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Plantwise Technical Factsheet

poplar and willow borer (Cryptorhynchus lapathi)

Host plants / species affected
Alnus glutinosa (European alder)
Alnus incana (grey alder)
Betula (birches)
Populus alba (silver-leaf poplar)
Populus berolinensis
Populus deltoides (poplar)
Populus interamericana
Populus nigra (black poplar)
Populus simonii (Simon poplar)
Salix alba (white willow)
Salix caprea (pussy willow)
Salix fragilis (crack willow)
Salix purpurea (purple willow)
Salix triandra (almond willow)
Salix viminalis (osier)
List of symptoms/signs
Stems  -  internal feeding
Stems  -  lodging; broken stems
Stems  -  visible frass
Whole plant  -  frass visible
Whole plant  -  internal feeding
Symptoms
Initial larval activity is revealed by a thin, powdery frass coming out from very small holes in the bark of young stems and branches. Later, when the larva ages and penetrates into the wood, the frass becomes coarser and whitish, and sap exudes from the wound. Plant reaction, when present, enhances the girdling trend of the galleries in the stem.
Prevention and control
Elimination of the infestation sources has to be considered unlikely and almost impossible, as the pest is largely distributed on spontaneous poplars and willows and on the crowns of older trees.

Attention has to be paid to the sanitary protection of poplars and willows in nurseries, in order to prevent diffusion of the pest to stands by infested nursery stock. Young plants can be chemically protected and checked in order to eliminate the infested ones.

Chemical protection is generally also needed in young poplar stands when high-quality wood has to be obtained (Italy, Spain, France, Hungary). Protection in older stands is useless as trunks over 15-20 cm in diameter are unlikely to be attacked and damaged. Organophosphate or pyrethroid insecticides are commonly used. Pest control can be achieved by spraying trunks against adults (Dafauce, 1965; Lapietra and Arru, 1973) or young larvae (Schvester and Bianchi, 1961; Lapietra, 1972; Cavalcaselle and De Bellis, 1983; Allegro, 1997). In the latter case, very high mortality levels are reached when larvae are still feeding on bark tissues and before they penetrate into the wood; moreover, the trunks have to be abundantly wetted by the chemicals. In countries where C. lapathi overwinters as larvae, nursery plants can be effectively treated in winter using pyrethroid insecticides (Lapietra and Allegro, 1986); this technique is particularly useful in order to prevent the passive distribution of the pest to stands by infested nursery stock.

Biological control of the pest is possible by injecting entomopathogenic nematodes (Cavalcaselle and Deseo, 1984; Hou et al., 1992a) or fungi (Cavalcaselle, 1975) into the larval galleries. C. lapathi larvae control by X-ray radiation has also been carried out (Cavalcaselle and De Bellis, 1968, 1970).

Physical barriers have been tested, and proved to be effective in preventing C. lapathi adults climbing the trunks of trees (Allegro, 1990).
Impact
C. lapathi is considered to be an economically important pest in Belgium, France, Italy, Spain, Turkey, Yugoslavia, Hungary, China, Korea, Japan, USA and Canada (Nef and Menu, 1994).

It is mostly injurious in countries where poplars (and secondarily willows) are grown with the aim of producing high-quality wood, mainly for plywood and furniture industries (Italy, Spain, France, Hungary). In Italy it has been estimated that 180 tons of insecticides are sprayed annually in poplar stands against the pest, at an expense of about 1,000,000 Euros, one-third of the total management cost (Allegro, 1997).
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