Indiana Department of Natural Resources sent this bulletin at 08/11/2021 08:25 AM EDT
Weekly Review for August 11, 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.
After two months of mainly dealing with gypsy moth, I have been able to get out in the field and get some inspections done. In a nursery that mainly grows maple, I was seeing tar spot. It varied in severity from heavy on some of the Norway maple varieties to light on the red maple varieties. Other diseases I saw included Septoria leafspot on oak leaf hydrangea, juniper tip blight on juniper, apple scab on crabapples to varying degrees depending on the variety, apple scab on serviceberry, and powdery mildew on Diablo ninebark and serviceberry. At a daylily and hosta grower I saw hosta anthracnose and daylily leaf streak. Bagworm populations are high this year and I did notice them on arborvitae at one of the nurseries. Other insects include white pine weevil on Eastern white pine, oak leafminer and oak spider mites on bur oak, Japanese beetle on roses and serviceberry, lacebug on serviceberry, and flea beetle damage on weigela.
When I finished a nursery inspection I stopped to check out a walnut tree that was covered with gypsy moth eggmasses and was happy to find the egg parasitoid, Ooencyrtus kuvanae, busy at work. These parasitoids are small wasps that lay their eggs in the eggs of the gypsy moth, killing the egg before it has a chance to hatch.
Ren Hall (Nursery Inspector & Compliance Officer) - RHall@dnr.IN.gov
I saw a group of pear trees with a bad case of fireblight with dark cankers, scorched leaves, and shepherd’s crooks on the ends of the branches. These trees may still be saved if the grower prunes out the blighted branches several inches under the cankers when the trees are dormant this winter, although once it reaches the main trunk it’s too late to save.
Last week, I saw a lot of larger bagworms while out doing nursery inspections. Other interesting finds were catalpa hornworm on catalpa trees and whitefly pupae on the undersides of leaves of many trees including maples, lilac, ash, and linden.
Ken Cote (Nursery Inspector & Compliance Officer) - KCote@dnr.IN.gov
Only 0.53 inches of rain in the last two weeks at my house. Many areas are becoming dry in the southern part of the state. I am seeing a lot of fall webworm, but I am also seeing numerous honey locust trees infested with mimosa webworm in the Bloomington area. This can cause significant damage to trees fairly quickly and it is often very objectionable to clients. Look for brown leaves that are lightly webbed together. This insect does not produce as much webbing as fall webworm, but it can turn entire trees brown.
I am also starting to see symptoms of leaf blotch fungus on my red buckeye. Look for brown necrotic areas on the leaf tissue. This type of damage on buckeye can be caused by environmental leaf scorch as a result of dry conditions, bacterial leaf scorch (Xylella fastidiosa) or a fungal infection, Guignardia leaf blotch. These symptoms all look very similar to one another in the field and a lab diagnosis is needed to distinguish which problem you really have. Interestingly, I had an identification of a leaf spot on Yoshino cherry as a Cercospora /Psuedocercospora species. This is causing significant leaf drop on Yoshino cherries in my region, but the symptoms of this leaf spot are exactly the same as the shot hole fungus. However, there is also a bacterial leaf spot that can cause similar symptoms on cherries. Remember, what we see in the field is a plant reaction to something. In many cases, similar symptoms can result from different pathogens.
Fall webworm populations are fairly high in scattered locations in northeast Indiana. The caterpillars make silken “tents” at the ends of branches on a wide variety of trees. Most of the tents I’ve seen have been on walnut, hickory, and persimmon. The caterpillars feed on the leaves inside the tents which help to protect them from predators. There are two generations a year of this insect in Indiana. The first generation appears in June with the second generation appearing in July and August. It typically doesn’t cause a lot of damage to trees so control measures are rarely needed. While inspecting nurseries in Allen County I observed redbud leaffolder caterpillars on redbud. These caterpillars fold a leaf over a stich it together with silk and feed inside the folded leaf. I also observed oak spider mites on bur oak; lace bugs on linden; moderate levels of redheaded flea beetle on hydrangea, Itea and weigela and pine needle scale on Scotch pine. As for diseases, tar spot has been getting heavier with the humid weather. Septoria leaf spot was heavy on ivory halo dogwood, as well as powdery mildew on flowering dogwood and possible Cercospora leaf spot on hydrangeas.
I have included a photo this week of leaf galls on pecan caused by the feeding of the pecan phylloxera insect. For more information, please see Purdue Extension’s publication Managing Insect Pests of Nut Trees.
