Entomology & Plant Pathology Weekly Review, August 21, 2024
Indiana Department of Natural Resources sent this bulletin at 08/21/2024 09:01 AM EDT
Weekly Review for August 21, 2024
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.
I’ve included a photo of oleander scale on jostaberry. These are armored scales, see this link for a management guide on scale insects.
I also had a nursery with a small outbreak of white-marked tussock moth (Orgyia leucostigma) caterpillars feeding on some crabapple trees. Early instar caterpillars will skeletonize leaves and as they grow larger they will consume whole sections of them. This moth overwinters in the egg stage and eggs are laid in a mass near cocoons. Outbreaks don’t usually require treatment on deciduous trees. However, since damage occurs quickly, outbreaks on conifers can cause extensive damage and warrant control.
A couple of interesting things to note this week. I happened upon a pair of polyphemus moths mating which is always a treat to see. I also happened upon a fairly heavy patch of a type of midrib leaf gall on shingle oaks.
As I have been reporting, I’m seeing more of the ever-present herbicide damage including oaks, redbud, Kentucky coffee trees, and river birch (only river birch is pictured below to save space). I had several comments and questions about herbicide damage from last week so I would point everyone to this document by Ohio State University explaining the issue.
I also only just spotted my first monarch two weeks ago and last week I found my first monarch caterpillar on some of my swamp milkweed. This past winter was the second lowest overwintering count for monarchs in Mexico. I harp on habitat a lot and many folks I talk with have a hard time wrapping their head around pollinator habitat planting and management. It just so happens that there is a pollinator habitat management workshop coming up on Sept. 24 from 8:30 a.m. until 3:30 p.m. in Danville. You can sign up for the workshop at this link.
Lastly for a bee related link, here is a talk by Dr. Kristen Traynor – Reading the Hive.
Most commonly I associate ‘shepherd’s crook’ symptoms on species in the Rosaceae family when they are infected with the bacterium that causes fire blight. However, this past week I noticed another pathogen that causes this terminal shoot blight on a group of aspen, Populus tremuloides, at a local nursery. A fungus, Venturia populina, was identified as the cause by the Purdue Plant & Pest Diagnostic Lab.
Symptoms of Venturia leaf and shoot blight include a variety of brown to black leaf spots and blights on leaf tips and margins. During wet summers, these necrotic areas expand rapidly, killing whole leaves and shoots. Control includes pruning to remove as many dead shoots and small branches as possible from the canopy, as the pathogen will readily overwinter in any diseased material that remains.
It is quite normal to find fascinating galls on oak and other shade trees this time of year and it is important to know that they are generally not harmful to the overall health of your tree. Feeding of cynipid wasp larvae caused this cluster of wedge-shaped galls on this swamp white oak (Quercus bicolor). As the wasp larvae feed and develop, the swelling gall provides protection to the wasps inside. This gall has two common names, the pine cone oak gall or lobed oak gall (Andricus quercusstrobilanus). Throughout the summer, this gall goes through a color change from pink or red to yellow and finally to brown.
