Indiana Department of Natural Resources sent this bulletin at 06/09/2021 08:23 AM EDT
Weekly Review for June 9, 2021
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.
Megan Abraham (Division Director & State Entomologist) - MAbraham@dnr.IN.gov
The DNR has learned of a new pest that has been introduced to the United States through the nursery industry. The box tree moth (Cydalima perspectalis) feeds primarily on boxwood species, however alternate hosts include both burning bush and holly. First reports of an infested nursery in Canada a few weeks ago have led to the discovery that several states have received potentially infested material. several of those locations shipped stock to other states. There are reports that track at least a few plants from the infested nursery of origin to the state of Indiana. At this point the DNR has NOT confirmed the existence of this pest in Indiana but we do want to alert the nursery industry and homeowners of the potential for this pest to spread and what to do if you spot it. Box tree moths are difficult to distinguish from native moths in our environment. However, the damage they create is quite distinguished from other species. Caterpillars of this species can cause heavy defoliation and will even attempt to feed on the bark if the plant has been stripped of its leaves. In addition, the caterpillars tend to spin silken webs to hold leaves together to form areas protected from predators in which to feed. For more information on this pest see the USDA Box Tree Moth Page or the USDA Pest Alert. As always, please contact your nursery inspector with any suspicious finds.
Here are photos of two issues found during a group inspection that several of us did together last week. Included is a photo of ‘Green Giant’ arborvitae showing tip dieback from Arborvitae Needle Blight caused by the fungus Phyllosticta thujae. The symptoms from this fungal disease are the larger browned tips on the ends of the foliage. There are other smaller brown spots of damage randomly around on the foliage that is caused by other injury, possibly mite damage, but the source of those injuries is unknown. Also included is a photo of aphid injury to apple, showing the tightly curled leaves from feeding damage.
Ren Hall (Nursery Inspector & Compliance Officer) - RHall@dnr.IN.gov
Last week, I helped at a nursery inspection in Hamilton County and had a few interesting finds. The first was downy mildew on ‘Pugster Pink’ butterfly bush. Initially I thought the yellow mottling on the leaves was probably caused by a virus, but I sent a sample to Purdue’s Plant & Pest Diagnostic Lab (PPDL) where they were able to diagnose the problem as downy mildew. I also came across the worst ambrosia beetle infestation I have seen so far on honey locust. There were hundreds of “frass toothpicks” on each tree, and my coworker Vince used a knife to dig out one of the tiny beetles. Lastly, I found an infestation of what looks to be Japanese maple scale on ‘Moraine’ sweetgum trees. They were covering most of the trees’ trunks. I haven’t come across this pest too often and hadn’t heard of it infesting sweetgum, but I did find a good publication by University of Maryland Extension listing hosts of Japanese maple scale and sweetgum was listed. We also saw the scale insect on several other species of trees nearby including crabapples.
Cool and damp weather the last few weeks have made a haven for things like downy mildew. Sometimes it’s not as obvious as powdery mildew since the symptoms can be variable depending on what it’s infecting. Below, you can see some Nanho Blue butterfly bush showing some leaf disfiguration and discoloration. Purdue Plant & Pest Diagnostic Lab confirmed downy mildew. We had this same pathogen at several locations in central Indiana. Purdue Extension has a great resource for anyone needing to manage downy mildew. It can be found at extension.purdue.edu/extmedia/bp/bp-68-w.pdf and is a good read. When dealing with things like downy or powdery mildew, sanitation is a critical part of managing the disease.
The weather this spring has also been conducive for anthracnose. Anthracnose is used to describe a group of related fungal diseases. Anthracnose can infect many different species, but most here in Indiana are probably familiar with anthracnose on sycamore trees. This year, I’ve been seeing it more and more on maple trees. It can be quite unsightly but in most cases it is an aesthetic issue. In extreme cases, a severe infection could cause premature defoliation which can add stress to the tree.
