Indiana Department of Natural Resources sent this bulletin at 08/25/2020 01:08 PM EDT
Weekly Review for Aug. 25, 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.
Elongate Hemlock scale (Fiorinia externa) is something that I’ve only seen on Christmas evergreen decorations, but we did find it in a nursery on stock that originated out of state. This native of Japan and China is a pest mostly of eastern hemlock, but it can also be found on fir and occasionally spruce, Douglas fir, and pines. The scale feeding can cause yellowing of needles that starts on the interior lower branches moving upwards as populations increase. Mechanical control is best done from November through mid-April and consists of removing and destroying heavily infested trees prior to bud break. If control is to be achieved through spraying, the best time to apply dormant oil is just prior to bud break. When first crawlers are active, typically in late May/early June, a systemic insecticide spray may be effective. The general recommendation is to spray three to four times over a 12-week period, but never more than four times per season. As with all treatments, it’s critical to read and follow all labels.
Red-headed flea beetle (Systena frontalis) continues to be active in central Indiana. These tiny native insects have a big appetite and can cause a lot of unsightly damage as adults feeding on foliage and can be an occasional pest of crops like corn and alfalfa. Larvae feed on roots and stems in the soil.
Ren Hall (Nursery Inspector & Compliance Officer) - RHall@dnr.IN.gov
Over the past couple of weeks, I’ve been seeing lots of fall webworm on trees along the highways and at nurseries. I’ve also found foliar nematodes on several types of plants (including coral bells and false sunflower, Heliopsis). I found Rose of Sharon with large black/brown circular water spots on the leaves that Purdue’s Plant Pest and Diagnostic Lab (PPDL) diagnosed as Phytophthora. Other recent finds: Pine needle scale on pine trees at a nursery, pine-oak gall rust and possible Diplodia tip blight on Scotch Pines at a Christmas tree grower, Rhizosphaera pini on white fir at another Christmas tree farm, and large milkweed bugs on butterfly weed.
These were found earlier than this past week. First, I was called out to property where the owner said one of his hard maple trees, a sugar maple, was dead and it had white worms coming out of it. At first I thought it was an ash and the owner misidentified the tree but after talking to him for a minute it was clear he knew his trees and it was indeed a maple. Upon arrival I found a dead sugar maple with loads of white frass around the base of the tree and in every bark crevice. It turned out to be a mass attack by one of the granulate ambrosia beetles. There were a few tell-tale pitch tubes left on the tree, but the landowner said that there were hundreds at one point. That explains the “white worms” that I found so perplexing.
More recently, I have been doing a bunch of work at the pollinator garden at the fairgrounds. One of the black cherry trees didn’t make it this past year and I hadn’t spent the time to investigate why, but two weeks ago I made a visit and the second black cherry tree had thousands of globs of sap along the stem and larger branches. I immediately suspected bark beetles, which I confirmed by removing one of the masses of pitch that showed the gallery entrance of a beetle. Upon checking the dead tree, I concluded bark beetles had killed it the previous year. I’m not really sad to see either of these trees go as they both caused shade issues as well as having thousands of cherry seedlings to remove each spring.
I’ve said often over the years it actually takes a lot to kill an established tree. I wrote about one such tree in the Weekly Review on July 2, 2012. This red maple stood next to a house that burnt to the ground. It took a lot of damage from the heat of the fire, but survived. I am sure that some corrective pruning and crown cleanup might have helped, but here we are eight years later…
