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Shark tree and vine herbicide label expected in 2003

Shark, an "environmentally soft" contact herbicide for control of broadleaf weeds and certain sedges on tree and vine crops, is moving toward California registration anticipated in 2003.

According to Jim Knabke, research biologist, FMC Corp., Clovis, his company has been working with the product, whose common name is carfentrazone ethyl, for several years. Under the commercial name Aim, it is registered on a dozen crops outside California.

Speaking at the recent 53rd Annual Conference of the California Weed Science Society in Monterey, Knabke said it has low toxicity to aquatic weed and mammalian species and acts on target weeds by breaking down cell walls.

Control is best when weeds are less than four inches tall, and fiddleneck and nightshades are among weeds highly sensitive to it.

"It is among a group of products that the target weeds have no known resistance to, and you can use it for a total vegetation control program with Roundup or paraquat," said Knabke.

Shark may be registered in California on other crops before trees and vines. Company officials say they expect state registration on rice this year and on cotton in 2002.

Milestone awaits Another speaker at the conference, Ronnie Turner of DuPont, said his company's herbicide, Milestone, is not expected to gain registration this year, while review of additional technical data requested by EPA continues.

Turner said the testing on the water-dispersible, granular formulation is expected to take about one year to complete.

Meanwhile, pursuit of federal registrations is arranged in three tiers. The first is grapes, citrus, and vegetation management; the second is cherries, plums, prunes, and nuts; and the third is coffee, blackberries, asparagus, and sunflower.

Azafenidin, the common name for Milestone, controls weeds such as common groundsel, barnyardgrass, sowthistle, spotted spurge, common malva, bearded sprangletop, and others by disrupting cell membranes.

It is said to provide four to eight months of residual weed control, depending on weather conditions and weed pressure. Although it is mainly a pre-emergence material, it does have some postemergence activity as well. It has been evaluated successfully in combination with some of the most commonly used postemergence herbicides and showed no reduction of activity.

Milestone requires rainfall or sprinkler irrigation for activation, and Turner said its volatility is very low, 1,000 times less than that of Roundup. It breaks down primarily by microbial degradation and has a half-life in California of 129 days.

Conference speaker Phil Phillips, Ventura County farm advisor, detailed the glassy-winged sharpshooter, vector of Pierce's Disease of grapes, and its relationship to weed species.

The insect has a preference for broadleaf vegetation in vineyard middles, and although it does feed on grasses, it does not lay eggs on grasses, he said.

Most vineyard cover crops, important to prevent soil erosion and promote water penetration, really have no significant impact in the insect or the bacterium it transmits, he said.

Sharpshooters overwintering in citrus or other evergreens, he said, fall to the ground during freezes. "Then, as daytime temperatures warm up, they crawl or fly to the first green material they can find. Often this is sowthistle or mallow, where they may feed for weeks on end until temperatures warm and they move back into the citrus."

In vineyards having cover crops of bermudagrass, another host for the disease, Phillips said, populations of red-headed or blue-green sharpshooters, also vectors of the disease, may be expected.

However, their populations do not reach the high numbers of the glassy-winged sharpshooters seen in recent seasons.

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