Fertilizer needs can be determined by 3 ways: observing visual symptoms, using soil tests, and using tissue (petiole) analysis. Because each method has advantages and limitations, all 3 should be checked on a regular basis. Petiole analysis is one of the best tools available to monitor the nutrient status of your grape varieties. Unfortunately, grape producers do not often use it. Tissue analysis serves two purposes: determine the nutrient status of the vine; and identify a suspected nutrient deficiency observed in the vineyard. By using tissue analysis, growers have a better handle on their fertilizer program and usually end up cutting costs since fertilizers are applied only as needed. Here are answers to commonly asked questions about petiole analysis:
Why petiole test if I did the soil test?
When should I do the test?
"Routine assessment": In the Midwest, mid-July through mid-August is the ideal time for petiole sampling for several reasons. Sampling during this time period gives a better measure of Potassium (K). Potassium levels are especially critical for wine grapes since they are correlated with wine quality (high fruit K leads to high pH and thus unstable wines); there is less vineyard activity (if there is such a thing!) during this time of year and more time for petiole sampling; and most importantly, the standard optimum level of each nutrient is based on research of nutrient levels at this time of year. It is recommended collecting petioles about 10 weeks after bloom but before harvest.
What are the most common nutrient deficiencies in vineyards?
What can I expect from the lab?
Take Home Message
Here are the slides from the Wisconsin Grape Growers Association's Spring Vineyard School, March 24, 2017, presentation titled "Vine Nutrition" - A major role in the life of your vineyard.
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