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Astrid Kubatsch, Heiner Grüneberg and Christian Ulrichs

Schefflera arboricola was held in light- and temperature-controlled chambers for 6 months under three light intensities of 10 μmol·m–2·s–1, 20 μmol·m–2·s–1, and 80 μmol·m–2·s–1 measured as photon flux density (PFD). Plants also received three temperature regimes: 15 °C, 20 °C, and 25 °C. Reduced light intensity significantly decreased fresh and dry weight and increased chlorophyll content, but did not affect leaf thickness and palisade and spongy mesophyll parenchyma. High temperatures reduced fresh weight and significantly increased chlorophyll content and leaf thickness. The authors conclude that reduced photosynthetic energy flow at low light intensities (10 μmol·m–2·s–1, 20 μmol·m–2·s–1) could not be buffered by a downregulation of energy-consuming processes. Therefore the life span and quality of S. arboricola is reduced at such PFD values, especially at higher temperatures. Plants lose their marketability within 6 months.

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Luise Ehrich, Christian Ulrichs and Heiner Grüneberg

Because South African Iridaceae have a high potential as new floricultural crops, four spring-flowering geophytic species originating in the Cape Floral Region were investigated. A total of 900 corms for each Freesia laxa, Sparaxis ×tricolor, Tritonia deusta, and Tritonia securigera were exported from South Africa during dormancy in 2 subsequent years. Experiments in Berlin, Germany, focused on storage conditions after export and different temperature and light intensity regimes for forcing, in particular their effect on plant habit, inflorescence induction, and flowering success. The results showed that after export, dormancy could be further maintained in storage at temperatures above 20 °C. Temperature was found to be the main criterion to successfully realize flowering after planting; cultivation at 13 °C at night was essential with temperatures of 17 °C and above possible during the day. During summer months, the failure of inflorescences in the terminal bud to develop completely, or the abortion of flower primordia within the corms, was the result of the high temperatures present. Also, low natural light levels during fall months could be linked to flower abortion of the investigated species. However, the results indicate that if forced as pot plants for the European fall and winter, the low temperature requirements of the investigated species during cultivation could represent substantial energy savings for future growers.

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

Since the 1900s, diatomaceous earth (DE) has been used as an alternative to chemical insecticides in stored product protection. New silica and DE formulations offer expanded possibilities for use in horticultural crops. However, many crop pests are found on the leaf underside and this is especially challenging when using silica because the substance must have direct contact with the insect to be effective. We tested three application techniques with three formulations of silica to evaluate their efficacy against different developmental stages of mustard leaf beetle (Phaedon cochleariae Fab.) and the cabbage worm of the large white butterfly (Pieris brassicae L.) on the host plant species pak choi (Brassica rapa ssp. chinensis L.). Formulations were applied manually with a powder blower, with an electrostatic spray gun, and in a closed chamber also working with electrostatic forces. The silica formulations used in the biotests were Fossil Shield 90.0s®, AE R974®, and a formulation developed at Humboldt University Berlin called AL-06-109. All formulations contained at least 60% silicon dioxide. Significant differences in efficacy were detected with different application methods and/or silica formulations. AL-06-109 electrostatic cabin-applied was the most effective combination. All formulations, if applied electrostatically, resulted in good coverage and in high plant protection against insect pests. Dusts applied manually were unevenly distributed and easily removed by wind from leaf surfaces. Electrostatic application with a spray gun resulted in even particle distribution on plants, but overspray was high. To accomplish even coverage without wasting so much active material, an enclosed mobile chamber with an electrostatic spray system and an attached exhaust system was developed.