highly refined petroleum spray oils and of ambient vapor pressure on net CO2 assimilation (A) and stomatal conductance of water vapor (gs) of single grapefruit (Citrus paradisi Macf.) leaves were investigated. Overall, gs of various-aged leaves was decreased by a large leaf-to-air vapor pressure difference (VPD). In the first experiment, oils with midpoint distillation temperatures (50% DT) of 224, 235, and 247C were applied with a hand atomizer at concentrations of 0, 1%, and 4% oil emulsions in water and 100% oil, all with 0.82% surfactant (by volume). There was a tendency for oils of the two higher DT to decrease net gas exchange during a subsequent 12 days, but significant differences could not be attributed to oil DT. Both A and gs were reduced by the two higher concentrations of oil mixtures. In the second experiment, a commercial airblast sprayer was used to apply the 224C oil at 4% or the 235C oil at 2% and 4% mixtures plus surfactant under field conditions. There were no significant effects of oil treatments on net gas exchange of leaves either measured under moderate VPD outdoors 1 day after spraying or under low VPD in the laboratory 2 days after spraying. No visible phytotoxic symptoms were observed in either experiment.

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Marc van Iersel

Transplanting can result in root damage, thereby limiting the uptake of water and nutrients by plants. This can slow growth and sometimes cause plant death. Antitranspirants have been used to minimize transplant shock of vegetables. The objective of this research was to determine if antitranspirants are useful to reduce transplant shock of impatiens (Impatiens wallerana Hook.f.) seedlings in the greenhouse. Seedling foliage was dipped in or sprayed with antitranspirant (Vapor Gard or WiltPruf) and shoot dry mass was determined at weekly intervals. Antitranspirants reduced posttransplant growth of impatiens as compared to untreated plants, possibly because of a decrease in stomatal conductance, leading to a decrease in photosynthesis. The two dip treatments also caused phytotoxic effects (necrotic spots) on the leaves. In a second study, leaf water, osmotic and pressure potential were determined at 2, 9, and 16 days after transplant. Application of antitranspirants (as a dip or spray) decreased water and osmotic potential compared to control plants. The results of this study indicate that antitranspirants are not useful for minimizing transplant shock of impatiens under greenhouse conditions.

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Marc W. van Iersel and Bruce Bugbee

Dibutylurea (DBU), a breakdown product of benomyl, may be partially responsible for the previously reported phytotoxicity of the fungicide Benlate DF. We quantified the effect of DBU on the growth of two popular bedding plant species, petunia (Petunia × hybrida) and impatiens (Impatiens wallerana Hook. f.). DBU reduced photosynthesis of both species, and its effect strongly depended on the amount of DBU applied. The effects of DBU were most apparent 2 to 4 days after treatment, at which time 1.20 g·m-2 (corresponding to 10% DBU in Benlate DF at maximum labeled drench rate) inhibited photosynthesis completely. DBU also decreased flower number and caused marginal necrosis. DBU effects were more pronounced in low relative humidity. Benlate DF containing 3.1% DBU and an equivalent amount of reagent grade DBU had similar effects on photosynthesis and petunia necrosis. Our results showed that DBU is responsible for at least part of the phytotoxic symptoms that can be caused by Benlate DF. However, other ingredients or breakdown products may also contribute to the phytotoxic symptoms of Benlate DF.

