Twospotted spider mite - cultural control

Twospotted spider mite has a very large host range and is found on many ground cover plants and shelter trees around orchards. It often moves from weeds in the ground cover into the trees when drought conditions and high mite numbers prevent further weed growth. It may also move from species of shelterbelt trees which host twospotted mite on to fruit crops. Wind is important in the dispersal of this mite. Good control of weed species that host twospotted spider mites will substantially reduce the probability of mites infesting the fruit trees in mid and late summer. Maintaining healthy green ground cover in the inter-row space will also help to reduce the probability of twospotted mite dispersal into the trees.

The alternative host plants of twospotted spider mite are not only a source of the mites, but are also a reservoir of their natural enemies. Care should be taken not to destroy these reservoirs by spraying the weeds or shelter with chemicals toxic to the predator species.

The choice of pesticides for all purposes in the orchard has a major influence on the survival of the natural enemies of twospotted spider mite, and is especially critical for the two most important predatory mites, Phytoseiulus persimilis and Galendromus occidentalis, and the ladybird Stethorus bifidus.

Apple varieties and tree nutrition affect the total numbers of eggs laid by twospotted spider mites. This may present some opportunities for cultural control through variety selection and the use of fertilisers. Higher nitrogen levels in the leaves of its host plants results in greater egg laying by twospotted spider mite.