Using Plant Growth Regulators to Promote Bud Break in Grapes

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Matthew Fidelibus and Stephen Vasquez, University of California

Inadequate chilling may lead to poor and erratic budbreak. Photo by Peter Christensen, used with permission of UC Regents.

During winter, grapevines, like other deciduous fruit trees, must experience a period of cool temperatures to resume growth in the spring. Normal winter weather in most temperate regions typically provides adequate chilling, but grapes grown in warm climates may receive inadequate chilling, resulting in delayed and erratic bud break. Insufficient chilling can be overcome by application of hydrogen cyanamide (H2CN2), the active ingredient in DORMEX® (DORMEX Co. USA, Fresno, CA). Hydrogen cyanamide is generally applied to vines after pruning, about four to eight weeks before bud break. Late applications (less than four weeks before bud break) may injure the buds and reduce bud break. Cyanamides are highly toxic, so take great care to follow all safety guidelines outlined in the label.

Caution: Plant growth regulators (PGRs), including hydrogen cyanamide, are classified as pesticides and are subject to the same rigorous regulatory framework. Plant growth regulators may not be approved for grapes in certain regions, or for particular cultivars of grapes. The unapproved use of PGRs on grapes may result in contaminated crops with illegal pesticide residues, so readers should seek guidance from a qualified local pest control advisor before applying any PGR or other type of pesticide to their grapes.

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Reviewed by Eric Stafne, Mississippi State University and Jim Wolpert, UC Davis