Biological control of the bulb mite Rhizoglyphus robini by the predatory mite Hypoaspis aculeifer on lilies : Implementation in practice

The bulb mite Rhizoglyphus robini is a serious pest of lily bulbs. To control this pest growers use acaricides together with cultural measures, e.g., hot-water treatment (2 hours 39°C or 41°C ) and storage of the bulbs at -2°C. To reduce the use of acaricides, possibilities for biological control with the predatory mite Hypoaspis aculeifer were investigated. Application of hot-water treatment to lily bulbs or acaricide treatment preceding bulb propagation by 'scaling' decimated populations of bulb mites and virtually eliminated populations of predatory mites. Earlier experiments under laboratory and semi-commercial conditions showed that release of predatory mites at the start of the propagation phase resulted in the control of bulb mites. Encouraged by these results, experiments were carried out at five bulb farms to assess the performance of biological control relative to and in combination with other cultural measures. The following experiments were carried out: (1) no additional treatment (control), (2) hot-water treatment (control), (3) release ofH. aculeifer, (4) hot-water treatment and release of H. aculeifer, (5) acaricide treatment (pirimiphos-methyl), (6) hot-water treatment and acaricide (pirimiphos-methyl) treatment. When bulb scales were mixed with vermiculite and packed in plastic, complete control of R. robini was achieved by acaricide treatment, whereas biological control led to decimation of the pest population. However, when peat was used as packing medium biological control gave more satisfactory results than acaricide treatment. It is concluded that a combination of hot-water treatment and biological control can replace acaricide application to control the bulb mite in lilies during the propagation phase