WINETECH Technical Yearbook 2020

Indigenous leafhopper transmits aster yellows

Thus far, the indigenous leafhopper Mgenia fuscovaria is the only confirmed vector of the phytoplasma that causes aster yellows in South Africa. Aster yellows is a phytoplasma disease which causes serious yield loss. Severely in- fected grapevines may have to be replaced within two to four years, therefore aster yellows has been classified as a quarantine disease. Phytoplasmas are transmitted by leafhoppers, psyllids and planthoppers. WHAT DOES THE VECTOR LOOK LIKE? It is a fairly large, robust leafhopper (adults are 4-6 mm long). Adults can be recognised by the whitish spot in the centre where the forewings join, as well as by the black insides of the hind legs (photo 1). The legs of live leafhoppers are pale green, but the colour fades to brown when dead (photo 2). Immature leafhoppers or nymphs are pale to bright green and in older nymphs the wing buds and dark colouration on the insides of the hind legs are already visible (photo 3). HOST PLANTS Researchers at ARC Infruitec-Nietvoorbij in the Southwestern Cape (Wellington, Slang- hoek and Wabooms River) found that the leafhopper occurs year round on two ever- green plants, namely wild vine or Cliffortia odorata and wild bramble or Rubus spp. which usually grows along watercourses. In the Olifants River Valley (Vredendal vicini-

AUGUST 2020

ELLEUNORAH ALLSOPP 1 & KERSTIN KRÜGER 2 : 1 ARC Infruitec- Nietvoorbij, Stellenbosch; 2 University of Pretoria, Pretoria KEYWORDS: Aster yellows, vector, leafhopper, Mgenia fuscovaria , monitoring

PHOTO 2. Adult Mgenia fuscovaria : The green colour has faded to brown, but the whitish spot on the wings, black insides of the hind legs and stippling pattern on the fore wings are still visible.

PHOTO 1. Adult Mgenia fuscovaria with characteristic whitish spot (a) in the middle of the forewings and black insides of the hind legs (b).

WINETECH TECHNICAL YEARBOOK 2020 52