Central WI Forest Health

Invasive insects threaten Wisconsin hemlock

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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.

Trees sought for EAB biocontrol efforts

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The U.S. Department of Agriculture’s (USDA) Biological Control Facility is seeking donations of living green ash trees from Wisconsin landowners. Infested live trees are needed to rear the parasitic wasps that prey upon emerald ash borer (EAB) eggs and larvae. 

USDA staff in Brighton, MI rear stingless, parasitic wasps for release in EAB-infested states. Currently, the biological control facility rears four species of wasp, three of which attack EAB larvae and one that attacks eggs. Finding and harvesting living green ash infested with EAB is a vital part of the biocontrol program, allowing staff to breed EAB colonies from adult beetles. These colonies then support the rearing of almost a million parasitic wasps each year. To learn more about the USDA’s EAB Program, read the EAB Story Map.

The stingless wasp Spathius agrili lays up to 20 eggs on its host. Eggs hatch and the larvae feed and eventually kill the EAB larva.

The stingless wasp Spathius agrili lays up to 20 eggs on its host. Eggs hatch and the larvae feed and eventually kill the EAB larva.

Another wasp, Tetrastichus planipennisi, lays its eggs inside EAB larvae where they feed and develop into red-eyed pupae before completing their lifecycle.

Another wasp, Tetrastichus planipennisi, lays its eggs inside EAB larvae where they feed and develop into red-eyed pupae before completing their life cycle.

The facility is looking for donations from properties that meet the following criteria:

  • Live green ash between 8-20 inches diameter
  • 25 or more suitable ash trees
  • Trees may show signs of decline but must be alive
  • Located in southeastern and eastern Wisconsin north up to Green Bay

USDA staff will conduct landowner site visits after leaves have budded in spring. If a site meets most of the criteria, staff will return in late summer to peel back bark of trees one by one. This is the EAB larval evaluation method used to determine infestation levels. Trees are then selected for harvest based on that methodology.

USDA staff evaluate ash trees for harvest by cutting a ‘bark window’ to estimate the degree of infestation from the live EAB larvae they see.

USDA staff evaluate ash trees for harvest by cutting a ‘bark window’ to estimate the degree of infestation from the live EAB larvae they see.

Harvests will occur weekdays from September to May. The USDA will arrange the harvests, including selecting subcontractors and paying for the work. Sites are remediated to pre-harvest conditions to the best of the contractor’s ability.

Lands enrolled in Wisconsin’s Managed Forest Law (MFL) or Forest Crop Law must file a MFL Cutting Notice (Form 2450-132) 30 days prior to cutting. Contact your local Tax Law Forestry Specialist for assistance.

All private landowners must submit a county cutting notice prior to harvest. This cutting notice is separate from the MFL cutting notice and should be filed with the county clerk. Learn more about cutting notices at this DNR webpage.

For more information about the USDA program and if you are interested in participating, contact Paul Nelson at paul.m.nelson@aphis.usda.gov or 734-732-0025.

Revised EAB insecticide guide now available

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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.

Salt spray injury on conifers observed in spring

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By Paul Cigan, forest health specialist, Hayward, Paul.Cigan@wisconsin.gov, 715-416-4920

A particularly active winter weather season has left white pine and other conifer species along many of Wisconsin’s roadways with salt spray injury this spring. These salt deposits draw water out of the foliage, causing them to dry out and turn brown, often beginning at needle tips and progressing down to the needle base. Browning is most heavily concentrated on branches facing the road, lower portions of tree crowns and foliage that remained above the snowline.

Browning is likely to intensify as the weather continues to warm this spring, and heavily damaged needles may die and prematurely fall off. Successive years of damage can leave branches sparse of foliage and cause branch dieback.

Salt spray from de-icing salts applied to roadways may drift and settle onto vegetation within 150 feet of a roadway. Injury can be prevented or reduced by placing physical barriers such as snow fencing, plastic or burlap around conifers in fall. Salt residues can also be rinsed off with water during periods of warm weather prior to bud break. More information about salt damage to plants can be found in this UW–Madison Division of Extension publication.