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D. Casey Sclar, Daniel Gerace, Andrea Tupy, Karen Wilson, S. Aaron Spriggs, R. Jason Bishop, and Whitney S. Cranshaw

Experiments conducted in greenhouse and field environments investigated the acute and chronic phytotoxic effects of several house-hold and commercially available soaps, detergents, and oils applied to tomato (Lycoperiscum esculentum Mill.). In addition, the effect of these treatments on greenhouse whitefly, Trialeurodes vaporarium (Westwood), was investigated. In the greenhouse experiments, the number of whiteflies observed was negatively correlated with phytotoxicity (i.e., higher phytotoxicity = fewer whiteflies). Ivory Clear detergent at two rates of application (0.5% or 2.0%) caused the greatest phytotoxicity to seedling tomato plants. Addition of vegetable oils to a 0.5% Ivory Clear detergent solution did not affect phytotoxicity to the plants. While commercially available insecticidal soap (M-Pede) and a neem seed extract (Margosan-O) had little phytotoxicity, they provided only a slight reduction of whitefly populations. A field experiment conducted in the absence of insect pressure showed phytotoxic effects to tomato plants as a result of continued treatment with New Ivory detergent. Significantly lower yield from this treatment resulted from reduced flower and/or fruit production. None of the other compounds in the field experiment significantly affected the yield of tomato plants.

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Nathaniel A. Mitkowski and Arielle Chaves

phytotoxicity to turfgrasses when applied in high heat, at rates above label, on warm-season grasses, or on annual bluegrass ( Poa annua L.) greens; DMI fungicides also affect the gibberellic acid synthesis pathway in plants ( Bigelow et al., 1995 ; Buchenauer

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Jaime A.Teixeira da Silva

Filter paper types significantly affected the growth, development and differentiation of chrysanthemum and tobacco stem thin cell layers (TCLs) from in vitro plantlets. Three different filter paper types, normally with varied uses in plant biology, showed varying morphogenic-altering and antibiotic-buffering capacities. Advantec #2 and Whatman #1 significantly stimulated root, shoot and callus formation while Whatman #3 inhibited them, as compared to TCLs placed directly on agar. Filter paper buffered the phytotoxic effect of antibiotics kanamycin and cefotaxime, substances commonly used in genetic transformation experiments, up to as much as 50%, independent of species or genotype. In both `Lineker' and `Shuhou-no-chikara' chrysanthemum cultivars, Advantec #2 and Whatman #1 filter papers stimulated embryogenesis but in tobacco all three filter paper types significantly reduced embryogenesis and explant survival.

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Timothy K. Broschat and Kimberly K. Moore

Zonal geraniums (Pelargonium ×hortorum) from seed and african marigolds (Tagetes erecta), which are known to be highly susceptible to Fe toxicity problems, were grown with I, 2, 4, or 6 mm Fe from ferrous sulfate, ferric citrate, FeEDTA, FeDTPA, FeEDDHA, ferric glucoheptonate, or ferrous ammonium sulfate in the subirrigation solution. FeEDTA and FeDTPA were highly toxic to both species, even at the 1 mm rate. Ferrous sulfate and ferrous ammonium sulfate caused no visible toxicity symptoms on marigolds, but did reduce dry weights with increasing Fe concentrations. Both materials were slightly to moderately toxic on zonal geraniums. FeEDDHA was only mildly toxic at the 1 mm concentration on both species, but was moderately toxic at the 2 and 4 mm concentrations. Substrate pH was generally negatively correlated with geranium dry weight and visible phytotoxicity ratings, with the least toxic materials, ferrous sulfate and ferrous ammonium sulfate, resulting in the lowest substrate pHs and the chelates FeEDTA, FeDTPA, and FeEDDHA the highest pH. The ionic Fe sources, ferrous sulfate and ferrous ammonium sulfate, suppressed P uptake in both species, whereas the Fe chelates did not. Fe EDDHA should be considered as an effective and less toxic alternative for the widely used FeEDTA and FeDTPA in the production of these crops.

