Hello, We had what seemed to be birch catkin bugs since midsummer, ALL over our birch trees. Every single leaf had about 100 individuals, plus all the catkins, plus every leaf of the concord grape vine nearby. They smell when crushed. They rained all over the yard constantly so we couldn’t eat there, etc. Is there a way to limit their reproduction so there won’t be so many next year? Will they keep increasing, or is there a cycle of some years having more and some having fewer? Info appreciated! Thank you.
Thank-you for contacting Toronto Master Gardeners with your question. Your infestation sounds very annoying and has obviously impacted your enjoyment of your garden!
It certainly does sound as though your problem is birch catkin bugs, or birch catkin feeders (Kleidocerys resedae). These small bugs are oval, about 1/8 inch long and reddish-brown. As you note, they emit a strong, unpleasant odour when crushed. They are especially attracted to white-barked birch trees. Adults overwinter in leaf debris and old catkins. They emerge in spring, mate and lay eggs, then die. The eggs hatch and nymphs begin to grow and feed on birch catkins, beginning in mid-summer. They are mature by the end of August. In heavy infestations, such as yours, they may begin to feed on leaves by the end of the summer and into the fall (even the leaves of other plants such as azaleas and rhododendrons). On sunny days in early fall, they may cluster on the sides of buildings . If they accidentally find their way into the house, it is best just to let them die naturally so as to avoid the smell emitted when they are crushed. The damage to the leaves is not usually severe enough to cause a problem and it comes late in the season, after the trees have sequestered the energy needed for the winter. The primary food source of the bugs is the seeds in the catkins, and this does not harm the tree. In fact, university-based websites such as University of Minnesota and University of Wisconsin do not recommend any treatment for birch catkin bugs.
In this article in Laidback Gardener , there are a few suggestions for reducing the problem. The author also points out that natural predators such as mites and fungi generally annihilate significant populations so that there is a cyclical downturn in numbers after a few years of large numbers of bugs.
The other suggestions for control are the removal of lower branches of the trees so that people do not brush the infested areas and end up with bugs on them, and a strong spray of soapy water (again, this may only be useful on easily reached lower branches). Maintaining good tree health and ensuring that the trees are well irrigated during periods of drought will be key to your trees remaining strong in spite of the infestation. A final recommendation is the clean up any leaf and catkin debris around your trees in fall in order to reduce places for the adults to overwinter, and then shredding the leaves to kill the bugs before using the leaves for mulch.
I hope these suggestions help your situation a bit. Let’s hope that you will see a cyclical down turn next year after your bumper year this season!
October 4, 2023