Red pine shoot with needle tip browning from salt spray injury.

Red pine shoot with needle tip browning.

White pine tree with salt spray injury concentrated on limbs of the lower crown that are facing the roadway.

White pine tree with salt spray injury.

White pine seedlings with salt spray injury concentrated on tissues above the former snowline.

White pine seedlings with salt spray injury.

 

Protect oaks from oak wilt by waiting to prune

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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. 

Treat your valuable ash trees against EAB

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

Spring is the best time to evaluate valuable ash trees and determine if they should be treated to protect them from emerald ash borer (EAB). Emerald ash borer is currently the most damaging threat to trees in the state, killing more than 99 percent of the ash trees it infests.

Insecticide treatments to prevent EAB infestation are usually applied between mid-April and mid-May, so it is important to start planning now. The first thing homeowners should do is check their ash trees for signs of infestation. Woodpecker damage is easy to see this time of year and is often the earliest visible sign of EAB. Photos of other signs and symptoms can be found on the DNR EAB website.

Ash trees with woodpecker "flecking" indicate EAB infestation.

Signs of EAB infestation include woodpecker damage where the birds pick away ash tree bark to feed on larvae.

Emerald ash borer has become so widespread that homeowners should consider treating valuable ash trees no matter where they are in Wisconsin. The highest risk of EAB infestation is within 15 miles of a known infestation, but it is widely believed that there are additional, undetected EAB infestations throughout the state. To see a map of known EAB infestations, visit the Wisconsin EAB website.

While the best time to treat ash trees is before they are infested, treatments of infested trees can still be successful if done while EAB populations within the tree are low or moderate. Some ash trees may be too heavily infested to save or they may have other problems that make them poor candidates for treatment.

Trunk injection treatment for EAB. Credit: Matthew Karst.

Trunk injection treatment to protect against EAB. Credit: Matthew Karst.

You should consider several factors when deciding whether to treat your ash trees. Insecticide treatments can be costly, but the investment may be worthwhile if you consider the many benefits that healthy yard trees provide, including higher property values, better air quality, shading and cooling for homes and more. Removing and replacing your ash trees is another option and may be the best choice for heavily infested and lower value trees. For trees that you decide are worth saving, however, the cost to treat may still be less than removing and replacing them with other species. This factsheet from UW-Extension can help you decide whether a tree is worth treating.

If you decide to treat, or if you want to discuss treatment options with a professional, call a certified arborist or search online and in phone books for other businesses. Check the credentials and insecticide applicator certification of any business before hiring them to treat your ash trees.

Treatments are not economically practical for ash found in woodlots. Any questions about woodlot management should be directed to a professional forester.

Despite the cold winter temperatures in late January and early February, don’t postpone treatment of ash trees. Weather data and collection of overwintering EAB larvae at two sites in Waukesha County predict high insect survival rates in most of the state. Female beetles can lay up to 200 eggs, so EAB populations will quickly rebound from any mortality that occurred due to cold weather.

More information about EAB and management options can be found through the Wisconsin EAB website.

Prepare for the return of gypsy moths

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

Gypsy moth eggs should start hatching in a few weeks as temperatures continue to warm. Homeowners should survey their trees for egg masses and either treat or remove the eggs now to help protect trees from defoliation and reduce future caterpillar populations.

Property owners should start by looking for the egg masses. They can be found on nearly any outdoor surface, including tree trunks, undersides of branches, buildings, firewood piles and other outdoor objects. They are tan-colored lumps about the size of a nickel or quarter. Each egg mass can contain 500 to 1,000 eggs that will soon hatch into hungry caterpillars. While statewide gypsy moth numbers are currently low, isolated trees and locations may have high populations.

Gypsy moth larvae hatch from egg masses on outdoor bowl.

Gypsy moth larvae hatch from egg masses on outdoor bowl.

