Noticed these small worms on a River Birch which has had many leaves eaten. I...
Noticed these small worms on a River Birch which has had many leaves eaten. I believe they may be Sawfly larva but not sure. New leaves are growing and it's late in the year. Any treatment needed? If so, what, when they return next year. Thanks
You are correct. They look like Dusky birch sawfly. There are two generations per year in Maryland, first in April and May and then again July through early fall. This time of year they really aren't a big deal.
Next season, if its a small group, you can just squish them or prune out the affected branches and dispose of them.
If the population is plentiful, you can kill them when they are small with a good coverage of horticultural oil or insecticidal soap.