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A Technical Guide for Wine Producers
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RECENT ARTICLES | WYNBOER HOME
Wood Borers in Vines: A New Pest or a Climatic Phenomenon?
Elleunorah Allsopp (photo) & Muriel Knipe, ARC Infruitec-Nietvoorbij, Stellenbosch
During the past two years there have been many enquiries concerning small holes bored in vines and a jelly-like secretion that emanates from these holes. In other instances, shoots, arms and even trunks of vines have been permeated by tunnels in which larvae, pupae and even adult beetles have been found.
Cause of the phenomenon
The culprit is a small wood borer called Xyloperthodes cf. incertus. This little beetle belongs to the family Bostrichidae. It is an indigenous wood borer which completes its entire life cycle in wood. The larvae prefer moribund or dead wood, whereas the adults also attack living wood. Only the adult beetles, that can fly, leave the wood to disperse to other hosts. The beetle tunnels in and lays its eggs. When the larvae hatch, they tunnel in the wood until pupation, which is completed in the wood.
If the beetle attacks a vine that is still robust and healthy, the vine starts to secrete the jelly-like substance as soon as the beetle starts to bore in the trunk or shoot. The jelly swamps the beetle and often expels it from the hole. The jelly also seals the hole so that wood rotting fungi are unable to penetrate. This secretion, which appears resinous when dry and solidified, is the vine's own protection mechanism and should therefore not be rubbed off or removed. As long as the vine still secretes this jelly, the wood borer poses no real threat to the vine.
If, however, the vine is stressed and unable to produce the jelly, for example due to drought, the beetle may succeed in tunnelling around the circumference of the shoot, effectively ringbarking it. The distal part of the shoot dries out and creates an ideal environment for the beetle's larvae to develop.
Various other factors may cause a vine to be stressed to such a degree that it is no longer able to secrete the jelly when attacked. These include soil physical problems, such as an impenetrable layer that results in poor root development, nematode infection which causes the root system to become less effective since hair-roots are attacked, and fungi or bacteria that colonise the vascular tissue of the vine, thus impeding water supply to the distal parts of the vine.
Xyloperthodes cf. incertus therefore does not kill vines - it is, mostly, the symptom of another, underlying problem.
Why the sudden proliferation of this problem?
This wood borer has always been present in vineyards and over the years there have been sporadic enquiries about the jelly-like secretions that are usually noticed in autumn or winter. In our opinion, the enormous increase in the occurrence of Xyloperthodes cf. incertus is due to the unusually warm, dry climatic conditions experienced in the Western Cape during the past few seasons. The summers and autumn periods have been exceptionally dry and warm, the winter rains arrived very late and fell over a relatively short period. Moreover, we have not experienced the prolonged periods of wet, cold winter weather to which we are accustomed. These factors benefit the survival of the wood borers, seeing that there is now a lot of dry wood in their immediate surroundings in which the larvae can develop. The drought conditions, often combined with other underlying problems, result in many stressed vines that are unable to protect themselves against attacks from the wood borers.
What can be done about the situation?
For further enquiries, contact Elleunorah Allsopp at (021) 809-3007 or email allsoppe@arc.agric.za.
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