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Plantwise Technical Factsheet

apple blossom weevil (Anthonomus pomorum)

Host plants / species affected
Malus domestica (apple)
Pyrus communis (European pear)
List of symptoms/signs
Inflorescence  -  external feeding
Leaves  -  external feeding
Symptoms
The typical indication of attack by A. pomorum results from feeding by larvae inside the flower bud. Infested flowers are dome-shaped with brown petals closing together, which are typically called "capped blossoms". Besides larval damage to flowers, feeding on host plants by active adults early in the season also results in small circular holes on newly growing leaves and buds.
Prevention and control

Cultural Control

Tree bands made of burlaps or corrugated cardboard may be used to trap overwintering or dormancy-site seeking adults (Miles, 1923). In Russia, tree-bands treated with insecticides have been used (Korchagin, 1974), although there have been no extensive studies on the effectiveness of this method.

Biological Control

A. pomorum is attacked by a variety of natural enemies including predators, parasitoids, fungi, bacteria and nematodes. Imms (1918) and Miles (1923) emphasized the importance of these natural enemies in suppressing populations in England. In Lithuania, Rilishkene and Zayanchkauskas (1985) reported that parasitization by Pteromalus grandis, predation by birds, and infection with fungi, bacteria and nematodes appeared to be important in reducing the abundance of A. pomorum.

To date, however, biological control of A. pomorum has primarily focused on the survey and documentation of field attack rates of the larva by natural enemies, particularly hymenopterous parasitoids. Few efforts have been directed towards conserving and augmenting these natural enemies for the control of the pest.

Chemical Control

Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:


Impact
A. pomorum was recorded as a major apple orchard pest in Europe prior to World War II (1939), ranking second only to the codling moth (Cydia pomonella) in importance (Ormerod, 1890; Massee, 1925; Régnier, 1925). After World War II, its importance was dramatically reduced in commercial orchards, as a result of the extensive use of broad-spectrum insecticides for controlling key fruit pests (Blommers, 1994). Recently, however, its pest status has increased in commercial apple orchards in many regions of Europe, necessitating control measures specifically required to control weevil damage (Wildbolz, 1992). This pest problem is especially apparent in IPM or biologically-managed orchards where selective pheromones, pathogens and/or insecticides are primary tactics for the control of major fruit pests.

Crop losses caused by A. pomorum result primarily from heavy losses of flowers by larval damage. Although light infestations may be considered potentially beneficial by thinning fruit in years when flowers are abundant, populations and damage of this insect are aggregated within orchards and usually grow to unacceptable densities in successive years (Blommers, 1994). Reijbroek (1983) studied the relationship between flower damage by A. pomorum and fruit yield loss in the Netherlands and recommended a provisional treatment threshold of approximately 10% blossom loss, although this treatment threshold may vary with different apple cultivars. Tret'yakov (1991) also published a formula for calculating yield losses based on blossom infestation rates.
Related treatment support
 
External factsheets
Bayer CropScience Crop Compendium, Bayer CropScience, English language
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