Defoliation of Tree and Bushes
Roughly 6 years ago I lost a Maple tree due to an unknown reason. Last year I lost a Currant bush due to a similar reason. This year my Snowball bush, Linden tree, and Birch tree are all infected with what seems to be the same problem. It looks like the leaves are being eaten. I see tiny black dots (possibly eggs) on the underside of leaves. On my Currant bush I noticed a tiny green worm/caterpillar. On the Birch tree I found multiple bugs (see attached photo). I cannot find anything on the Snowball bush. It is the most affected. Please advise what the pest is and how to treat. Thank you!
Livingston County Michigan
Sorry for the slow response. It can be confusing, but different pests (insects, disease pathogens, etc.) can cause similar symptoms. More often, biological pests will have a limited host range, so it is unlikely that the same biological pest would destroy all of those species in your landscape. Though of course, there are exceptions and pests with pretty wide host ranges (things can never be too simple). Still, I think it's unlikely that the same pest is causing issues on all of the types of plants you mentioned. Environmental issues are a different story, so think about the drainage, soil quality, light conditions, etc. in your yard, in terms of what might be harming multiple plant species.
That looks like a viburnum snowball bush, so I'm guessing that the pest to blame there is the viburnum leaf beetle. Keep looking for the larvae, then soon the beetles, and later in the season, the egg masses. Please see this article: What’s eating my viburnums and how can I stop it? from MSU Extension
With the birch and the linden I am less sure what the issue is, but I wouldn't worry about it as much unless you're seeing very severe defoliation. Otherwise healthy trees can tolerate some feeding and defoliation. If you're concerned you can try to support overall tree health with proper nutrients and watering during drought stress. You might want to consider getting a soil test to make sure your soil has the proper amounts of nutrients for trees and shrubs. See homesoiltest.msu.edu
You can also consider consulting with an ISA-certified arborist, and I would suggest doing so before treating large landscape trees. (ISA = International Society of Arboriculture) You can search for an ISA-certified arborist near you at https://www.treesaregood.org/findanarborist/arboristsearch .
Plus, here are a couple more resources:
Basswood/Linden > Leaves > Dots, spots, or blotches on leaves from U. of Minnesota Extension
Birch (Betula) Leaf Feeders from the U. of Kentucky Dept. of Entomology
Please let me know if you have further questions.