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Nitrogen compounds promote even grapevine bud break

California grape growers want to start growing seasons like a dozen Thoroughbreds lunging with pent up energy out of a starting gate in unison.

They want an even, strong bud break that will ensure a harvest of evenly ripened, quality fruit.

However, like jockeys guiding horses, grapevine buds often need a little help, particularly where there is a shortage of chilling hours, generally in coastal areas and in the southern California desert.

Hydrogen cyanamide (Dormex) has been used for years to break dormancy on fruit crops worldwide to compensate for a lack of winter chilling. The first successful registration of Dormex on U.S. was on table grapes in 1992 in California's Coachella Valley.

Although hydrogen cyanamide had been used for several years to break dormancy, the California Department of Pesticide Regulation (DPR) and the Environmental Protection Agency forced the manufacturer of Dormex, SKW Trostberg Ag of Trostberg, Germany, to register the compound as a plant growth regulator after field problems surfaced.

Registered statewide

It is now registered statewide for use on all grapes because the Coachella Valley is not the only place where there is a lack of chilling hours for grapevines. California's central coast is one area the University of California has identified as virtually identical to Southern California in a dearth of chilling hours with one big difference — the threat of spring frost.

Dormex not only breaks vine bud dormancy, it can advance bud break up to three weeks. That is not a problem in the desert but it could spell disaster for coastal wine grapes subject to frost, according to Western Farm Service pest control adviser Mike Hollarman of Paso Robles, Calif.

In 2002 and last season Western Farm Service's agronomist Jack May began screening Dormex, a product called Erger, and well known fertilizer CAN-17 on California coastal varieties. He discovered that Dormex advanced bud break, but evenness of bud break was marginal. There were phytoxicity problems with Erger when used with a penetrant-adjuvant.

Results encouraging

CAN-17 with adjuvant Break-thru promoted more uniform bud break, which is what coastal grape growers need often.

Results were encouraging, and WFS and Wilbur-Ellis submitted a registration package to DPR, which had ruled in 2000 that any nitrogenous compound applied to dormant plant material to influence bud break is a plant growth regulator/pesticide and as such must be registered. However, before DPR would approve it, the state agency wanted EPA to register it. However, EPA concluded calcium nitrate does not have to be registered as a pesticide because it is a nutrient.

That created a dilemma for DPR, but EPA would not budge from its decision.

DPR considered giving calcium nitrate a state label alone, but finally decided to abide by EPA's decision that calcium nitrate need not be registered as a pesticide — specifically a PGR — as long as it was not labeled as a PGR. It was DPR's version of don't tell, don't ask.

That puts marketers of nitrogenous compounds marketed to enhance uniform bud break in a quandary. Nevertheless, WFS is moving forward with grower meetings in January to detail impressive, independent research that shows these compounds can even bud break. Joining in these meetings will be cherry growers, who have also been using calcium nitrate to improve bud break.

Hollarman and WFS marketing manager Jim Dana of Santa Maria expect coastal grape growers in San Luis Obispo and Santa Barbara counties to expand use of calcium nitrate to enhance bud break once they see what it can do to even bud break.

Hollarman explained that a lack of sufficient chilling can result in very light crop loads. Uneven bud break also creates problems in fungicide application timing, uneven bloom and ripening the crop at the end of the season.

Season-long problems

“Uneven bud break creates season long management problems” said Hollarman. “You can have bunches two weeks to a month behind other bunches on the same vine because of uneven bud break.”

Growers often leave extra canes at pruning to compensate for a possible short crop caused by low chilling. “If there are adequate chilling hours and the vines set a big crop, a growers is faced with the cost of hand thinning extra bunches to achieve premium quality,” said Dana.

“What growers in this area want is not eight tons of fruit, but four tons of high quality fruit,” said Hollarman, adding that when there is an oversupply of wine grapes, if is often quality that sells grapes.

WFS will be marketing two calcium nitrate products, “BudBreak” and “EvenBreak.”

“Dormex is a good product. Clearly, if you want to advance bud break, nothing touches it. However, with the threat of frost in the coastal vineyards, growers are putting vineyards at risks if they advance bud break two to three weeks ahead of normal,” said Western Farm Service's marketing manager Jim Coburn.

“We can have frost in this area until June 1,” explained Hollarman.

WFS tried CAN-17 as the calcium nitrate base combined with a unique organo-silicone surfactant that improves penetration in the wood. “This surfactant is a relatively new technology,” said Coburn. This combination at recommended rates is about $50 per acre, about a fourth of the cost of Dormex.

In trials conducted by WFS agronomist Jack May, the product WFS now calls “BudBreak” significantly improved bud break uniformity in coastal wine grape varietals.

In 2003, May encountered very low chilling hours with some vines sending out shoots in the second week of January.

With green material showing, Hollarman knew CAN-17 would cause leaf burn, so Dana and Hollarman developed a foliar formulated calcium/potassium material they call EvenBreak for use on foliage that would provide safety and still achieve even bud break.

Bud break week

“It is for use literally the week of bud break when you have those seasons when the leaves never fall off the vines,” said Dana.

Surprisingly, neither nitrogen formulation significantly advances vine vigor. “They do not change vigor of the plant by more than a couple of inches. When you have an even bud break, energy goes into the buds,” explained the PCA.

As always, coastal grape growers will be keeping a running tally of chilling hours. However, there are new tools available come spring to give a uniform bud break regardless of what that tally may be.

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