WINETECH Technical Yearbook 2020

ty) researchers from the University of Pre- toria found that this leafhopper occurs on various weeds in and around vineyards, and that they also overwinter on weeds, such as nettles ( Urtica sp.), henbit dead-nettle ( Lamium amplexicaule ) and yellow sorrel ( Oxalis pes-caprae ). SEASONAL OCCURRENCE Data from yellow sticky traps adjacent to wild host plants in the Wabooms River Val- ley and Wellington area showed that Mge- nia numbers generally peaked in spring (September/October), with a subsequent peak in autumn or early winter (May/ June). Very few to no Mgenia were found on traps in the adjacent vineyards, even when numbers peaked in spring. Further- more, M. fuscovaria was not the most abundant leafhopper – other leafhopper species that do not transmit aster yellows were generally more numerous. The phyto- plasma which causes aster yellows was not detected in wild brambles adjacent to the vineyards in the Western Cape. In the Olifants River Valley sticky trap catches in a vineyard heavily infected with aster yellows revealed that Mgenia num- bers peaked in September and February on grapevines and in June on weeds in vineyards. The numbers were generally considerably higher than in the Southwest- ern Cape, particularly when the vineyard was heavily infected with aster yellows and

M. fuscovaria was the most abundant spe- cies. Research at the University of Pretoria showed that M. fuscovaria preferred grape- vines infected with aster yellows to healthy plants and that the leafhopper can also transmit the phytoplasma to wheat, maize and the cover crop triticale. MONITORING Leafhoppers should be monitored weekly throughout the year, using commercially available yellow sticky traps, for timing of control measures, such as weed manage­ ment in winter or timing of foliar sprays during the growing season. In areas of high risk for aster yellows, at least two sticky traps should be used per vineyard block. RECOMMENDATIONS The numbers of M. fuscovaria in vineyards in the Southwestern Cape were very low. Since the first aster yellows infection was reported in the Wabooms River Valley, no new infections have been reported. In the Olifants River Valley, where new infections are still being reported, producers are advised to monitor vineyards for the presence of M. fuscovaria. If the leafhopper occurs, particularly where aster yellows infected vines are present in the same or adjacent vineyard, leafhoppers should be controlled with a registered chemical to prevent spreading of the disease. Weed control, especially during winter when leafhoppers overwinter on

the weeds, is very important to reduce leafhopper numbers. Only certified, disease-free planting material should be used when establishing new vineyards. In theWestern Cape aster yellows can be successfully limited and eliminated by destroying infected vines and only using certified, disease-free planting material. SUMMARY The indigenous leafhopper Mgenia fuscovaria is the only confirmed vector of the phytoplasma which causes aster yellows. New infections are still being reported in the Olifants River Valley. Regular monitoring of leafhoppers with yellow sticky traps, control of leafhoppers, weed control, as well as the use of certified, disease-free planting material for establishing new vineyards, are required to contain the disease in this region. ACKNOWLEDGEMENTS This research was funded by Winetech, the ARC and NRF – projects WW 05/23, UPKK01, UPKK02, UPKK03, THRIP Technology and Human Resources for Industry Programme (THRIP), as well as TROPICSAFE, the European Union’s Horizon 2020 research and innovation programme under grant agreement number 727459, project “Insect-borne prokaryote- associated diseases in tropical and sub­ tropical perennial crops” TROPICSAFE.

PHOTO 3. Mgenia fuscovaria nymph with wings buds (v) clearly visible. The insides of the hind legs are also starting to appear black.

For more information, contact Elleunorah Allsopp at allsoppe@arc.agric.za.

WINETECH TECHNICAL YEARBOOK 2020 53