Successful bio-control of the strawberry mite Phytonemus pallidus with the predatory mite Neoseiulus cucumeris in organic outdoor production of strawberries (Fragaria × ananassa Duch.) in Sweden.

Use of the predatory mite Neoseiulus cucumeris (Oudemans) (Acaraci: Phytoseiidae) showed strong potential for control of the strawberry mite Phytonemus pallidus (Banks) (Acari: Tarsonemidae) in outdoor organic strawberry production. The experiment was carried out at Ranna Experimental Station, Skovde, Sweden (58°27'N, 13°51'E). Two cultivars, 'Honeoye' and 'BF949603' (a new cultivar from Balsgard, SLU Sweden), were treated with N. cucumeris three times during spring and summer 2007, to control P. pallidus. Number of strawberry mites and fruit yield were measured in the 2007 growing season. In plots where N. cucumeris had been released, there were significantly fewer P. pallidus in 'Honeoye', in July and August. This in turn significantly improved the yield in 'Honeoye', with 88% higher production of first class fruits when treated with N. cucumeris. In 'BF949603' there was low incidence of P. pallidus in 2007 and consequently no effect on yield. Earlier experiences of N. cucumeris use in outdoor production of strawberries in Sweden have varied widely. The efficacy of N. cucumeris depends on temperature and the current recommendation is to delay the first release of predatory mites until the risk of low night temperature is over, i.e., until the beginning of June. This study shows the importance of early and repeated temperature-adapted release of predatory mites for successful biological control of P. pallidus in organic outdoor production of strawberries.