Northeast WI Forest Health

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.

Additional oak wilt found in several areas in Vilas County

A number of new oak wilt infections have been identified in Vilas County this summer.  I’m waiting on results for a few more samples, and have several more trees to go and collect samples from, so there will probably be additional reports to come.

Cloverland Township, Vilas County, had its first oak wilt identified this year.  Unfortunately, oak wilt was first introduced to this site last year when the harvest extended into the high risk period, and the storm damage that we had in May allowed oak wilt to infect many new trees at the site this spring.

In Arbor Vitae Township, northeast of Woodruff, there are a number of new sites where oak wilt has been identified; some of these are right on the southern border of Boulder Junction Township.  And several wilting trees have been identified along Nabish Lake Rd in Boulder Junction and Plum Lake Townships.

As I said, I’m still waiting on a few more results, as well as needing to collect from a few trees that were recently reported to me.  Oak wilt is generally not common in the northwoods so if you see wilting oaks in July or August, please report them.  To minimize new infections of oak wilt it’s important not to prune, wound, or harvest during the high risk period in the spring, April 15 – July 15 in the north.  For more information about minimizing the risk of overland spread of oak wilt, or for info on controlling oak wilt infections that are already present, check out the Wisconsin DNR oak wilt page.

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

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.

Spruce needle rust

Spruce trees turn orangish or pinkish when spruce needle rust is sporulating.

In some areas of the northwoods, the blue spruce are turning pink or orange, and the black spruce and white spruce are turning pale yellow.  What is going on?  This is spruce needle rust, which infects the current year needles.  Problems were noted in northern counties in 2013, 2014, 2015, and now again this year (Forest, Oneida, Vilas Counties).  This fungus enjoys a moist spring, so this year it’s doing well.  As a rust it has an alternate host, probably a shrub in the heath family like Labrador Tea.  The infected needles will drop prematurely.  No treatment “cure” is available for the already infected needles.  Preventative fungicide treatments for yard trees could be done next spring and early summer to protect new emerging needles, but must be done before symptoms appear.  Repeated treatments are necessary as the fungicide must coat the needle to protect it and has to be reapplied after it washes off or weathers off.

Spore pustules of the spruce needle rust fungus erupt from spruce needles.

Spore pustules of the spruce needle rust fungus erupt from spruce needles.

 

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.

Oak leaf tier and oak leaf roller

Oak leaf rollers and oak leaf tiers fold over or roll leaves which protect them from predators.

Oak leaf rollers and oak leaf tiers fold over or roll leaves which protect them from predators.

Last month I reported on a location in Marinette where oak leaf tier and oak leaf roller were defoliating oak. Since then I had a report of this same combination of pests causing defoliation near Rhinelander. Typically this defoliation is not severe, but when the leaves are rolled up or folded in half it can make it look like the defoliation is more severe.

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

Of historical interest, 25 years ago (1992) and 50 years ago (1967)

25 years ago – 1992

  • Frost – On June 20, the temperature dropped to 25°F in many locations throughout Wisconsin. This caused injury to several tree species including: black ash, balsam fir, red pine, northern pin oak, and spruce in northwestern Wisconsin, and red pine and northern pin oak in Oneida and Vilas counties, north-central Wisconsin. Severe damage to new shoots of white spruce and balsam fir Christmas trees occurred in Taylor, Langlade, Oneida, Lincoln and Oconto counties. Injury to hardwoods often caused defoliation. Conifers affected by the frost had curled and crooked shoots that eventually died. In Vilas County, most of the injured red pine and oak did not reflush. In Eau Claire County, western Wisconsin, spruce, black walnut and several species of pine were injured. Seedling and sapling-size red pine were injured in Clark and Chippewa counties. Balsam fir, white spruce and white pine Christmas trees in northern Wisconsin were also injured by the early summer frost. Severe loss of new growth.
  • White Grubs – Phyllophaga In Marinette County, (Section 16, T30N, R20E) high numbers of white grub larvae were observed in plantings of ash, maple, oak and walnut. These trees were being planted in alfalfa. In Portage county, (NWNW, Section 4, T21N, R7E) all larval stages were present at the time of planting red pine in sod on a 13 acre area. In Washburn County, heavy mortality occurred in a red pine planting due to white grub feeding. Heavy numbers of grubs were reported in new tree plantations in Door, Kewaunee and Manitowoc counties. The adult stage of white grubs, the May and June beetles, were observed in large numbers at night in urban areas in Oconto, Marinette and Marathon counties. Progeny of these beetles could produce heavy damage to nearby young tree plantings in the next two years.

