Spotting the Uninvited

By Mark Stock

Winemaking is an ongoing teeter-totter ride shared by man and Mother Nature. Vineyard crews and winemakers are always outweighed in power and scope by nature herself, but are extremely adaptive and can create balance out of her sometimes-unfair ways. Outside of unfriendly weather, pests may be the most disruptive natural - or unnatural, depending on origin - vineyard foe Oregon grapegrowers face.

The newest character in the cast of viticultural villains is an insect no bigger than an eighth of an inch. And although the Spotted Wing Drosophila (Drosophila suzukii) caused no major damage to the '09 harvest, the fruit fly had only just been discovered locally that year. Some legitimate concern is already mounting for the 2010 crush. Because the fly prefers healthy, ripened fruit - as opposed to rotting fruit like many insects - it is still uncertain what kinds of problems this pest may bring with it. Vintage 2010 is only just underway.

Originally from Asia, this particular fruit fly has carved a grim reputation in Hawaii and Spain. California was the state to spot the pest in 2008 in cherries and berries. According to the Oregon Department of Agriculture, up to 65 adults can emerge from a single cherry. Their prolific nature is troubling, as the females lay close to 400 eggs over a lifetime. Researchers in Japan have witnessed 15 generations of the Spotted Wing Drosophila population over the course of a single growing season (April through November).

The state of Oregon issued over $200,000 in funding for research and pest monitoring after the Spotted Wing Drosophila was found in blueberries in 2009. Oregon State's Horticulture Department is a big part of the investigation, and fruit farmers throughout the valley are encouraged to share findings. Fortunately, Oregon farmers run many generations deep and have encountered winged dilemmas like this before. 

Phylloxera, Glassy-Winger Sharpshooters and Mealybugs are among the many arthropods that have caused considerable damage to area vines. Yet, with early detection and a viticulture scene that grows wiser every year, grape farmers will hopefully squash the Spotted Wing Drosophila before it even takes flight.

Test Your Vines

Adapted from Oregon State University

As a young potential threat, Oregon growers are urged to test their own sites to determine just how big the problem may be. With the following supplies, you can determine how your fruit is faring.

You'll need: clear plastic cup(s), fitted plastic cap(s), yellow sticky trap card(s), metal hanger(s) or wire(s), and apple cider vinegar or sweet wine.

1. Drill four to five 3/16- to 3/8- inch holes in side of container for entry of the flies. Leave 3-inch pour space for vinegar.

2. Cut a cross section in the top of the lid to allow hanging of the sticky trap.

3. Affix a twist-tie or wire to the top of a yellow sticky card, and affix to the top of the lid for easy removal.

4. Pour 1½-inch apple cider vinegar in the bottom of the cup, making sure to keep the sticky trap above the liquid. 

5. Close the top and place the traps in areas you wish to monitor in the vineyard.

6. One trap will service one acre. Place in or near the fruiting wire of the trellis or on the ground later in the season where thinned fruit may exist.  

Observe the catch in your trap(s). These flies are bigger than average fruit flies. A magnifying glass will help identify the signature spot on the wing of this drosophila (males only) and their red eyes. Females lack these characteristics and instead have saw-like ovipositors on their backsides. It's advised you refer to management guidelines provided by Oregon State University (see links below) if Spotted Wing Drosophilas are found.

Signs of Infestation

From the Oregon Department of Agriculture

• Small puncture wounds on the fruit.

• Soft fruit, starting at puncture scar.  Secondary pests may cause additional damage at this point. 

• Small, pale maggots in fruit.  

Links
swd.hort.oregonstate.edu • wine.oregonstate.edu/files/files/drosophila%20zudikii.pdf ipm.ucdavis.edu/EXOTIC/drosophila.html  

Mark Stock, a Gonzaga grad, is a Portland-based freelance writer and photographer with a knack for all things Oregon.