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T.K. Hartz and C. Giannini

Windrows of municipal yard and landscape waste at three commercial composting sites in California were sampled at ≈3-week intervals through 12 to 15 weeks of composting to observe changes in physiochemical and biological characteristics of importance to horticulture. Initial C, N, P, and K content averaged 30%, 1.3%, 0.20%, and 0.9%, respectively. Carbon concentration declined rapidly through the first 6 to 9 weeks, while N, P, and K remained relatively stable throughout the sampling period. Few viable weed seeds were found in any compost. A high level of phytotoxicity, as measured by a tomato (Lycopersicon esculentum Mill.) seed bioassay, was observed at only one site; overall, the degree of phytotoxicity declined with compost age. Short-term net N immobilization (in a 2-week aerobic incubation) was observed in nearly all samples, with an overall trend toward decreased immobilization with increased compost age. In a 16-week pot study in which fescue (Festuca arundinacea Shreb.) was grown in compost-amended soil, net N mineralization averaged only 2% to 3% of compost total N content. Neither composting site nor duration of composting significantly affected either N mineralization rate or fescue growth. Growth of vinca (Catharanthus roseus Don.) in a blend of 1 compost : 1 perlite increased with increasing compost age. Overall, at least 9 to 12 weeks of composting were required to minimize the undesirable characteristics of immature compost.

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Edward W. Bush, Wayne C. Porter, Dennis P. Shepard, and James N. McCrimmon

Field studies were performed on established carpetgrass (Axonopus affinis Chase) in 1994 and 1995 to evaluate plant growth regulators (PGRs) and application rates. Trinexapac-ethyl (0.48 kg·ha-1) improved turf quality and reduced cumulative vegetative growth (CVG) of unmowed and mowed plots by 38% and 46%, respectively, in 1995, and suppressed seedhead height in unmowed turf by >31% 6 weeks after treatment (WAT) both years. Mefluidide (0.14 and 0.28 kg·ha-1) had little effect on carpetgrass. Sulfometuron resulted in unacceptable phytotoxicity (>20%) 2 WAT in 1994 and 18% phytotoxicity in 1995. In 1995, sulfometuron reduced mowed carpetgrass CVG 21%, seedhead number 47%, seedhead height 36%, clipping yield 24%, and reduced the number of mowings required. It also improved unmowed carpetgrass quality at 6 WAT. Sethoxydim (0.11 kg·ha-1) suppressed seedhead formation by 60% and seedhead height by 20%, and caused moderate phytotoxicity (13%) in 1995. Sethoxydim (0.22 kg·ha-1) was unacceptably phytotoxic (38%) in 1994, but only slightly phytotoxic (7%) in 1995, reduced clipping yields (>24%), and increased quality of mowed carpetgrass both years. Fluazasulfuron (0.027 and 0.054 kg·ha-1) phytotoxicity ratings were unacceptable at 2 WAT in 1994, but not in 1995. Fluazasulfuron (0.054 kg·ha-1) reduced seedhead height by 23% to 26% in both years. Early seedhead formation was suppressed >70% when applied 2 WAT in 1994, and 43% when applied 6 WAT in 1995. The effects of the chemicals varied with mowing treatment and evaluation year. Chemical names used: 4-(cyclopropyl-x-hydroxy-methylene)-3,5 dioxo-cyclohexane-carboxylic acid ethyl ester (trinexapac-ethyl); N-2,4-dimethyl-5-[[(trifluoro-methyl)sulfonyl]amino]phenyl]acetamide] (mefluidide); [methyl 2-[[[[(4,6-dimethyl-2-pyrimidinyl) amino]carbonyl] amino] sulfonyl]benzoate)] (sulfometuron); (2-[1-(ethoxyimino)butyl-5-[(2-ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one) (sethoxydim); 1-(4,6-dimethoxypyrimidin-2yl)-3-[(3-trifluoromethyl-pyridin 2-yl) sulphonyl] urea (fluazasulfuron).

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Thomas M. Kon, James R. Schupp, Keith S. Yoder, Leon D. Combs, and Melanie A. Schupp

combination of damaged floral tissue and reduced photosynthesis due to leaf injury. In some experiments, ATS caused unacceptable leaf phytotoxicity ( Byers, 1997 ; Embree and Foster, 1999 ), which resulted in reduced fruit growth ( Wertheim, 2000