Forest Health News

Protect Oak Trees From Oak Wilt By Pruning After July, Not Before

Posted on by eleanorvoigt

By Don Kissinger, DNR Urban Forester, 715-348-5746 or Don.Kissinger@wisconsin.gov; Paul Cigan, DNR Forest Health Specialist, 715-416-4920 or Paul.Cigan@wisconsin.gov

The Wisconsin Department of Natural Resources (DNR) urban and forest health specialists recommend not pruning or cutting oaks from April through July to protect oak trees from the often fatal oak wilt disease.

The spring season often draws property owners outdoors to soak up rays of long-awaited sunlight, breathe in some fresh air and begin seasonal yard maintenance and cleanup projects. While spring is a time to dust off yard tools like rakes, shovels and weed clippers, when it comes to the health of oak trees, keeping those chainsaws and trimming tools a safe distance away will go a long way to ensure that your trees stay healthy for many more spring seasons to come.

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

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

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Treat Your Valuable Ash Trees Against Emerald Ash Borer

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Bill McNee, Forest Health Specialist, Oshkosh. Bill.Mcnee@wisconsin.gov or 920-360-0942

Property owners with healthy, valuable ash trees should consider treating them with insecticide this spring to protect against emerald ash borer (EAB). The pest is currently the most damaging threat to trees in Wisconsin, killing more than 99% of the ash trees it infests.

Woodpecker damage during the winter is often the first sign that an ash tree is infested. Now is an excellent time to consider insecticide protection because the treatments are typically done between mid-April and mid-May once leaves begin to return.

Treatments on already-infested ash trees are more likely to be successful if the trees have low or moderate levels of woodpecker damage.

An ash tree branch with bark missing after woodpeckers attacked it while looking for larvae to eat.

This ash tree branch in West Allis has been attacked by woodpeckers looking for larvae to eat.

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Look For Gypsy Moth Egg Masses And Prepare For Hatch; DATCP Slow-The-Spread Treatments Announced

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By Bill McNee, DNR Forest Health Specialist, Oshkosh, Bill.Mcnee@wisconsin.gov or 920-360-0942

Typically, gypsy moth egg masses hatch in April as temperatures warm. Now is a great time to do an egg mass inspection to look for unknown infestations and treat or remove any masses within reach. Each mass can result in 500 to 1,000 leaf-eating caterpillars.

Egg masses are tan-colored lumps and vary from about the size of a nickel to a quarter. They can be found on many outdoor surfaces such as tree trunks, the undersides of branches, buildings, rocks, fences, retaining walls, firewood piles and picnic tables.

Gypsy moth egg masses on the underside of a maple branch

Gypsy moth egg masses on the underside of a maple branch. 

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Stalactiform Stem Rust Of Jack Pine

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By Todd Lanigan, DNR Forest Health Specialist, Eau Claire. Todd.Lanigan@wisconsin.gov or 715-210-0150

Stalactiform stem rust, which occurs in the Lake States and Canada on jack pines, was recently found in western Monroe County. Before this discovery, the only place I have seen stalactiform stem rust in Wisconsin was Adams County in the mid to late 1990s.

Rust diseases can be identified by the galls’ shape and location and by cankers present on the trees. On jack pine seedlings and saplings, stalactiform stem rust can cause elongate swellings on branches or the main stem (trunk).

A jack pine with stalactiform stem rust galls that squirrels have chewed on

A jack pine with stalactiform stem rust galls that squirrels have chewed on.

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Oak Wilt Vectors Emergence User Interface Now Available

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By Kyoko Scanlon, Forest Pathologist, Kyoko.Scanlon@wisconsin.gov or 608-235-7532 and Elly Voigt, Forest Health Communications Specialist and Lab Technician, Eleanor.Voigt@wisconsin.gov

Oak wilt is a serious disease of oaks that spreads to new areas when insects carrying oak wilt fungal spores land on a fresh wound of a healthy oak tree. To prevent oak wilt infections, it is important to avoid pruning, wounding and harvesting of oaks when these insects are abundant.

