Aster Yellows and vector monitoring in the Wabooms river/Slankhoek and Robertson areas
De Klerk, C A
De Klerk, C A
Aster Yellows is a phytoplasma disease that was only recently identified in three viticulture areas in South Africa. It causes serious yield losses and eventually kills the vines. No measures are known to control this disease which is transmitted by a leafhopper of the genus Mgenia. To prevent spreading of the disease, the vector has to be controlled chemically. Many of the mother blocks that supply grafting material for the grapevine industry are situated in these Aster Yellows infested areas (Wabooms River/Slanghoek). The aim of this project was to monitor the occurrence of the Mgenia leafhopper and of Aster Yellows symptoms in vineyards in the Wabooms River and Slanghoek areas, as well as vineyards in the Robertson area where chemical control for leafhoppers was applied. This would indicate if leafhopper control was successful and if this prevented spreading of the disease.
Yellow sticky traps and a motorised vacuum sampler were used to collect leafhoppers in the vineyards. Aster Yellows symptoms were visually assessed. Leafhoppers were examined under a binocular microscope for identification. In the Wabooms River area no Mgenia or Aster Yellows symptoms were found in mother blocks. In the known Aster Yellows infected area, disease symptoms and Mgenia were found in only two vineyards.
In the area between the mother blocks and the disease-infected area Mgenia occurred in several blocks, but no Aster Yellows symptoms were found. It seems, therefore, that the disease is still restricted to a small area, but that the vector occurs in a much wider area and near to the mother blocks. This is a great risk and the situation needs to be monitored on a regular basis.
In the Robertson area eight blocks on six farms showed symptoms of Aster Yellows and low numbers of the Mgenia leafhopper occurred in all of them. At present the infested area in Robertson is very small in comparison to the whole production area. It is thus of utmost importance to ensure that the disease does not spread throughout the whole Robertson area. Regular monitoring of the situation is therefore a priority.