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Richard McAvoy and Bernard Bible

Bract edge burn (BEB) starts as a necrosis on veins near the margins of mature bracts. Typically, BEB first appears at anthesis and symptoms progress over time. In 1993, the incidence of BEB on plants sprayed with sodium silicate (Na2SiO3)—490 ppm Si at weekly intervals during bract development—was compared to unsprayed controls using the cultivar Supjibi. BEB appeared soon after anthesis on unsprayed plants, and, by 309 days post-anthesis, 11.5% of the bracts on unsprayed plants had BEB, but only 0.4% of the bracts on Na2SiO3-treated plants had symptoms. Calcium levels in bract margins were similar (0.194% in both treatments. In 1994, the following spray treatments were applied weekly from 31 Oct. to 5 Dec. (initial anthesis) to the cultivars Supjibi and V-17 Angelika White: CaCl2 (400 ppm Ca), Na2SiO3 (50, 100, 150, or 200 ppm Si), DI H2O (sprayed control), or unsprayed control. Both cultivars developed similar BEB symptoms and responded similarly to all treatments. One week post-anthesis, 5.7% of the bracts on unsprayed plants (averaged for both cultivars) developed BEB and 2.5% of the bracts on sprayed controls developed BEB, but only 0.19% of the bracts on CaCl2- or Na2SiO3-treated plants developed BEB symptoms. By 5 weeks post-anthesis, the incidence of BEB was similar for plants sprayed with CaCl2 and Na2SiO3 at 100, 150, or 200 ppm (1.1%, 6%, 6.7%, and 5.7%, respectively); but higher on sprayed controls (22%), and still higher on unsprayed plants (28.5%).

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Richard J. McAvoy

Lilium longiflorum Thunb. cv. Ace grown without plant growth regulators and plants drenched with 0.5 mg a.i. ancymidol per pot following shoot emergence were compared to plants growing in a medium containing uniconazole-impregnated amendments. Uniconazole was applied at rates of 0.18, 0.018, and 0.0018 mg a.i. per pot using either impregnated rockwool (RW) or copolymer acrylamide acrylate (CA). Two other treatment groups received a uniconazole drench at potting (0.018 or 0.0018 mg a.i. per pot). Impregnated CA resulted in undesirably short lilies (i.e., plants <1.5 times the height of the pot) when 0.18 mg uniconazole per pot was incorporated into the medium; effective height control was obtained with CA at 0.018 mg/pot; no height control was observed at 0.0018 mg/pot. Similarly, final height of lilies grown in medium containing uniconazole-impregnated RW decreased as the rate of uniconazole increased. Pre-emergence potting medium drenches with uniconazole (0.018 and 0.0018 mg a.i. per pot) did not significantly affect lily growth and flowering. Ancymidol drench was less effective at retarding stem length and plant height than medium incorporation of 0.18 mg uniconazole. Flowering was not significantly affected by any treatment. Chemical names used: a-cyclopropyl-a-(4-methoxy-phenyl)-5-pyriimidine methanol(ancymidol);B-[(4-cyclophenyl)methyl]-a-(1,1-dimethylethyl)1 H-1,2,4-triazole-1-ethanol(paclobutrazol);(E)-(p-chloro-phenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-1-penten-3-ol(uniconazole).

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Richard J. McAvoy

Poinsettias, Euphorbia pulcherrima Willd. cvs Lilo and Diva Starlight, were exposed to either warm day-cool night or cool day-warm night greenhouse temperature regimes. Day time temperatures were imposed between 900 to 1600 HR. Within each temperature regime, poinsettias were grown single stem or pinched and drenched with either 0.04 or 0.08 mg a.i. uniconazole per 1.6 1 pot or grown as untreated controls. Light levels (PAR) and potting medium and plant canopy temperatures were continuously monitored.

Over the course of the study, the day-night temperature differential (DIF), in the plant canopy, averaged 4.2C in the warm day regime and -1.4C in the cool day regime. The average daily temperature was lower (16.9C) in the warm day regime than in the cool day regime (18.7C).

DIF treatment significantly affected final leaf area, leaf and total plant dry weight, leaf area ratio and specific leaf weight, The DIF treatment by cultivar interaction was significant for final poinsettia leaf area, stem, leaf and total plant dry weight, break number and average break length. Uniconazole significantly affected final plant height, stem and total plant dry weight, break number, average break length and specific leaf weight. Uniconazole by DIF treatment effects were not significant,

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Richard J. McAvoy

Root-zone and plant canopy temperatures were continuously monitored as a poinsettia (Euphorbia pulcherrima Willd. ex JSI.) crop was grown in the greenhouse under warm day/cool night [(+) DT-NT] or cool day/warm night [(-) DT-NT] temperature regimes. Day temperatures were imposed from 0900 to 1700 hr. Light levels photosynthetic photon flux (PPF) and outside ambient air temperatures were also monitored. Temperature differences between the root-zone and plant canopy microenvironments were most extreme during the night-to-day and day-to-night temperature transition periods. The temperature difference between the plant canopy and the root zone following temperature transition periods had been previously identified as a critical factor affecting stem elongation. Overall poinsettia height was consistently shorter under the (-) DT-NT than under the (+) DT-NT environment.

