Preventing and Managing Spotted Wing Drosophila Infestation
Our recent mild winter raised concerns about the potential for early season spotted wing drosophila (SWD) damage to berries, which were further increased when South Carolina strawberry growers observed infestation last month.
We have now observed infestation in strawberries, blueberries, and blackberries collected from our research locations in North Carolina. Infestation rates are low (less than 1% in most cases), but these observations underscore the importance of proactive prevention of SWD infestation.
Growers of SWD hosts (blueberries, blackberries, raspberries, strawberries, and cherries) should begin preventative treatment when fruit becomes susceptible, when it starts to change color. Specific treatment recommendations can be found in the Southern Region Small Fruit Consortium Integrated Pest Management (IPM) Guides. This post from a few years ago has more information about timing SWD management.
Dealing with infestation if it occurs
Despite best efforts, SWD infestation may still occur. There is still zero tolerance for SWD infestation in fresh marketed fruit, which means that infested fruit is unmarketable. Here’s a quick summary of some key steps you should take in the event of SWD infestation:
1. Sample fruit regularly to detect infestation if it occurs. Sample fruit each harvest by either cutting them open and looking for larvae or soaking them in salt water (1/4 cup salt per gallon). The video below illustrates a salt test.
2. If you detect infestation, remove as much ripe and ripening fruit as possible and destroy it (by freezing, “baking” in the sun inside a clear plastic bag for a few days, or removing from the site). Eggs or larvae may be present in otherwise sound appearing fruit. Leaving this fruit means that potentially infested fruit is present and could be harvested.
3. Practice excellent sanitation. Thoroughly harvest all all ripe fruit and sell or destroy it (if it’s unmarketable). Do not discard culls in the field, and clean up after rain and u-pickers. Unpicked fruit is a reservoir for SWD larvae.
4. Store fruit cold post harvest for as long as possible. Most eggs and larvae do not develop further at temperatures below 40F, and some may die. If fruit are kept cold, any eggs that may been laid will not hatch, and some may die.
5. Begin or resume an aggressive (once per week if it does not rain, reapplication in the event of rain) spray program. Rotating between at least two modes of action will reduce the likelihood of resistance development.