The potential of silicate rock dust to control pollen beetles (Meligethes spp.)

Abstract: In organic agriculture, treatments with rock dusts for soil amendment, disease prevention, or insect control have a long tradition. Clinoptilolite (a naturally occurring zeolite) was tested against pollen beetle Meligethes spp. in organic and IPM oilseed rape fields in order to find a control strategy compatible with the guidelines for organic and IPM agriculture in Switzerland. Dust and spray applications were evaluated in several large-scale field trials from 2008 to 2011. Dust applications using 300-750 kg/ha pulverized Clinoptilolite (particle size < 0.1 mm; product Klinofeed, available from Unipoint, Switzerland) were applied using a drop-box fertilizer spreader or a Vicon pendulum spreader. For spray applications the same Clinoptilolite (product Klinospray) with a particle size of 0.017 mm was applied at rates of 30-50 kg/ha with a wetting agent (Heliosol, 2 l/ha; 600 l waster/ha) using a standard field crop sprayer. Two or three applications were conducted during the inflorescene stage (BBCH 51-57) depending on the rate of development of the oilseed rape plants.Under the dry and sunny weather conditions in 2009 and 2010, the treatments significantly reduced the number of pollen beetles by 50 to 80% until seven days after treatment (BBCH 51-54). Under the rainy weather conditions in 2008, no reduction of pollen beetles was observed. However, pollen beetles in treated plots showed a lower activity compared to beetles from the untreated control plots. In all experimental years flowering was visibly more intense in the treated than control plots. Pod setting on the main raceme was significantly increased in the treated plots. The yield was significantly increased by 23% in the experiments conducted under IPM conditions in 2010. However, no yield increase was observed in 2008 and 2009 under organic agricultural conditions.