Friday, June 26, 2009

Aster Yellows - Be prepared !!

Aster Yellows has been identified in on a number of farms between Lutzville and Klawer as well as in the Waboomsrivier area. These farms are currently under quarantine, current legislation requires a 5km radius.

Grapevine Yellows disease is caused by a wide variety of phytoplasmas. The
Yellows disease detected in the Western Cape is caused by Aster Yellows phytoplasma. Yellows diseases caused by this specific phytoplasma can also be found in Europe, Israel, North America, Chile and Tunisia. A phytoplasma is a small primitive bacterium without a cell wall that is systemic in the phloem of the plant. All organs can be infected namely the roots, trunks, shoots, buds, flowers and berries but phytoplasmas cannot be found in seed. Grapevine Yellows disease affects a wide variety of cultivars. Chardonnay is very sensitive but it can also be found on Chenin blanc, Colombar, Pinotage, Cabernet Sauvignon, Cabernet franc,
Shiraz, Merlot, Sauvignon blanc,
Ruby Cabernet, Pinot noir, Pinot gris and Riesling. Rootstocks do not show symptoms but can act as carriers. Yellows disease was detected in the following table grape cultivars in Greece and Israel: Waltham Cross, Italia, Queen of the Vineyard, Muscat d’Alexandrie and Alphonse Lavallee. Aster Yellows phytoplasma has a wide range of host plants (about 200) like weeds, cover crops, vegetables and flowers.

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