East Central WI Forest Health

Spider mites cause bronzing on oak leaves

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

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”

Tiny spikey aphids on maple leaves

These spikey aphids, marked with blotches of brown and tan, are maple aphids.

These spikey aphids, marked with blotches of brown and tan, are maple aphids.

As I wandered through the woods one day in September, I noticed some spots on a sugar maple leaf. When I flipped it over, I discovered tiny black dots on the underside. They looked like tiny flea beetles to the naked eye (they were very tiny), but I didn’t know of any flea beetles on maple. After putting them under the microscope, I discovered that my tiny bugs weren’t beetles at all, they were maple aphids! They are tiny, dark, and spiky! Cute little suckers! They weren’t doing any significant damage to the leaves that I could tell, although all the leaves in that area had at least a few aphids on the underside. I’ll watch this area next year to see if I can find them again.

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

 

Jumping galls cause defoliation on white oaks

Brown areas on these white oak leaves were caused by a heavy infestation of jumping oak gall.

Brown areas on these white oak leaves were caused by a heavy infestation of jumping oak gall.

Jumping oak galls caused by tiny wasps form on the underside of white oak leaves.

Jumping oak galls caused by tiny wasps form on the underside of white oak leaves.

If you were in Waupaca County this summer, you probably noticed that large white oaks were looking pretty brown. They were being defoliated by a tiny gall wasp called jumping oak gall (Neuroterus saltatorius). The small galls, which develop around tiny larvae on the undersides of oak leaves, fall off the leaves in late summer. Continue reading “Jumping galls cause defoliation on white oaks”

Acorn weevils

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

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.

 

What is causing hardwood species to appear off-color?

Numerous issues are causing various hardwood species to become off-color this summer.  Below I’ve listed a few issues that I’m seeing.  Most of these issues do not require any control or any mitigation if your trees are showing these symptoms.

Anthracnose causes irregular dead areas on ash leaflets.

 

Anthracnose – irregular dead brown blotches on oak leaves and ash leaflets, caused by the fungal leaf disease anthracnose, is making some oaks and ash appear to be browning.  Phone calls with concerns about dying trees have been coming in.  Symptoms are typically worse in the lower crowns, and the ash I’ve seen with this issue in Marinette, Oconto, and Vilas Counties have very thin looking crowns.

 

Browning areas on this aspen leaf are caused by aspen blotch miner.

Browning areas on this aspen leaf are caused by aspen blotch miner.

Aspen blotch miner – all ages of trembling aspen are being impacted by aspen blotch miner this year.  Aspen crowns appear thin, leaves appear off-color from a distance, “blisters” form on the underside of the leaf, and eventually the leaves curl and brown of the leaves.  This is the 4th year in a row that I’ve noticed defoliation by this insect.  This year, similar to past years, I’ve seen it in Oconto, Marinette, Florence, Forest, Oneida, and Vilas Counties.  Tiny larvae spend their entire life feeding within the leaf and pupate within the area that they mined out.  Moths emerge in August and spend the winter in a protected place.

The winding galleries of aspen leafminer make the tree appear grey from a distance.

The winding galleries of aspen leafminer make the tree appear grey from a distance.

 

 

Aspen leaf miner – for those leaves that aren’t heavily infested with aspen blotchminer, they are often infested with aspen leaf miner.  Aspen leafminer is another tiny larvae that spends its life feeding within the leaf, but they create picturesque winding trails that give the leaves a pale appearance.

 

Balsam poplar browning – a couple of things are going on with the Balsam poplar in Brown and Oconto Counties, including a leaf disease and aspen blotch miner.  The trees are thinnest in the lower crowns, but the upper portions don’t look too hot either.

This birch leaf shows both the feeding of Japanese beetles (which don’t eat the veins of the leaf), and a brown blotch where birch leafminer was feeding.

This birch leaf shows both the feeding of Japanese beetles (which don’t eat the veins of the leaf), and a brown blotch where birch leafminer was feeding.

Birch dropping leaves – every year about this time birch will drop a portion of their leaves.  Many of those leaves don’t appear to have much damage on them.  But there is certainly leaf damage if you look closely at birch.  The primary issue that I’ve been seeing this year in Brown, Oconto, Oneida, Shawano and Vilas Counties is from birch leafminer.  Dead blotches on the leaves may make you think anthracnose, but holding the leaves up to the light you will discover you can see through them and see signs of insect activity inside the leaves.

