Indiana Department of Natural Resources sent this bulletin at 08/03/2022 07:10 AM EDT
Weekly Review for August 3, 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.
I was able to get out and do a few inspections last week. I have been noticing bagworm in landscape arborvitae but it wasn’t until last week that I found it in a nursery. It was scattered throughout a planting of arborvitae. I showed the nursery owner and it was probably at the stage where he could get rid of them by hand picking them off. I saw Zimmerman pine moth in a group of older white pine. Japanese beetles were still causing scattered feeding damage on rose, linden, river birch and hollyhock. Flea beetle damage was on weigela and hydrangea.
Spongy moth adults are about done flying for the year, so those that have had problems will probably see the egg masses. They can be treated with horticultural oil labeled for the treatment of egg masses. I have seen the egg parasitoid, a tiny wasp that lays its egg in the spongy moth’s. Hold off treating egg masses until the first hard frost to let that parasitoid attack and kill some of those eggs.
I have not seen nearly as much Japanese beetle damage in east central Indiana as has been reported in other areas. The most feeding damage I saw was adjacent to a trap set to protect garden center plants. It was far enough away from valuable stock that it worked and the grapevines in the fence row were not of any concern. I have seen a small amount of woolly aphids on various species. None of the populations I saw were in high enough numbers to cause damage to the woody plants they were feeding on.
Ken Cote (Nursery Inspector & Compliance Officer) - KCote@dnr.IN.gov
Thankfully, we are getting some good rain. Surprisingly, there are still some areas that only received an inch or less last week and they are quickly drying up again. With the consistent warm weather and unusual periods of low relative humidity, spider mites continue to be a problem on many plants. Severe injury from two-spotted spider mites was found on Crocosmia. This plant is very susceptible to both thrips and spider mites.
Stippling that leads to leaf yellowing and eventually browning can be seen in the photo below. I am also finding maple mites in the field, but I am not seeing much damage yet in the locations I have inspected. Look for light stippling and adults and eggs near the veins on the undersides of leaves. I encountered some significant sawfly feeding injury on perennial hibiscus, but I was not able to find any larvae at this time. Look for the interveinal defoliation on hibiscus leaves in late spring or early summer. I also found an abundance of milk weed bugs feeding on swamp milkweed. Look for orange and black insects. You can often find both adults and nymphs feeding gregariously on the seed pods of milkweed. They never seem to cause many issues with their host. I do not recommend treating them in order to protect monarchs from encountering an insecticide.
I am continuing to see pockets of fall webworm in the landscape and forested areas of my region. However, populations are not too serious. One note is that I am just starting to see mimosa webworm beginning to feed on honey locust. I hope to have some good pictures next week.
During an inspection last week I found necrotic areas on hosta leaves that were constricted by the veins. At this time of year I often observe necrotic areas caused by leaf scorch and possible other foliar diseases. However, when the leaf damage is restricted by the veins, this is an indication that foliar nematodes may be present. I got laboratory confirmation that the tissue was indeed infected with foliar nematodes. Control of nematodes can be difficult.
During the last four years I continue to see needle cast on large white pines in my region. Symptoms do not usually appear until late May. Both red band and brown spot needle cast have been confirmed on samples I submitted to the Purdue Lab. I have been watching this problem for some time now. Interestingly, I have only had one encounter of needle cast on a white pine in a nursery setting. The species of needle cast was Ploioderma.
The problem I am seeing on white pine is occurring in forested areas and large white pines in the landscape. The trees seem to grow out of the damage, but in some cases I have observed bark beetle infestations on white pines that have had repeated infections of needle casts. It is hard to determine if the needle cast infection caused the stress on the trees and allowed for bark beetle infestation or if it was a combination of stress factors that caused both the needle cast and bark beetle issues at the same time.
