Disease

Oak Mortality Increases In 2023

Posted on by akabelowsky
Photo of a bur oak tree more than 100 years old showing canopy dieback and epicormic branching due to twolined chestnut borer

A bur oak more than 100 years old exhibits canopy dieback and epicormic branching caused by twolined chestnut borer. / Photo Credit: Wisconsin DNR

By Michael Hillstrom, DNR Forest Health Specialist, Fitchburg
Michael.Hillstrom@wisconsin.gov

White, red and bur oaks have been experiencing increased mortality in Wisconsin and neighboring states over the last few years.

The causes of mortality are varied, but two-lined chestnut borer (TLCB) is the most common culprit. Wisconsin has switched from a period of historically wet years (2017-2020) to drought conditions that have become more severe each year (2021-2023). Add in frost damage, storm damage, increased growing season length and aging forests and the environmental recipe exists for stressed oaks that are more susceptible to attack by insects and diseases.

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Balsam Fir Mortality Similar To 2018 And 2020

Posted on by akabelowsky

Linda Williams, DNR Forest Health Specialist, Woodruff
Linda.Williams@wisconsin.gov or 920-360-0665

Photo of balsam fir tree prematurely turning brown and red.

Scattered balsam fir trees in the Northwoods have suddenly turned brown and red this spring. / Photo Credit: Linda Williams, Wisconsin DNR

Scattered balsam fir trees in some areas of northern Wisconsin have suddenly turned rusty red to brown and are dying. These trees are not being impacted by spruce budworm and typically die with a full complement of needles.

The symptoms resemble what was observed in 2018 and 2020. So far, the number of trees being reported is smaller than what was seen in 2018 or 2020. Reports are still coming in, but they seem to be concentrated in northern areas of the state where we had extensive snowfall in late winter.

Continue reading “Balsam Fir Mortality Similar To 2018 And 2020” →

Watch For Brown Spot Needle Blight

Posted on by akabelowsky
Photo showing white pine with yellowing needles.

White pine with yellowing needles; new growth is not affected. / Photo Credit: Wisconsin DNR.

By Linda Williams, DNR Forest Health Specialist, Woodruff; Linda.Williams@wisconsin.gov or 920-360-0665

White pine in north central Wisconsin, as well as scattered areas elsewhere in the state, have many needles that are bright yellow. Brown spot needle blight (Lecanosticta acicula, previously known as Mycosphaerella dearnessii) is the primary suspect, although samples have been sent to the Wisconsin Department of Natural Resources (DNR) Forest Health laboratory to determine if other fungal species are present.

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Heterobasidion Root Disease Approaches

Posted on by akabelowsky

By Alex Feltmeyer, Forest Health Specialist, Plover, Alexandra.Feltmeyer@wisconsin.gov or 715-340-3810

A Heterobasidian root disease fruiting body at the base of a white pine sapling

A Heterobasidion root disease fruiting body is found at the base of a white pine sapling in the understory. Photo: Wisconsin DNR Forest Health

Heterobasidion Root Disease (formerly annosum root rot or Fomes root rot) is a serious disease of conifers that causes reduced height, shoot and diameter growth along with thin and yellowish/red foliage, ultimately causing mortality.

The disease becomes established in a new stand when spores of the fungus land on freshly cut stumps made by any forest management that creates cut stumps. After the disease becomes established, it spreads underground through root systems into adjacent trees. In this way, we often find pockets or groups of trees in various stages of decline.

Movement through the root systems contributes to significant spread throughout stands of conifers, impacting the regeneration of conifers within these pockets.

Mortality usually starts occurring three to eight years after a thinning operation. During this time, perennial fruiting bodies of the fungus begin to develop around the base of cut stumps or dead trees.

Continue reading “Heterobasidion Root Disease Approaches” →

Wisconsin DNR 2022 Forest Health Annual Report

Posted on by patricialindquist

By Becky Gray, Forest Health Team Leader, Rebecca.Gray@wisconsin.gov

The Wisconsin Department of Natural Resources’ Forest Health team recently completed the 2022 Forest Health Annual Report. The report summarizes impacts from pests, diseases and weather on the health of Wisconsin’s forests. Highlights from 2022 include:

  • Spongy moth’s rising numbers and evaluation of control techniques;
  • emerald ash borer continuing to spread and kill ash trees;
  • possible new biological control of buckthorn; and
  • drought and flooding impacts alongside insect infestations.

