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  • Author or Editor: Douglas A. Cox x
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'Annette Hegg Brilliant Diamond' plants were cultured under Mo stress conditions by using an unlimed sphagnum peat and perlite potting medium and by supplying all trace elements but Mo in the fertilizer solution. Plants were untreated or sprayed with solutions of 1, 10, or 100 μg Mo·liter-1 5, 8, or 11 weeks after pinching. Untreated plants developed foliar symptoms of Mo deficiency (interveinal chlorosis, marginal necrosis, and marginal curling) and leaf tissue contained Mo below the critical level of 0.5 μg·g-1 and NO 3 -N above 1.0%. At 5 or 8 weeks all Mo spray concentrations prevented deficiency symptoms, increased tissue Mo, and reduced tissue NO 3 -N. Some symptoms were visible when plants were treated at 11 weeks. Mo sprays at this time did not eliminate the symptoms but reduced the number of leaves showing symptoms to about one-half that of untreated plants when the experiment was ended 15 weeks after pinching.

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Seed geranium (Pelargonium × hortorum, Bailey ‘Jackpot’) was grown in 10-cm pots in a peat-pine bark-perlite medium and fertilized with solutions of (NH4)2SO4 (AS), NH4NO3 (AN), Ca(NO3)2-4H2O (CN), CO(NH2)2 (UR), or Osmocote 14N–6.2P–11.6K (OS). Shoot and root growth and shoot N were greatest with AN and least with AS. Greatest N loss by leaching occurred with AS and CN; leaching loss was less with AN and OS and least with UR. In all treatments form of N in leachate reflected N source applied. Proportion of N not accounted for by analysis (lost as a gas) was greatest with AS and UR.

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Six cultivars of poinsettia (Euphorbia pulcherrima Willd. ex Kl.) were grown in unlimed growth medium consisting of equal volumes of sphagnum peat and perlite. Plants received fertilizer solutions supplying Mo at either 0.0 mg·liter-1 (-Mo) or 1.0 mg·liter -1 (+Mo). In the –Mo treatment, moderate to severe symptoms of Mo deficiency (marginal and interveinal chlorosis, marginal necrosis, and downward curling of the margins) developed on the middle-aged and some recently matured leaves of `Annette Hegg Brilliant Diamond' and `Eckespoint Lilo', while some interveinal chlorosis occurred on the same leaves of `Gutbier V-17 Angelika'. No symptoms appeared on `Gross Supjibi', `Peace Regal Velvet', and `Peace Noel'. All cultivars were symptomless in the + Mo treatment. In the –Mo treatment, upper, recently matured leaves of the symptomatic cultivars and two of three symptomless cultivars had Mo concentrations at or near the critical level for deficiency; however, nitrate reductase enzyme activity was higher and NO3-N was lower in the leaves of symptomless cultivars than of symptomatic cultivars.

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`Annette Hegg Brilliant Diamond' poinsettia (Euphorbia pulcherrima Willd. ex Kl.) was grown in an unlimed growth medium consisting of equal volumes of sphagnum peat and perlite and received a fertilizer solution supplying all micronutrients except Mo. Plants were untreated or foliage was sprayed with solutions of 1, 10, or 100 mg Mo/liter 5, 8, or 11 weeks after pinching. Untreated plants developed foliar symptoms of Mo deficiency (marginal and interveinal chlorosis, marginal necrosis, and downward curling), and leaf tissue contained Mo below the critical level of 0.5 μg·g-1 and NO3-N > 1.0%. Treatment at 5 or 8 weeks largely prevented deficiency symptoms, increased tissue Mo, and reduced tissue NO3-N. Molybdenum deficiency symptoms were in the early stages of development on the day of treatment when plants were sprayed at 11 weeks. Molybdenum sprays at this time increased tissue Mo and reduced tissue NO3-N but did not eliminate the symptoms. However, when the experiment was completed 15 weeks after pinching, the number of leaves showing symptoms was about one-half that of untreated plants. Increasing the concentration of Mo in the spray solution increased the concentration of Mo in the leaves but had no effect on NO3-N.