Birch look brown – defoliation from Japanese beetle in Minocqua/Woodruff area is causing the birch to appear tan.  Defoliation is more significant in the lower canopy, but some trees are heavily defoliated top to bottom.  Japanese beetle is something that you may want to do some treatments for.  There are many options for treatments, whether excluding them with netting, or using insecticides against the adults, using traps for the adults, or using insecticides or fungal biocontrol against the larvae.           UW Extension has a great document with more info on Japanese beetle control.

A young black cherry turns red. While some are being defoliated by lacebugs (causing them to turn red), others like this one have very little defoliation.

A young black cherry turns red. While some are being defoliated by lacebugs (causing them to turn red), others like this one have very little defoliation.

Cherry lacewing and cherry turning red – I’m not quite sure what’s going on with all of the cherry.  Some of them are turning reddish in color because they are being defoliated by Cherry Lacebug (Oconto County), but others don’t seem to have any damage that I see (Marinette and Oconto Counties), so I’m not sure why they’re turning red.

Maple early fall color – check out Todd Lanigan’s article  which highlights the high water levels that are causing stress to lowland trees.  Many maples growing in these lowlands are already turning a rich shade of red due to water stress.

Brown blotches on these oak leaves are not anthracnose. The tiny oak leafminer lives within the leaf, feeding on the leaf material. The damaged area eventually turns brown.

Brown blotches on these oak leaves are not anthracnose. The tiny oak leafminer lives within the leaf, feeding on the leaf material. The damaged area eventually turns brown.

 

Oak leafminer – in Minocqua/Woodruff area I was noticing some oaks were looking a bit brown, which I assumed was probably anthracnose.  Always good to double check these things!  Once I stopped to check it out I discovered activity from oak leafminer was to blame, causing dead brown areas where the insects feed within the leaf.

 

Defoliation by oak skeletonizer will leave a layer of cells, which appear like parchment paper if you hold the leaf up to the light.

Defoliation by oak skeletonizer will leave a layer of cells, which appear like parchment paper if you hold the leaf up to the light.

 

 

 

Oak skeletonizer – scattered light levels of defoliation have been seen in nearly every county in Northeast and East Central Wisconsin.  Oak skeletonizer defoliates oak leaves by scraping off a single layer of the leaf, leaving a parchment-like layer on the leaf which turns pale tan.  Holding these leaves up to the light makes it clear that they’re defoliated.

A willow leaf is brown where willow flea weevil larvae have been feeding inside the leaves.

A willow leaf is brown where willow flea weevil larvae have been feeding inside the leaves.

 

Willow browning – although we started this spring with some willow scab that caused significant defoliation, the current issue is the leafmining action of the larvae of willow flea weevil.  This is the fourth consecutive year that Brown, Calumet, Marinette, Shawano, and Oconto Counties have experienced significant defoliation of willow from this insect.  I’ve also noted this in a few willow in Florence and Langlade Counties this year.

 

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

Fall webworm

Fall webworm started showing up around the middle of July.

Fall webworm web

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 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

Elm sawfly with uncommon pink coloration

Elm sawfly is the largest sawfly found in North America and has the disturbing habit of falling out of trees when you walk under the tree.  They feed on willow and elm, although in Wisconsin I’ve only seen them causing noticeable defoliation on willow.  They may also feed on birch, aspen, basswood, and maple.  Most people don’t notice the damage until the larvae begin to migrate down and gather near the base of the tree.  Larvae will overwinter as pupae on the ground and emerge as adults the following year.

Pink form of the elm sawfly larvae crawls on the bark of a tree. Photo by Ricky Keller.

Elm sawfly larvae are typically yellow; it is uncommon to find the pink form. (Photo by Ricky Keller)

Larvae grow 1 ½ – 2 inches long and are usually a bright yellow color with a black strip down their back, although occasionally the pink form is found.  Adults are a large, dark brown sawfly that looks like a cross between a horse fly and a wasp.  Usually defoliation is localized to a single tree or group of trees.  Spraying a general insecticide or soapy water should kill these sawflies if you think control is warranted, but these late season defoliators rarely do serious damage to the trees that they defoliate.

