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.
By Don Kissinger, DNR urban forester (Wausau), Don.Kissinger@wisconsin.gov, 715-359-5793 and Paul Cigan, DNR forest health specialist (Hayward), Paul.Cigan@wisconsin.gov, 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.
“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, https://dnr.wi.gov/, and search for “oak wilt” or “firewood.” Additional information about proper pruning techniques is available from community foresters or by searching for “tree pruning.”
By Paul Cigan, DNR forest health specialist (Hayward), Paul.Cigan@Wisconsin.gov, 715-416-4920
The DNR Forest Health Program just released a new oak wilt video to educate the public about this deadly fungal disease that kills oak trees. In addition to the 3.5 minute video, a 30 second video trailer is also available:, each video may also be accessed from the Wisconsin DNR’s oak wilt webpage.
The videos, which are hosted on YouTube, may be shared through any networks of professional and public contacts who may benefit from viewing this resource. Please post the video on your organizational websites as an additional information source. Promotion of the videos is underway, including print ads in newspapers in several northern counties, DNR Facebook page posts, and an informational flyer distributed in northern counties. If you are interested in distributing flyers, please contact me or Jodie Ellis at Jodie.Ellis@wisconsin.gov for copies. Contact your regional forest health specialist for more details about prevention, detection, and management of oak wilt.
Written by: Linda Williams, forest health specialist, Woodruff. Linda.Williams@wisconsin.gov, 715-356-5211 x232.
A new Wisconsin Wildcard is available on beech bark disease (BBD). Wisconsin Wildcards are pocket-sized, collectible informational pieces available at Wisconsin state parks. The BBD Wildcard may be viewed at https://p.widencdn.net/clz4yw/Beech-bark-disease-wildcard and ordered by emailing a request to Forestry.Webmail@wisconsin.gov (ask for publication no. FR-218x).
Beech bark disease will eventually become a problem wherever beech is found. The native range of American beech (Fagus grandifolia) extends into the eastern third of Wisconsin. BBD is the result of a relationship between exotic scale insects and a Neonectria fungus. The disease was first identified in Wisconsin in 2009. Currently, the only known area of the state which has experienced mortality from BBD is Door County.
The scale insects feed by inserting their mouthparts through the bark on the trunk and branches and sucking the sap from the tree. The fungus, which “hitchhikes” on the scale insects’ bodies, enters the tree through those wounds. The tiny scale insects secrete a white waxy protective covering; when scale populations explode and there are millions of scales on a tree, the tree can appear white from a distance, making it resemble a birch tree. As the fungus enters the tree at numerous points and dead spots under the bark (called cankers) form, the tree becomes weakened, leading to a risk of “beech snap.” Beech snap can occur unexpectedly when the tree still has a full canopy of leaves remaining. Beech snap can create huge problems for park and campground managers who are trying to keep guests safe; there is no way to predict when a tree is going to fail from BBD.
Eventually, the insects and disease take their toll and the beech trees decline and die. Any age of beech tree can be infested, so in stands with significant beech mortality, regenerating trees will become infested as well as mature ones. The good news is that three to five percent of American beech trees are resistant to BBD. Michigan has identified and propagated such trees for a number of years, and have established a seed orchard of resistant trees. BBD is not yet as established in Wisconsin, but already we’ve been able to identify a couple of resistant trees in the area where BBD has killed many trees.
For more info on beech bark disease, visit Wisconsin DNR’s webpage on BBD.
Written by: Linda Williams, forest health specialist, Woodruff. Linda.Williams@wisconsin.gov, 715-356-5211 x232
Winter is a great time to look for cankers on trees, so I thought I’d highlight one this month that you may have noticed but not recognized. Most of you probably know Nectria as “the target canker” because growth patterns give the canker face a series of rings, expanding outwards as the canker ages, causing it to resemble a target. But on basswood, the cankers can appear very different at first glance. On basswood, it may look like there are small “explosions” that occurred under the bark. The bark may be popped out a bit, may have oddly shaped outward growths, and it may or may not be clear that it’s hollow underneath the bark. When you peel away the outer bark and all the gnarly growths, you do end up with a typical Nectria canker face, but on basswood, you often have to dig to get to it. Accompanying photographs show the “bark explosion” appearance that you might notice, as well as what it looks like when you remove the bark.
Nectria cankers are perennial, meaning they grow a little each year. They are made of solid wood (not decayed wood unless another fungus has caused the damage). They typically have staining associated with them; this can cause degrade in lumber value of your final product. If the cankers occur on small branches they can grow to girdle the branch, but the cankers found under the “bark explosions” on the main stem of basswood trees are not typically going to be able to cause that level of damage, and will instead simply continue to grow for many years.
Although this article focused on Nectria on basswood, the fungus can infect a number of other hardwood species. In those other species, you won’t find the “bark explosions” that you see on basswood, and instead will typically find a target shaped, open-faced canker.
The Division of Forestry’s forest health team recently updated another forest health fact sheet about conifer bark beetles. Like the oak wilt and hickory dieback and mortality fact sheets revised earlier this year, the conifer bark beetle publication offers information about biology, impact, prevention and management of the insects. The conifer bark beetle fact sheet is available on the DNR’s forest health webpage.
