Statewide Forest Health

White pine weevil – old and new damage

By Linda Williams, forest health specialist, Woodruff.; 715-356-5211 x232

The terminal leader of this young white pine was killed by white pine weevil.

The terminal leader of this young white pine was killed by white pine weevil. Photo: Linda Williams

White pine weevil is an insect that can attack and kill the terminal leader on white pine, jack pine, and spruce trees. Terminal leaders killed last year may remain on the tree until spring, although they commonly break off during winter. Adult weevils are now out laying eggs on terminal leaders, just below the expanding buds. After the eggs hatch, the larvae will bore just under the bark of the terminal and feed, moving downward as they progress. As buds expand this spring, they will quickly run out of water and food due to damage caused by larval feeding, and the terminal leader will begin to wilt, curl, and die. Continue reading “White pine weevil – old and new damage”

Porcupine and squirrel damage on trees

By Linda Williams, forest health specialist (Woodruff).; 715-356-5211, x232

During winter and early spring, damage to trees caused by porcupines and squirrels is evident in some areas. As spring arrives, new green leaves will mask the destruction.

This red pine had the bark stripped off it by a porcupine, which has wider incisors than a squirrel.

This red pine had the bark stripped off it by a porcupine, which has wider incisors than a squirrel.

Porcupine and squirrels feed on the bark of trees, stripping it from branches and main stems. Stripping bark can girdle trees, resulting in branch dieback which shows up the year following the damage. If the branch isn’t completely girdled, it will start to grow callus tissue over damaged areas in an attempt to recover.

This maple bark was eaten by a squirrel. You can see where the tiny incisors scraped the bark down to the wood.

This maple bark was eaten by a squirrel. You can see where the tiny incisors scraped the bark down to the wood.

Both porcupines and squirrels feed on bark in the crowns of trees, so how can you tell which one is doing the damage if you don’t catch them in the act? The size of the teeth marks left in the wood is one clue. A gray squirrel’s incisors leave marks between 1.3 to 1.7 mm wide, while a porcupine’s teeth marks are nearly triple that, from 3.6 to 4.8 mm wide. You should also consider the species of tree being debarked: squirrels prefer maples while porcupines will feed on oak, pine, maple, and even spruce, as well as other species.

Rabbits, mice, and voles can cause similar damage to that caused by squirrels and porcupines, but damage will be located near the base of the tree instead of in the crown.

Another type of tree damage seen in late spring is when squirrels clip 4 to 6 inches off the tips of spruce branches, apparently to consume tasty buds. They drop the remainder of the branches to the forest floor, leaving a carpet of branch tips under spruce trees. I have yet to observe squirrels doing this, but the carpet of branch tips they leave prompts calls from concerned landowners each spring.

Spruce branch tips litter the ground where squirrels dropped them after clipping them from the tree. Although it can look alarming it rarely does enough damage to affect the overall health of the tree.

Spruce branch tips litter the ground where squirrels dropped them after clipping them from the tree. Although it can look alarming it rarely does enough damage to affect the overall health of the tree.

UW Extension offers a brochure about squirrels, including control options to share with landowners having trouble with these critters.

You can be a star!

by Jodie Ellis, communications specialist (Madison).; 608-266-2172

Invasive Species Action Month in Wisconsin will be held this year in June. To celebrate, the Wisconsin DNR is teaming up with partners for the “Protect the Places You Play” video challenge. We are looking for video entries from the public (no longer than two minutes, please) that show how you or your group help prevent the spread of invasive species. The winning video’s producer will be invited to attend the Wisconsin Invasive Species Council’s Invader Crusader Awards ceremony on June 6 at Olbrich Botanical Gardens in Madison. Submissions must be received no later than Monday, May 15.

Entries will be voted on by visitors to the DNR’s Facebook page. Voting will be open from May 16 through 25. For instructions on entering your video, see the 2018 Video Challenge page on the Council’s website. Need some inspiration? See last year’s winning submission.

EAB biocontrol releases continue in 2018

By Mike Hillstrom, forest health specialist (Fitchburg).; 608-513-7690

In 2018, the Wisconsin DNR will complete its eighth year of releasing tiny, stingless wasps as biocontrol agents to help manage emerald ash borer. Columbia, Dane and Grant counties are slated for first-time releases this year, and there will be new release sites in Brown, Door and Sheboygan counties. The wasps will be released for a second year at established sites in Brown, Green, Jefferson, Milwaukee and Sheboygan counties. The same wasps that were released in 2017 will be used this year: Tetra sticus planipennisi, Spathius galinae and Oobius agrili.

Tiny adult Spathius galinae wasps are released near an infested ash tree where they will look for EAB larvae to parasitize

Adult Spathius galinae wasps venture out to find some tasty EAB larvae to parasitize.


Map showing the numerous biocontrol sites for emerald ash borer established in southern and eastern Wisconsin since 2011.

