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Carrie E. Green and David R. Hershey

Fundamental research on mineral nutrition of azalea has been restricted due to the lack of a model experimental system for growing azaleas in solution culture. The need to maintain a clean root system dictates that azalea cuttings be rooted in solution. A propagation system (HortScience 24:706) was used to root 10-cm long terminal shoot cuttings of azalea `Delaware Valley White' under intermittent mist in a greenhouse. Cutting bases were dipped in 8,000 mg/liter K-IBA for 40 seconds before rooting. Rooting percentages after 7 weeks were 6, 10, and 50% for rooting solutions of tap water, modified 20% Hoagland solution, and 2mM CaCl2, respectively. After an additional 5 weeks the rooting percentage had increased to 83% in the 2 mM CaCl2 treatment. Three other azalea cultivars were found to root much slower than `Delaware Valley White'. Acclimatization of rooted cuttings to the normal greenhouse environment is essential to prevent leaf necrosis and is accomplished by gradually reducing the misting frequency prior to removal from under intermittent mist.

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Carrie E. Green and David R. Hershey

Fundamental research on mineral nutrition of azalea has been restricted due to the lack of a model experimental system for growing azaleas in solution culture. The need to maintain a clean root system dictates that azalea cuttings be rooted in solution. A propagation system (HortScience 24:706) was used to root 10-cm long terminal shoot cuttings of azalea `Delaware Valley White' under intermittent mist in a greenhouse. Cutting bases were dipped in 8,000 mg/liter K-IBA for 40 seconds before rooting. Rooting percentages after 7 weeks were 6, 10, and 50% for rooting solutions of tap water, modified 20% Hoagland solution, and 2mM CaCl2, respectively. After an additional 5 weeks the rooting percentage had increased to 83% in the 2 mM CaCl2 treatment. Three other azalea cultivars were found to root much slower than `Delaware Valley White'. Acclimatization of rooted cuttings to the normal greenhouse environment is essential to prevent leaf necrosis and is accomplished by gradually reducing the misting frequency prior to removal from under intermittent mist.

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Lori A. Black, Terril A. Nell, and James E. Barrett

Dormant-budded `Gloria' azaleas (Rhododendron sp.) at various maturity levels (one, eight, or 32 individual open flowers) were moved from the greenhouse to postproduction rooms. Postproduction rooms were maintained at 21 ± 1C, relative humidity 50% ± 5%, and 12 hours of daily irradiance at 12 μmol·s–1·m–2 from cool-white fluorescent lamps to simulate home conditions. Using predetermined categories, the number of tight, showing-color, candle, and open-flower inflorescences were recorded. After 2 weeks postproduction, plants chosen at the start of postproduction with eight or 32 individual open flowers had the best flowering uniformity and flower color. In a second experiment, azaleas with one, eight, or 32 individual open flowers were placed into simulated transport for 4 days at 16 ± 1C. Plants with one individual open flower had greatest longevity, but those with eight open flowers had the best overall postproduction performance. In a final experiment, azaleas at similar maturity levels were placed in simulated transport at 5, 16, or 27C for 2, 4, or 6 days. After 2 weeks postprodudion, there was no difference due to simulated-transport temperature or duration on flowering performance or flower color. Longevity was good for plants held 2, 4, or 6 days at 5C and for plants held for 2 days at 16 or 27C.

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R.C. Beeson Jr.

Elaeagnus pungens Thunb., Ligustrum japonicum Thunb., Photinia ×fraseri `Red Top', and Rhododendron sp. `Fashion' (azalea) growing in 10.4-liter containers were irrigated only at dawn with overhead impact sprinklers or pulse-irrigated three or four times each day with a drip system. Plant water potential was measured diurnally each week for 24 weeks, and growth was measured at the end of the growing season in December. Overhead irrigation resulted in less growth of all species than plants maintained near 100% container moisture with pulse irrigation. With the exception of photinia, more growth was associated with significantly lower daily accumulated water stress. Water stress of overhead-irrigated plants was generally not severe enough to cause stomata1 closure.

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Yuefang Wang, S. Kristine Braman, Carol D. Robacker, Joyce G. Latimer, and Karl E. Espelie

Epicuticular lipids were extracted from the foliage of six deciduous and one evergreen azalea genotypes (Rhododendron sp.) and identified by gas chromatography-mass spectrometry. The relationship of leaf-surface lipid composition with measures of resistance to azalea lace bug, Stephanitis pyrioides Scott, was evaluated. Each genotype had a distinct epicuticular lipid composition. The major surface lipid components from all test taxa were n-alkanes and triterpenoids. In the most resistant genotypes [R. canescens Michaux and R. periclymenoides (Michaux) Shinners] ursolic acid, n-hentriacontane, and n-nonacosane were the most abundant epicuticular lipids. The lipids present in largest proportion among all susceptible deciduous genotypes tested were α-amyrin, β-amyrin, and n-nonacosane. The proportions of the lipid components from the same plant of each genotype varied between spring and fall samples. Among classes of lipids, n-alkanes, n-1-alkanols, and triterpenoids had significant correlations with azalea lace bug behavior on host plants. Among individual components, heptadecanoic acid, n-hentriacontane, oleanolic acid, ursolic acid and one unknown compound (with major mass spectra 73/179/192/284/311) were significantly negatively correlated with host plant susceptibility to azalea lace bug, as measured by oviposition, leaf area damaged, egg and nymphal development, and nymphal survivorship. Triacontanol, α-amyrin, β-amyrin, and three unknowns were significantly positively correlated with host plant susceptibility. Acceptance or rejection by azalea lace bug to a particular plant may be mediated by a balance of positively and negatively interpreted sensory signals evoked by plant chemicals. This study indicated that the high levels of resistance observed in R. canescens and R. periclymenoides may be due to the lesser amount or the absence of attractants and stimulants for feeding or oviposition.

