INTEGRATION OF BIOLOGICAL MITE CONTROL AND CONVENTIONAL INSECT CONTROL IN STRAWBERRY

A 3-year project (2004-2006) aimed to improve integration of biological control of the strawberry tarsonemid mite (Phytonemus pallidus) and the normal plant protection practices in perennial outdoor strawberry production. Two chemicals, methiocarb and abamectin are available for strawberry tarsonemid mite control in Finland before flowering and after harvesting. In the meantime, only biological control is possible. Besides, pyrethroids and organophosphates are used to control insect pests, often just before flowering. The main obstacle to integrate biological control is the sensitivity of predatory mites to these insecticides, because long waiting periods needed to ensure the survival of predators may lead to far too late introductions of predators. Two species of predatory mites, Neoseiulus cucumeris and Neoseiulus barkeri were applied in strawberry fields using variable timing and waiting periods from the preceding insecticide treatments. Ca. 1-1.5 million predatory mites per ha were introduced once during the season. Monitoring of the mite situation was based on leaf samples which were collected 2-6 times during the seasons. The results showed that the integration of biological mite control and chemical control of insects is possible but requires more knowledge of the situation in the field than mere chemical control. Monitoring of pest insects may enable earlier timing of insecticide treatments and hence earlier introductions of predators. Insecticides with low persistence should be chosen if sprayings are delayed. Introductions of predators early enough when strawberry tarsonemid mite populations are still low are essential. Late season leaf sample inspections will support the decision making of possible complementary acaricide treatments after harvesting time.