Indiana Department of Natural Resources sent this bulletin at 07/21/2020 09:53 AM EDT
Weekly Review for July 21, 2020
This informal report by the Division of Entomology and Plant Pathology is designed to update the Nursery and Greenhouse industry of insect and disease pests the Division has been encountering on a week to week basis and as a way to give a “heads up” of things to be on the lookout for. Comments and questions about this report are welcome and can be sent to your respective Inspector.
This past week I saw the effects of White Pine Weevil in both white pine and Norway spruce. Bag worms were spotted at multiple locations and are still very active (double check your sprays because at two separate nurseries I still found viable bagworms post spray). I am starting to see the effects of drought stress and things like a heavy oyster shell scale infestation on the pictured red maple is the straw that broke the camel’s back. Still not seeing much Japanese beetle damage even on things like linden and grape. A lot of folks have been asking where the monarchs are but I saw quite a few of them this week. The one pictured is laying an egg in the milkweed patch at the State Fairgrounds.
Ken Cote (Nursery Inspector & Compliance Officer) - KCote@dnr.IN.gov
I received over an inch of rain last evening at my home and some western parts of my region received up to 5 inches of rain, while areas to the east received very little precipitation. Bagworm is causing serious damage to main landscape plants. During the last week I am seeing increasing levels of mimosa webworm on honey locusts. Look for leaves that are being webbed together, especially on cultivar Sunburst. The webbing is not as heavy as the webbing that occurs with fall webworm. I have not seen this pest become a problem for a while, but damaging populations were seen in both Monroe and Bartholomew counties during the last week. While looking for mimosa webworm, I came across large honey locust that had dieback and corky nodules coming out of the bark. I shared the photos with the Purdue Diagnostic Lab and it was thought that they may have been a result of herbicide injury. This was likely the case since the trees were growing along a power line right of way.
I am also seeing damage from locust leafminer on black locust. This beetle species will cause black locust to look brown in appearance from a distance. It is a blotch leafminer and does not cause the winding damage pattern like serpentine leafminers. Adults are orange and black in color, but not always that easy to find. Black locust typically recovers from this pest and it typically does not cause major issues for trees other than the cosmetic injury. Bark beetle activity was found on white pine. This can happen to trees that are undergoing drought stress or trees that are in a wet location that cause root damage, which mimics drought stress. Look for trees that are turning an off-green color, and then browning out. Close examination of the trunk will reveal small holes and sawdust coming out of the trees. The best thing to do is to cut down and destroy heavily infested trees so the bark beetle does not spread to other trees in close proximity.
It was another first for me this week. I found a population of Catalpa hornworm (Ceratomia catalpae) doing what they do best. There were late and earlier instars all feeding heavily on Catalpa trees in Wayne County. The same trees also were home to some early nymph brown marmorated stink bugs.
I have sent red oak samples to PPDL this year. No pathogens were found, so the report came back “environmental issues.” But I want to dive into the case a bit deeper. The nursery had planted 20 bare-root red oak trees. They have lost between four and six of these trees per year since planting them. Not far away is another red oak planting which looks fantastic. The nursery owner told me something interesting about these trees. The failing group was purchased from a nursery in Oregon. The others were sourced from Indiana.
If you look up the native range of red oak, you will see that it is a Midwest/East coast tree that ranges from Maine down to Alabama, over to Arkansas and up to Minnesota. That covers USDA cold hardiness zones 3-8. Given the large native range, I would suspect that red oak has an equally large genetic variability based on the climates and soils of where a specific line or ecotype calls home. Oregon (zone 8-9 on the coast) is not native red oak range, so where were these trees collected from? Were they just a poor match to Indiana growing conditions? We’ll never know for sure, but it is a possible explanation. This also sets up a case for sourcing plant material as locally as possible.
Finally, I want to climb on a soapbox. I found “Assorted Tropical Bush” for sale in a box store. There were no tags on any of the plants. 312 IAC 18-4-5 requires plants to be individually labeled with the common name, botanical name, and hardiness zone. I could have placed a stop sale order on about a third of the plants at that store for violation of this rule. Interestingly, almost all of these plants came from one vendor in Florida, so the decision was made to contact the supplier through the Florida Department of Agriculture rather than make the enforcement on the store. I’m seeing more and more mislabeled and unlabeled nursery stock. Aside from the inconvenience to inspectors, missing tags deny customers a critical gateway to botanical knowledge. Without the information provided on tags many customers are likely to decide against a purchase.
Ren Hall (Nursery Inspector & Compliance Officer) - RHall@dnr.IN.gov
A couple weeks ago I spotted European elm scale on an elm tree in the landscape in Marion County. The tree was heavily infested and looked pretty scraggly compared to the neighboring (uninfested) elm trees, and on closer inspection I saw honeydew and sooty mold on leaves and branches, twig dieback, and scales covering the bark of the infested tree’s limbs. I found woolly apple aphids on twigs of several hawthorn trees at a nursery in Jackson County a couple of weeks ago as well.
This past week I saw hackberry trees at a nursery in Tippecanoe County with symptoms of island chlorosis, which is caused by a virus. The leaves have blocky yellow and light green blotches with distinct borders delineated by the leaf veins. Lastly, I found heavy infestations of oystershell scale on several cultivars of red maple at a nursery in Hendricks County last week. The scale insects were completely covering the bark of the trees’ trunks and branches, and were also found on the leaves along the veins. There was noticeable twig dieback and blackening of the bark on the trees even from a distance, and up close it was clear that every inch of the trees was covered with scales.
