WINETECH Technical Yearbook 2020

PHOTO 8. Sowthistle.

PHOTO 9. Sticky bristle grass.

ACKNOWLEDGEMENTS Kerstin Kruger, Elleunorah Allsopp, Winetech, Tropicsafe (www.tropicsafe.eu/ tropicsafe/ ), and Jeff Joubert (photos).

It is also important for the producer to know which plant species, apart from grapevines, can act as host for the phytoplasma which causes aster yellows. This includes well- known agricultural crops like tomatoes, wheat, maize and triticale. Wild radish, per- iwinkle, common iceplant, white goosefoot, blackjack, sowthistle, stinging nettle and sticky bristle grass are weeds in which the phytoplasma has also been detected through laboratory testing (see photos).

which addresses all three aspects of the disease triangle, namely the phytoplasma responsible for the disease, the Mgenia fuscovaria leafhopper species which spreads the disease, and finally the infected grapevine or alternative host species which acts as infection source. Photo 1 shows a grapevine with typical aster yellows symptoms. Control measures include the monitoring of leafhopper numbers with the help

of insect traps (photo 2), planting only certified plant material, the removal of infected vines or infected parts of vines, and effective weed and vector control. These control measures are summarised in the aster yellows management table (table 1). This table serves as a guide to ass i st producers wi th planning and decision-making and also l ists the registered products permitted for leafhopper control.

For more information, contact Gert Engelbrecht at gerte@vinpro.co.za.

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