Indiana Department of Natural Resources sent this bulletin at 08/17/2022 07:30 AM EDT
Weekly Review for August 17, 2022
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.
Here are a few things I saw this past week while inspecting in Allen and Dekalb Counties. I saw several red maple trees at one nursery where high winds had broken off the tree at the graft. You can clearly see the callus tissue in the photos below. Redbud leaf roller was causing damage on redbud. These caterpillars are hard to take pictures of because when you unfold the leaf they typically fall to the ground. Bagworm had totally striped a spruce tree of all its needles, and an elderberry borer was found feeding on the foliage of elderberry.
Ken Cote (Nursery Inspector & Compliance Officer) - KCote@dnr.IN.gov
During the last few weeks, I have continued to encounter mite problems. Recently I found mite actively feeding on pin oak. I was not sure of the exact species, but the mites were feeding on the top sides of the leaves and causing stippling and leaf browning. Coarse stippling and leaf browning was also found on ‘Winter King’ hawthorns. This type of damage may look similar to mite injury, but the stippling is coarser in texture and is actually caused by lace bugs feeding on the undersides of leaves. When leaves are turned over black colored adults, nymphs and fecal spots can be seen on the undersides of leaves. I also observed a very large population of leafhoppers causing serious injury to grapes. This pest also causes a coarse stippling, but the damage can extend beyond just the feeding damage caused by leafhoppers. Certain species of leafhoppers can transmit a bacterium called Xylella fastidiosa. This is the causal agent for bacterial leaf scorch on oak, elm, maple and horse chestnut, but it also causes Pierce’s grape disease. All the aforementioned pests have one thing in common; they have piercing sucking mouth parts.
Recently, I am starting to see an increase in damage cause by the mimosa webworm on honey locust in the Monroe County area. Look for the ends of leaves that are tied together and become brown. This Lepidopteran pest can be quite damaging and, in some years, can result in damage to the entire canopy.
Bark beetles were found causing serious injury to white pines. This is quite common on white pines that have drought stress and can occur on trees of any age. Bark beetles tend to infest trees that are stressed by drought or by root rot that can mimic drought stress on the top portion of the plant.
Look for trees that have an off green color, yellowing or browning. Close examination of the trunk will reveal small circular exit holes and sawdust. However, exit holes may be more difficult to see in raining weather or large trees with bark fissures. The best thing to do is remove severely infested trees from the area.
Leaf spot disease are quite common at this time of year on a number of ornamental hosts. Recently I encountered symptoms of angular leaf spot (Pseudocercopsora), on Japanese tree lilac in my region. This disease is becoming more common in my region and in some cases is causing early defoliation on trees. Look for black angular leaf spots on infected trees. Leaf spots possibly cause by Cercospora were found on honey locust. In the past I have had this identified as Cercospora condensata. I occasionally see this fungus cause early leaf drop on infected trees, but I do not encounter it every year. Early signs of Tubakia leaf spot were found on red oak in my region. Look for leaf spots and browning areas on the leaves of infected trees. This tends to be a late season infection that occurs later in the year than anthracnose. Sever infections can leave trees with an unsightly appearance.
I use the word “possible” to describe these diseases because I do not have lab confirmation on these samples. In the field, I am observing symptoms that I believe to be caused by a particular pathogen. However, always remember that symptoms are an expression of the plant’s reaction from the presence of an infection. Laboratory diagnosis is necessary to isolate exactly which pathogen is causing the symptoms. A similar example would be humans experiencing a fever. Fever can have a number of causes, both biotic and abiotic. I hope to have some more pictures in the future.
Fall webworm (Hyphantriacunea) is making itself known right now. Everything I’ve seen has been in second or third instar and I haven’t noted significant damage. In the few cases I have seen it where management is necessary, a small pruning cut has been the easiest way to discard. For homeowners, it’s important to remember his pest is more of a nuisance than anything as in most cases no real damage is done to the tree. The caterpillars are important food sources for birds, spiders and some predatory insects.
I have also found cryptomeria scale feeding on several fir species. This armored scale feeds on the underside of needles on all true firs and causes chlorotic damage to needles. August into the first week of September is treatment window for spray control of this pest. Mechanical control (removal of heavily infested trees) can take place during winter months until bud break. When removing trees from fields, wrap in tarps or plastic to limit possibility of spreading pest to other trees. If treating chemically, don’t use a broad-spectrum insecticide that will also kill beneficial insects that can help control populations of scale.
I wanted to share something that I haven’t seen in nursery stock in previous years.I had a grower with hardy fig in small pots and they had Bird’s nest fungus (Family Nidulariaceae) growing in the pots. Attached to the fig leaves of several plants were the spore bodies (or peridioles) from the fungus in the pots.The peridioles get launched from the fungal cups through water splash and stick to the surfaces on which they land. The Bird’s nest fungus will not harm the nursery stock plants.
