Spotted Wing Drosophila (SWD) Detected in Grapes and Berry Crops in Indiana
Bruce Bordelon, Department of Horticulture and Landscape Architecture and
Rick Foster, Department of Entomology, Purdue University
We have been monitoring the population of spotted wing drosophila (SWD) across the state with traps this season. Throughout June and July only a few adults were captured in traps. Over the past few days, however, the numbers of adults and incidence of damage to fruit has increased dramatically. SWD has been found attacking grapes and berry crops at Purdue research farms in Vincennes and Lafayette and in commercial plantings elsewhere. SWD is attacking any berry or grape that has softened and begun to ripen.
One of the most recent invasive pests affecting fruit producers is the spotted wing drosophila (SWD), Drosophila suzukii Matsumura (Diptera: Drosophilidae). This insect is a serious pest of soft fruits such as blackberries, raspberries, blueberries, grapes, strawberries, cherries, and peaches. It can also infest apples, apricots, and tomatoes that are damaged.
There are many species of native vinegar flies that are attracted to ripe, over-ripe, or decaying fruit. SWD, on the other hand, is capable of infesting healthy fruit in the field because of the presence of a serrated ovipositor that allows the female fly to cut through the skin of many soft fruit to lay her eggs inside. Most fruits become attractive for oviposition as they begin to turn color during ripening and sugar levels increase.
This pest is apparently a native of Japan and was discovered causing serious crop injury in California in 2008. Since that time, the spotted wing drosophila has spread throughout many of the continental states. The detection in Michigan in the fall of 2010 was the first confirmation that this insect had reached the North Central region. SWD has since been found in a number of North Central states. The first confirmed record of SWD in Indiana was on October 16, 2012 in a home garden in Blackford County in east-central Indiana although we have undocumented reports of infestations earlier in 2012.
Detection: On grape berries, look for small puncture wounds that may or may not be leaking juice. Cut open, peel, or smash the berry and look for larvae. The larvae are white and small, about the diameter of mechanical pencil lead (0.5 mm) and about 2 mm long. There may be several in each berry. In addition, look for small white larvae on the surface of berries. We have observed an abundance of larvae on the outside of berries after an insecticide was applied in research plots recently.
On raspberry and blackberry, tease open or smash the fruit carefully and look for larvae. Any overripe or soft fruit is likely to be invested. As with grapes, there can be several larvae in each berry.
Control: Even though this is a new pest in our region, there are recommended control measures in the 2013 Midwest Small Fruit and Grape Spray Guide. Since the Spray Guide was published we have learned more about insecticide efficacy against this pest thanks to work by Rufus Isaacs at Michigan State University.
Several insecticides are registered for use on berry crops and many are effective against SWD. The following table lists the recommended products. It is important to consider the pre-harvest interval (PHI) when applying any pesticide close to harvest.
Table: Efficacy of insecticides for control of Spotted Wing Drosophila
In our opinion, Mustang Max is the insecticide of choice due to excellent efficacy and short (1 day) PHI. It is limited to six applications per season so growers may need to rotate with another product. Delegate/Radiant would be a good alternative as it also has good efficacy and a 1-day PHI and is a different mode of action from Mustang Max.
If growers find any damage or evidence of infestation, we suggest you spray immediately to try to knock down the population. You will likely need to make a second application a few days later to kill the new adults that emerge after the initial application.
See Facts for Fancy Fruit Vol 13 Issue 6 July 3, 2013 (pdf file) for more info about SWD.
Note: A restricted-use product may be bought and used only by a certified applicator or persons under the direct supervision of a certified applicator. Commercial and private pesticide applicators must keep written records of all applications involving restricted-use pesticides for at least two years from the date of application. Restricted Use Pesticides can only be purchased and applied by certified pesticide applicators. Growers are qualified to use RUPs because they have passed the core exam and have a current permit.
Click image to enlarge
SWD puncture wound on grape (Bruce Bordelon)
SWD puncture wound on grape close-up (Bruce Bordelon)
SWD larvae under skin of grape (Bruce Bordelon)
SWD larvae on outside of grape (Bruce Bordelon)
SWD larvae on grape pulp (John Obermyer)
SWD larvae inside blackberry (John Obermyer)
SWD fly on unripe raspberries (John Obermyer)
SWD larvae inside raspberries (John Obermyer)