Enhancement of biodiversity (Natural enemies)

Flowering plants

Many wild flower species attract insects that are predators or parasitoids of fruit pests. The plants may provide a food source in the form of nectar or pollen, or plant feeding insects feeding on them may constitute alternative prey or hosts. Adult hoverflies are the main natural enemies attracted, often in considerable numbers, by such wild flowers. Their larvae are important predators of aphids. Examples of flowering plants are:

• Flowering herbs should be sown repeatedly during the season, ideally to ensure a continual succession of flowering from May to September.
• They should be sown round the headland of the orchards or even in the strip under the trees if competition with the tree for moisture or nutrients is not a problem.
• This latter option is likely to be impractical in most situations.

Species diverse alleyways

The alleyways in orchards should be sown with a mixture of grasses and annual and perennial flowing plants.

• If white clover is included, this will help provide nitrogen for the tree.
• The use of broad-leaved herbicides in alleyways should be avoided.
• The frequency of mowing should be reduced as much as possible to allow taller species to grow, flower and set seed.
• The species composition should be chosen to suit the soil type.
• A wide range of mixtures is available from specialist seed suppliers (e.g. Emorsgate Seeds, King’s Lynn, Norfolk).
• Avoid species that are likely to harbour important pests (e.g. docks harbour dock sawfly, mayweed harbours common green capsid) or which are likely to seed in the weed-free (herbicide) strip under the tree and be difficult to control with herbicides.

Hedgerows and windbreaks

Woody species in hedgerows and windbreaks and their understory vegetation can act as important sources of natural enemies of apple pests but can also harbour important pests of apple.

• They can provide alternate prey for predatory insects or other food sources such as pollen and nectar.
• They can harbour various apple pests such as apple blossom weevil (Anthonomus pomorum) and winter moth (Operophtera brumats).
• Several moderately important apple pests occur on other woody plants in the family Rosacae, including hawthorn (Crataegus sp), rowen (Sorbus aucuparia) and whitebeam (Sorbus sp).
• In general, it is probably best to avoid hawthorn because it does harbour damaging pests such as the apple fruit rhynchites weevil as well as the bacterial disease fireblight, to which several modern apple varieties are very susceptible.
• Willows (especially Salix caprea and S. cinerea), hazel (Corylus avellana), common alder alder (Alnus glutinosa) and birch (Betula sp.) as well as nettles (Urtica dioica) provide food sources for anthocorid bugs (Anthocoris nemoralis and A. nemorum) which are important predators of aphid pests of apple.
• In general, insufficient is known about the best woody species for hedgerows and windbreaks but probably a diverse range of species avoiding species that harbour important apple pests, such as hawthorn, is probably the best strategy.