If egg masses are found, there are two options to help reduce pest numbers. Available at many garden centers and retail stores, horticultural oils that suffocate the eggs can be directly applied to the masses. These are most effective when temperatures are above 40 degrees and a return to freezing is not imminent.  Alternatively, egg masses within reach can be scraped into a can of soapy water and left to soak for a few days before being discarded in the trash.

Insecticide treatments may be appropriate for larger trees that have many egg masses. Some types of treatment are done before eggs hatch, and some are done while the caterpillars are small. Property owners looking to hire a business to treat large yard trees this spring should contact them soon. A list of certified arborists is available on the Wisconsin Arborist Association website. Additional businesses offering insecticide treatments may be found online or in a phone book. Questions about woodlot management should be directed to a professional forester.

Additional information about management options for homeowners, including sticky barrier bands and burlap collection bands, is available at the Wisconsin gypsy moth website.

Don’t change EAB plans due to cold weather

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

The recent frigid temperatures in late January and early February are likely to kill many overwintering emerald ash borer (EAB) larvae, but the tree-killing pest isn’t going away. The insulating properties of tree bark keep the larvae warmer than the outdoor air temperature, and wind chills do not affect the larvae because they are sheltered. The pest is also adapted to subzero temperatures based on its native range in eastern Asia where cold winters are common.

Prepupal larva seen during post-polar vortex sampling to assess larval mortality.

Overwintering prepupal larva, from February 2019 in Brookfield, WI.

On the morning of January 31, many parts of Wisconsin had low air temperatures between -30 and -35 degrees F. In places where it was this cold, scientific studies predict that most EAB larvae will be killed. Where low temperatures were between -20 and -30, larval mortality is likely to be lighter. Overwintering larvae were examined about 1 week after the cold snap in Brookfield (Waukesha County), where the low was -26, and few of the larvae were observed to have physical signs of freezing damage. Many of the larvae began moving within three days of being brought indoors. However, physical damage to the larvae may not yet be apparent, and normal-looking larvae may ultimately die from the cold temperatures.

Populations of the pest are likely to rebound, since each female beetle that emerges this summer will lay as many as 200 eggs. It is not currently known if larval mortality will significantly delay ash tree decline and mortality, although this may occur in areas that experienced the lowest temperatures. A cold spell in early 2014, that was not quite as cold, had no noticeable impacts on EAB spread or ash decline/mortality in areas known to be heavily infested.

The introduced biological controls of EAB, commonly known as “EAB wasps,” are at least as cold-tolerant as EAB. It is expected that these wasps will persist in and around release sites and continue parasitizing EAB eggs and larvae.

Forestry experts do not recommend changing EAB management plans solely due to the cold weather.

  • Continue to look for EAB in ash trees. Woodpecker damage is a good sign that an ash tree is infested with EAB or other pests.
  • Insecticide treatment of high-value ash trees near known infestations should be continued this spring.
  • Don’t delay tree removals or timber harvests that are already scheduled. Giving non-ash tree species more time to grow means that the future impacts of EAB will be reduced.
  • Continue planting non-ash tree species.
  • To help slow the spread of EAB, review firewood rules in Wisconsin. Buy firewood in the local area where you plan to burn it or buy Wisconsin-certified firewood that has been treated to eliminate pests. Certified firewood is often available at DNR-managed properties or you can buy from an independent certified firewood dealer.

Additional information about emerald ash borer, insecticide treatments and forest management can be found online at www.emeraldashborer.wi.gov.

Ice, snow and deep frost: winter creates problems for trees

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By forest health specialists Linda Williams, Woodruff, Linda.Williams@wisconsin.gov, 920-360-0665; Mike Hillstrom, Fitchburg, Michael.Hillstrom@wisconsin.gov, 608-513-7690; Alex Feltmeyer, Plover, Alexandra.Feltmeyer@wisconsin.gov, 715-340-3810

Heavy ice and snow loads can cause significant problems for trees. Branch tips and whole branches may break under heavy loads, and in windy conditions entire tree tops can come crashing down.