Biological control sites for emerald ash borer in Wisconsin 2011-2018. Figure by Bill McNee.

Phomopsis galls

By Linda Williams, forest health specialist (Woodruff).; 715-356-5211, x232

Large swellings on the branches of this oak are caused by the fungus Phomopsis.

Large swellings on the branches of this oak are caused by the fungus Phomopsis.

Winter and early spring are great times to look for galls on trees. Some galls, including phomopsis galls, can get very large and, because there are often many galls on a single tree, they are easily spotted from a distance. Phomopsis galls are woody swellings caused by a fungus which range in size from very small to larger than a person’s head. They occur on hickory, northern red oak, maple, and a few other tree species. Infections are usually localized to a single tree with neighboring trees being completely unaffected, or a small group of trees may be infected. Occasionally, larger infection centers can be found.

It is suspected that genetic variability plays a role in the susceptibility of individual trees, but a lot is still unknown about this fungus. There is no known treatment for Phompsis galls other than to prune them out and dispose of them; many people choose to simply live with them. If left on a tree, galls may eventually cause dieback or girdling of infested branches, but some trees live for many decades with galls on their main stems. The presence of galls does not necessarily mean the rapid death of a tree, which is especially true for oak trees: they seem to survive for decades with very large galls present on the branches.

Historical Forest Health News – 1993 and 1968

News from 25 years ago (1993)

Jack pine budworm Choristoneura pinus (Rohwer)

Area of defoliation by jack pine budworm in 1993 shaded in black.

Area of defoliation by jack pine budworm in 1993 shaded in black.

“This defoliator erupted in northern and central Wisconsin to cause moderate to heavy defoliation on 400,000 acres of jack pine. This was the second year of defoliation in Clark, Eau Claire and Jackson counties, and first year defoliation in Monroe County. The largest areas of defoliation were in the northwest where periodic outbreaks are expected. Heavy defoliation occurred in Adams, Juneau, Wood, Clark, Eau Claire, Jackson and Monroe counties. Light feeding was apparent in the Conover area of Vilas county. In Oconto county a 90-acre planting of sapling white pine suffered heavy terminal and upper lateral defoliation. Spotty light to moderate defoliation occurred in Oconto and Marinette counties in the northeast. Defoliation in Marinette county was heaviest in over-mature natural stands of jack pine stands in Silver Cliff Township (Sections 22, 23, 27, 26, 34, 35, T34N, RISE).

In Juneau and Wood counties, tree mortality is expected to be high because many trees lost 90 to 100 percent of their foliage. Salvage harvests were scheduled in the defoliated stands that were predicted to suffer heavy mortality. Some of the harvests in the central and westcentral counties were in potential conflict with the protection of the Karner blue butterfly, a newly listed endangered species. Guidelines were developed to survey for the Karner Blue and for its food plant, blue lupine. The guidelines also contain procedures to prevent damage to known Karner Blue habitat during harvest operations. Many defoliated stands that were scheduled for salvage harvests were surveyed. Late season egg mass surveys revealed a 33% decline from 1992 levels in the northwestern counties portending a decrease in populations and defoliation in 1994. In western and central Wisconsin, the egg mass surveys indicate the budworm populations should remain high in 1994. Egg mass surveys in Wood County averaged 5.8 egg masses per plot. Egg mass surveys in Marinette county indicate defoliation will likely be spotty and variable in intensity again in 1994.”

Continue reading “Historical Forest Health News – 1993 and 1968”

Forest health zones restructured

by Jodie Ellis, communications specialist, Forest Health team (Madison); 608-266-2172

The number of Forest Health (FH) specialist positions in the state was recently reduced by one, going from seven fulltime positions to six. To reflect this change, the forest health zonal map was restructured to spread coverage between five forest health specialists (the FH specialist position for the Central zone, while not eliminated, remains vacant). The new assignments went into effect on April 3, 2018.

To contact a forest health specialist, please refer to the revised map below:

  • Northwest zone: Paul Cigan (Hayward), 715-416-4920,
  • Northeast zone: Linda Williams (Woodruff), 715-356-5211 x232, Also covering Lincoln, Shawano, Menominee, Waupaca and Oconto counties in the Central zone
  • West Central zone: Todd Lanigan (Eau Claire), 715-839-1632, Also covering Taylor County in the Central zone.
  • Southeast zone: Bill McNee (Oshkosh), 920-360-0942,
  • South Central zone: Michael Hillstrom (Fitchburg, WI), 608-513-7690, Also covering Marathon, Wood, Portage, Adams, Waushara, Marquette and Green Lake counties in the Central zone.
  • Central zone: vacant
Restructured Forest Health zones

Restructured Forest Health zones

A fulltime FH specialist position, which had been vacant, was eliminated as part of the reduction of six positions from the Division of Forestry in the recent state budget. Because of the increased work load on the five remaining FH specialists, the FH program has permanently reduced or eliminated some of its services to customers to keep the staff’s work load at manageable levels.

