SWD has been a concern to the fruit industry since its arrival in California from Asia in 2008. By 2010 the pest was being detected in soft skinned berry crops from coast to coast throughout North America. In 2012, berry crops in Michigan were severely damaged--especially the highly vulnerable raspberry crop. But much has been learned about SWD since 2012, as horticultural crop researchers and cooperating fruit farmers shifted into high gear to understand the new pest and to devise effective strategies for control.
Spotted Wing Drosophila is fruit fly--a close relative to our common "vinegar fly", that tiny pest that hovers around your kitchen during the summer months as you process your dill pickles. Vinegar flies normally only "attack" soft over-ripe or rotting fruits. What makes SWD different is its unique serrated ovipositor, which enables it to saw its way into the stronger skin of healthy fruit to lay its eggs.
One of the challenges for controlling SWD is the fact that it is a multi-generational insect, able to mature from an egg laid, to an adult fly capable of laying eggs, in a ten day cycle. Population increase is logarithmic, and can become explosive during the later summer season. As the produce industry maintains a "zero tolerance" for the presence of insect larva in fresh fruit, only the most diligent farmers will likely be able to meet the standard for marketable fresh berries--especially raspberries--given the current presence of SWD in the surrounding environment. It is true that some farmers across the country are choosing to get out of the raspberry business, unwilling or unable to rise to the SWD challenge. Others, however, choose to tackle the problem, work with the researchers, and apply what is being learned with a willingness to modify their management practices and harvest/marketing strategies in an effort to control the pest. Many are succeeding.
At HIGHLAND VALLEY FARM, a first step was to abandon plans to grow late fruiting or fall fruiting raspberry varieties. Early fruiting raspberries are less pressured by SWD. A second step was to learn how to best scout for the pest, a management tool that has been refined and improved almost annually by researchers as they continue to develop better traps, more effective lures, and modify threshholds for injury. We also control the pest habitat by keeping thoroughfares closely mowed, hedges well pruned and open to sunlight using a "vee" trellis to spread the canes. When scouting indicates an increasing pest presence, we spray. Both organic and benign conventional chemical controls are available with zero or one day re-entry or harvest restrictions.
ALL raspberry fruit is harvested on an every other day basis at our farm. If pick-your-own customer turnout is light, we will pick any ripe fruit left in the field. Raspberries we pick are immediately cooled and refrigerated, and we advise our PYO customers do the same. Refrigeration will immediately arrest any SWD eggs that might be present, preventing those eggs from hatching. During the harvest period, raspberry fruit is sampled in the field several times a day. As soon as a single live lava is detected, the raspberry pick-your-own harvest is curtailed for the season. Our late season raspberries are then machine harvested on an every-other-day basis and immediately frozen for later processing use.
If you want to pick raspberries this season, they will be available--as delicate, sweet, and attractive as you remember them. My advice to would-be raspberry pickers is know what your farmer is doing to manage Spotted Wing Drosophila, come early in the season, come early in the day, and refrigerate or, better yet, consume or process your harvest as soon as possible. There is no fruit more special than fresh red raspberries!