Tiny Holes in Black Currant

Asked June 30, 2018, 3:29 PM EDT

Hello, I want to harvest my black currant (I think it's a Crandall) and all the berries have tiny, scab/hole marks, are lumby and almost deflated feeling, but without being dried. It's hard to see from the photo. I'm guessing it's a bug problem, any idea what kind and what I can do next year? The white currant doesn't have the same problem but instead dropped most of it's fruit before it could ripen :(

Multnomah County Oregon

1 Response

Thank you for the image. I think your suspicion that the fruits have been attacked by insects is accurate. My best long-distance guess is that the culprits are either the currant fruit fly (Euphranta canadensis, also called the gooseberry maggot) or the spotted wing drosophila.

In both instances, the maggots ("worms") develop inside the berries which then typically drop prematurely from the shrub. Both insects survive the winter in organic debris on the soil as well as several inches deep in the soil.

It's best to verify who's active by rearing out the adult flies. To do so, collect a handful of potentially affected berries; put them into a clear container for which you fashion of lid from paper toweling secured with a rubber band. Set on the kitchen counter, out of direct sunlight, while you wait until the adults appear, perhaps several weeks.

If it’s the currant fruit fly, it will be somewhat smaller than a house fly and will look like the images here: https://bugguide.net/node/view/470944.

If the spotted wing drosophila, they’ll closely resemble the small nuisance fruit flies that congregate near over-ripe fruit.

For now, collect and discard all affected and fallen fruits in the trash.

No pesticides are registered for home-use against currant fruit fly but one which is used against the drosophila is: spinosad. You’ll need to read labels to determine which product to obtain. The adult flies are the target. Also, be certain to check the berries carefully, then remove and discard all that are affected.

Unfortunately, neem is only 25 percent effective. (Hardly worth the effort.)

You might consider starting a new planting in a clean area in the fall. Once there, you can protect them next season, and beyond, with floating row cover. See “How to Install Floating row Cover” -- http://cru.cahe.wsu.edu/CEPublications/FS089E/FS089E.pdf .

Caution: If row cover is used in the existing planting area, it will trap the adults when they emerge from the soil in April. Definitely not a good thing!