Predicting when these insects emerge in spring can be difficult as their emergence is highly weather-dependent and spring weather varies significantly year to year. The good news is that a new online interface is now available to provide users with localized information about the emergence status of the two most important insects that transmit oak wilt in Wisconsin. Because the interface uses a degree-day model constructed from insect trapping data and actual weather data, it is useful to refine the beginning of the periods when pruning, wounding and harvesting of oaks should be avoided.

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Porcupine Damage Easily Seen In Winter

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By Todd Lanigan, Forest Health Specialist, Eau Claire. Todd.Lanigan@wisconsin.gov or 715-210-0150

Porcupines can damage both conifer and hardwood trees by eating their bark. On sunny days, the bright, white wood where the bark has been stripped readily stands out in the forest, especially on hardwoods. Porcupines can remove large areas of bark, at times enough to completely girdle the trunk or branches. This causes the tree to die from the girdle point upwards on the trunk or outwards on the branch.

Trees and branches that are not entirely girdled will continue to grow and callus tissue will begin to grow over the wounds. On hardwoods, the trunk or branches that are nearly girdled may leaf out in the spring, only to have those leaves suddenly wilt and die as hot weather hits because the tree cannot move enough water to keep the leaves alive. On conifers, the needles may wilt and turn reddish-brown in hot weather. There are no treatment recommendations for porcupine damage.

fresh porcupine damage on a red pine

Porcupine feeding damage on red pine. Photo by Linda Williams, Wisconsin DNR

Snow Fleas Come To The Surface

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By Todd Lanigan, Forest Health Specialist, Eau Claire. Todd.Lanigan@wisconsin.gov or 715-210-0150

Snow fleas are a species of springtails that are active during the winter and are generally found in groups where their dark-colored bodies stand out against the white snow. While often observed in late winter or early spring, they also come to the surface on warm winter days. Cold weather drives snow fleas back below the surface to wait for better weather. 

Many snow fleas on snow.

Easily mistaken for specks of dirt or debris, snow fleas are tiny soil-dwelling animals that gather on the surface of the snow on warm winter and spring days.

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Revised Factsheets, Guidelines Now Available

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By Elly Voigt, DNR Forest Health Lab Technician and Communications Specialist, Eleanor.Voigt@wisconsin.gov

The Wisconsin Department of Natural Resources (DNR) has just released several updated publications, including the annual update of the Heterobasidion root disease and oak wilt factsheets and guidelines. Updated versions can be found on the DNR’s forest health webpage by clicking the links below:

     – Heterobasidion root disease factsheet
     – Heterobasidion root disease guidelines
     – Oak wilt factsheet
     – Oak harvesting guidelines

Minor revisions were also made to the environmental cause of tree damage and conifer bark beetle factsheets. Visit the DNR webpage here for other forest health publications.

For more information on forest health, visit the DNR webpage, or talk to your regional Forest Health Specialist.

Wisconsin DNR 2020 Forest Health Annual Report

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By Elly Voigt, DNR Forest Lab Technician and Communications Specialist, Eleanor.Voigt@wisconsin.gov

The cover page of the 2020 Annual ReportThe Wisconsin Department of Natural Resources’ Forest Health team recently completed the 2020 Forest Health Annual Report. The report summarizes impacts from pests, diseases and weather on the health of Wisconsin’s forests. Highlights from 2020 include:

• An update on emerald ash borer in Wisconsin, including newly confirmed counties
• New township detections of oak wilt
• Flooding and tornado damage
• Summary of state nursery studies

For access to the report, visit the link here.

Learn More About Rime Ice And Winter Tree Damage

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By Mike Hillstrom, DNR Forest Health Specialist, Fitchburg, Michael.Hillstrom@wisconsin.gov or 608-513-7690 and Brian Wahl, DNR Forestry Specialist, Fitchburg, Brian.Wahl@wisconsin.gov or 608-225-7943

During Wisconsin’s first week of 2021, a beautiful weather phenomenon occurred: rime ice. Rime ice forms when the tiny water droplets in fog freeze on trees and other objects. Hoarfrost, a similar phenomenon that occurs without fog, can form when water vapor in freezing air contacts a surface. The best news is that these winter conditions should not concern tree health when we emerge from the winter fog in spring.

A close-up photo showing rime ice on crabapple branches

Rime ice on a crabapple tree.

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