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Tanja Mucha-Pelzer, Reinhard Bauer, Ekkehard Scobel, and Christian Ulrichs

. Naturally occurring silicas [e.g., diatomaceous earth (DE)] have already been verified for their insecticidal properties in the field of stored product protection by numerous authors ( Athanassiou et al., 2003 ; Dowdy, 1999 ; Ebeling, 1971 ; Fields and

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Jonathan M. Frantz*, Dharmalingam S. Pitchay, James C. Locke, and Charles Krause

Silica (Si) is not considered to be an essential plant nutrient because without it, most plants can be grown from seed to seed without its presence. However, many investigations have shown a positive growth effect if Si is present, including increased dry weight, increased yield, enhanced pollination, and most commonly, increased disease resistance, which leads to its official designation as a beneficial nutrient. Surprisingly, some effects, such as reduced incidence of micronutrient toxicity, appear to occur even if Si is not taken up in appreciable amounts. The literature results must be interpreted with care, however, because many of the benefits can be obtained with the counterion of the Si supplied to the plant. Determining a potential benefit from Si could be a large benefit to greenhouse plant producers because more production is using soilless media that are devoid of Si. Therefore, Si must be supplied either as a foliar spray or nutrient solution amendment. We investigated adding Si to New Guinea Impatiens (Impatiens hawkeri Bull), marigold (Tagetes erecta), pansy (Viola wittrockiana), spreading petunia (Petunia hybridia), geranium (Pelargonium spp.), and orchid (Phalaenopsis spp.). Using SEM, energy dispersive X-ray analysis, and ICP analysis, Si content and location was determined. This information and other growth characteristics will be used as a first step in determining the likelihood of using Si as a beneficial element in greenhouse fertilizer solutions for higher quality bedding plants with fewer agrochemical inputs.

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Richard J. McAvoy and Bernard B. Bible

Silica sprays (Na2SiO3 or SiO2·nH2O) markedly reduced the incidence and severity of bract necrosis (BN) of Euphorbia pulcherrima Willd. cv. Supjibi Red compared to plants not sprayed with silica. BN has been associated with low Ca concentrations or high K: Ca ratios in tissues of bract margins. Silica had no effect on Ca or K concentrations in bract margin tissues, and BN was not associated with the macro- or micronutrient composition of bract margin tissues. Sixteen days after initial anthesis, nontreated and deionized-water-sprayed poinsettias developed a higher incidence of BN than did plants sprayed with Na2SiO3 or CaCl2. However, sprays of 3.56, 5.34, and 7.12 mm Na2SiO3 were as effective as 9.98 mm CaCl2 sprays in protecting against BN of `Supjibi Red' and `Angelika White' bracts for up to 30 days after initial anthesis. `Supjibi Red' developed a higher incidence of bract necrosis than did `Angelika White', but both cultivars showed a similar response to the treatments and similar symptoms of necrosis. In both cultivars, initial symptoms appeared as small necrotic lesions on bracts at the looped ends of lateral veins that displayed a closed-vein pattern after the plants reached initial anthesis.

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Loong-sheng Chang, Chun-yen Yeh, and Chien-hwa Liao

Race 1 of Plasmodiophora brassica isolated from high altitude of vegetable production district induced clubroot on cabbage, and Chinese cabbage. Inoculation of race from northwestern coast of Taiwan resulted clubroot of Chinese cabbage neither in cabbage. The addition of bark slag or silica slag significantly decreased clubroot infection and increased the weight of Chinese cabbage in the infected field. The addition of 3 gram slaked lime +1 gram KC1 +1.78 gram ammonium sulfate + 1 gram calcium superphosphate at 500 gram soil 2 month after transplanting increased dry wight of cabbage and decreased infection root hair followed by inoculation of race 1.

