Practices to manage chestnut orchards infested by the Chinese gall wasp

Abstract

The rapid spread of the Chinese gall wasp (Dryocosmus kuriphilus Yasumatsu) in Italian chestnut growing areas is causing new criticisms. In this context, in addition to a clear plant suffering due to the wasp infestation, the dangerous recurrence of chestnut blight and the sudden spread of Gnomoniopsis sp., a coloniser of galls but also the etiological agent of nut brown rot, must be considered. Therefore, it is very important to increase the plants’ vigour and prevent their decline. Preliminary experiments were carried out in different Italian regions between 2010 and 2011. Organic plant fertilizers were applied to plants showing middle or high defoliation levels caused by the wasp attacks. The observations carried out during the growing season indicate a good vegetative restart in the treated plants compared to the untreated controls, in all the situations and independently of the fertilizers applied. Most of the treated plants (between the 75% and the 100%) showed an evident improvement in the canopy vegetation, while the untreated controls were always classified in the worse classes of crown condition. These preliminary results highlight the efficacy of this kind of treatments for infested chestnut stands. This strategy, which is based on the preliminary evaluation of the plant vigour (following the proposed scale of attack severity and lack of foliage), consists in a manuring treatment at vegetative restart, which can be repeated in the following years in dependence on the results obtained. Moreover, pruning may be suggested only to manage the development of plants showing a definite recovery. The gall wasp pullulation requires new management strategies aimed at preserving the chestnut orchards, in order to avoid the chestnut cultivation to be marginalized or abandoned.

Keywords

• Management
• Decline
• Manuring