50 years ago – 1967

  • Pissodes approximatus Damage by this weevil was associated with red pine plantings on poor sites or frost pockets in the Northeast Area. The most severe infestations were found in Marinette, Oneida and Vilas counties during surveys for Scleroderris lagerbergii (Gremman).
  • White-Pine Weevil, Pissodes strobi (Peck). Populations were generally low in all areas of the state. About 10% of the leaders were infested in a small white pine planting in Washburn County (Section 8, T41N, Rl3W). A few terminals of Norway spruce and Scotch pine Christmas trees were infested in Langlade and Oconto county plantations, and survival of weevils was poor in the east central counties. Heaviest infestations were reported from the West Central Area where 20% to 30% of the current leaders were infested in a few white pine plantations and averaged 10% to 15%.  Although no white pine weevil control projects were conducted in the West Central Area this year, additional insecticide test plots were established on Black River State Forest plantations. Further investigation of a reported white pine weevil attack on red pine in Trempealeau County reported in 1966 (p. 7, Annual Report 1966) appears more likely to have been the work of Pissodes approximatus Hopkins. Large numbers of these weevils were found on stumps of red pine, cut for Christmas in the fall of 1966, when the site was re-examined in the spring of 1967. Older stumps showed evidence of previous attacks typical of P. approximatus.  Evaluation of evidence available indicated that terminal attacks in 1966 occurred because breeding P. approximatus populations exceeded available stump areas and overflowed to the stems and terminals of living trees.

Content taken from the Forest Pest Conditions for Wisconsin Annual Reports from 1967 and 1992.

Defoliation by rose chafers and Japanese beetles is showing up.

Rose chafers and Japanese beetles are starting to cause problems in some areas this summer. So far reports and damage are generally light for Japanese beetles, but in some areas rose chafer defoliation is noticeable. 

Rose chafers are beetles that can defoliate many plant species. They have fairly long legs, and are a dusty mustard color.

Rose chafers are beetles that can defoliate many plant species. They have fairly long legs, and are a dusty mustard color.

Rose chafer defoliation was reported from Florence, Marinette, Oconto, Vilas, and Waupaca counties this year. Rose chafers are more common in areas with sandy soil where they will lay their eggs. The eggs hatch into white grubs which live in the soil and feed on grass and weed roots. My books inform me that birds can die if they eat adult rose chafers because of a poison in the beetles that affects the heart of small, warm-blooded animals. For information on rose chafer control, check out UW Extension publication A3122.

The last significant defoliation that I noted from rose chafer was in 2012, and before that it was 2005. These beetles feed on a wide variety of plants and prefer blossoms, but they will skeletonize leaves as well. Control is difficult because the adults are good fliers and can easily fly in from neighboring areas to re-infest your freshly sprayed plants. 

Japanese beetle populations will emerge in southern Wisconsin first, typically by the first part of July. Some areas of the state have building populations while others, like the Madison area, may have populations that exploded in the past and are more stable now. These insects are occasionally mistaken for EAB because they have some metallic green coloring near their heads.  More commonly people will refer to the multicolored Asian ladybeetles as Japanese beetles, but the ladybugs are ladybugs and Japanese beetles are scarab beetles.

Japanese beetle adults feed on the flowers and leaves of over 300 plant species, including trees, shrubs, and herbaceous plants. They can cause significant defoliation. The larval stage of Japanese beetle is a white grub that lives in the soil and feeds on plant roots.  University of Wisconsin Extension has a Japanese beetle webpage including information on the damage caused by the adults, the damage caused by the white grubs, and control measures that are useful on the adults and the larvae. 

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