One of the most effective naturally occurring insecticide powders is diatomaceous earth (DE), which contains above 96 % of silica (silicon dioxide SiO2). In recent days, the possibility to use new improved DE formulations for plant protection in horticulture has been the focus of research. For aphids and other under-leaf insects only insecticides deposited on leaf undersides are effective. We tested electrostatic application of different silica containing dusts onto the cruciferous crop pak-choi (Brassica chinensis). The materials tested were Fossil Shield 90.0s, Advasan, Biobeck PA910, and a formulation newly developed by the Urban Horticultural Section at Humboldt University called "Al-06". Silica materials were tested for their effect on plant photosynthesis and efficacy against the mustard beetle (Phaedon cochleariae F.). All materials have been effective in contact experiments against tested insects. However, significant differences were observed between materials after application onto plant leaves. Fossil Shield, Advasan, and Al-06 application resulted in a good coverage and in high protection against the mustard beetle. Biobeck PA910 was easily removed by wind from leaf surfaces and did not protect the plants well. However, photosynthesis has been reduced in treated plants and remained at a lower level even after dust removal. Experimental results are critically discussed in the view of future potential for crop protection programs.