All creatures, great and small love, love, love the vineyard this time of year. As the fruit ripens, all manner of critter turns up to feast: mammals, fowl, insects. The largest critters are relatively to control — a good fence does the job of excluding deer, though the fence is probably not large enough to keep out a determined bear. Smaller mammals like opossum and raccoon in years past would go under the fence, but this year we reinforced the fence with another layer of rodent wire that was buried a foot in the ground. This was supplemented with an electrified strand run around the perimeter at the top of the fence to discourage climbers.
Birds are another matter — mostly songbirds and crows, but turkey will feast if they can get over the fence. Bird netting deters, but it doesn’t eliminate the damage. This is supplemented with a bird scare device from Bird Gard that plays recordings of birds in distress and hawks in attack. Balloons that supposedly look to them like creatures with large eyes are deployed around the vineyard, but these must be moved often to keep them on their toes. Still, you put the damn things up, and next thing you know the birds are back, ignoring them.
A New Threat: Spotted Wing Drosophila.
The smallest, and latest threat is the most insidious — the dreaded Spotted Wing Drosophila (Drosophila suzukii), a pest native to China, Japan and Korea that made its way to Hawaii in the 1980s, then turned up in California in 2008, making its way to Oregon, Washington and British Columbia. In 2009 it was found in Florida, in 2010 it turned up in the Carolinas, Utah, Michigan, and Wisconsin; and in 2011 in Virginia, New Jersey, Pennsylvania and New England. It’s found in Europe, too — primarily in France, Italy and Spain.
The Spotted Wing Drosophila is all about fruit. It feeds on and lays eggs in apples, blackberries, blueberries, cherries, nectarines, peaches, pears, plums, grapes, raspberries, and strawberries. It loves cherries early in the season, and its favorite host late in the season is grapes. They are extremely prolific; research in Japan shows that as many as 13 generations may hatch per season, and a female may lay as many as 300 eggs during its lifespan. Needless to say, the potential population size is huge.
What is unique about D. suzukii is the female’s serrated ovipositor, which she used to deposit 7 to 16 eggs in ripening fruit. The eggs hatch within three days, and the maggots feed on the fruit. Crop losses can be massive.
Insecticide sprays are ineffective against the maggots, since they are protected within the fruit, so control measures target the flies. But you eliminate one generation of flies and the next rises Phoenix-like from the berries a few days later, requiring weekly toxic sprays to keep them under control. Applying these every three days isn’t desirable — these things are extremely toxic, and that would likely exceed the recommended rate of application. That malathion is especially wicked. Effective, certainly, perhaps too much so — it is particularly hard on bees. Using it feels like resorting to napalm, although a week later the vineyard is again swarming with life. Trapping simply isn’t feasible, and neither is netting. There is no easy answer.
They don’t seem to have made it to Charlotte County — yet. There is a lively discussion among growers about ways to cope, ranging from experimental sprays in the fruit zone of a natural kaolin clay product called Surround (“the flies seem to prefer darker berries — what if we mask them?”), to planting “bait” patches to lure them away from the more desirable crops. Lots of interesting ideas are being bandied about, but for now control unfortunately devolves to chemical means — insecticides.
Besides being toxic, there are many factors to consider when selecting an insecticide: the pre-harvest interval (the the length of time that must be included when it is applied prior to harvest), the number of sprays allowed per season (often very few are allowed, according to the label instructions), the minimum number of days between applications, the re-entry interval (the number of hours or days that must elapse before workers are allowed to work in that field), the mode of action (how it works), whether active through contact or if it needs to be ingested; whether it is rain-fast or not; and its impact on beneficial insects such as bees, spiders and mantids. And the various products need to be rotated to prevent the target insect from developing resistance.
Interestingly, in 2012 Oregon Cooperative Extension published recommendations for dealing with the pest in cherries that mentioned control measures employed in Japan (2012 Spotted Wing Drosophila in Sweet Cherry). That document noted that when conventional insecticide treatments are not an option, such as for organic growers, and “if fruit from pollinizer varieties matures earlier than the main variety and the pollinizer fruit will not to be picked and sold, then pick and remove pollinizer fruit at least one week before harvest of the main variety. This will prevent the SWD from emerging from the pollinizer fruit during the main variety harvest. Fruit removal is a critical control step for organic growers because of the lack of known effective organic insecticides. Conventional growers can suppress SWD on pollinizer fruit by insecticide applications.” There are numerous other guides from nearly every state grappling with this foe, easily found with a search on Google.
It all sound like tilting at windmills. Napalm, anyone? Carpet bombing seems the only solution, with all of its unpleasant repercussions. What a war . . .