Statewide Forest Health

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.

Flooding affects forest stands across state

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

It’s another wet year in many parts of Wisconsin with water levels in lakes and rivers remaining very high. Seasonally wet areas are staying wet for longer, and areas that have not been wet for years are flooding or experiencing rising ground water levels. DNR forest health staff are increasingly noticing tree mortality due to these hydrologic issues. This occurs because flooding and high water reduces the amount of oxygen in the soil, depriving trees with submerged roots of the oxygen needed for growth and respiration. Along with submerged roots, trees can also die from uprooting and from subsequent insect and disease attack following flooding stress.

Trees being impacted by river flooding.

Trees being impacted by river flooding.

It may become necessary to conduct salvage harvests in flooded stands. Of course, the flooding also makes site access difficult. This is particularly concerning in stands where salvage harvests are needed to capture value, such as stands impacted by insects like emerald ash borer and eastern larch beetle.

Please let your local forest health specialist know if you are seeing flood-damaged stands. It is recommended to keep setting up salvage sales where appropriate. Access to wet or flooded sites can be difficult and may require frozen ground conditions if the site is expected to remain wet in the near-term.

Find your local forest health specialist on the DNR forest health webpage and learn more about flooding damage and mitigation with this resource from UW-Madison Division of Extension.

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.

 

Native caterpillars not a major concern for trees

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

Eastern tent caterpillars (ETC) are hatching and beginning to feed on host trees, including cherry, apple and crabapple. Landowners and homeowners may notice the white silken tents forming in branch forks. Although they form unsightly tents, ETC is a native insect so management is not typically necessary. Even completely defoliated trees will put out new leaves within a few weeks.

A group of eastern tent caterpillars warm themselves on white silk tent before leaving to feed on black cherry leaves.

If landowners want to remove the tents the best time to do so is early morning or evening when the caterpillars are inside. Unless it is raining, eastern tent caterpillars leave their tents each morning to feed throughout the day before returning at night. Caterpillars can be removed either by hand if they are within reach or with a rake if they are high in the tree. They can then be killed by soaking them in soapy water or sealing them in a trash bag. Insecticides are rarely necessary but should penetrate inside the tent if used. Do not prune branches, burn tents or soak them with WD-40. These methods are more harmful to the tree than ETC defoliation and are not recommended.

For more information on eastern tent caterpillar, read this factsheet from UW-Madison Division of Extension.

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!”

Branch tips littering the ground under your trees?

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

Have you been noticing branch tips scattered on the ground beneath spruce, fir or pine trees this spring? You may be seeing one of a few things – damage from small animals or breakage caused by the harsh winter we had. Fortunately, the damage from either is unlikely to do serious harm to your trees. 

Spruce branch tips found on ground were clipped from tree by squirrels.

Spruce branch tips found on ground were clipped from tree by squirrels.

Continue reading “Branch tips littering the ground under your trees?”

Invasive insects threaten Wisconsin hemlock

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

Two invasive insects, hemlock woolly adelgid (HWA) and elongate hemlock scale (EHS), pose serious threats to Wisconsin’s hemlock trees. Although neither insect is established in Wisconsin, both insects have been found in recent years on infested nursery stock or live tree material that was shipped into the state. Fortunately, these introductions were detected and the plant material destroyed. But with HWA established in hemlock stands of several Michigan counties along Lake Michigan, natural spread to Wisconsin is anticipated.

Because of the risk, forest health staff from the Department of Natural Resources (DNR) and the Department of Agriculture, Trade and Consumer Protection (DATCP) are conducting surveys for early detection of these pests. Both pests could appear in many settings including urban and rural forests, yard trees and holiday tree plantations so everyone has a role to play in looking for these pests and reporting what they see.

HWA and EHS both feed on tree needles with sucking mouthparts. When populations are large enough, this feeding causes excessive fluid and nutrient loss, leading to declining tree health. Both insects can be found together on infested hemlock trees.

A group of adult hemlock woolly adelgid covered in white waxy filaments feeding on hemlock needles.

Characteristic white wax coating of adult hemlock woolly adelgid.

There are a few key ways to spot these insects. HWA is most obvious in winter when white, wax-covered adults are present. You may also see hemlock foliage turning gray-green in color as tree health declines. Adult EHS have a waxy cover and feed on the underside of hemlock, spruce and fir needles. Damage from EHS appears as yellow banding on needles. Crowns appear progressively thinner as infested needles die and fall off prematurely. Both insects also have tiny immature crawlers that may be seen moving on infested trees.

Tiny adult scales protected with a waxy cover feed on needles causing yellow banding.

Adult elongate hemlock scale and yellow needle banding (Credit: WI DATCP).

If you suspect you’ve found either HWA or EHS, please report it immediately to your local DNR forest health specialist. For more information about HWA, visit the DNR and DATCP webpages. To learn about EHS, visit the DATCP webpage.

Revised EAB insecticide guide now available

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

Title page of revised insecticide guide.The North Central Integrated Pest Management Center has released the third edition of its widely distributed guide, “Insecticide Options for Protecting Ash Trees from Emerald Ash Borer.” This updated document addresses frequently asked questions and shares new information about insecticide options that are not covered in the guide’s previous edition from 2014. To review the most current recommendations and study results regarding insecticide use for EAB, download the report here.