Feed the vine to feed the crop
The months of July and August can have significant implications on the overall success of a winegrape crop. During this time, the vines are balancing the needs of the fruit, with the needs of the vine health. Mild water stress can help promote uniform ripening with minimal long-term consequences, while severe water stress can have immediate and irreversible consequences on both the vine and the fruit. Severe water stress can cause the collapse of vegetative tissues and reductions in berry size, sugar accumulation and increase susceptibility to sunburn of berries (Grape Pest Management, UCANR). When vegetative tissues are compromised, the vine loses some ability to cool itself, to conduct photosynthesis, and to transport carbohydrates to the ripening fruit. Subsequently, cell division in the berries subsides, sugar accumulation terminates, and berries can dehydrate and wither. Water stress is sometimes used to drive brix up late in the season, but this effect is only due to the relative ratio of carbohydrates to water, not that accumulation of carbohydrates actually increases. Therefore, when severe water stress occurs, berry health and weight are compromised to meet the brix requirements of the contract.
There is a better way! Vines have the inherent programming to balance the needs of the plant with the needs of the fruit, however, these processes can be turned “on” or “off” depending on the nutrition levels of the plant relative to the demand of the crop load. As the stress of ripening fruit and maintaining vine health coincide, we need to consider critical elements that can effectively support both processes. Calcium and potassium support proper functioning of the guard cells of stomata to regulate internal tissue temperatures and indirectly support photosynthesis. Nitrogen, magnesium, and zinc support the development of chlorophyll molecules to carry out photosynthesis and produce carbohydrates (or sugars). Lastly, phosphorous aids in the transport of carbohydrates to the berries.
These processes do not occur in isolated events. Proper balanced nutrition is required to enable all of these processes to function simultaneously to support your end goals of yield and quality year after year. Crop nutrition programs should be built based on the needs of individual fields.
