Many species of natural enemies in fruit trees seek refuges as a daily sheltering place or an overwintering site. The sites that they seek are often cracks or crevices in the bark, but young fruit trees with smooth bark offer far fewer refuges of this kind than large old trees. This deficiency can to some extent be counteracted by the provision of artificial refuges such as Wignests and bottle refuges. Unfortunately, artificial refuges can provide winter shelter for some pest species (e.g. apple blossom weevil adults). However, their benefits greatly outweigh their disadvantages.
- Bottle refuges may be made from 1 or 2 litre plastic drinks bottles. The bottom of 1 litre bottles is removed. 2 litre bottles are cut in half.
- Each bottle or bottle half is filled with a roll of corrugated cardboard made from a strip 15 cm wide by about 1.3 m long.
- A short wire is pulled through the plastic near the base to secure the cardboard.
- The bottles may be suspended from branches or attached tightly to trunks, branches or tree stakes with wire (open orifice facing down so they don’t fill with rain water).
A wide variety of other types of refuge may be used.
- One simple and inexpensive method is to tie extra lengths of hollow plastic tree tie round the stake. The open ends are favoured refuges for many predators.
- Sick bands tied round the tree trunk provide excellent refuges for many overwintering natural enemies including importantly predatory mites.
- Unfortunately, they also provide overwintering sites for several important pests, notably for codling and tortrix moth larvae. For this reason, trunk bands have to be cleaned out of pests in the winter which makes them less than ideal as refuges for overwintering natural enemies.
Ideally, every apple tree in the orchard should be provided with a refuge. However, the labour required for provision of bottle refuges in intensive orchards is likely to be prohibitive.
- The refuges should be left on the tree continuously.
- In summer they will provide daytime shelter for numerous earwigs as well as spiders, predatory flower bugs (anthocorids) and ladybirds.
- In winter, earwigs are in the soil but the refuges are occupied by predatory bugs, lacewings, spiders, ladybirds and many other beneficial insects.