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Aspen Leaf Diseases Responsible For Thin Crowns

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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Red Oak Irony

By Paul Cigan, DNR Forest Health Specialist, Hayward, paul.cigan@wisconsin.gov or 715-416-4920

Red oak trees in many areas of northern Wisconsin are aptly fitting their name as many crowns exhibit a red hue this summer.

A red oak tree with a red and green leaves.

Red oaks are producing a second flush of leaves following oak leafroller defoliation in spring, resulting in trees with red-looking crowns. Photo: Wisconsin DNR

Widespread defoliation by oak leafrollers in May and June has led many oaks to generate a second set of leaves after being stripped. New expanding leaves often display a prominent red color that gives the tree crown a stark reddish appearance from afar.

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Eyes On Beech Leaf Disease

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

Forest owners and land managers should be on the lookout for beech leaf disease (BLD), a destructive disease of beech trees. The disease is primarily found on American beech (Fagus grandifolia) but can also be found on ornamental species like European, Oriental and Chinese beech (F. sylvatica, F. orientalis and F. engleriana).

Multiple symptomatic beech leaves showing dark striping between lateral veins on the underside of the canopy.

Symptomatic striping seen from under the canopy. This photo was taken in Ohio. Photo: Wisconsin DNR

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Pine Sawyer Beetle: A Noteworthy Native

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

This time of year, you may see black beetles with long antennae flying around, especially in areas with pine trees. These slow, ungainly flyers are a native longhorn species called white-spotted sawyer beetle, also known as pine sawyer.

Pine sawyers are black beetles with long antennae.

Pine sawyer adult male. Photo: Wisconsin DNR

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Troubled White Pines: Disease And Thinning

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

Scattered white pine in Oneida and Vilas counties had significant amounts of needles that turned light tan or pale yellow this spring. Those needles have mostly dropped from trees, leaving them quite thin.

Some white pine needles are tan colored due to Lophodermium infection.

Tan-colored needles infected with Lophodermium. Photo: Wisconsin DNR

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Hungry, Hungry Japanese Beetles

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

Japanese beetles (Popillia japonica) are an invasive insect that feed on many plant species. They skeletonize leaves, which means that they eat the material between the veins and often leave lacy veins that turn brown and curl.

An adult beetle on a leaf.

Japanese beetle adult. Photo: Wisconsin DNR

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Tubakia Leaf Disease Mimicking Oak Wilt

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

Tubakia leaf spot (Tubakia dryina) is a leaf disease that typically affects the lower canopy of oaks. It caused some issues in 2021 and is affecting red oak trees in north-central Wisconsin this year as well.

Oak leaves with abnormally-shaped brown blotches.

Tubakia creates abnormal blotches and spots on oak leaves that can coalesce. Photo: Wisconsin DNR

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Summer Of Spongy Moth

By Andrea Diss-Torrance, Invasive Insects Program Coordinator, Madison, Andrea.DissTorrance.wisconsin.gov

Spongy moth* (formerly known as gypsy moth) populations are entering an outbreak phase in southern Wisconsin due to last year’s dry, hot weather. This pest is rising most rapidly in oak-dominated areas, especially in landscaped spaces with turf and high human activity (i.e., parks, picnic areas, campgrounds and yards). This open ground and human disturbance deter spongy moth’s predators and diseases.

Large, defoliated yard trees along road in neighborhood.

Oak trees are more vulnerable to defoliation in disturbance-heavy environments. These oak trees in Middleton, Wisconsin are facing heavy defoliation by spongy moth. Photo: Wisconsin DNR

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