Read the report here.

2022 Forest Health Annual Report

Sign Up For Oak Wilt Vector Emergence Estimate Daily Email Notification

Posted on by patricialindquist

By Kyoko Scanlon, Forest Pathologist, Fitchburg, Kyoko.Scanlon@wisconsin.gov or 608-235-7532

Oak wilt is a serious disease that occurs when insects carrying oak wilt fungal spores land on a healthy oak tree’s fresh wound. To prevent oak wilt infections, it is important to avoid pruning, wounding and harvesting oaks when these insects are abundant, generally from April through July. Predicting exactly when these insects start to emerge in the spring can be difficult as their emergence is highly weather-dependent, and spring weather varies significantly from year to year.

In 2021, the Oak Wilt Vectors Emergence Thermal Model tool, a unique estimation tool, was developed as a collaborative project between the University of Wisconsin-Madison and the Wisconsin DNR to help with these predictions. This online tool offers localized recommendations about the emergence status of the two most important insects that transmit oak wilt in Wisconsin. The interface uses a degree-day model (Jagemann et al., 2018) constructed from insect trapping data and actual weather data, which helps refine the beginning of the periods when you should avoid pruning, wounding or harvesting oaks.

A screen shot of the oak wilt vector emergence homepage where the location and date data is entered to model growing degree days.

UW Extension’s Oak Wilt Vectors Emergence Thermal Model can help predict when oak wilt vectors may be coming. Photo Credit: UW Extension

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Bur Oak Blight Confirmed In Fond du Lac County

Posted on by brenna.denamur

By Bill McNee, DNR Forest Health Specialist, Oshkosh, bill.mcnee@wisconsin.gov

Recent lab examination has confirmed bur oak blight in Fond du Lac County. The disease affects only bur oaks and is caused by the fungus, Tubakia iowensis.

Map of Wisconsin counties where bur oak blight has been confirmed.

Map of counties where bur oak blight has been confirmed. Map credit: Wisconsin DNR.

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Moving Firewood Can Spread Invasive Species

Posted on by brenna.denamur
An image of an insect walking away from burning firewood in a forest with the caption, “Buy it where you burn it.”

Don’t Move Firewood, The Nature Conservancy

October is Firewood Month! Help prevent the spread of invasive insects and diseases by buying firewood where you burn it.

Firewood Scout can help you find local firewood for sale.

See the DNR website for more information on invasive species and forest health. Continue reading “Moving Firewood Can Spread Invasive Species” →

Check Conifer Trees For Severe Root Disease

Posted on by brenna.denamur

By Michael Hillstrom, DNR Forest Health Specialist, Fitchburg, michael.hillstrom@wisconsin.gov

Considered one of the most destructive diseases of conifers in the northern hemisphere, Heterobasidion root disease (HRD) is very difficult to control once established in a forest. Infestation of a conifer stand may significantly impact stand management, making early detection essential.

A pine stump with a Heterobasidion root disease fruit body with old brown growth in the center and new, bright white growth along the edges.

A Heterobasidion root disease (HRD) fruit body with new white growth observed in the fall. Photo: Wisconsin DNR

Continue reading “Check Conifer Trees For Severe Root Disease” →

Aspen Leaf Diseases Responsible For Thin Crowns

Posted on by brenna.denamur

By Linda Williams, Forest Health Specialist, Woodruff, Linda.Williams@wisconsin.gov or 920-360-0665

Northeastern Wisconsin saw thin and defoliated aspen trees in early summer this year due to a few diseases. A sample from Marinette County turned up Alternaria leaf and stem blight, Venturia leaf and shoot blight and Phyllosticta leaf spot. Venturia was also noted in central Wisconsin, causing shoot blight, which kills the terminal leaders (growth buds) of young aspen.

Aspen trees with leaves damaged by leaf disease..

Aspen crowns were thin due to multiple leaf diseases. Photo: Wisconsin DNR

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