Program services that have been reduced or eliminated include:

  • The DNR’s gypsy moth suppression program, which addressed population surges in areas of the state where gypsy moth is already established. This program was already in the process of being deactivated when the FH specialist position was cut. (NOTE: The Slow The Spread program, which is managed by the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP), remains active. It targets gypsy moth populations in the western part of the state where gypsy moth has not yet established.)
  • Site visits to confirm EAB at the township level (digital images will be used for identification instead)
  • Site visits and digital diagnostics of small acreage (less than 10 acres) for private landowners

Forest Health team members must also reduce the number of outreach presentations provided to the public.

Please contact Rebecca Gray, Forest Health team leader, with any questions at or by phone at 608-275-3273.

How are communities handling EAB across Wisconsin?

The Wisconsin Department of Agriculture, Trade, and Consumer Protection (DATCP) has recently issued a statewide quarantine for emerald ash borer (EAB), regulating the pest in Wisconsin. Since the menace has already affected 48 of Wisconsin’s 72 counties, many municipalities have been acting on EAB management plans they set into place, including the City of Racine and Ozaukee county have been managing the pest.

Continue reading “How are communities handling EAB across Wisconsin?”

Protect oak trees from oak wilt by waiting until after July to prune

By Don Kissinger, DNR urban forester (Wausau),, 715-359-5793 and Paul Cigan, DNR forest health specialist (Hayward),, 715-416-4920

To protect oak trees and help prevent oak wilt, the Wisconsin Department of Natural Resources advises people to avoid pruning oaks on their property from April through July.

Spring and early summer pruning makes oak trees vulnerable to oak wilt, a fatal fungal disease that rapidly kills trees in the red oak group and weakens those in the white oak group. Any tree damage during this time creates an opening that exposes live tree tissue and provides an opportunity for the oak wilt fungus to infect the tree.

The red oak group includes northern pin oak, northern red oak, red oak and black oak; the white oak group includes bur oak, swamp white oak, white oak and English oak.

Pin oak (Quercus palustris)

Pin oak (Quercus palustris)
Photo: Gary Fewless, University of Wisconsin, Green Bay

“It takes only a few minutes for beetles that carry oak wilt spores to land on a fresh wound and infect your tree,” said Paul Cigan, DNR forest health specialist in Hayward.

Property owners with oak trees are encouraged to check with their municipality to find out if there are local oak wilt ordinances which may have different pruning restrictions.

The use of tree paint or a wound dressing is not normally recommended on pruning cuts or wounded surfaces on most trees. But for damaged oaks, the use of such products are suggested from April through July. An immediate light painting of wounds or cuts on oak trees during this time helps protect against the spread of oak wilt by beetles.

Don Kissinger, a DNR urban forester in Wausau, said there are also other important reasons to avoid pruning many kinds of deciduous trees in spring beyond concerns about oak wilt.

“Spring is the time when tree buds and leaves are growing, leaving the tree’s food reserves low,” Kissinger said. In general, the best time to prune trees is in winter.

Oak wilt and other diseases move easily on or in firewood logs year-round. To protect trees in general, don’t move firewood long distances, or only use firewood labeled as Wisconsin-certified.

As of January 31, 2018, oak wilt has been found in all Wisconsin counties except Douglas, Bayfield, Ashland, Iron, Forest, Taylor, Door, Kewaunee, Calumet, and Manitowoc counties. Several of these counties contain the highest abundance of healthy and productive oak forests in the state. Taking recommended precautions with living oak trees and keeping firewood local to prevent the spread of oak wilt will help keep them that way for years to come.

More information is available online at the WI DNR website, including a recently released video on oak wilt. Visit the DNR website,, and search for “oak wilt” or “firewood.” Additional information about proper pruning techniques is available from community foresters or by searching for “tree pruning.”

SPECIAL REQUEST from DNR’s Forest Health Team

Thank you to those kind subscribers who have already completed the Forest Health News Survey which was emailed in March. If you haven’t had a chance to take the survey, we ask that you do so now.

Our goal at Forest Health is to provide you with helpful information on pest, disease and invasive plant issues in the state in a timely manner. To help us improve our usefulness to you, please click here to take the survey.

The survey will take about 10 minutes to complete. Your individual responses will be kept confidential. All responses will be compiled and analyzed as a group; a summary of the survey results will be available to you this spring. If you own forested land in Wisconsin, you will need to refer to the zonal map which you will find at the beginning of the survey.

We would be grateful if you will complete the survey by April 15, 2018. If you have any questions or concerns about the survey or wish to provide additional comments about Forest Health News, please contact Jodie Ellis at or at 608-266-2172.

Thank you for taking the time to complete this survey. It is much appreciated.