Written by: Mike Hillstrom, forest health specialist, Wisconsin Dells. Michael.Hillstrom@Wisconsin.gov; 608-513-7690
In late summer and early fall I had a few calls about younger spruce with yellow needles. These trees were typically 8-20 years old and were a very yellow color, with new foliage emerging a green color but quickly fading to yellow. There are two things that came to mind this year. The first thought is that we’ve had a very wet year. All year long roots were often in saturated or very moist soil. Consequently. the yellowing could be a sign of nutrient deficiency, specifically nitrogen, due to the saturated soils. The second possibility is a disease called SNEED (an abbreviation for ‘spruce needle drop’), which I typically see on heavier soils.
SNEED in spruce is thought to be caused by the fungus Setomalonomma holmii. Pathogenicity of the fungus has not been proven, but it is the primary fungus present on trees with a particular suite of symptoms. Spruce with SNEED have current year needles that are a nice green color, but older needles will be yellow or yellow/green in color. Black fruiting bodies will look like pepper sprinkled generously on the twigs of the affected branches. Old needles, although not showing any fruiting bodies, will drop from the tree prematurely, and repeated years of this will cause the tree to thin, decline, and can lead to mortality. I’ve seen this primarily in plantations of white spruce on heavy soils, but have also seen it in blue spruce plantations; it’s reported in Norway spruce as well. I don’t know of any sure-fire chemical options to prevent infection or to help the trees recover. Management typically involves removing the most affected trees in the plantation, minimizing stress, and minimizing standing water or waterlogged soils where possible.
Written by: Linda Williams, forest health specialist, Woodruff. Linda.Williams@wisconsin.gov; 715-356-5211, x232.
Past reports from the 1992 and 1967 WI DNR Forest Health Annual Reports
25 years ago – 1992
“European fruit lecanium (Parthenolecanium corni (Bouche))
Heavy infestations of this scale insect were reported on sugar maple twigs in Vilas and Price counties.
Jack pine budworm (Choristoneura pinus (Rohwer))
The outbreak in the northwestern counties, which began in 1991, exploded this year (Figure 16). Over 114,000 acres of jack pine were heavily defoliated in Douglas, Bayfield, Washburn and Burnett counties. Egg mass surveys indicate extremely high numbers of jack pine budworm. The area of defoliation may increase in 1993. The present defoliation is not expected to cause significant mortality except in Highland Township, but another year of heavy defoliation in the same stands could cause 10-15 percent mortality. In Highland Township, Douglas County, extremely severe feeding produced significant. mortality and top dieback on several thousand acres of jack pine. Most of these stands are being harvested this winter. Moderate to heavy defoliation also occurred in Jackson, Juneau, Eau Claire, Marinette (1,650 acres), Vilas (2,960 acres) and Oconto counties. In Marinette County, 20 acres of 70-year-old jack pine were cut to release young jack pine and white pine. Jack pine budworm was causing severe top mortality. Evidence of budworm in the northern portion of the Monroe County Forest was observed on 35-40 year old jack pine (Sections 4, 9,16, T19N, R3W). DNR foresters have silvicultural guidelines available to manage budworm-prone jack pine stands.”
Oak wilt, a deadly fungal disease affecting the red oak group, was recently detected in Sheboygan County for the first time. Wood samples were collected from adjacent symptomatic oak trees on the Kettle Moraine State Forest – Northern Unit in the Town of Mitchell after the trees were spotted by DNR Forestry staff. The presence of Ceratocystis fagacearum, the fungus causing oak wilt, was confirmed through a DNA test done at the DNR Forest Health Lab and DNA sequencing done at the UW-Madison Biotechnology Center. On-the-ground control options are currently being examined.
Oak wilt is a common disease in the southern two-thirds of the state, but has been
increasingly found in the northern counties. DNR staff have recently reported first community detections in these northern counties already known to have the disease:
- Langlade County – Town of Langlade
- Sawyer County – Town of Edgewater
- Washburn County – Town of Stone Lake
Oak wilt has been found in all Wisconsin counties except Ashland, Bayfield, Calumet, Door, Douglas, Forest, Iron, Kewaunee, Manitowoc and Taylor.
Additional information about oak wilt can be found at the DNR Forest Health website.
Written by Bill McNee, DNR Forest Health Specialist, Oshkosh. Bill.McNee@wisconsin.gov; 920-360-0942
In August, I reported that we’d found oak wilt in Cloverland Township in Vilas County, in Arbor Vitae Township northeast of Woodruff, (on the southern border of Boulder Junction Township), and along Nabish Lake Road in Boulder Junction and Plum Lake Townships.
So, what’s new since then? Another tree killed by oak wilt was identified on the western side of Plum Lake in Plum Lake Township in Vilas County; another tree died in Washington Township just north of the city of Eagle River. I’m still waiting on results from a suspicious tree in northern Three Lakes Township in Oneida County. In many cases spring storms, which occurred during the high-risk period for overland transmission of oak wilt, were to blame for new oak wilt infections. But in some cases, disease was due to logging or pruning that occurred during the high-risk period for overland transmission of oak wilt. It’s important to know where oak wilt is and to minimize your risk.
For more information, visit the DNR oak wilt web page.