Chapter 31

Crop Estimation in Vineyards

Factors Affecting Wine Grape Yields

Vine Health

Yields are strongly affected by management practices (e.g., irrigation, fertilization, canopy management) and biotic stress (i.e., disease or insect pest damage) that affects vine balance and health.

Site Capability

Typically, areas with soils that have high water-holding capacity (such as clay or silt) and organic matter content (>2%, which is associated with nitrogen), along with optimal growing season length (more than 180 frost-free days) and warm average temperatures (daytime highs between 75 and 95 degrees F, 24 and 35°C), result in a greater potential for a large crop load.

Weather Conditions

Overcast, wet, cool or hot weather can result in “poor” fruit set and loose clusters. An extended period of low (<59°F, 15°C) or high (>90°F, 32°C) temperature could interfere with the development of pollen and pistil during the flowering process or the development of the ovule after fertilization.

Cropping History

Overcropping a vine can lead to a decrease in the vine’s carbohydrate reserves (which are necessary for overwintering and spring growth) and a reduction in potential bud fruitfulness.

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