For several years the glassy-winged sharpshooter has caused headaches for California growers, and it was just recently trapped in Oregon. John Aguirre is the new executive director of the Oregon Association of Nurserymen and I asked him about GWSS and its impact on the West Coast.

Q. First off, what is the glassy-winged sharpshooter and why is it dangerous to the nursery industry on the West Coast?

A. The glassy-winged sharpshooter (GWSS) is a large insect, almost 1/2 inch long, and is a part of a family of insects known as sharpshooters, such as the smaller blue-green sharpshooter. GWSS gets its name from its transparent wings. It's a direct threat to grape vineyards and almond trees because it can transmit a bacterium, called Xyllela fastidiosa, which causes Pierce's disease in grapevines and almond leaf scorch in almond trees. The GWSS is also thought to cause oleander leaf scorch disease.

Here in Oregon, we don't see GWSS as a direct economic pest to nursery stock and don't anticipate the insect will affect the quality or quantity of nursery material coming from the state. But, because a lot of nursery stock is considered host material for the GWSS, movement of nursery stock could be restricted.

Q. How big a threat is GWSS to the West Coast wine industry?

A. Pierce's disease is considered a major threat to vineyards. That's why California and Oregon have responded aggressively with quarantine and control programs. The disease has been present in California grape vineyards for a long time, and in the 1880s an outbreak destroyed 40,000 acres of grapes in Southern California. But the introduction of GWSS to California meant that a dramatically more effective vector was introduced to spread the disease. GWSS moves faster and farther than other sharpshooter species and it feeds on older parts of the grapevine, thus infecting a part of the plant where the Pierce's disease bacterium can overwinter.

Q. How long has GWSS been in California, and is it true that the insect is native to the Southeast? How come the insect isn't a problem there?

A. GWSS is thought to have first entered California as eggs on plants. The first adult GWSS collected in California was near Irvine in 1989. Early on, GWSS was confused with another sharpshooter, the smoke tree sharpshooter. GWSS is believed to be a key vector of X. fastidiosa to peach trees and grapevines in Florida, Georgia and South Carolina. GWSS and Pierce's disease aren't as great a concern in the Southeast for the simple reason that the wine industries in those states do not compare in importance to California or Oregon. There is concern that the GWSS could pose a serious threat to Florida and California citrus if a Brazilian citrus disease known as citrus variegated chlorosis is introduced to the United States.

Q. When was GWSS detected in Oregon and how many of the insects have been found in Oregon at this point?

A. In early August, the Oregon Department of Agriculture and the Oregon wine industry grew increasingly concerned about the potential threat of the GWSS and Pierce's disease. When we in Oregon saw the concern in California over the GWSS and the aggressive response of the California Department of Food and Agriculture, we began to discuss what threat it may pose to Oregon. In simple terms, the ODA thought Oregon should apply the same restrictions against California nursery stock originating from areas in that state with GWSS that Californians were applying.

In late August and early September three adult GWSS associated with shipments of California nursery stock were trapped in Oregon's Willamette Valley. ODA quickly launched an eradication program to assure that the insect did not spread. We remain optimistic that our long, wet winters will prevent Pierce's disease and the GWSS from becoming established in Oregon.

Q. When did Oregon impose a quarantine and what has been the immediate impact?

A. Oregon imposed a temporary, emergency quarantine at the beginning of September. The quarantine covers a lengthy list of plants that are recognized as host material for the GWSS and its eggs.

Basically, the quarantine provides that plant material coming to Oregon from areas known to have established, reproducing populations of the GWSS must first be sprayed with a registered pesticide effective at killing all stages of the insect. The quarantine is more rigorous for grapevines. All shipments into Oregon of California grapevines must first be treated for GWSS and a representative sample from the shipment must be tested for Pierce's disease.

We haven't noticed any major impacts on the movement of nursery stock between California and Oregon. Obviously, the quarantine means higher costs, some delays in shipping and more paperwork for some nursery operations, which are not insignificant issues. But, the effort is well worth it to prevent the introduction of GWSS in Oregon.

Q. Have these impacts been similar to what the California quarantine had on growers in that state?

A. Because Oregon doesn't have any established populations of GWSS and Pierce's disease hasn't been found here, our growers haven't suffered the same costs and difficulties that the California industry has experienced.

Q. Are members of the wine industry finger-pointing at the nursery industry and blaming us for this problem?

A. Certainly, when your livelihood is threatened, finger-pointing can and does occur. The fact is, the agricultural community in Oregon has done a good job of sticking together on this issue. I know of no OAN member that would dismiss or want to ignore the concerns of Oregon's wine grape industry. At the same time, I believe Oregon wine grape growers, some of whom are members of the OAN, recognize the importance of this industry to Oregon and the need to be able to receive California plant material and in turn to export plants to other states, at an economic price. The appearance of GWSS as a threat in California is simply another chapter in the story of global plant trade and the pests that threaten our plant resources.

Q. To this point, has the nursery industry been portrayed as the bad guy through this whole ordeal?

A. I can't speak for the California nursery industry, except I know the California Association of Nurserymen has excellent leadership and they are very much on top of this issue. From our perspective in Oregon, no one has been painted as a bad guy. Everyone in our state with an interest in this issue has stepped up to the plate and responded positively. Moreover, no one in Oregon views the California industry as a bad guy. The fact is events like the GWSS are going to happen. What counts is how we respond. And, to date, I think the response in Oregon has been excellent.

Q. We seem to be walking a fine line. Is there a juggling act between doing the right thing and protecting our own interests? What are we doing to make sure that we aren't being forced to take unnecessary or useless actions?

A. Well, you have it right. There is a fine line between responding aggressively and effectively to legitimate pest and disease threats versus responding in a way that unnecessarily restricts the movement of plants. In Oregon, an emergency 90-day quarantine was put into place and ODA is certain to extend that quarantine into the foreseeable future. But we clearly recognize that we have to answer some basic questions that will affect how we ultimately respond. Can the GWSS overwinter in Oregon and does it have the potential to become established? What is the northernmost range for Pierce's disease and can it become problematic in Oregon or further north? What are the most effective eradication and control strategies for GWSS? Great efforts are being made to marshal the necessary resources to research and answer these questions. With research and better knowledge we can refine our quarantine polices.

Q. What's next? Is there any chance of eliminating the GWSS problem or is it something we'll have to deal with indefinitely?

A. Two things will determine what has happened next. We gain new knowledge from research and use it to control or eradicate the GWSS, or the bug expands aggressively into areas where it is not now established. Oregon in the winter is good for nursery plants, but I don't think it's a hospitable place for the GWSS. So, we don't expect to see the GWSS become established here. Clearly, we have to add the GWSS to the long list of pests and diseases that command our attention in this industry. But, the more important issue is to make certain that this industry, working with and through the American Nursery & Landscape Association, participates effectively in the broader debate on a wide range of phytosanitary issues.

Q. What can we learn from this situation and apply to future pest infestations?

A. I think there are two important things to learn. Close cooperation between state agriculture officials and the nursery and greenhouse industries within their respective states is extremely important. In Oregon, the nursery and greenhouse industry enjoys a very strong, positive relationship with our department of agriculture. Because of that relationship we could work closely with our agricultural officials with confidence and trust. When a biological threat arrives on the scene, you don't want your state's response to devolve into a political battle among agricultural groups. You want an agricultural community that can quickly come together to deal with an issue of mutual concern.

Send this article to a friend

Enter your e-mail address:


Enter your friend's e-mail address:


Click the image below to send:

© 2000 Branch-Smith Publishing