Spotted wing drosophila infestations can quickly turn a ripe, marketable piece of fruit into a mushy disaster. Controlling this tiny, invasive pest requires a multipronged approach that includes insecticide treatments, cultural controls and postharvest pest management.
An invasive pest, the spotted wing drosophila is native to mainland Asia and was first detected in the United States in 2009.
“Spotted wing drosophila populations are now established everywhere berry crops are grown,” says Dr. Hannah Burrack, an entomologist with North Carolina State University.
Optimize cultural controls
Adjusting cultural control practices can help manage this costly pest.
Dr. Burrack’s research, presented at the 2019 Southeastern Fruit & Vegetable Conference, documented higher spotted wing drosophila infestations in the middle of blackberry bushes. While additional pruning can reduce infestation rates in blueberries, studies have not found that to be true in blackberries and raspberries.
A cultural control practice that holds promise is harvest frequency. Picking fruit every two days results in reduced infestations compared with picking every three days.
“Harvest frequency has the potential to reduce infestation of the fruit. Infestations are further decreased by daily picking of fruit,” she says.
Target insecticide timing
Preventive insecticide applications, made at optimum times, are critical to controlling spotted wing drosophila.
According to North Carolina State University research, low but detectable fly populations are generally found in berry production from early in the growing season to midsummer. Populations tend to explode later in the summer and coincide with fruit ripening. Berries are most susceptible to spotted wing drosophila damage when they are changing color or pinking-up. At highest risk for damage are blackberries and raspberries, while fruiting blueberries are also at high risk for damage.
“Cane berries are spotted wing drosophila’s preferred host when available,” Dr. Burrack says. “We are growing an attractive host crop when infestation is likely because of high populations of spotted wing drosophila. Risk is directly related to population size.”
Managing risk requires managing pest populations with insecticides when fruit is most susceptible to insect damage and when spotted wing drosophila flies are more active. That means focusing control sprays at dawn or dusk when flies are most active.
A season-long management strategy with multiple modes of action is key to long-term control and minimizing resistance development. Including Delegate® WG insecticide in your program — with a one-day preharvest interval in cane berries and blueberries and a unique mode of action — enables better control of spotted wing drosophila and other damaging pests during harvest when control is critical to fruit quality.
Delegate contains spinetoram — an innovative active ingredient that delivers fast knockdown of a wide range of yield-robbing insects, including leafminer, leafroller, thrips, spotted wing drosophila and several worms.
Delegate effectively controls insects and worms through translaminar, contact and ingestion activity. A Group 5 insecticide, Delegate offers a unique mode of action that is ideal for insecticide resistance management. It has minimal impact on beneficials and does not flare mites. Delegate also offers growers convenience, with a short four-hour re-entry interval, providing maximum management flexibility.
Keeping harvested fruit as cold as possible for as long as possible can also improve fruit marketability.
On-farm cold storage is a critical spotted wing drosophila control tool for growers because the pest stops developing at 35 degrees F, says Dr. Burrack.
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