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.

Zusammenfassung Amorphe silikathaltige Stäube, in ihrer natürlich vorkommenden Form als Diatomeenerden oder synthetisch produziert, werden im Vorratsschutz und in der Tierhaltung seit Jahren zur Bekämpfung von Schadinsekten und Parasiten eingesetzt. Neue Formulierungen lassen auch einen möglichen Einsatz gegen Schädlinge im Gartenbau erwarten. Um Schädlinge auch an Blattunterseiten zu bekämpfen, wurde versucht, ein natürliches Silikat elektrostatisch auf Blätter von Brassica chinensis zu applizieren. Dabei ließen sich siliziumdioxidhaltige Stäube nicht mit Tribo-Sprühgeräten aufladen und es musste auf Korona-Sprühgeräte zurückgegriffen werden. Mit diesen gelang es, gleichmäßige Schichten einer Diatomeenerde auf Blätter zu applizieren und die Schichtdicke zwischen 25-125 µm zu variieren. Die insektizide Wirkung im Petrischalenversuch mit je 20 Kornkäfern (Sitophilus granarius (L.)) unterschied sich dabei nicht für Schichtdicken von 50-100 µm und 100-125 µm. Eine Silikatschichtdicke von 25-50 µm führte zu einer niedrigeren Mortalitätsrate. Die Applikationen führten bereits innerhalb von zwei Stunden zu einer Reduktion der Kohlenstoffdioxidabsorption von 45%. Dieser Wert schwankte über einen Zeitraum von C. Ulrichs (u) · T. Mucha-Pelzer · I. Mewis sieben Tagen zwischen 45 und 73%. Auch nach einem Entfernen des Staubes blieb die Kohlenstoffdioxidabsorption der Pflanze um 19-28% reduziert. Dieses spricht für ein Eindringen der Silikatpartikel in die Stomata, wo diese zu Verstopfungen führen bzw. eine reduzierte Transpiration sowie Fotosyntheseleistung bewirken.Schlüsselwörter Silikate · Diatomeenerde · Sitophilus granaries · Elektrostatische Applikation Plant protection with silica particles: Electrostatic application and impact of particle layer density on the insecticidal efficacy Abstract Natural occurring amorphous silica is ubiquitous on the earth in soils and sediments. Both, natural derived silica and synthetically produced amorphous silica are used against stored product pests and parasites in animal houses. New formulations, active even under higher relative humidity's can be possible used against horticultural arthropod pests. Since many horticultural pests hide on the undersides of leaves and silica is a physical contact insecticide, an appropriate application method is needed. This paper reviews electrostatic application of natural derived amorphous silica to Brassica chinensis leaves. Due to the inherent high volume resistivity of silica powder, induction charging was ineffective for electrostatic powder coating. Corona charging involves a reliable current source, but typically is inefficient in charging the powder particles and creates a high density of free ions between the gun and grounded substrate as well as within the coating layer. These factors resulted in poor coating quality and inefficient particle deposition. The best leave coating was archived using tribo charging. Here we have been able to apply 1 3 30 Gesunde Pflanzen (2008) 60:29-34 coatings with different thickness. While a silica coat...

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