Reducing the incidence of fungal diseases
Grapes are subject to attack from a wide range of pests and diseases. Black rot, Botrytis, downy and powdery mildew are all caused by wet weather and if allowed to move from the leaf to the grape can cause considerable wine grape yield loss and quality deterioration.
The most effective control is through protective fungicide applications, opening up the grape crop canopy can reduce disease pressures. A balanced crop nutrition programme will also reduce the incidence of fungal diseases.
Crop nutrition and fungal diseases
Potassium and Nitrogen
One key benefit from getting the potassium:nitrogen ratio right, is the reduction of fungal diseases in wine grape, such as Botrytis. When leaf nitrogen levels are high, plant growth increases and the concentration of plant exudates (e.g. sugar and amino acids) in the fruit rises. When combined with low Potassium-levels (N:K ratio over 2.5) this stimulates the spread of the disease on leaves and fruit. By balancing the nitrogen and potassium levels,(N:K ratio around 1.2) the effects of Botrytis have been seen to minimize.
The K:N ratio effect on disease is dependent upon the absolute level of both nutrients. So, for example there will be no benefit from an increased potassium concentration on the level of Botrytis where high, or excessive, N-levels also occur at harvest.
Calcium
Calcium is beneficial in aiding plant resistance to diseases such as Botrytis on the vine. It does so by strengthening the cell wall membrane, thereby reducing disease impact, and also by directly inhibiting the activity of a specific pathogen enzyme (polygalacturonase), which dissolves the middle lamella of cell walls. Calcium sprays applied pre-veraison to the fruit are most effective.
Recommended Yara fertilisers for grapevines
Related articles
Increasing grape berry size
While smaller grapes may produce a more intensely flavoured, quality wine, the grower needs to balance this with the need for a high yield from well-sized berries on his vines.
Improving grape quality
The aim of any grower is a high yielding, top quality wine grape that satisfies the wine-maker. Both yield and quality are strongly influenced by nutrition.
Managing grape sweetness
The amount of sugar in the grape influences potential alcohol content after fermentation, and the amount of residual sugar remaining in the wine.
Influencing total acidity in grapevines
A certain level of acidity is considered important to the taste of any wine. This can be influenced by crop nutrition
Influencing wine grape colour
Growing temperature and grape variety are the major factors that influence the wine’s eventual color.
Nutrient deficiencies-Wine Grape
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