Forest Health News

Another Year Of Spruce Budworm Defoliation

Posted on by brenna.denamur

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

Spruce budworm is a native insect with periodic outbreaks that defoliate spruce and balsam fir in the Midwest. While these caterpillars have pupated and moths are already emerging to mate and lay eggs, spruce budworm defoliation is now becoming noticeable in northern and central Wisconsin as clipped needles stuck in caterpillar webbing turn rusty red.

Dark colored spruce budworm caterpillar feeding on new balsam fir foliage.

Spruce budworm larvae had webbed together the new growth. Note some clipped needles in the webbing that will turn rusty red in color. Photo: Wisconsin DNR

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Spiny Oak Sawfly And Red Oak: A One-Sided Love Story

Posted on by brenna.denamur

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

The spiny oak sawfly feasts again. While defoliation by this insect is common in understory oaks, this year, lower branches of overstory oaks have also seen damage. All damage so far has been observed on red oaks. Previously we saw a widespread outbreak in 2005 with lesser reports of damage in 2007, 2016, 2017 and 2021.

A small caterpillar on the underside of an oak leaf.

Spiny oak sawfly larvae. Photo: Wisconsin DNR

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Hairy Spring Caterpillars – Which One Do You Have?

Posted on by brenna.denamur

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

Wisconsin has a few leaf-eating caterpillar species that are out early in the spring. Forest tent caterpillars, eastern tent caterpillars and spongy moth caterpillars cause varying levels of tree damage and are often mistaken for one another.

A group of many forest tent caterpillars on the bark of a tree.

Forest tent caterpillars congregating on the trunk of a tree. Photo: Wisconsin DNR

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On The Lookout For Oak Wilt Fruiting Bodies

Posted on by brenna.denamur

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

Have you ever seen an oak wilt fruiting body? Oak wilt is a fungal disease that kills trees in the red oak group (northern red oak, northern pin oak, black oak and other oaks with points on their leaves). Trees in the white oak group (white oak, burr oak, swamp white oak and other oaks with rounded leaves) are more resistant to the disease, but branches or branch tips can still be killed.

A small crack in tree bark that indicates an oak wilt pressure pad is underneath.

Oak wilt pressure pads can create a crack in the bark, allowing beetles to get into the spores. Photo: Wisconsin DNR

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June To October: Oak Wilt Watch!

Posted on by brenna.denamur

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

An image of two red oak leaves that are part brown and part green, symptomatic of oak wilt infection.

Typical browning leaf symptoms of red oak trees infected with oak wilt. Photo: Wisconsin DNR

Now is the time to watch for oak wilt! Symptoms typically appear in southern Wisconsin in late June and in northern Wisconsin during July. Watch for browning leaves starting at the top of the canopy and progressing downward. Most leaves will fall from infected trees as they die, typically within two to four weeks.

Several management methods are available to contain oak wilt pockets, so consult your local forest health specialist for guidance on your best options.

The forest health team is also working to evaluate new control methods. Rapid response is currently being tested to more formally evaluate if a new oak wilt infection in a single tree can be stopped before it reaches the roots and spreads to nearby oaks. There is observational data that this method works, but more formal tests are desired. Continue reading “June To October: Oak Wilt Watch!” →

I Spy… Browning White Pine Stands Along Roads

Posted on by brenna.denamur

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

As you begin your summer travel, you may notice that many white pine trees along northern Wisconsin roadways have a lot of brown needles on them. Although it may seem concerning, most of these trees are sending out new needles as we speak.

Three young conifers with varying levels of browning needles

Different conifer species can be impacted differently by salt spray. The white pine in the middle also shows lower branches that are green because they were protected by snow. Photo: Wisconsin DNR.

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When It Rains, It Spores! Orange Spore Horns Emerge

Posted on by brenna.denamur

By Ethan Wachendorf, DNR Forest Health Lab Technician, Fitchburg, ethan.wachendorf@wisconsin.gov or 608-273-6276

Have you noticed orange, jelly-like growths on cedars this spring? These growths may look like tiny octopus creatures with legs extending all directions, but they’re actually spore horns caused by a fungus.

Orange jelly-like horns extending 1/2 inch long and 1/8 inch in diameter on cedar

Orange jelly-like spore horns caused by cedar-apple rust fungus. Photo: Wisconsin DNR

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Basswood Thrips: Tiny Terrors Of Basswood Leaves

Posted on by brenna.denamur

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

Introduced basswood thrips are tiny, invasive insects that feed inside tree buds in early spring. Leaves are then deformed when they expand and can look like frost or wind has damaged them.

A long and thin introduced basswood thrips rests on the underside of a small green leaf.

An adult introduced basswood thrips on the underside of an emerging basswood leaf. This photo is enlarged under a microscope. To the naked eye, they appear as tiny black specks on the underside of the leaf. Photo: Wisconsin DNR

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White Trunk Rot In Aspen Trees

Posted on by brenna.denamur

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

White trunk rot (Phellinus tremulae), sometimes called aspen trunk rot, is a fungus that causes decay columns to form in aspen. The fungus enters the tree through branch stubs, wounds or small dead branches that remain on the tree. Perennial conks, or fungal bodies, then grow from these sites.

A cross section of the trunk of an aspen with significant decay in the center and a fruiting body conk on the side of the wood.

White trunk rot causes decay in aspen trees. Note the conk (fruiting body) from the fungus on the left side of the pic. Photo: Wisconsin DNR

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Slow Oaks And Maples With Too Many Seeds And Not Enough Leaves

Posted on by brenna.denamur

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

Maples

Have you noticed any maple trees that appear brown or reddish and have fewer leaves than usual? The seeds, not the leaves, make the tan/red color. Those seeds are so plentiful this year that they can easily be spotted from a distance.

Reddish tan maple trees with thin canopies.

Maples with heavy seed crops may appear tan or reddish due to the color of the seeds and having very few green leaves in the canopy. Photo: Wisconsin DNR.

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