Disease

Insects and disease in storm-damaged trees

On July 19 & 20, two separate lines of severe thunderstorms swept across Wisconsin causing significant forest damage in numerous counties. Straight line winds in excess of 100 mph and 16 documented tornadoes caused extensive damage to trees including main stem breakage, branches and tops broken, tipping and root damage and complete uprooting of trees. After the storms passed, the first order of business was to check on people, clear and open roads and make sure damaged homes were secured. As those tasks were completed, thoughts then turned to the damaged forests.

Map of damage assessment across land ownership types. From 2019 storms in northern Wisconsin.

Coarse-scale damage assessment from recent storms in northern Wisconsin. Percent damage and number of acres affected were estimated during ground and aerial surveys.

Some insects and diseases can take advantage of storm-damaged trees and cause long-term damage to forest stands. Continue reading to learn more about these issues, how to deal with them and how to contact professionals who can help landowners make decisions about their land.

Aerial view of extensive damage to aspen stands. Landscape of trees leaning from high winds.

Aerial view of aspen trees leaning from high wind in storm event.

Pines are first priority

Storm-damaged pine stands should be a landowner’s top priority when deciding where to start. Salvaging pine is much more urgent than oak or other hardwood stands because damaged pines will quickly begin to stain, and insects and disease will rapidly infest the damaged trees.

Broken and leaning pine trees following storm event. Damaged trees are more vulnerable to bark beetle attack.

Bark beetles quickly attack leaning, broken or uprooted pines.

Native bark beetles such as red turpentine (Dendroctonus valens) and pine engraver (Ips pini) will rapidly attack damaged trees that are leaning, broken or uprooted as well as fresh logs in log decks. Bark beetles will continue to attack storm-damaged trees and can move on to attack healthy pine once their populations grow. For more info on bark beetles, check out the WI DNR bark beetle factsheet.

White-spotted sawyer (Monochamus scutellatus) is another native beetle that will move in when a pine tree is nearly dead (or freshly cut). If you’ve ever stood by a conifer log pile and heard scratchy chewing noises, you were listening to this native pine sawyer.

Armillaria is a fungus that attacks the roots of storm-damaged trees. Tree mortality from armillaria root disease won’t show up until 1-3 years after the storm.

The bottom line to minimize insect and disease issues is to harvest your pines as soon as possible after the storm. Check out this printer-friendly factsheet for more information about salvage harvests, pests and replanting in storm-damaged pine stands.

Heterobasidion root disease in pine and spruce

Heterobasidion root disease (HRD), previously known as annosum, is a serious fungal disease of conifers, particularly pine and spruce. Infected trees decline and eventually die. Infection occurs when a spore lands on a freshly cut stump and germinates. Once in a stand, the disease can move from an infected stump to nearby trees through root contact, eventually killing those neighboring trees.

If a pine or spruce stand is within 25 miles of a known HRD pocket and a harvest or salvage will be done, it is recommended to treat pine and spruce stumps with a preventative fungicide within 24 hours of the tree being cut. To find out if you’re within 25 miles of a known HRD pocket, check out the interactive HRD web map.

When salvaging storm-damaged trees, it may be difficult to quickly find a logger who is certified to apply pesticides or one who has the equipment to spray the stumps as they are being cut. It may also be impractical or impossible for logging equipment to cut and treat those trees that are down or broken. Although efforts should be made to arrange preventive stump treatment, under this type of emergency harvesting, treatment of stumps at the time of harvest may not be practical. Refer to the HRD guidelines and the modifications that reference salvage (Chapter 3, Modification 4, and Chapter 4, Modification 4). For more information about HRD, visit the DNR HRD webpage.

Hemlock borer

Hemlock borer (Melanophila fulvoguttata) is a flatheaded wood-boring beetle whose immature stage bores into stressed or recently killed hemlocks. Storm-damaged hemlocks provide a good breeding ground for hemlock borers, and their populations grow large enough that they attack living hemlocks. To avoid hemlock borer attack on living hemlocks, promptly salvage windblown hemlock following a storm event. If you must thin standing trees around living hemlocks, the intensity of thinning should be as light as possible.

Oaks and other hardwood stands

Distribution of oak wilt in Wisconsin showing sparse distribution in most northern counties.

