Pristine, the new, soon-to-be-registered dual mode of action fungicide from BASF, was the “grand winner” in George Leavitt's Madera County, Calif., powdery mildew control grape trials this year.
Last year the winner was a combination of Flint and Quintec. The latter is another new mode of action material from Dow AgroSciences expected to be available next season as well.
Sovran and Rubigan, Flint and Elite, Sovran and Rally, Kaligreen in combination with Flint, Elite and Nordox, Flint alone alternated with a tank mix of Flint and Elevate; Quintec alone and Rally and Quintec all controlled powdery mildew statistically as well as Pristine.
Where Pristine became the grand winner is that in the trial where Pristine alone was at 28-day intervals — longest in the trial — it reduced powdery mildew to less than 1 percent. None of the others reached that level, however, all those statistically in the same ball park as Pristine in providing more than adequate powdery mildew control to satisfy winery contracts.
The trial was held in one of the most susceptible powdery mildew vineyards in the valley, a Carignane vineyard is surrounded by water just east of Madera where Leavitt each year subjects fungicides to the most rigorous powdery mildew test possible.
Carignane, along with Cabernet Sauvignon and Chardonnay, is one of the most susceptible powdery mildew varieties grown in the state. They are also the only known survivors from a powdery mildew epidemic that virtually wiped out European wine grapes decades ago.
Leavitt, veteran UC Cooperative Extension farm advisor in Madera who is often referred to as “Mr. Powdery Mildew” in the San Joaquin Valley for years of research on the most devastating disease of grapevines said growers have a boatload of good powdery mildew products to select from systemics to contacts. Making them work is the key. That requires proper timing and coverage, especially in the case of contacts, and thoughtful resistance management by rotating compounds with different modes of action.
“I often hear growers say ‘my neighbor gave me powdery mildew’” said Leavitt. “Your neighbor's vineyard may give you more spores and increase the severity of the problem in your vineyards, but if you have powdery mildew it is not because of your neighbor. It is because you slipped up on spray intervals or did not put material on correctly.
“Powdery mildew can be controlled,” he said. To prove his point, he said the untreated check in his Carignane trial vineyard has not been treated in more than a decade. In some years, the vines in the check have been all but killed by powdery mildew, “yet six inches away powdery mildew had been controlled with properly timed treatments.”
This year the untreated vines fared better because Leavitt called 2003 an “average” year for powdery mildew severity. However, it started out bizarre weather-wise. “It was an unbelievable start. I did not think we were going to ever see summer,” he said. “We went from winter to two weeks of spring and then summer.”
It was in those two weeks of spring that powdery mildew “exploded.”
The powdery mildew risk index model developed by UC to help growers decide when to begin treating for powdery mildew triggered early in the year
“The model kicked off twice early and then went down quickly to zero both times,” said Leavitt.
“Growers who treated right away were okay. Those who could not get into the vineyards because of irrigation water or for other reasons waited, had mildew,” said Leavitt.
Leavitt recommended that growers wait after the second trigger incident because the index was indicating a low level of powdery mildew. In hindsight, Leavitt said his recommendation should have been to treat after the second time that the index reached 60.
The index adds and subtracts points based on canopy air temperatures of between 70 and 85 degrees for six hours.
While any new fungicide is welcome, particularly ones with new modes of action to fit into a resistance, Pristine is unusual.
It is the only one effective in a 28-day spray interval. It also may have application beyond in-season powdery mildew control.
Helpful on raisins
Last season, Leavitt sprayed it on raisin trays left in a vineyard until late November to test it as a mold inhibitor. This is three months later than anyone would leave raisins drying in the field. The raisins treated with Pristine were “pretty clean” even toward Thanksgiving.
While that is not applicable, he said it indicated Pristine could be useful as a raisin saver for dried-on-the-vine (DOV) raisins when rain is expected.
“I think there also may be an application for Pristine to hold Crimson Seedless on the vine later in the season,” said Leavitt. “We already cover the vines with plastic, but if we could extend harvest until Nov. 1-15 by using Pristine to keep rot from forming it might give us a better marketing window for Crimson.”
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