Black spots on cherries

Asked June 24, 2016, 10:06 PM EDT

Second year in a row, my cherry tree cherries have black spots, and do not taste good. What are they? The birds won't even touch them. I rent and have enjoyed the cherries since living here, up til two years ago, when the spots started. Thank you.

Linn County Oregon

1 Response

Hello and thank you for using Ask and Expert. Though not possible to confirm from the photo, I suspect your cherries are infested with Spotted Winged Drosophila larvae. This is caused by a small vinegar fly (fruit fly) laying eggs inside of ripe and overripe fruits. The males of this species have small black spots on the tips of their wings. This is a newer invasive pest that was first identified to be in Oregon in 2009. This critter originated in Japan and has long been a pest of fruits in Asia. The following website will take you to an Oregon State University Extension document that describes this fruit fly’s damage to various fruits and discusses cultural controls to help manage the impact of this critter to your garden.

Basically it calls for cleanup of ALL fruit not harvested or eaten. Leaving fruit on the ground could lead to a heavy infestation, one source I read said as many as 65 adults have emerged from a single cherry. (When picking my cherries I also remove fruit partially eaten by birds and put it in the trash in sealed bags). Putting the discarded or damaged fruit into a sealed plastic bag and leaving it out in the sun for several days to kill the larvae inside the fruit and disposing of the still sealed bags. Do not compost infected fruit as the flies can survive and re-infest your fruits next year. This fly attacks cherries, blueberries, blackberries, plums, raspberries, grapes, and strawberries. If your fruiting plants are near to native vegetation the fly can also survive on things like elderberries and wild blackberries. The pest can continue to multiply as fruit after fruit ripens in the garden each season. Stepping on small fruits on the ground to speed their desiccation and monitoring for the adults are also talked about. To verify that it is indeed the Spotted Winged Drosophila (SWD) fruit fly take a sample of cherries with the black spots into your Master Gardener information desk for verification. If the larvae are present the master gardeners on duty should be able to find them. The Master Gardener desk is located in the OSU Linn County Extension Office in Tangent, 336030 McFarland Road. Phone is 541-967-3871. I recommend calling before you leave to make sure a Master Gardener is on duty.