Counties shown in red have oak wilt throughout the county, although it may not be in every stand. Oak wilt is not common in northern Wisconsin.

Don’t rush – deterioration of oak is not an immediate concern. A thoughtful approach to salvaging your oak stands will be more beneficial in the long term. Oaks with broken roots or major branch/stem breakage may be attacked by the native two-lined chestnut borer (Agrilus bilineatus). Larvae of this beetle bore under the bark of oaks and can girdle and kill branches or entire trees. Branch mortality or whole tree mortality due to this insect will show up 1-3 years after a major stress event like these storms.

 The good news is that the July 19 and 20 storms occurred after the high-risk period for new oak wilt infections. Oaks are highly susceptible to infection by the oak wilt fungus (Bretziella fagacearum) during spring and early summer (April 15 – July 15 in the north and April 1 – July 15 in southern Wisconsin). Oaks in the red oak group will be killed completely while just a branch may die on white and bur oaks.

If salvage of stands with oak will occur next spring during the high risk period, please see the oak wilt guidelines for information on harvesting to minimize introduction of oak wilt There is a guideline modification for salvage harvesting that you could consider, so check out the guidelines to decide what is best for your property. Read more about oak wilt on the DNR oak wilt webpage.

What to salvage

Uprooted trees, and those with completely broken tops, will die and should be salvaged. Standing trees with some broken branches are judgment calls. A general rule is to salvage the tree if more than 50% of the crown or top is broken, but there may be situations when these damaged trees could be left to help your forest recover. A professional forester can help you with these determinations. Trees that are leaning may have broken roots or broken stem fibers and should be considered for salvage. Check locally for wood disposal sites or refer to the DNR page on cleaning up storm debris.

Firewood

Storm-damaged trees can be utilized for firewood, but you should be careful not to move firewood long distances and risk introducing invasive species like emerald ash borer, gypsy moth and oak wilt to new areas. Instead, let the firewood age in place and burn it locally. For more information, visit the DNR firewood page. Always use proper protective equipment when operating a chainsaw.

Continued monitoring

Trees do not recover from stresses very quickly. Dieback, and even mortality associated with the storm, could continue for 2-3 years. Hail damage associated with the storms may not be apparent until next spring. You should continue to monitor your storm-damage stands for several years, especially if additional stresses occur in the year or years after the storm damage (such as a drought, defoliation, etc.). If you notice trees dying in the year following the storm or even two years after the storm, you should discuss this with your forester.

Replanting when do you start over?

If you have a pine stand that was salvaged and you plan to replant to pine on that site, wait!  Pales weevil (Hylobius pales) is a native insect that will infest freshly cut pine stumps. That alone is not a concern, but as new adults emerge from stumps, they must do a “maturation feeding” on conifer twigs, which can girdle them. If the only “twigs” available are the seedlings that you just planted then they will feed on those, possibly killing the seedling and causing extensive failure of your new planting. Wait for the second springtime following your salvage/harvest before you replant. Example: you salvaged your stand in August 2019, you should not replant until the spring of 2021. Another example: you salvage your stand in May 2020, you should not replant conifers on that site until spring of 2022.

Talk with a professional

If you’re still unsure of how to proceed with making decisions about the storm damage on your land, you should contact a professional forester or forest health specialist for insect and disease questions. You can also find lots of resources and information on recovery from the storm at the Wisconsin DNR storm damage page. Major storms like this can devastate a landscape and deal a crushing blow to the family forest. Discussing your options with a forester and creating a game plan that will benefit you and your land will start you on the road to forest recovery.

Aerial view of extensive storm damage surrounding a home in Wisconsin.

Storm damage was extensive in numerous counties. For scale, note the house near the center of this photo.

Please report damage to white and bur oaks

By Mike Hillstrom, forest health specialist, Fitchburg, Michael.Hillstrom@wisconsin.gov, 608-513-7690; Alex Feltmeyer, forest health specialist, Plover, Alex.Feltmeyer@wisconsin.gov, 715-340-3810; and Paul Cigan, forest health specialist, Hayward, Paul.Cigan@wisconsin.gov, 715-416-4920

Forest health staff are again noticing health issues with white and bur oaks in 2019. A few trees with dieback in 2018 were recently resurveyed and were found to have recovered well. However, variable symptoms are appearing again in some areas. Forest health staff are conducting site visits to determine if the causal agents are the same as in 2018. Last year, leaf damage resulted from leaf fungal pathogens and twig damage was caused by Botryosphaeria fungi and gall wasps.

