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Fungicides curb garlic rust in trials

Rust disease struck the California garlic industry during the cool and wet conditions of 1998, in some cases hard enough to cut yields in half and reduce value per acre by nearly three-quarters.

Tests that year by Richard Smith and Steve Koike, Monterey County farm advisors, showed that fungicides Folicur and Quadris gave protection when applied in advance of extensive development of the disease.

A Section 18 registration for Folicur for use on garlic was issued in 1998 and has been renewed each year since. Registration of Quadris is pending with the California Department of Pesticide Regulation.

Fungicide applications have typically begun in late January when the disease appeared, but Smith said some adjustments in timing could be made.

The disease, Puccinia allii, does not kill garlic plants outright but can sharply reduce the weight of bulbs. It persists even after the conditions initiating it are absent.

At the recent Garlic and Onion Seminar at Five Points, Smith said, “It showed up in dramatic fashion in 1998 during the El Nino weather pattern. We had never seen it before, but it was reported along the coast in the 1940s to a lesser degree than we saw in 1998. The disease came again the succeeding two seasons but was less severe.”

Check 30 varieties

In their 1999 trials Smith and Koike looked for resistance in more than 30 garlic varieties inoculated with the fungus. Although susceptibility varied, they did not find adequate resistance in any of the cultivars. Varieties having less susceptibility were from foreign sources.

Recalling 1999 and 2000 seasons on the coast, Smith said some plots intentionally left untreated with Folicur developed rust to the high levels of 1998. In a trial in King City, 50 bulbs from Folicur-treated plots weighed 8.3 pounds, while 50 from untreated plots weighed 4.3 pounds.

“It's probably similar to the situation with late blight of tomatoes or powdery mildew on peppers.”

“It's probably similar to the situation with late blight of tomatoes or powdery mildew on peppers,” Smith said. However, he added, in the San Joaquin Valley, many fields not treated with Folicur in 1999 and 2000 failed to develop the rust to serious levels.

“This indicates,” Smith said, “that an important environmental component may be involved with the disease development of garlic rust in the various parts of California.”

While garlic is highly susceptible, onions and chives are less susceptible. Leek, elephant garlic, and shallot are not affected by the disease. It continues to be a problem in the Salinas area on green onions, whose market depends on blemish-free leaves.


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