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Richard McAvoy and Bernard Bible

One factor in the development of poinsettia (Euphorbia pulcherrima Willd. ex Klotzch) bract necrosis is plant nutrition. Twenty poinsettia cultivars were grown as 15-cm single-pinched plants in Metro mix 510 with standard commercial practices for irrigating, fertilizing, and pest control. Seventy days after initial anthesis, plants were harvested and the number of necrotic and healthy bracts recorded. Mineral nutrients in bract margins were determined. The only nutrient that had a significant relationship to incidence of bract necrosis across the 20 cultivars was bract B content (R 2=49.5%, P< 0.001). This suggests that cultivars with lower bract B content are more susceptible to bract necrosis. Using `Supjibi' plants grown in the Metro mix 510, we applied topical sprays of B (0, 4, or 8 mm) weekly during bract development or once at initial anthesis (8 mm). Also a weekly drench treatment of B (10 mm) was applied initially at bract color change and continued for 2 more weeks. By 42 days after initial anthesis, all B treatments averaged together reduced incidence of bract necrosis from 33.1% for controls to 10% for plant receiving B treatment. The B drench treatment resulted in leaf scorching and there was some leaf tipburn with the 4 and 8 mm B weekly sprays. The single spray (8 mm B) treatment at initial anthesis caused no injury. Although B sprays are not a replacement for Ca sprays as a control for bract necrosis, the results suggest a role for B in the etiology of bract necrosis.

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Bernard Bible and Richard McAvoy

Poinsettia (Euphorbia pulcherrima Willd. ex Klotzch) bracts are susceptible to postharvest disorders like the pathogen Botrytis cinerea and the abiotic disorder bract necrosis that degrade plant appearance. `Freedom Red' and `Supjibi' poinsettias were grown hydroponically with Ca concentrations of 0.5 or 4 mm. Forty days after initial anthesis, plants were harvested and their bracts subdivided into true-bracts and transitional-bracts for determination of incidence of botrytis lesions and bract necrosis. Mineral nutrients in bract margins were determined only for true-bracts. Margin Ca concentrations were relatively high in true bracts only for `Supjibi' plants exposed to 4 mm Ca solutions. Botrytis incidence was increased for transitional-bracts but not true-bracts for both cultivars by plant exposure to low (0.5 mm) Ca solutions compared to control (4 mm Ca) plants. The smaller the poinsettia roots relative to shoots, the higher the incidence of botrytis for `Freedom Red' transitional-bracts and `Supjibi' true-bracts. Botrytis incidence was higher on transitional-bracts (13%) than on true-bracts (3.5%) for both cultivars exposed to low Ca, whereas the incidence of bract necrosis on `Supjibi' was the same on true-bracts and transitional-bracts in either Ca solution. Bract necrosis was not evident on `Freedom Red' plants in either the 0.5 or 4-mmmm Ca solutions, however for `Supjibi' exposure to low Ca solutions increased incidence of bract necrosis from 5.5% for controls to 19.3%. The effect of Ca stress applied to poinsettia roots was genotype dependant for bract necrosis but not for botrytis.

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Bernard Bible and Richard McAvoy

Incidences of poinsettia (Euphorbia pulcherrima Willd. ex Klotzch) bract disorders like the pathogen Botrytis cinerea and the abiotic disorder bract necrosis are related to nutrient stress. `Supjibi' poinsettias were grown hydroponically with four Ca-B combinations of 0 or 4 mm Ca added with either 5 or 120 μmol B added. Forty-one days after initial anthesis, plants were harvested and their bracts subdivided into true-bracts and transitional-bracts for determination of incidence of botrytis lesions and bract necrosis. Mineral nutrients in bract margins were determined for leaves, transitional-bracts and true-bracts. Leaf margins had the highest concentrations of Ca and B. Margins of transitional-bracts had substantially lower concentrations and margins of true-bracts the least. The low Ca (0 mm) or low B (5 μmol) treatments greatly reduced the concentrations of these elements, respectively, in all three tissue types. The low Ca-low B treatment increased the incidence of bract necrosis on true-bracts from 1.9% on controls (4 mm Ca, 120 μmol B) to 27%. Low Ca treatment increased bract necrosis on transitional-bracts from 1.6% on controls to 24.3%. Bract necrosis incidence was the same on true-bracts and transitional-bracts, whereas the incidence of botrytis was higher on transitional-bracts than on true-bracts. Botrytis incidence was increased for true-bracts and transitional-bracts by plant exposure to low Ca solutions compared to plants in 4 mm Ca. Low Ca reduced growth in roots, but not shoots. Ca and B stress to roots increased the incidence of bract necrosis on true-bracts, while only Ca stress increased incidence of botrytis.