Please report any white or bur oak issues you notice to your local forest health specialist.

Same bur oak in June 2019 showing good recovery with only minor dieback.

Same bur oak in June 2019 showing good recovery with only minor dieback.

Bur oak with moderate crown dieback in June 2018.

Bur oak with moderate crown dieback in June 2018.

Professionally-designed HRD guidelines now available

Cover page of HRD guidelines documentThe professionally-designed version of the Heterobasidion root disease (HRD) stump treatment guidelines is now posted on the DNR’s HRD webpage. The revised stump treatment guidelines, developed to reduce the risk of introduction and spread of HRD in Wisconsin, were implemented January 1, 2019. The content is the same as the guidelines that were approved last year, but this document has a layout that is much more user-friendly. Explore the new look of the HRD guidelines.

 

Watch for signs of oak wilt

Linda Williams, forest health specialist, Woodruff, Linda.Williams@wisconsin.gov, 920-360-0665 

Trees in the red oak group (those with points on their leaves) that were infected with the oak wilt fungus this spring will rapidly drop their leaves from July to September and be dead by fall. This wilting and dropping of the green leaves happens quickly. Once it starts, the tree will drop most of its leaves within just a few weeks.

Tree dying from oak wilt with rapidly dropping leaves.

Tree dying from oak wilt with rapidly dropping leaves. The tree was injured in May, attracting the beetles that help spread the fungus, and the tree was dead by the end of the year. Photo was taken in August.

Red oak leaf from infected tree. Leaves are often green at the base, with the outer portions of the leaf appearing water-soaked or brownish.

Red oak leaf from infected tree. Leaves are often green at the base, with the outer portions of the leaf appearing water-soaked or brownish.

Continue reading “Watch for signs of oak wilt”

Protect yourself from ticks and tickborne illnesses

Bill McNee, forest health specialist, Oshkosh, Bill.McNee@wisconsin.gov or 920-360-0942

Adult deer tick. Credit: Scott Bauer, USDA Agricultural Research Service, bugwood.org.

So far this spring we are off to a busy tick season, with many reports and photos being sent in to DNR staff. Ticks can be found year-round in Wisconsin but are most active from May to September. Some species, including the deer tick responsible for Lyme disease, carry infectious diseases that elevate them from mere nuisance to serious health threat.  Lyme disease is most often spread by very small, immature ticks known as “nymphs.” Adult deer ticks can also transmit Lyme disease, but because they are larger, they are more likely to be discovered and removed compared to the tiny nymphs which can be as small as a chia or sesame seed.

Continue reading “Protect yourself from ticks and tickborne illnesses”

Needle and leaf diseases are back!

Mike Hillstrom, forest health specialist, Fitchburg, Michael.Hillstrom@wisconsin.gov, 608-513-7690

It’s nearly summer and the usual cast of disease characters are on the scene following wet spring conditions. Rhizosphaera needlecast and other needle diseases impacting spruce continue to be a major concern for landowners and homeowners. Diseases in hardwoods are also popping up. For more information on needle and leaf diseases affecting trees in Wisconsin and resources to learn more, click below to read full article. 

A row of spruce trees with dead branches and missing needles caused by Rhizosphaera needlecast.

Spruce trees impacted by Rhizosphaera needlecast.

Continue reading “Needle and leaf diseases are back!”

Protect oaks from oak wilt by waiting to prune

By Don Kissinger, urban forester, 715-348-5746, don.kissinger@wisconsin.gov and Paul Cigan, forest health specialist, 715-416-4920, paul.cigan@wisconsin.gov

To protect oak trees from the often-fatal oak wilt disease, don’t prune, cut or injure oak trees from April through July. 

Pruning and cutting oaks in spring and early summer leaves them vulnerable to oak wilt, which rapidly kills trees in the red oak group and weakens those in the white oak group. Any damage during this time, including broken branches caused by storms, exposes living tree tissue beneath the bark and provides an opportunity for the oak wilt fungus to infect the tree.

Sap-feeding beetles introduce the disease by carrying oak wilt spores from infected trees or firewood to fresh wounds. Healthy oaks can become infected in as little as 15 minutes after the creation of a wound. 

