Indiana Department of Natural Resources sent this bulletin at 06/07/2023 07:39 AM EDT
Weekly Review for June 7, 2023
This informal report by the Division of Entomology & Plant Pathology is a commentary on insects, diseases, and curiosities division staff encounter on a week-to-week basis. Comments and questions about this report are welcome and can be sent to your respective Inspector.
This past week I had someone show me something that was new to me. The questioner thought it may be some sort of scale infesting their red oak, but I took one look at it and knew it was a cynipid wasp (gall former). I had to do some research to figure out which one and it turned out to be Callirhytis quercusgemmaria (no common name that I could find).
Normally gall makers do not cause extensive damage but in this case, they have extensively damaged the main stem. I am curious if this will cause enough structural weakness to cause stem failure in the future.
I also realized this past week that I have not sent out the updated treatment thresholds from the Honey Bee Health Coalition (HBHC). The old standard stated that if you do a mite wash and get a 3% mite load (9 mites per ½ cup bees, which is roughly 300) you should treat. The new recommendations put out by HBHC suggest treating at an infestation level of 1-3% depending on the stage of colony development and time of year. You can find the full document, Tools for Varroa Management, online.
During a nursery inspection in southern Indiana this past week, the presence of honeydew on the upper leaf surface on Fagus grandifolia caught my eye. After a few moments of close inspection, I spotted the culprits: a group of giant bark aphids, Longistigma caryae, feeding on the bark of the tree. These aphids feed on a variety of deciduous species, suck tree sap, and only occasionally cause serious damage.
This aphid is the largest species in North America, measuring up to 6 mm-long (1/4 inch). Their body is brownish gray with black spots helping them to camouflage when present and feeding. Their long legs, which makes them appear even larger, give them a spider-like appearance.
The good news is the lack of rain has reduced the occurrence of many foliar diseases. The bad news is I’m already seeing moisture issues cropping up in nurseries, especially in containerized stock. Be diligent with watering as the dry weather continues.
I mentioned aphids last week and I am continuing to see them. Crabapples, red oaks, spirea and roses are frequent hosts. I’ve found a few scale issues here and there as well. This week, I found my first bagworm of the season, though interestingly it was on basswood.
There seems to be a lot of galls forming over the last week or so as well. Galls, especially those on leaves, typically do little damage to the plant but stir up alarm with homeowners. Maples and oaks are the usual hosts, but I found one this week that I do not see very often – linden wart gall midge.
