Scientists of Wageningen UR Greenhouse Horticulture expect that some indigenous predatory mites could play a significant role in biological pest control in summer flowers. The variation in the spontaneous occurrence of these predatory mites, however, showed large differences per season and per location. Commercially available predatory mites can in any case be deployed for the control of thrips and red spider mites in summer flowers. Occasionally, it will be necessary to apply chemical products as supporting measure.
During the past two years scientists did put out predatory mites in Delphinium, Alchemilla, Veronica, rose hip and chrysanthemum against thrips, red spider mites, and white mites (Tarsonemidae). Development of pest and predatory mite population was followed by counting and identification of the sampled predatory mites. The predatory mites Neoseiulus cucumeris and Amblyseius andersoni were put out, where necessary supplemented with the predatory mite Phytoseiulus persimilis against red spider mites. Syngenta Bioline provided the predatory mites.
Differences per crop
The study showed that Alchemilla and Delphinium are suitable plants for predatory mites. Such mites are already frequently occurring spontaneously on these plants. Neoseiulus cucumeris was also found to be present spontaneously in these crops, as well as related indigenous predatory mites. Little is yet known, however, about the significance of these indigenous mites as regards biological control. When Neoseiulus cucumeris does not yet occur in these crops, there is a good chance of infestation after introduction. Sulphur evaporation in greenhouses, however, may put a spoke in the wheel.
No large numbers of predatory mites are found in chrysanthemum, rose hip, and Veronica; this does not change after the release of predatory mites. Sometimes predatory mites from a completely different family were found, especially in chrysanthemum, and sometimes also in Veronica. Very little is yet known about these predatory mites.
Provisional advice
These and other observations show a wide variation between seasons and locations as regards the spontaneous occurrence of predatory mites. More observations are required to gain more insight into this phenomenon. Some of the indigenous species that were found are seriously expected to be able to play a significant role in the biological control of pests such as white mites, red spider mites and thrips in certain crops. Only further research can provide more clarity about such possibilities.
The advice – with the current knowledge – is to put out the predatory mite Neoseiulus cucumeris in case of thrips infesatation, although not all crops are equally suitable for these predatory mites. The predatory mite Phytoseiulus persimilis is most suitable against red spider mites. Selective pest and disease control chemicals must be selected in biological control systems.