Farmer vs. Ant

By JULISSA McKINNON, Register Staff Writer

This growing season grape farmers have a new and organic weapon in their ongoing war against exotic and troublesome Argentine ants.

As the weather warms, ants come out of winter hiding and begin tending and defending the vine mealybug -- a tough-to-spot, slime-secreting vineyard scourge.

To date the tiny yet formidable vine mealybug has infested approximately 500 of Napa Valley's 45,000 vineyard acres, according to the Napa County Agricultural Commissioner's Office. The tiny insect has posed the biggest threat to Napa Valley's sustainable and organic grape-growing trend, in part because Argentine ants have been busily fighting off the mealybug's natural predators. The ants not only defend the mealybugs but sometimes move them to more protected locations so the ants can feed off the mealybug's honeydew secretions.

This spring, for the first time, prospects look more promising for growers committed to environmentally-sound ant control.

Using a new liquid ant bait recently approved by the California Department of Pesticide Regulation, growers could expect to see a decline in ant numbers after a year or two. Ant bait researchers assure the time lag is for the better.

"We're trying to kill them slowly," said Monica Cooper, a researcher with UC Berkeley's ant control studies. "We want them to keep coming back and feeding it to the colony because these colonies are so big it takes a long time" to infiltrate, Cooper said.

The liquid ant bait is not only organic, it's also designed to target the entire ant colony rather than killing individual ants, according to researchers. Argentine ants, which are strictly liquid feeders, are lured by the high-sugar content in the liquid bait, which is also laced with deadly traces of boron -- a certified organic pesticide. Though people can purchase mushroom-shaped bait stations now on the shelf, researchers have taken to fashioning containers out of PVC pipe, which are then placed at the base of an infested vine.

Up until recently, the most common way of exterminating Argentine ants had been killing individual ants on contact by spraying the highly toxic pesticide chlorpyrifos, more commonly known as Lorsban or Dursban. According to the California Department of Pesticide Regulation, the insecticide may be fatal if swallowed or absorbed through the skin and poses environmental hazards to water, wildlife, birds, fish, bees, livestock, people and aquatic organisms.

In recent years growers committed to avoiding heavy-impact pesticides were getting frustrated trying to stop ants with "sticky glue and adhesives," said Katey Taylor, the viticulturist for Domaine Chandon who also leads the Vine Mealybug Workgroup.

"It wasn't practical on a commercial scale," Taylor said of the glue and other adhesive crusades.

Julian Malone, a project technician working with a Central Coast sustainable vineyard team, estimates building your own PVC bait station to be $8 to $10 cheaper per station.

Researchers intentionally gave the ant bait a low toxicity so that worker ants live long enough to share the poisoned feed with the queen ant and ant larvae -- which they feed.

Beating back the Argentine ant paves the way for growers to begin relying on the mealybug's natural predators to tame the white and waxy pest. A mealybug destroyer known as the Australian ladybug preys by hitting the mealybug, piercing it and sucking the juice out of it.

Then there are the parasitic wasps that lay their eggs inside the bodies of the adult mealybug. As the new wasps hatch, they naturally feed on the mealybug.

But with ants guarding the mealybugs, natural predators seldom make it past a mass ant ambush to their mealybug meal.

"Ants are very successful at driving off predators. They're like little soldiers," Taylor said.

Spring Mountain Vineyard has been working with UC Berkeley researchers to test the effectiveness of the mealybug's predators. So far the experiment suggests the natural mealybug enemies show some promise as a reliable form of biological control.

After getting ants under control, Taylor said, introducing the mealybug natural predators may become a much more viable way of beating back the soft-bodied pest.

"Ants have been preventing us from using biological control to control the vine mealybug," Taylor said. "We want to be sustainable. We prefer using good bugs vs. bad bugs."

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