Get ready for SWD in your small fruit

If you grow small fruits such as raspberries and blueberries, be on the lookout for spotted wing drosophila (SWD). A relatively new insect, SWD, is once again poised to make its appearance in Chippewa Valley gardens.

SWD is native to Asia, and was first detected in mainland United States in California, in 2008. It has since spread throughout the U.S., and has become the most economically important insect pest of berries.

Male SWD have dark spots on the outer margins of their wings. Female SWD have a saw-like ovipositor (organ for laying eggs) that they use to cut the skin of ripe or ripening fruit, and deposit eggs inside the fruit. Once eggs hatch, the larvae are found inside the fruit.

Sounds yummy, doesn’t it?

To care for your small fruit crop, you should begin controlling them. A small amount of SWD can cause a large amount of damage on the fruit, by laying eggs in multiple berries. Gardeners growing strawberries, raspberries, blueberries, grapes and other soft fruits, should plan ahead to decide how they will manage SWD and order any remaining supplies before SWD populations grow.

Strawberry, honeyberry, summer-bearing raspberry and blueberry growers, should be monitored closely at this time, as those crops are either already in-season, or will be soon.

Good management of SWD involves a mix of cultural, preventative and chemical (either organic or synthetic pesticide) practices. For home gardeners with small fruit plantings who are willing to tolerate some damage, it may be sufficient to avoid most SWD damage without pesticide application, by using preventative methods.

Based on a 2019 survey data by University of Minnesota researchers, daily harvest is the most common SWD management method among raspberry growers. Additionally, a Michigan State study has found that harvesting every one to two days significantly decreases berry infestation rates, compared to berries harvested every three days.

Another preventive practice is to refrigerate the berries right away. In addition to harvesting frequently, refrigerating the berries as soon as possible after harvesting, prevents the fruit from degrading, even if it has already been impacted by SWD.

Get bad fruit out of the garden as soon as possible. Removing and destroying infested or dropped fruit, stops the eggs and larvae from turning into adult flies, potentially reducing the SWD populations in the field. You can also disrupt their habitat.

Landscape fabric, mowing and heavier pruning may, in theory, reduce SWD populations by making the garden less hospitable to them. SWD retreat to cool plant canopies and grassy areas during the hot parts of the day. Furthermore, they are poor fliers and do best under less windy conditions. Therefore, minimizing these habitats may help decrease SWD pressure.

The use of netting structures around the crop to exclude SWD may also help in keeping SWD out of the planting. This is a technique that can be used by either gardeners or farmers, because it can be scaled up or down to fit the needs of the grower.

Organic insecticides and repellents are effective to control SWD. Spinosad is available to home gardeners and is considered the most effective organic pesticide option for SWD at this time. Gardeners should have a couple products on hand and not rely heavily on Spinosad for SWD control, as resistance can develop.

Pyrethrins like Pyganic can be used as well, however Pyganic is not as effective as Spinosad. You may ask about essential oil repellents. Research is ongoing in this area and no recommendations can be made at this time. While neem oil can be used for SWD, its efficiency is considered poor.

Because organic insecticides are limited and can be very expensive, organic gardeners are encouraged to develop more robust approaches for management of SWD, involving nonchemical (cultural and preventative) practices listed above.

Synthetic pesticides are available to home gardeners for SWD management and are limited. Sevin (carbaryl) is the most easily accessible synthetic pesticide for SWD for home gardeners. Carbaryl is a broad-spectrum insecticide and will also kill pollinators.

If using a synthetic insecticide, remember to read and follow the label! Those wishing to use carbaryl should follow guidelines for protecting pollinators, such as spraying in the early morning or evening.

Controlling SWD in your garden is challenging and it can be done with a mix of cultural, preventative and, if needed, chemical options.