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Richard McAvoy and Bernard Bible

Bract necrosis (BN) in poinsettia is thought to be caused by a localized calcium deficiency in the margins of bracts. Both calcium and silicate sprays can suppress the post-anthesis development of BN if applied repeatedly during bract development. However, studies conducted in 1993 and 1994, with BN-susceptible scions (`Supjibi') grafted onto either `Supjibi' rootstock or the BN-resistant `Annette Hegg Dark Red' (AHDR) rootstock, failed to support the calcium hypothesis. In these studies, higher calcium concentrations were found in the margins of `Supjibi' bracts on `Supjibi' rootstock, then in `Supjibi' bracts on `AHDR' rootstock, even thought the incidence of BN was highest on plants with `Supjibi' rootstock. These studies suggested that non-nutritional factors (possibly hormonal factors) may play a role in BN. In 1995, `Supjibi' plants were produced in the greenhouse, and at initial anthesis, were sprayed once with either deionized (DI) water, benzyladenine (BA) (100 ppm), or daminozide (2000 ppm). At initial anthesis, plants in all treatment groups showed a low level of BN (0.75% of bracts with symptoms). Four weeks after initial anthesis, 18.5% of bracts on DI water sprayed plants and 38.7% of bracts on daminozide treated plants had developed BN; but BA treated plants developed BN on only 1% of bracts. At final harvest (38 days after treatments were applied), BN was evident on 3.4% of BA-treated bracts, 28.7% of DI-treated bracts, and 46.3% of daminozide-sprayed bracts.

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Richard McAvoy and Bernard Bible

Bract necrosis (BN) first appears at anthesis, and symptoms become more numerous and severe with time. Previously, we reported that 3.6 mm sodium silicate (Na2SiO3) sprays, applied during bract development, were as effective as 10 mm CaCl2 sprays at suppressing BN on `Supjibi' and `Angelika White', but only for several weeks after initial anthesis. While applying Na2SiO3 during bract development dramatically suppressed BN (7.2% of bracts with BN 46 days after anthesis vs. 33.4% for untreated plants), applying Na2SiO3 after anthesis is ineffective (35.7% BN). In 1995, suppression of BN was evaluated on `Supjibi' plants sprayed with similar concentrations (2 or 4 mm) of Na2SiO3 and CaCl2; treatments were compared to unsprayed poinsettias, or plants sprayed with either deionized (DI) water, 4 mm SrCl2, 4 mm NaCl, 4 mm MgCl2, or a solution of Na2SiO3 plus CaCl2 (1 or 2 mm each). At harvest (38 days after initial anthesis), 40.6% of the bracts on unsprayed plants and 35.8% of the bracts on DI water sprayed plants had BN. In contrasts, only 5.3% of the bracts on the 4 mm CaCl2 treated plants and 5.9% of the bracts on 4 mm Na2SiO3 treated plants had BN. Plants sprayed with 4 mm SrCl2 or the combination of 2 mm Na2SiO3 plus 2 mm CaCl2 developed BN on 7.8% and 9.2% of bracts, respectively. NaCl and MgCl2 sprays (4 mm) were not as effective (29.6 and 26.4% BN) as Ca, Si, or Sr sprays at suppressing BN over the duration of this study.

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Richard J. McAvoy

`Rose Grenadine' and `Buckaroo' garden chrysanthemums [Dendranthema ×grandiflorum (Ramat.) Kitamura] were produced in 15-cm pots in the greenhouse and fertilized with either 550 or 1000 ml of a 15 mol·m-3 N solution at each irrigation. The nutrient solution applied to half the pots contained a wetting agent (WA), and the remaining pots received no WA. Core samples were removed at 15-cm increments to a depth of 90 cm from the soil beneath the pots. The average leaching fraction (LF) from pots receiving a WA was 0.29 but was 0.26 from pots receiving no WA. However, WA did not affect the leachate NO3-N concentration or the total NO3-N deposited on the soil beneath; these were most influenced by LF. After week 2, NO3-N concentration in the upper 15 cm soil layer was 3.4 times higher with a high LF than with a low LF (30 and 8.8 g·m-3 respectively). At week 10, the NO3-N concentration in the 30 to 45 cm soil layer averaged 71.9 g·m-3 under the high LF and 35.5 g·m-3 under the low LF. Total N and NO3-N in the potting medium was higher in the low LF pots than the high LF pots, while NO3-N was higher in the medium of pots irrigated without WA than with WA. Final plant shoot mass was higher in pots irrigated to a high LF or without WA than in pots irrigated to a low LF or with WA.