Sap-feeding beetle on diseased oak tree in Sawyer County.

Sap-feeding beetle on diseased oak tree in Sawyer County.

The trees most likely to die from oak wilt infection are in the red oak group, including northern pin oak, northern red oak, red oak and black oak. The white oak group is more likely to survive infection and includes bur oak, swamp white oak, white oak and English oak.

Tree paint or wound dressing is not normally recommended on pruned or wounded surfaces, but for damaged oaks an immediate light application of these products may be the only defense against oak wilt infection from April through July.

Pruning in spring can be damaging to any deciduous tree because their energy reserves are low as they produce new buds and leaves following the winter months. In general, the best time to prune is in winter when trees are dormant. 

As of January 31, oak wilt has been found in all Wisconsin counties except 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 will help keep them that way for years to come.

Oak wilt and other diseases move easily on or in firewood logs year-round, so keeping firewood local, or purchasing Wisconsin-certified firewood, is another important component of protecting trees and keeping forests healthy. Visit the DNR firewood page for more information and a directory of certified firewood vendors.

More information, including a recently released oak wilt video, is available at the DNR oak wilt page. Additional information about proper pruning techniques is available from community foresters or through DNR resources such as this tree pruning poster

Revised Heterobasidion root disease guidelines now available

The Wisconsin Department of Natural Resources has released updated guidelines to reduce the risk of introduction and spread of Heterobasidion root disease (HRD) in Wisconsin through preventive stump treatments. The revised guidelines became effective on January 1, 2019, and a professionally designed version will be available soon. Woodland owners are strongly encouraged to work with a professional forester to make management decisions about HRD and preventive stump treatments.

Pocket of HRD-caused thinning and mortality in red pine plantation, Grant County.

Pocket of HRD-caused thinning and mortality in red pine plantation, Grant County.

Heterobasidion root disease is one of the most destructive diseases affecting conifers in the Northern Hemisphere. In Wisconsin, HRD is most commonly found in pine and spruce plantations. Infection by the wood-decaying Heterobasidion irregulare fungus kills living tissues and leads to growth loss and tree mortality. Spores landing on a fresh cut pine or spruce stump will infect that stump and root system and spread via root contact to neighboring trees, killing them as it invades their root systems. This pattern of spread creates pockets of dead and dying trees that expand outward. Growth reduction of trees leads to economic losses for plantation owners, and mortality of trees, including seedlings and saplings, has long-term implications for future stand composition and management.

The HRD stump treatment guidelines are designed to help make decisions about the use of preventive stump treatments when harvesting a stand. These treatments limit disease introduction by preventing fungal spores from developing on the exposed surfaces of newly cut stumps.

Cutting bar on logging equipment spraying blue chemical used in HRD stump treatments.

Pesticides used in stump treatments can be applied using logging equipment (blue mist exiting through nozzles in saw bar) or backpack sprayer.

Stump treatments are typically recommended between April 1 and November 30 if a stand is within 25 miles of a known HRD infection site and the stand is more than 50% pine and/or spruce. However, there are other factors to consider when deciding whether to use the preventive stump treatments. Certain situations when you may not need to treat stumps, referred to as “Exceptions” and “Modifications” in the guidelines, consider variables such as economic feasibility, landowner risk tolerance, unexpected weather patterns and future desired stand composition. Highlights of the revised stump treatment guidelines include:

  • Timing of treatments and general distance recommendations did not change from older guidance
  • Addition of spruce as a species recommended for stump treatment
  • Additional Exceptions and Modifications where treatment may not be necessary
  • For private landowners with a higher risk tolerance, a 6-mile radius from known infection sites can be considered when evaluating whether to apply treatments
  • Even if a stand is considered at low risk for HRD infection, woodland owners should carefully consider the potential impacts to their stand if preventive treatments are not used and HRD becomes established

Along with the guidelines, a web-based HRD map viewer has been launched. This interactive map displays confirmed HRD locations and 25-mile and 6-mile radius buffers around HRD locations. The purpose of this map is to help users determine whether a stand is within either the 25 or 6-mile buffers where stump treatments are recommended. You can enter an address or GPS location, turn map layers on and off, and zoom in and out to an area of interest.

If you would like more information about HRD or these guidelines, visit the DNR HRD webpage or talk to your regional forest health specialist.

