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Grapevine tissue sampling at veraison

As a follow up to yesterday’s post on scouting your vineyard for system disease and/or nutrient imbalance symptoms…

Grapevine tissue (leaf blades and/or petioles) sampling is a good, objective indicator of nutrient status in your vineyard.

Many southeastern US vineyards will be entering veraison over the next couple weeks. Veraison (commencement of ripening, sugar accumulation, and coloration) represents one of the stages that nutrient guidelines have been developed for evaluating vine nutrient status. The other growth stage in which nutrient guidelines have been developed is at bloom. This brings into question “which stage is best?”… See below for some considerations that I hope will help you decide.

Veraison in Chambourcin

When to collect grapevine tissues?

Within-season. There are two phenological (growth) stages for which grapevine nutrient guidelines have been developed: bloom and veraison. Bloom, also called “flowering”, is the stage at which flower caps fall from the flower clusters. Veraison is the stage at which grape berries soften (white cultivars) or become colored (red cultivars) and transition to ripening. Since mineral nutrient concentrations fluctuate in vine tissues over the growing season, leaf blades or petioles should be sampled at bloom or at veraison to routinely monitor vine nutrient status. Sampling at bloom may allow time for nutrient adjustments to be made within the current growing season, although the success of post bloom fertilization depends on many factors including method of application, properties of material used and weather conditions. Sampling at veraison is better for diagnosing macronutrients such as nitrogen (N), phosphorus (P), and potassium (K) due to the high concentrations of these nutrients during bloom and their relative mobility within the plant.

Over seasons. Leaf blade and petiole sampling should be conducted on a routine basis to monitor nutritional health before a given nutrient limits crop yield or substantially reduces vine growth. It is unnecessary to sample soils every year. However, conducting tissues tests annually (or every other year once you have sufficient experience with a given block) ensures that fertilizer inputs are catered to optimize vine nutrition and meet production goals for each vineyard block. Routine tissue sampling is thus recommended for Georgia vineyards. It is important to collect samples at the same growth stage each year to avoid errors that result from seasonal fluctuations in nutrients. It is helpful to monitor vine growth at the time of sampling, as well as keeping records of yield and pruning weights for each block to aid in the interpretation of tissue test results. Nutrient concentrations in plant tissues can be diluted by rapid growth. Tissue tests are used also to diagnose suspected nutrient deficiencies or toxicities encountered in the vineyard. We recommend collecting a tissue sample from both symptomatic vines and a separate sample from healthy vines nearby, if at all possible, when diagnosing potential nutrition problems. Samples from the healthy vines should be collected from leaves of the same age as those displaying symptoms.