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Nine cultivars were grown in a 1:1 sphagnum peat and perlite medium with no limestone or trace element fertilizer. Fertilizer solutions of 300 ppm N and K (calcium nitrate and potassium nitrate) and 24 ppm Mg were applied at every watering. Solutions supplied all trace elements and either 0 or 1 ppm Mo. Moderate to severe foliar symptoms of Mo deficiency developed on `Annette Hegg Brilliant Diamond' and `Eckespoint Lilo' with 0 ppm Mo. Symptoms did not occur with 1 ppm Mo. No Mo deficiency symptoms developed on the other 7 cultivars which included `Supjibi', `Gutbier V-17 Angelika', `Peace Regal Velvet', and `Cheers!'. With 0 ppm Mo these cultivars generally maintained higher levels of nitrate reductase enzyme activity and lower tissue nitrate levels than the 2 showing symptoms.

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Paclobutrazol (PBZ) was applied to `Mustang' geranium (Pelargonium × hortorum L.H. Bailey) as a single growth-medium drench at 0.06 mg a.i./pot or as a single foliar spray at 100 mg·liter-l when the plants had three to four expanded true leaves (34 days after sowing). At these rates, PBZ caused excessive growth suppression but plants flowered earlier than untreated controls. A single foliar spray of gibberellic acid (GA) at 100 mg·liter-l applied 0 (same day), 7, 14, or 21 days after PBZ reversed the growth suppression caused by PBZ. Plants treated with GA30 or 7 days after PBZ were as tall or taller and flowered at the same time as or later than the untreated (no PBZ, no GA3) controls. Plants treated with GA, 14 or 21 days after PBZ were shorter and flowered earlier than untreated controls but were taller than plants treated with PBZ alone. Response to GA3 was similar whether PBZ was applied as a drench or as a spray. Chemical name used: (+)-(R*,R*)-β([4-chlorophenyl]methyl)-α-(1,1-dimethylethyl)-1 H -1,2,4-triazole-1-ethanol (paclobutrazol).

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To test the effects of fertilizer concentration and growth medium electrical conductivity (EC) on the growth of New Guinea impatiens (Impatiens sp. hybrids or I. platypetala Lindl.), plants of `Selenia' were grown 70 days in a commercial soilless medium and irrigated with solutions of 20N-4.3P-16.6K at concentrations of 0.5, 1.0, 1.5, or 2.0 g·liter-1. In a fifth treatment (“delay”), no fertilizer was applied for the first 14 days after planting, then 0.5 g·liter-1 was applied for the next 14 days, followed by 1.0 g·liter-1 until the end of the experiment. Measurements of shoot dry weight and growth medium EC were made at 14-day intervals. Differences in dry weight between fertilizer treatments became significant (P = 0.0001) 42 days after planting. Over the 70-day experiment, plants grew most with 0.5 g·liter-1 and delay treatments. High fertilizer concentrations (1.5 and 2.0 g·liter-1) caused the most growth suppression and resulted in increasing growth medium EC with time. An EC of ≈1.5 dS·m-1 or higher was associated with suppressed growth beginning 42 days after planting. A mild chlorosis developed on the leaves of some plants at the two highest fertilizer concentrations.

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To test the effect of soluble salts on the growth of New Guinea impatiens (Impatiens platypetala), `Selenia' was grown for 70 days in a soilless medium and irrigated with solutions of 20N-4.3P-16.6K at rates of 0.5, 1.0, 1.5, or 2.0 g·liter-1. A fifth treatment was no fertilization for the first 14 days, 0.5 g·liter-1 for the next 14 days and 1.0 g·liter-1 till finish. At 14-day intervals shoot dry weight and growth medium soluble salts were measured. By 42 days after planting, differences between treatments were statistically significant with respect to dry weight. Over a 70-day period, growth was greatest with 0.5 g·liter-1. The 1.0 g·liter-1 treatment caused a similar growth response. Plants in delay treatment responded similarly to 0.5 and 1.0 g·liter-1. Higher rates, 1.5 and 2.0 g·liter-1, caused growth suppression and resulted in soluble salts buildup in the growth medium. Soluble salts levels of 1.5 dS·m-1 and above suppressed early growth. Results show that during the first 42-56 days of growth, New Guinea impatiens are sensitive to soluble salts and levels over 1.5 dS·m-1 are cause for concern.

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