Biologisk bekaempelse af spindemider og trips paa pottegerbera.
1994
Enkegaard A. | Broedsgaard H.F.
The influence of relative humidity and density of spidermites (Tetranychus urticae) on the outcome of biological control of spidermites with predatory mites (Phytoseiulus persimilis) on potted gerbera (Gerbera jamesonii, cv. 'Hummingbird') was investigated at 20 deg C. The influence of the presence of thrips (Frankliniella occidentalis) and minute pirate bugs (Orius majusculus) on biological control of spidermites, as well as the influence of mites on biological control of thrips, were likewise investigated. The results have shown that biological control of spidermites with predatory mites is possible on potted gerbera. By introducing predatory mites in a ratio of 1:3500 or more, relative to the number of spidermites, an almost complete extermination of spidermites both on leaves and in flowers was achieved within 4-5 weeks. Differences in the outcome of the biological control at 45% and 85% relative humidity, respectively, were not observed. Biological control of spidermites was influenced by the presence of thrips and minute pirate bugs. When only pirate bugs were present together with spidermites and predatory mites, the pirate bugs ate some of the predatory mites, hereby delaying their control of the spidermites. The spidermites consequently achieved a higher density before the arrestment of their population increase. The population development of spidermites became remarkably different when both thrips and pirate bugs were present together with spidermites and predatory mites. By a predatory action on spidermite eggs, the thrips were able to keep the density of spidermites very low until the introduction of beneficials. After their introduction, the spidermite population was quickly reduced as a result of the action of the predatory mites. These were not hampered by the presence of pirate bugs, as these in situations with all four species clearly prefer to eat thrips before mites. Furthermore, the results have shown that biological control of thrips with minute pirate bugs is possible on potted gerbera. By introducing pirate bugs in a ratio of l:l50 or more, relative to the number of thrips, the thrips population was reduced to less than 1 per leaf and approximately 5 per flower within 6-7 weeks. The efficacy of the pirate bugs was not influenced by the presence of neither spidermites nor predatory mites.
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