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Though results are preliminary, representing only the first year of work, a research project studying micronutrient utilization by juice grapevines has found that timing and the combination of nutrients can make a difference in plant response.

Washington State University soil scientist Dr. Joan Davenport and her colleagues at WSU’s Irrigated Agriculture Research and Extension Center at Prosser are evaluating the micronutrient utilization of boron, copper, and zinc in Concord grapes by comparing foliar to broadcast application, timing (early leaf stage or bloom), and micronutrient combinations.

Micronutrient availability is often an issue in eastern Washington’s high pH soils, said Davenport. “Our soils are so alkaline that they tie up the micro­nutrients, and the micronutrients then don’t get to the plant.”

Boron affects fruit set, and is involved with pollen germination and pollen tube development; while zinc is essential to normal leaf development, shoot elongation, and fruit set. Copper is involved in enzyme reactions and plant energy ­relations.

The project is based on recent work done by Suphasuk “Bird” Pradubsuk, a graduate student of Davenport. Pradubsuk excavated Concord vines throughout the growing season and analyzed macro- and micronutrient levels in plant parts to determine when and how much the grape plant used.

Foliar response

Results from the first year of study indicate that the grapevines showed a yield response to foliar applications compared to broadcast, on the ground applications, Davenport said.

Also, she observed an effect from foliar sprays of copper applied at bloom, but not at prebloom or the young leaf stage. Boron was very effective when sprayed at the young leaf stage.

Additionally, the study has shown that combining boron, zinc, and copper into one spray is not as effective as boron sprayed alone or ­copper alone.

Up to now, juice grape growers have relied on experience and products that are commercially available when making foliar applications, she said, adding that this research should give growers quantifiable data in which to base their micronutrient applications.

“Most of the micronutrient foliars that growers are putting on are nutrient blends—what I call vegetable soup mixes. The cocktail blends tend to be whatever the fertilizer salesman has available and often were developed for another crop.”

The research suggests that blends of micronutrients might not be as effective as when they are applied separately, she said. “With cocktail blends, you’ve got all this other stuff that you may not need, and in fact, it might not do anything or not work as well.”

Davenport acknowledges funding support for this research from the Washington State Concord Grape Research Council.