Freezing rain on February 4, 2019 covered trees around the state with a ¼” thick layer of ice. The weather then turned bitterly cold, leaving the ice stuck to the branches, weighing them down and straining the trees. Following that event, a snow storm affecting most of the state led to more ice, snow and damage to branches. 

Tree branches covered in 1 inch of ice.

These extraordinary ice formations may look light and frosty, but they add a lot of weight to tree branches and can cause branch breakage.

Some trees are more susceptible to winter damage. Small trees can be particularly prone to injuries caused by heavy ice and snow. They can bend so far over from the weight that their tops are near or even touching the ground. In some cases, their stems may break at ground level causing the entire tree to fall over. Other vulnerable trees include those with ingrown bark at branch unions. This type of branch union is weak and more likely to split under heavy loads.

White pine saplings bent over from weight of ice on branches.

These young white pines were coated in ice, causing them to bend over. They may not rebound well after the ice and snow melt.

White pine sapling weighed down with snow, causing significant branch droop.

The heavy snow on the branches of this young white pine have caused the branches to droop and the top to bend over significantly. Heavy snow loads can cause branches to break.

While forest trees are just as prone to winter damage, yard trees present the most safety hazards and should be seen by an arborist as soon as damage becomes evident. Storm-damaged trees may have dangerous features such as hanging branches, branches under tension, spring poles and cracks in the main stem. Depending on the damage, some yard trees may also require pruning to correct their form and protect them from future injuries. Due to the dangers associated with storm-damaged trees, consider having a professional arborist or logger do your tree pruning or removal.

Tree roots can be damaged in cold weather too. In areas of southern Wisconsin, a lack of snow during some of this winter’s cold snaps has forced the frost deep into the ground. Some of you may recall the winter of 2002-2003 when we had very little snow and frost went 5’ deep in many parts of the state. Not only did it freeze septic systems and water lines that winter, but it also damaged tree root systems by killing some of the fine roots and root tips that grow deep below the surface and prefer not to freeze. Trees that lost a significant number of roots experienced crown dieback and stress that led to insects and diseases attacks, including two-lined chestnut borer on oak and Armillaria root rot on conifers. Deep freeze damage to tree roots is not often the single cause of tree stress or death but is more often one of several stress agents that leave trees more susceptible to insects and diseases. Fortunately, the deep frost can be pulled out of the ground, and some of the damages avoided, if there is enough snow cover for the remainder of the winter.

For more information on how snow and ice can impact trees, check out these resources from Wisconsin [PDF] and Minnesota. Contact a certified arborist or DNR forester if you want to discuss management options for storm-damaged trees.

Revised emerald ash borer guidelines now available

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

The Wisconsin Department of Natural Resources has released updated guidelines to aid woodland owners and managers in managing ash stands in light of the invasive emerald ash borer (EAB). The guidelines that became effective on January 1, 2019 reflect new research, increased pest detections and the anticipated transition to a statewide EAB quarantine (which occurred in March 2018).

Forestry professional and landowner standing in hardwood stand assessing conditions.

Landowners should work with professional foresters to make management decisions related to EAB on their land.

The silvicultural guidelines are intended to help make informed stand-level decisions regarding management of stands that are not yet infested by EAB and stands that are already impacted by the tree-killing beetle. They should be used along with other materials, including best management practices and other guidance documents, to develop appropriate management plans. 

The revised guidelines include recommendations to:

  • Implement management plans as soon as practical, across all of Wisconsin, to reduce a stand’s ash component to no more than 20%. More management options are likely to be available by taking immediate action
  • Review existing management plans to determine if they need revision due to changes in EAB distribution, stand condition, market prices, etc.
  • Diversify woodlands with site-appropriate tree species
  • Utilize merchantable ash before trees are infested or killed. It may be appropriate to retain some live ash on site for ecological benefits, species diversity, wildlife habitat, temporary cover or seed production

The guidelines also place a greater emphasis on assessing stand and site conditions before making management decisions. The document offers stand management alternatives for both upland and lowland stands, while recognizing that conversion of lowland ash stands to other forest types will be impractical in many cases.

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