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R.C. Beeson Jr. and G.W. Knox

Volume of water captured in a container as a function of sprinkler type, spacing, plant type, and container size was measured for marketable-sized plants. Percent water captured was calculated and a model to predict this value derived. Percent water captured was inversely related to the leaf area contained in the cylinder over the container when containers were separated, and with total plant leaf area at a pot-to-pot spacing. This relationship was independent of leaf curvature (concave vs. convex). Canopy densities were less related to percent water captured than leaf areas. Irrigation application efficiencies separated by spacing ranged from 37% at a close spacing to 25% at a spacing of 7.6 cm between containers. Container spacing, canopy shedding, and possibly some canopy retention of water later lost by evaporation were determined to be the main factors associated with the low efficiencies. The results suggest that higher irrigation application efficiencies would be maintained only if plants were transplanted to larger containers before reaching maximum canopy size rather than spacing existing containers to achieve more room for canopy growth.

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Tongyin Li, Guihong Bi, Richard L. Harkess, Geoffrey C. Denny, Eugene K. Blythe, and Xiaojie Zhao

.0 lb N/yard 3 resulted in lower shoot dry weight and shoot height of Rhododendron sp. ‘George Tabor’, and 1.5 lb N/yard 3 was recommended for resin-coated controlled-release fertilizer (Nutricote 17N–3.1P–6.7K, 180 d at 77 °F) ( Million et al., 2007

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William M. Womack, Terril A. Nell, and James E. Barrett

Dormant-budded `Prize' azaleas (Rhododendron sp.) were held at 2C, 7C, 13C, or 18C for 1, 2, 4, 6, 8, or 10 weeks then forced in walk-in growth chambers (29C day/24C night). Holding at 2C delayed flowering by 5-7 days over 7C and 13C. Plants held at 2C, 7C, or 13C for at least 4 weeks had approximately 50% buds showing color at marketability (8 open flowers). Plants held at 18C never exceeded 35% buds showing color at marketability. Increase in buds showing color was not apparent for plants were held at 7C, 13C, or 18C for more than 6 weeks; however, holding at 2C resulted in increasing percentages of buds showing color for holding periods longer than 6 weeks. Plants chilled at 13C and 18C showed significant increases in bud abortion after 8 or 10 weeks of cooling with most plants never reaching marketability (8 open flowers). These plants also had an increased proliferation of bypass shoots during cooling and forcing over other treatments.

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Geraldine J. Cashion and Thomas H. Yeager

Multiple branched liners of Rhododendron sp. cv. Duc de Rohan were potted in 3-L containers using a 5 pine bark: 5 Florida peat: 1 sand medium (by volume) amended with Prokote Plus (20N–1.3P–8.3K, 9.2 kg·m–3) and placed on one of five treatment platforms (1.2 × 2.4 m) in a commercial nursery in Manatee County, Fla. Treatments were 88 plants per square grid with containers touching (T1), 44 plants per square grid with containers touching (T2), 44 plants per square grid with containers touching in rows and 15 cm between rows (T3), 22 plants per square grid with containers touching (T4), and 22 plants per square grid with 15 cm between containers in rows and 15 cm between rows (T5). Irrigation was applied by overhead impact nozzles (0.13 cm/0.5 h) before collecting runoff. Runoff volume was measured and ppm nitrate N determined on day 6, 23, 38, 63, 92, 161, 189, 217, and 274. Average nitrate N ranged from 97 ppm for T1 to 10 ppm for T5 and corresponded to volumes of 19 and 20 L, respectively. Volumes were not different due to spacing or number of containers; however, nitrate N increased linearly with container number when containers were touching (T1, T2, and T4). Nitrate N in runoff was similar for the same number of containers regardless of spacing.

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Robert G. Linderman and E. Anne Davis

Phytophthora ramorum, while thought to be primarily an aboveground pathogen, can be introduced into soilless potting media in the nursery industry as sporangia or chlamydospores and remain undetected while disseminated geographically. Inoculum of this pathogen, both North American (A-2 mating type) and European (A-1 mating type) isolates, was used to infest potting media components or soil, using either sporangia, chlamydospores produced in vermiculite culture, or dry infected `Nova Zembla' rhododendron (Rhododendron sp.) leaf pieces. Vermiculite chlamydospore/oospore inoculum of P. citricola, P. cactorum, and P. citrophthora were included for comparison. Survival was determined monthly by leaf disc baiting or direct plating on selective medium. Results indicated that P. ramorum survived in most media components or soil for up to 6 months when introduced as sporangia, or up to 12 months as chlamydospores. However, it was not detected at all from infected rhododendron leaf pieces by either detection method. These results show that P. ramorum can survive in potting media if introduced as sporangia or chlamydospores, and accordingly the pathogen could be disseminated geographically without being detected visually.