So do we need to worry about SWD?
The short answer is yes… SWD adult females have a serrated ovipositor that allows them to cut into nearly ripe and ripe fruit to lay their eggs inside. The larvae then hatch out inside the fruit, rendering it unmarketable. Typical vinegar flies only attack over-ripe and rotting fruit, whereas this insect will attack fruit just before it’s ready to be harvested. Furthermore, wounds in the fruit can also be a pathway for disease organisms to enter. It generally attacks thin-skinned fruit. In Nova Scotia we need to be concerned about it becoming a pest of: blueberries, blackberries, raspberries, strawberries, cherries, plums, peaches, currants and perhaps grapes (mainly table varieties). The verdict is still out on cranberries, but it’s felt that the skin and flesh of cranberries may not be as appealing as those of the softer fruits. Generally, early season crops are not at risk because it takes a while for population levels to build; right now the biggest concern is for fall bearing raspberries and blackberries, blueberries (high and low bush) and day neutral strawberries.
If you grow any of the crops mentioned and are wondering how to monitor for this pest, there are a number of options. Commercial traps are available for purchase, that catch the adults to determine if they are in your area. You can also make your own trap using a plastic container or bottle with a tight fitting lid. To do so, pour a little apple cider vinegar into the bottle, then punch a few small holes above the vinegar line (approx. 1-2cm apart) and check regularly to see if you have caught any of the adult flies. You can check out some models for homemade traps at http://www.ipm.msu.edu/SWD/SWD-monitor.htm. Place the traps in the fruit zone; if your crop is strawberries, place them on the ground. If it’s raspberries, hang them off your trellis system. If you are concerned they may already have infested your fruit, you can do a salt water test. Collect approximately ½ pint of fruit that is ripe (but not overripe) and put it in a large Ziplock bag. Cover the fruit with a salt water solution made up of 1 part salt to 4 parts water. Allow it to sit for 5 minutes and if they are infested you will see small white larvae float to the surface of the water.
Once you’ve confirmed that you have SWD on your farm, what can you do about it? Because this is a relatively new pest in Canada, the PMRA has granted emergency use registrations for a number of insecticide products on a number of fruit crops. In Ontario the recommendation is that if trap catches have confirmed that adults are active in your area, you should consider any of your soft fruit crops at risk and treat accordingly with one of the emergency use registered insecticides. A further precaution is to remove all ‘old’ fruit from the field after harvest and destroy it to reduce the overwintering population of SWD. And of course keep yourself informed because this is a relatively new pest, and there is new information being released all the time.
If you wish to find out more information about SWD, check out our Perennia website for information in our crop specific blogs as well as a new factsheet on the products that have received emergency use registration for this pest. There is also a great summary of this pest on the OMAFRA website: http://www.omafra.gov.on.ca/english/crops/facts/pest-alert-swd.htm
For more information contact Rachael Cheverie, MSc, P. Ag, CCA Horticulturalist Specialist at Perennia at: cell: 902-890-2566 or at rcheverie@perennia.ca
