Technical Yearbook 2023

Manganese deficiency Manganese deficiencies manifest first on the basal leaves. Light yellowing/chlorosis of the interveinal areas, while veins remain dark green in colour (photo 8). Symptoms are often evenly spread across the entire leaf blade. Symptoms remain in the yellow spectrum for both red and white grape varieties and therefore only a candidate for confusion in white grape varieties. Other diseases There are various other grapevine diseases that can be mistaken for GLRaV-3. Although discussion thereof is not in the scope of this text, it is important to acknowledge that insight into symptoms related to other grapevine diseases is critical. In this regard, the work on grapevine abnormalities by Prof Piet Goussard is an invaluable reference resource. Specifically, symptom confusion with GLRaV-3 diseases such as Esca (wood disease), Shiraz disease (virus), Shiraz decline (cause unknown) and Aster Yellows (phytoplasma) are all worth noting. Conclusion A successful leafroll disease management strategy relies heavily on the correct identification of GLRaV-3 vines. In addition to visual cues, uncertainty can be removed by testing leaf blades/petioles for nutrient deficiencies and/ or viruses. Generally, nutrient analysis is performed before véraison to allow for corrective action before harvest and GLRaV-3 testing after véraison to ensure optimal expression. Regarding the interpretation of visual cues/ symptoms, one must always bear in mind that there is a significant impact of environmental conditions on grapevine expression and both nutrient and GLRaV-3 symptoms may/ or not display seasonal variability. 

PHOTO 8. Manganese deficiency depicted by light coloured interveinal areas covering the entire leaf blade of Verdelho.

Reference https://www.wineland.co.za/leafroll-disease-or-deficiency-symptom/

For more information, contact Etienne Terblanche at etienne@vinpro.co.za.

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TECHNICAL YEARBOOK 2023