Unusual galls on bluberry shoots

Asked June 25, 2018, 2:11 PM EDT

I have two young blueberry plants of one variety and two young plants of a different variety. One variety set fruit this year, but the other variety set almost no fruit. Yesterday I noticed unusual growth lumps on the variety that did not set fruit. What are the lumps. Is it a disease of some type and should I trim them off, or treat them in some way? There is a lump on the end of about every branch on the one bush.

Ottawa County Michigan

1 Response

That is blueberry stem gall wasp. This pest has become very common in blueberry fields in Ottawa County over the last few years. It is a native pest which was more of a curiosity than a problem in the past. Blueberry growers are now forced to spray a lot more to control the Spotted wing drosophila fly which lays its eggs in ripening fruit. This increased spraying has apparently reduced the natural predators and parasites which kept this pest down.
Several varieties especially 'Jersey' and 'Liberty' seem to be especially attractive to the wasp. It lays its eggs in young stems during bloom when bees are active so chemical control sprays are out. Ottawa County growers prune them out and many are removing fields of 'Jersey' since the galls also reduce fruiting and pruning them all out takes time and costs a lot of money.
The only control is to remove the galls. If you have one bush with galls on all the shoots I would recommend you remove the bush.
Here is a link on control focused on commercial growers