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Pat Bowen, Jim Menzies, David Ehret, Lacey Samuels, and Anthony D.M. Glass

The effect of root or leaf applications of soluble Si on severity of grape (Vitis vinifera L.) powdery mildew [Uncinula necator (Schwein) Burrill] was determined. On potted plants, root-feeding at 1.7 mm Si had no effect on disease severity, but foliar sprays at 17 mm Si substantially reduced the number of mildew colonies that developed on inoculated leaves. Scanning electron micrographs showed that, on Si-sprayed leaves, hyphae did not develop in areas where thick Si deposits were present on the leaf surface; and where surface deposits were not present, Si was translocated laterally through the leaf and surrounded the appressoria. Leaves on plants that were fed Si via roots showed a similar deposition of Si surrounding the appressoria. On water-sprayed leaves and leaves from untreated plants, internal deposition of Si was more variable and generally less than on Si-sprayed or root-fed plants. Conidia germination and germtube development on agar media were weakly promoted by the presence of Si. Reduced severity of grape mildew by Si sprays may be partly due to a physical barrier to hyphal penetration and to a resistance response involving the lateral movement of Si and its deposition within the leaf at fungal penetration sites.

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Michael R. Evans, Bernard W. Krumpelman, Ramsey Sealy, and Craig S. Rothrock

Vinca (Catharanthus roseus) is a common annual bedding plant species that is susceptible to root and stem rot caused by Phytophthora nicotianae. The experimental design was a 6×2×1 factorial with a total of 12 treatment combinations that had five replications and was repeated twice. Vinca seeds were planted in the middle nine plugs of a 5×5 five-milliliter round plug tray filled with sphagnum peat (control) or peat amended with 2.1 kg/m3 calcitic lime, 5.9 and 7.3 kg/m3 potassium silicate alone and combined with 3.0 kg/m3 calcium sulfate. A peat control drenched with metalaxyl after inoculation was also included. After germination, when the seedlings had one true leaf, half of the treatments were inoculated with 500 cfu of Phytophthora nicotianae per plug cell while the other half remained uninoculated. The percentage of germination for the potassium silicate combined with calcium sulfate (KSCS) (79% and 78%) was similar to the control (86%) and the metalaxyl treatment (83%), whereas the potassium silicate alone had poorer germination (69% and 71%) and plant growth. The percentage of mortality for the KSCS treatment (6% and 14%) was similar to the metalaxyl treatment (9%) but was significantly less than the control (100%). The average dry shoot and root weights for the KSCS treatments (4.4 and 4.9 mg; 2.7 and 2.2 mg) were similar to the metalaxyl treatment (5.0 and 3.6 mg) and the uninoculated control (5.0 and 3.2 mg), but were higher than the potassium silicate treatment alone (2.1 and 1.6 mg; 0.7 and 0.6 mg).

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Richard J. McAvoy, Bernard B. Bible, and Michael R. Evans

The early onset of bract necrosis in poinsettia (Euphorbia pulcherrima Willd. ex. Klotzch) is characterized by small dark-stained spots that precede the development of enlarged necrotic lesions. Electron micrographs of adaxial epidermal and subepidermal tissues with early symptoms of necrosis revealed large, electron-dense deposits in cell vacuoles. These spherical bodies resembled condensed tannins observed in the epidermal tissues of peach and apple fruit. Chemical analysis of bract tissues confirmed the presence of condensed tannins. Furthermore, there were higher concentrations of condensed tannin in bract samples with 2-mm-diameter lesions than in samples with lesions <0.5 mm (equivalent to catechin concentrations of 59 and 13 mg·g-1 fresh mass, respectively). No tannin bodies were observed in parallel samples of healthy-appearing bracts in which only trace concentrations of condensed tannins were measured (0.2 mg·g-1 fresh mass). The evidence suggests an association between condensed tannin accumulation in localized areas of the bract and the early appearance of bract necrosis symptoms.

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Filippo Lulli, Claudia de Bertoldi, Roberto Armeni, Lorenzo Guglielminetti, and Marco Volterrani

canopy morphological parameters, and plant key constituents (mainly lignin and silica). These two common plant tissue compounds are often called upon to explain wear tolerance in both warm-season ( Trenholm et al., 2000 ) and cool-season turfgrass species

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Claudia Calonje, Chad Husby, and Michael Calonje

effort propagating and growing cycads in containers as well as in the ground. Historically, MBC has used a horticultural mix comprised of equal parts organic soil conditioner (Fafard Organic Soil Conditioner; Conrad Fafard, Inc., Agawam, MA), silica

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Bahlebi K. Eiasu, Puffy Soundy, and J. Martin Steyn

Araya et al. (2006) and Motsa et al. (2006) . The pots were filled with either silica sand or sandy clay soil (52:8:38 coarse sand, silt, and clay, respectively). Volumetric water-holding capacity of the silica sand was 9.7% at field capacity and 3