New northern oak wilt detections

By Paul Cigan, forest health specialist, Hayward. Paul.Cigan@wisconsin.gov; 715-416-4920 and Linda Williams forest health specialist, Woodruff. Linda.Williams@wisconsin.gov; 920-360-0665

Oak wilt (OW) was confirmed for the first time in Bayfield and Douglas counties and in 16 new northern townships in 2018. The new OW infections occurred on a range of properties, including county, tribal, private, U.S. Forest Service and Board of Commissioners of Public Lands. Wisconsin Department of Natural Resources (DNR) forest health staff are working proactively with affected property managers and landowners to address these infections and prioritize disease prevention and detection in the future.

 

Oak wilt distribution map. Confirmed counties are displayed in red. Confirmed townships are displayed in pink 6-mile square blocks.

The greatest risk of overland transmission in northern Wisconsin is from April 15 to July 15, when fungal spores readily infect open wounds. Most of these new cases occurred during this time frame due to stem and branch damage. The primary causes of damage were roadside brush clearing, pruning, lot clearing and storm-caused branch breakage. Fungal spores may have come from diseased oak firewood and unprocessed wood recently transported into these areas.

Image shows a group of oak trees. Northern red oak on far left is in wilting stage of disease (leaves on but wilting and dropping). Oak on far right has mechanical root collar injury. Dairyland Township, Douglas County.

OW disease center. Oak on far left was infected through belowground root contact with tree damaged in lot clearing (far right). Dairyland Township, Douglas County (photo taken by Paul Cigan).

If oak wilt is present in or within 6 miles of the county where you manage oak, your management activities may be affected by seasonal harvesting restrictions to reduce OW introduction and impact. Read DNR’s oak harvesting guidelines for more information and refer to the list below of new 6 square mile blocks by township and county to see if OW has been detected near your property.

Bayfield County
Barnes T45N R9W
Cable T43N R7W
Drummond T45N R8W
Douglas County
Dairyland T43N R15W
Gordon T44N R11W
Langlade County
Elcho T34N R11E
Langlade T33N R13E
Neva T32N R11E
Sawyer County
Couderay T39N R8W
Hayward T41N R8W
Hunter T40N R7W
Round Lake T41N R8W
Spider Lake T42N R7W
Vilas County
Boulder Junction T42N R6E
Lac du Flambeau T41N R5E, T40N R5E
St. Germain T40N R8E

Please report any suspected oak wilt infections to your local DNR forester or regional forest health specialist and learn more about oak wilt identification and biology on the DNR oak wilt webpage. To learn more about firewood rules and how you can help reduce transmission of pests and diseases, including oak wilt, visit the DNR firewood page.

10 oak leaves lain on downed log display bronze discoloration typical of oak wilt. Midrib and base of leaf are still green.

Bronzed leaves fallen from infected oak. Leaves were observed beneath infected northern red oak. Cable Township, Bayfield County (photo taken by Paul Cigan).

Heterobasidion root disease in Monroe County

By Todd Lanigan, forest health specialist, Eau Claire. Todd.Lanigan@wisconsin.gov; 715-210-0150

Heterobasidion root disease (HRD), formerly known as annosum root rot, was recently found in Monroe County for the first time in the town of Little Falls. With this detection, HRD is now known to occur in 28 Wisconsin counties.

HRD distribution map. Counties where HRD is present are shown in blue with most recently confirmed county shown in dark blue.

Fruiting bodies of the pathogen, Heterobasidion irregulare, were found on dead overstory red pine and both live and dead white pine saplings in the Big Creek Fishery Area. The 20-acre stand was a red pine plantation established in 1958 and last thinned in 2012. Wood samples were collected to isolate and identify the pathogen through microscopic identification at the Forest Health Lab in Fitchburg.

Image of multiple spores viewed under microscope. Conidiophores look like Q-tip heads.

Microscopic spores isolated from wood samples and confirmed as HRD in Forest Health Lab.

Based on this new find, a number of townships were added to the 25-mile buffer zones used in determining appropriate management activities according to the HRD Management Guide. There will be a one-year grace period for implementation of the guide in these townships.

The Forest Health Program has records of all confirmed HRD detections. If you suspect this disease is present in a stand, contact your regional forest health specialist.

For more information about HRD, visit the DNR Forest Health webpage.