Insecticide For Spotted Wing Drosophila

In December 2016, the spotted wing drosophila (SWD) was identified in the Lower Mainland of British Columbia. This news came as a surprise to many British Columbians, who haven’t seen this pest since the 70’s. SWD is a small (5mm) relatively new invasive fruit fly pest found in Europe that is known to have a detrimental effect on fruit and vegetable crops. The Spotted-wing Drosophila has inflicted a lot of damage on the local grape industry of San Joaquin Valley. As the name suggests, this fly resembles a fruit fly, but it has a wingspan of 1/8 to 1/4 inch and two distinctive spots on its wings. It is native to tropical and subtropical regions of Central and South America. The Spotted-wing Drosophila is an invasive species that was first documented in southern California in 2008.

Insecticide For Spotted Wing Drosophila

First reported in Kentucky in 2012, we found spotted wing Drosophila (SWD) to be widespread in the state by midsummer of 2013. This new invasive pest lays its eggs in the flesh of many types of soft skinned fruits, most commonly in small fruits and berries. Attack begins during the harvest period resulting in collapse of the fruit after harvest and small larvae in the fruit.

SWD is a serious threat to small fruit production, the adults lay eggs under the skin of otherwise sound fruit. This can result in small larvae in the fruit at harvest or just after harvest. In addition to damaging a large percentage of a crop, this pest also has the potential to upset customers and ruin markets. Blueberries, blackberries and raspberries are very susceptible to this new invasive pest. However, in the SE US, June-bearing strawberries have not experienced these large losses and have lower risk to SWD than other later-ripening small fruit crops.

Figure 1. A SWD female with the arrow pointing to its modified ovipositor and wing cross vein.

Trapping in 2013 in commercial plantings detected SWD in 20 counties in all regions of the state. While these traps detected flies before fruit infestations were observed, in other states traps have not been consistent in their ability to detect adult SWD activity prior to fruit infestations being detected. In many states, commercial growers have had much more consistent results using host susceptibility (fruit beginning to soften and turn color) to time SWD sprays for highly susceptible small fruit crops destined for fresh market rather than using trap catch results to initiate sprays.

Producers wanting to use traps should read Entfact-229, Spotted Wing Drosophila Biology, Identification, and Monitoring, for a description of the traps and their use. While we encourage growers to use traps, spray timing should be based on fruit susceptibility with highly susceptible mid-summer and fall crops. Traps can be made with materials commonly found at home.

Figure 2. A male SWD showing the wing spot and front legs ‘banding.’

In other states where SWD has become established, producers need to spray periodically during the harvest period to reduce losses. Because of this, producers need to coordinate their harvests and spray timing in order to comply with pre-harvest intervals (PHIs) and seasonal limits with the respective insecticides. As the small fruit crops are harvested several times a week, harvest schedules limit the types of materials that can be used. Insecticide trials in OR, WA, CA, MI, NJ, NC, FL have identified a number of effective materials to protect small fruit crops from SWD. Some insecticides in the organophosphate, pyrethroid, spinosyn, and carbamate classes have demonstrated good activity against SWD. The neonicotinoids have not been as effective as some other classes. Conventional and OMRI approved sprays are available. There are also a few materials in the registration pipeline that have been shown to be effective.

Cultural Controls

There are several cultural controls that may be helpful. The first is frequent harvest and clean picking, also referred to as sanitation. This requires removal of overripe and damaged berries from the planting at least every other day. Raspberries that are picked a bit on the pink side will continue to ripen. Pickers can use two buckets, one for the marketable berries and the other for culls. Burial of infested fruit has not been effective as the SWD can still emerge. To destroy SWD in cull fruit, place fruit in clear bags and leave them in the sun. This should kill any SWD that emerge from the culls.  Wine makers should manage pomace disposal to avoid issues with SWD and other fruit flies as well.

Post-Harvest Handling

Chilling of the fruit immediately after harvest is essential. Ideally fruit should be held just above their freezing point to not only arrest SWD development but to also kill many of the eggs and older larvae. However, even at 40F, SWD development is arrested and fruit quality preserved.

Wild Hosts

Removal of wild hosts (wild brambles, poke weed, mulberries, and honeysuckle for example) near commercial plantings may help but is not always practical or possible.

Insecticidal Control

While trapping can be used as a monitoring tool, commercial producers of highly susceptible small fruit crops should initiate SWD sprays when the fruit become susceptible. On these crops, the initial spray is applied a week before the expected first harvest. Sprays need to be in place prior to oviposition (egg laying), and coverage needs to be thorough as the adults often hide in the dense portions of the canopy. So, high pressure and spray volume will be needed to reach these difficult to reach spots and provide thorough coverage. Even the best of the insecticides will not consistently last more than 7 days so, at a minimum, weekly applications are needed. With heavy rains, sprays need to be reapplied.

Producers must rotate among insecticides with different modes of action (IRAC Group) to prevent/delay resistance. A general rule of thumb is to switch modes of action with each new pest generation, which would mean switching to a new IRAC insecticide group each week. Since this pest can complete a generation in less than two weeks, we need to switch modes of action weekly and have multiple types of insecticides available. With a limited number of modes of action available, we cannot afford to lose the effectiveness of materials to insecticide resistance.

Insecticide For Spotted Wing Drosophila

Spotted wing drosophila is an invasive species of fly that has been attacking the fruit industry for decades. The problem is particularly bad in California, where growers have lost $250 million to the pest since 2012.

One way to help combat this pest is by using insecticides. Insecticide should be applied as soon as possible after seeing the first signs of spotted wing drosophila infestation, because it can spread quickly and it’s hard to control once it has set up camp in a crop.

There are several types of insecticide available for use against the spotted wing drosophila: contact and systemic insecticides, organic pesticides, and biological controls (which use natural predators).

List Of Insecticide For Spotted Wing Drosophila