Control methods (Apple blossom weevil)

Chemical control

The usual method of control of apple blossom weevil is to apply a spray of a broad-spectrum insecticide against adults at bud burst when most adults have migrated into the apple crop but before significant egg-lying has occurred.

• The organochlorine insecticides DDT and HCH were traditionally used for this purpose and were highly effective but were withdrawn from use many years ago.
• Fatty acids (Flipper) is specifically recommended for control of apple blossom weevil on apple.
• Synthetic pyrethroids such as deltamethrin (Decis Forte) are also highly effective when used against other pests, but their use should be avoided as they are harmful to the orchard predatory mite Typhlodromus pyri and a wide range of other natural enemies.

Insecticide resistance

Resistance of apple blossom weevil to insecticides is not known and is unlikely to occur.

Cultural control

Young, dwarf apple trees have smooth bark, which provides few overwintering sites for the weevil in the orchard. Moreover, well-managed orchards have little leaf litter in which the weevils can overwinter, so most weevils overwinter outside the orchard in nearby woodland and hedgerows. The weevil is less of a problem in orchards that are not adjacent to woodland or hedgerows.

• Loss of even quite a high proportion of buds may be of limited importance on apple trees that have high numbers of apple buds and on varieties where damaged flowers do not continue to develop into mature fruits.
• Good tree management and nutrition will greatly reduce the impact of this pest.
• In organic orchards where the pest is especially troublesome, providing adequate nitrogen to the trees is important to maintain fruit bud numbers and quality.
• On a limited scale, it might be feasible to remove and destroy capped blossoms before the weevil completes its development and emerges. This could be done when hand thinning of fruitlets is done. This should reduce the risk of allowing damaged fruits to mature.
• On a limited scale, it might be possible to provide artificial hibernation sites for adults (e.g. trunk bands) in June before the weevil moves to its hibernation quarters. The artificial hibernation sites could then be removed and the weevils destroyed. This approach probably hasn’t been tried and may not be very effective.

Biological control

British Apples and Pears Ltd funded Niab to investigate the use of both entomopathogenic nematodes (Steinernema carpocapsae and Steinernema feltiae) and fungi (Beauveria bassiana and Metarhizium products) as possible means of controlling apple blossom weevil. 

Entomopathogenic nematodes

• Predatory nematodes have proved to be effective at controlling the larvae of other weevil pests such as vine weevil. 
• To be effective for apple blossom weevil larvae, they would need to penetrate the capped blossoms to reach the larvae hidden beneath. Nematodes can swim in films of water and when capped blossoms were removed and dipped in suspensions of the nematodes containing a wetting agent in the laboratory, 100% infection of larvae was achieved. However, when applied in the field, control was slower and incomplete although infection levels in the larvae reached 50% after nine days. 
• Further investigation is required before full recommendations can be provided to growers.

Entomopathogenic fungi

• Commercially available Beauveria bassiana, Metarhizium anispoliae and Metarhizium brunneum are already sold in the horticultural industry to control all life stages of various weevils.
• Niab carried out laboratory bioassays using Naturalis-L (Beauveria bassiana) and a Metarhizium product not yet registered for use, to assess if either was effective against apple blossom weevil.
• Although entomopathogenic fungi (EPF) infection of apple blossom weevil adults was achieved, the efficacy was low.
• Further research is required to optimise EPF use for apple blossom weevil control before these can be adopted by growers.