A mass emergence of winged ants.  Photo by Mike Kamke.

On August 29, and again in early September, a mass emergence of winged ants occurred in southern Vilas County and some areas of northern Oneida County. Mass emergences of winged adults are part of a reproductive strategy used by ants to overwhelm predators, in the hope that a few of the new queens will mate and establish their own nests. When weather conditions are right, winged individuals from many ant colonies in an area will emerge and fly away to mate and start their own nests.

Winged ants consist of large winged females and smaller winged males, but many folks that reported these insects were concerned that they were seeing swarms of wasps since most people aren’t accustomed to seeing ants with wings. Once new queens and males fly away from the nest, they will eventually drop to the ground, shed their wings, mate and start a new nest. These events are relatively rare for folks to see as they are very short lived, with the winged ants generally being gone within a day.

Mature northern red oaks killed by oak wilt in Sawyer County. Photo by Paul Cigan

Late-summer aerial and ground surveys revealed new oak wilt infections within northern red oak stands in Rusk, Sawyer and Washburn counties. Below is an update on the finds in each of the counties.

In Rusk County, aerial detection surveys led to the confirmation of 10 new infections on county forest property. Suspected factors for these infections include spring storm damage and latent detection of past infections caused by logging damage during unrestricted spring harvesting. The county forestry department continues to use cut-stump herbicide treatments to control below-ground transmission. They plan to continue follow-up monitoring of treated pockets and have reported encouraging results to date; only a few pockets treated between 2015 and 2016 contained newly infected oaks on or near the edge of the treatment zone.

Continue reading “Oak wilt update for Rusk, Washburn, and Sawyer counties” →

Round hard galls from oak bullet gall wasps can impact growth of young oaks if the population is high enough.

There are a lot of galls on oak. One that can cause some problems at heavy densities is the oak bullet gall. These galls, sometimes called rough bullet galls, can quickly become unsightly. I usually see them on burr oak and occasionally on swamp white oak. They are caused by a gall wasp. The galls start out green-colored, eventually darkening to brown as the season progresses and the gall wasp larvae grow inside. Continue reading “Oak bullet gall” →

Bronzing along the veins of this oak leaf is due to feeding mites.

In August and September, I observed bronzing due to mites feeding on some young swamp white oaks. The tops of the leaves were very bronzed along the main veins, while the undersides of the leaves remained unaffected. When looking at the leaves with my hand lens and under the microscope, I saw a very heavy infestation of mites. Mites suck plant juices from the cells of the leaf.

Continue reading “Spider mites cause bronzing on oak leaves” →

The round hole at the edge of the fallen acorn’s cap was created when an acorn weevil larva chewed its way out to find a place on the ground to overwinter.

In some areas of Oconto County, a large percentage of the acorns on northern red oaks dropped early. Most of those acorns were infested with acorn weevil, although at the time they dropped they looked whole. After sitting for a few days, acorn weevil larvae started to emerge in hopes of burrowing into the soil to find a place to spend the winter.

Adult acorn weevils have very long narrow snouts and feed on acorns that are still attached to the tree. They chew a small hole in the acorn, then lay an egg (or several eggs) in the hole. They then plug the hole with fecal pellets, camouflaging their work. The eggs hatch and larvae begin feeding within the acorns. In the fall, the acorn drops to the ground and the larvae chew their way out, after which they bore into the soil to spend the winter underground. There is a different species of acorn weevil that feeds on acorns that have already fallen.

Even though the acorns looked perfect when they dropped, the insects had already been at work on them. Floating acorns in water will allow you to sort out the ones that are damaged, even though you may not see damage on the outside.

Written by: Linda Williams, forest health specialist, Woodruff, (Linda.Williams@wisconsin.gov), 715-356-5211 x232.

Fall webworm started showing up around the middle of July.

Fall webworm web

This is a native insect that feeds on deciduous trees and shrubs, and it is makes an appearance every year in yards and forests. Fall webworm forms loose webbing over branch tips and if it is a small tree, the entire tree can be completely webbed.

Inside the webbing you’ll find caterpillars (alive and dead), partially eaten leaves and frass (caterpillar poop).

Fall webworm caterpillars

Fall webworm is more of a cosmetic problem than a tree health problem, but if you want to control them, the easiest way to do that is to open up the webbing. You can take a rake, fishing pole, long stick, or whatever and open up the webbing. This will allow predators to get at the caterpillars inside the webbing.  Or you can use the rake, fishing pole, etc. and roll the webbing up. Then peel the rolled webbing off and place the entire web in a container of soapy water for a couple of days. If you want to use an insecticide, you need to make sure the insecticide is labelled for caterpillars/fall webworm and the spray needs to penetrate inside the webbing. With all pesticides, the user needs to read and follow label directions. There is no need to prune off the branch. If the tree is healthy, the defoliation should not harm the tree.  You can find more information on fall webworm here. 

Written by: Todd Lanigan, forest health specialist, Eau Claire (Todd.Lanigan@wisconsin.gov)
715-839-1632