Phylloxera survey
Increasing reports of phylloxera infestations, even in vineyards where grapevines are grafted onto resistant rootstocks, led to SATI and Raisins SA contracting ARC Infruitec-Nietvoorbij to conduct a survey to determine 1. how widespread phylloxera occurs in the table- and dried- grape production regions, and 2. whether phylloxera contributes significantly to poor grapevine performance. Fine root samples were collected from five grapevines in each of 82 table- and dried-grape vineyards in the major growing areas of the Western and Northern Cape between 2020 and 2022.
This survey confirmed that phylloxera is present in all the major regions in the Western (Hex River Valley, Berg River Valley, including Piketberg, and Olifants River Valley) and Northern Cape (Orange River Valley) where table and dried grapes are produced. Galls were more numerous on grapevines grown on own roots, but small numbers of live phylloxera and galls were also present on resistant (R99, R110) and moderately resistant rootstocks (US 8-7, 143B, Ramsey, Paulsen). Despite the presence of phylloxera and root galls, production data did not show any significant impact on growth and yield that could be ascribed to phylloxera in the vineyards surveyed.
Implications
Resistant and moderately phylloxera resistant rootstocks allow small numbers of phylloxera to survive on roots, but these do not reach levels at which production is affected negatively. However, there is a risk of phylloxera numbers increasing to damaging levels should grapevines come under stress, which reduces vine vigour as well as rootstock resistance to phylloxera. If a vineyard became infested with phylloxera while planted with a resistant/tolerant rootstock and is then replanted using a susceptible rootstock, phylloxera could increase sufficiently to affect growth and yield negatively. Infested vineyards can also serve as reservoirs for phylloxera, from where it can spread by plant material and soil on implements to other vineyards and farms.
How do you know if phylloxerais present?
The best time to monitor vineyards for phylloxera is during summer (December to February) when phylloxera numbers peak and root galls are easily visible. Inspect fine roots for the presence of characteristic hook-shaped galls and send a sample of these roots for expert identification under a microscope, because phylloxera is not visible with the naked eye.
Recommendations
- Nurseries and growers should be aware of the potential risks posed by phylloxera and every effort should be made to ensure that planting material is free from phylloxera. Growers should insist that planting material be certified phylloxera-free.
- Phylloxera should be controlled in vineyards supplying rootstock material to nurseries and in nurseries. Systemic insecticides used for control of vine mealybug will also control phylloxera.
- If phylloxera is present in a vineyard earmarked for replacement, a systemic insecticide (such as those registered for postharvest mealybug control) should be applied after the last harvest to reduce the phylloxera population. Select a phylloxera-resistant rootstock for the new grapevines. Table 1 lists the phylloxera tolerance level of some of the common rootstocks, according to Loubser et al., (1987). The young grape-vines may not yet have sufficient vigour to resist any remaining phylloxera in the soil. Therefore, a systemic insecticide should be applied as a soil drench after budding to protect the young vines from being colonised by mealybugs and phylloxera.
References
Loubser, J.T., J.H.S. Ferreira en C.A. de Klerk. 1987. Weerstandbiedendheid van Wingerdonderstokke teen Knopwortelaalwurm, Filloksera, Kroongal en Phytophthora. Wynboer Tegnies No. 19: 4-6.
Featured image: Phylloxera on root gall