HHere you can see how large elm sawfly larvae are, and there are some slight color differences in these. Photo by Chris Plzak.ere you can see how large elm sawfly larvae are, and there are some slight color differences in these.  (Photo by Chris Plzak)

 

 

 

 

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

Venturia shoot blight in northern Wisconsin

Sapling aspen with withered, drooping shoot killed by Venturia shoot blight.

Venturia shoot blighted aspen shoot. Photo by Gerred Carothers.

Venturia shoot blight has been observed throughout northern Wisconsin this summer. Venturia shoot blight is one of the most common fungal diseases of aspen and is favored by cool, wet spring weather. 

The pathogen rapidly kills expanding terminal and lateral shoots, causing shoots to wither and droop. It also causes leaf necrosis, appearing as black circles of varying sizes, necrotic curling at the margins, or complete leaf death. The disease is most damaging to seedling and sapling aspen, where it can reduce height growth and cause temporary stem crooking as lateral shoots are released and compete for apical dominance.  Disease control is unnecessary in a forest setting.

Written by Paul Cigan, forest health specialist, Hayward (Paul.Cigan@Wisconsin.gov), 715-416-4920.

White spotted sawyer

Our native pine sawyer has a “spot” between the elytra (yellow arrow) that Asian longhorned beetle does not have. They also will appear dusty or pitted.

Our native pine sawyer has a “spot” between the elytra (yellow arrow) that Asian longhorned beetle does not have. They also will appear dusty or pitted.

White spotted sawyer, sometimes called Pine Sawyer, is a native longhorn beetle. It is often mistaken for Asian Longhorned Beetle (ALB). How can you tell the difference between our native beetle and ALB?  First of all, size: ALB is a big burly beetle, while our native sawyer beetle looks slim in comparison. Second, ALB has a very smooth shiny appearance with distinct white spots on black wing covers, whereas our native sawyer beetle will appear pitted or dusty, and the white spots may be less distinct or absent. Finally, our native beetle will have a nice white dot “between its shoulders” where the wing covers meet, and ALB does not have this. 

Adult pine sawyer beetles feed on the bark of twigs which can cause branch tip mortality.

Adult pine sawyer beetles feed on the bark of twigs which can cause branch tip mortality.

Pine sawyer larvae develop in weakened, recently dead, or recently harvested conifers. Larvae first feed in the phloem layer then progress to inner wood. They will pupate within the tree and adults will chew their way out leaving large round exit holes. Adults feed on needles and the bark of twigs. Areas this year which will attract white spotted sawyers include areas of storm damaged pine, and areas of conifer decline due to high water levels, as well as any other areas where conifers are stressed. 

If you find a beetle and are unsure whether it’s ALB or our native sawyer, please take some photos to send for identification. 

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

Poplar vagabond aphid

Poplar vagabond aphid feeding on the buds of aspen or cottonwood cause the tree to form a fleshy, hollow gall around the insects.

Poplar vagabond aphid feeding on the buds of aspen or cottonwood cause the tree to form a fleshy, hollow gall around the insects.

Galls caused by poplar vagabond aphid form at the ends of aspen and cottonwood branches. The galls are caused by aphids feeding at the tips of twigs. This feeding causes the tree to grow an elaborate structure that the aphids can live inside. One of the galls in the photo is broken open so you can see the aphids inside. This damage does not usually kill the tree, but reduces branch growth because the formation kills the terminal buds. The aphids feed during the spring and early summer within the gall, and then leave to feed on an unknown second host plant. When the aphids leave the gall it will turn brown and woody, and will remain on the tree for several years before weathering off. Adult aphids return later in the fall and lay eggs on the woody gall or in crevices in the bark. Eggs will hatch the following spring and repeat the process. For control, prune the galls prior to egg hatch early in the spring. Because the aphids return to the same trees with the original galls it is common to see a single tree heavily infested while a nearby tree will have no galls at all. I have always seen this problem in trees that are open grown, either along the edge of a stand, along a roadway or fence row, or in a yard. I’m not sure how much of a problem it is in the interior of a stand.

Poplar vagabond aphids, which are covered in a white waxy material, are protected inside the large hollow galls formed by the tree. They suck the trees’ sap.

Poplar vagabond aphids, which are covered in a white waxy material, are protected inside the large hollow galls formed by the tree. They suck the trees’ sap.

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