Technical Yearbook 2023

Nutritional disorders Temporary nutritional disorders are prevalent in many vineyards and can normally be corrected through targeted management practices. Even though the deficiency symptoms may be clear, the interventions should be guided by soil and leaf blade/petiole analysis to ensure corrective action. While deficiencies are well documented, toxicity and excess can also express symptoms that could be confused with GLRaV-3. Red discolouration of leaf edges can be caused by nitrogen toxicity (photo 4.1), while guttation in luxuriously growing vines can also cause damage to leaf edges (photo 4.2).

Potassium deficiency Potassium deficiency is often prevalent early in the season and symptoms include a yellow discolouration of the interveinal area (photo 5.1) and rolling of the leaf edges. Later in the season leaf edges may discolour completely and turn red (photo 5.2), including the area around the main veins.

PHOTO 5.1. Early season potassium deficiencies cause very lightly-faded interveinal yellowing in both red and white varieties e.g., Chardonnay.

PHOTO 4.1. Nitrogen toxicity on Cabernet Sauvignon, note the shiny leaf blade and the outer edge of the leaf turning red. In severe cases, leaf edges dry out as the season progresses.

PHOTO 4.2. Leaf edges and proximal tips browning due to guttation in vigorous Merlot vines. Guttation refers to the exuding of excess xylem at the leaf edges in low water deficit situations. The xylem charged with minerals dries and causes leaf scorch.

PHOTO 5.2. Late season potassium deficiencies in red varieties (example of Cabernet franc) manifest as a red discolouration at the leaf edges, note the slight yellowing on the inner part of the leaf and vines also turning red.

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TECHNICAL YEARBOOK 2023