WINETECH Technical Yearbook 2020

ROOTSTOCKS In South Africa, there was uncertainty re- garding which of the commercial grapevine rootstocks had resistance against ring nem- atodes. The analysis of soil samples from the Nemlab routine samples indicated that most of the samples received were from the rootstock Ramsey (60%), followed by those from the rootstock Richter 110 (15%). However, in terms of the mean number of ring nematodes per rootstock, the highest was found for the US 8-7 (24%), followed by Richter 110 (21%), Paulsen 1103 (14%), Richter 99 (14%), Ramsey (15%), and 101- 14 (12%), with the latter having the least number of ring nematodes (figure 3). Previous experiments indicated variable results under glasshouse conditions. How­ ever, Richter 110 was shown to be the most susceptible, with Richter 99 and Ramsey being the least susceptible.

CONCLUSIONS 1. The only nematode in the ring nema- tode group found during a recent sur- vey was the species C. xenoplax , proven by a recent survey and by the use of molecular techniques. 2. Ring nematode is widespread through- out all the different grape-growing ar - eas, with the presence of relatively high numbers, especially towards the relatively warm northern areas. 3. The attempts made at conducting glass- house experiments did not produce reliable results that gave a true picture, depending, as they did, on the avail- ability of perfect conditions, in terms of humidity, temperature and irrigation, for a period of at least six months. 4. An annual host is not currently available for the culture of large numbers of nematodes for experimental purposes.

5. Inference is possible from the Nemlab routine samples that all South Africa’s commercial rootstocks are susceptible to ring nematode, with only US 8-7 being notably more susceptible than the others. 6. Chemical control of ring nematode should prove not to be conducive to future soil health practices in vineyards. 7. In the development of different root - stocks selections, ring nematode should be included as an important criterion for selection. FUTURE PROSPECTS FOR RESEARCH A holistic approach should be followed in the control of ring nematode. Previous studies, conducted on the use of cover crops with biofumigation capability, showed a gradual decrease in the ring nematode numbers over the number of

years. The Nemlab routine samples showed that approximately 18% of the grapevine samples were free of ring nematodes. These vineyards might indicate specific management practices that are not con­ ducive to the increase of ring nematode numbers, so that they should be compared with the management practices of those vineyards that are severely infested with ring nematode.

For more information, contact Antoinette Malan at apm@sun.ac.za.

WINETECH TECHNICAL YEARBOOK 2020 40