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The Glassy-Winged Sharpshooter… It’s War!

by David on June 20, 2009

It sounds like some new, secret, stealth airship. And in fact, it is. But the war isn’t a military one. It’s agricultural. And it’s being fought in vineyards throughout California.

The glassy-winged sharpshooter is actually an insect, about one half-inch long. It feeds on the water-conducting tissue of over 35 different kinds of plants and crops, including table grapes and wine grapes.

The feeding itself isn’t the problem. The problem occurs when the insect carries harmful bacteria, Xylella fastidiosa, that causes diseases in plants, including almonds, oleander and alfalfa among others. Certain strains of Xylella can also seriously affect citrus and stone fruits, but we haven’t seen them in California so far. For grapes it means Pierce’s Disease, an extremely serious problem.

Here’s how it works: The sharpshooter feeds on an infected plant, and then transmits the bacteria when it feeds on the next plant. The bacteria get into the grapevine and multiply, spreading throughout the plant’s system, blocking the movement of water, nutrients and minerals. Growth is stunted, the leaves dry and turn yellow and the fruit colors prematurely. Eventually, as the vine becomes weaker, the grapes won’t ripen.

Worst of all, there’s no known cure for Pierce’s Disease – the only solution is to rip up infected vines and replant. So avoiding Pierce’s in the first place is paramount to growers which means fighting the glassy-winged sharpshooter.

Not a new battle, but one with a new seriousness…

Pierce’s Disease has actually been around for quite a while. Back in the 1880s, it wiped out 40,000 acres of grapevines in Southern California. And grape growers throughout the state have been suffering its consequences ever since.

The disease is known in all the southern grape-growing states, from Florida to California and down through Central America and the northern-most parts of South America.

Until recently, Pierce’s Disease was known to be carried by blue-green, green, and red-headed sharpshooters. But with the arrival of the glassy-winged sharpshooter, things got substantially more serious because the glassy-winged sharpshooter has the ability to spread Pierce’s faster than ever.

A stronger opponent…

It used to be that Pierce’s generally affected the perimeters of vineyards. But the glassy-winged sharpshooter changed all that, because it flies farther, faster and deeper into vineyards than its relatives. It flies in greater numbers, wreaking far greater havoc than other sharpshooters ever could. It’s also thought that, since this bug feeds lower on the plant, it could enable vine-to-vine spread of infection – something growers haven’t had to deal with before. If this occurs, they can expect the problem to increase exponentially.

Where did this new army come from?

Most believe the glassy-winged sharpshooter was accidentally introduced to Southern California as eggs on nursery stock. It was first noted in Ventura County in 1990. The growing region of Temecula, in northern San Diego County, noticed a problem back in 1996. By 1997, the damage was spreading like wildfire, and by August of 2000, between $12 and $14 billion of Temecula grapevines had been wiped out. From Temecula, the glassy-winged sharpshooter has worked its way north through several counties and has been sited In Solano County, just over the Vaca range from Napa County. A little too close for comfort.

New armor being developed…

The California Department of Food and Agriculture established a task force and research is underway in coordination with other state agencies, state universities and agricultural organizations to find effective weapons against the glassy-winged sharpshooter. One study, for example, is working to see if altering the nutrition of the grapevine will make it more resistant to Pierce’s.

At the minimum, grape growers maintain a vigilant lookout for the glassy-winged sharpshooter. In fact, citizens all over Northern California have been educated about the pest, through the distribution of pamphlets and brochures with photos and information. Growers are also monitoring their vineyards with sticky traps, and inspecting plants for the bugs and their eggs.

While pesticides are being used in large agricultural areas, biological controls are being studied where pesticide usage isn’t feasible or desirable. Goosecross Cellars, among many other growers in the Napa Valley, prefers to farm naturally and so chemicals aren’t considered an acceptable solution. Other potential solutions being studied include physical barriers, injecting vines with antibiotics and genetic engineering.
In the area of biological controls, we’ve seen great promise with the introduction of a tiny, stingerless wasp – a natural enemy of the glassy-winged sharpshooter. It was imported from Mexico, and has been released in various infested counties throughout California. The wasp parasitizes the sharpshooter by laying its eggs inside those of the sharpshooter. The newborn wasps eventually eat their way out. This has proven to reduce the glassy-winged sharpshooter population without introducing new problems. The hope is that they will reproduce successfully, find the glassy-winged sharpshooter larvae and will become permanent populations. Other parasitic beneficial insects are being tested and appear to be our best hope.
Wisely, Napa County has become a quarantined area, and any plant material entering the county is inspected for the glassy-winged sharpshooter. Residents of Napa County are strongly encouraged to purchase plants from nurseries within the county.

Make no mistake about it, for California’s $2.8 billion wine, raisin and table grape industry, this is war and it looks to be a long one. Those of us on the sidelines should keep our fingers crossed – and keep an eye out for the enemy, the glassy-winged sharpshooter.

For a color copy of the official University of California’s Pierce’s Disease Research And Emergency Task Force Glassy-Winged Sharpshooter Brochure, click here.

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