PHYLLOXERA – The enemy below

In 1886 the SA wine industry was nearly destroyed when phylloxera, an aphid-like insect which originates from wild grapevines in North America, was accidentally introduced into SA. The industry was saved only by the introduction of resistant rootstocks onto which the susceptible scion cultivars were grafted.

Life cycle and damage

Phylloxera (Daktulosphaira vitifoliae) is a sap-sucking insect, which feeds only on grapevines. It is a pest on wine, table and dried grapes. In SA it occurs primarily on grapevine roots and prefers soil with a heavier texture (i.e. not sandy soils). Where it feeds on the fine roots, characteristic galls or nodosities develop (Fig. 1), which weaken the root system and have a profound impact on grapevine performance. Infested vines decline gradually and eventually die. Phylloxera has a complex life cycle, but only wingless females that reproduce parthenogenetically (without mating) occur on grapevine roots in SA (Fig. 2). On some susceptible rootstock cultivars some of the females move onto the leaves where they feed and lay eggs in characteristic galls on the underside of leaves (Fig. 3). Phylloxera overwinter as first instar larvae or nymphs that are difficult to see, even under a microscope.
Phylloxera spreads via infested plant material or infested soil clinging to implements, vehicle tyres or shoes.

Resistant rootstocks

Vitis vinifera scion cultivars are highly susceptible to phylloxera, therefore they are normally grafted onto resistant or tolerant rootstocks. However, resistance to phylloxera is not absolute and can be affected by grapevine vigour, which can in turn be affected by soil type, climate and stress factors like heat, drought or the presence of other pests like nematodes. It would perhaps be more appropriate to call it tolerance rather than resistance.
A resistant rootstock growing under optimal conditions may tolerate high numbers of the pest, but under sub-optimal conditions resistance can weaken and the root system of the grapevine can be severely affected. The fact that phylloxera can still feed and reproduce on resistant rootstocks means that such vineyards can serve as reservoirs for the pest, from where it can be spread to other vineyards. Vigorously growing grape-vines with high levels of resistance can allow phylloxera to exist in the soil and when replanted, the young grapevines may not have sufficient vigour to resist the phylloxera present in the soil. Current status of phylloxera Nowadays most producers do not consider phylloxera resistance when choosing a rootstock, nor do they insist on plant-ing material being certified phylloxera free. In recent years researchers and consultants reported increasing numbers
of phylloxera infestations, even in vineyards where vines are grafted onto resistant rootstocks such as 99 Richter, 110 Richter and Ramsey.
Since the last phylloxera surveys were conducted 40 years ago, SATI and Raisins SA contracted ARC Infruitec-Nietvoorbij to conduct a survey in the major table and dried grape regions of the Western Cape (Berg River and Hex River Valleys), as well as the Olifants and Orange River Valleys.

Aims of the phylloxera survey

The aims of this survey are to determine (1) how widespread phylloxera occurs in the table and dried grape industries, and (2) whether phylloxera contributes significantly to poor grape-vine performance, with and without the presence of other factors that affect vine vigour and therefore also phylloxera resistance/tolerance.

All table and dried grape producers with vineyards on heavier soils (<60% sand) who suspect that phylloxera may be present in their vineyards are welcome to contact the research team. Researchers will arrange to visit the farm and take root samples in summer (Dec – Feb) when the root galls are clearly visible. All farm information will remain confidential. ✤

Fig. 1. Hook-shaped galls on fine roots due to phylloxera feeding

Fig. 2. Phylloxera on root gall

Fig. 3. Phylloxera galls on underside of grapevine leaves

For more information or to be included in the survey, contact Dr Elleunorah Allsopp at allsoppe@arc.agric.za or Mr Abraham Vermeulen at vermeulena@arc.agric.za