Forest Health News

Fall webworm activity in July

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By Todd Lanigan, forest health specialist, Eau Claire, Todd.Lanigan@wisconsin.gov, 715-210-0150

Fall webworm started showing up in early July. This native insect feeds on deciduous trees and shrubs and appears every year in yards and forests. It is often noticed first by the loose webbing over branch tips. It can even completely cover a small tree with webbing. If you look inside the webbing, you will find partially eaten leaves, frass (caterpillar poop) and both live and dead caterpillars.

Fall webworm caterpillars atop

Fall webworm larvae feed within webbed enclosures at branch tips. Credit: Courtney Celley, US Fish & Wildlife Service.

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Chlorosis: common causes and next steps in management

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Mike Hillstrom, forest health specialist, Fitchburg, Michael.Hillstrom@wisconsin.gov, 608-513-7690

Chlorosis, which is marked by yellow leaves with green veins, is a common tree and shrub issue in Wisconsin. It is often a result of a nutrient deficiency of iron and manganese. 

A chlorotic leaf has yellow leaf tissue with green veins.

A chlorotic oak leaf displays yellow leaf tissue with green veins.

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Reports of sudden balsam fir mortality

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Linda Williams, forest health specialist, Woodruff, Linda.Williams@wisconsin.gov, 920-360-0665

In early June we started getting reports of balsam fir trees rapidly changing from green to rusty red and dying in just a matter of weeks. Reports and observations are still coming in at the time of this writing, so this article gives a brief synopsis of what we’ve seen so far this year. Symptoms have been observed in some northern and central counties.

The top half of a balsam fir died rapidly this spring due to reasons we are still exploring.

Some balsam fir crowns died rapidly this spring for reasons still being explored.

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Report surviving elm in the forest

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You can help keep native elm trees in the forests of Wisconsin! The US Forest Service continues to work on a project to identify Dutch elm disease (DED)-tolerant American elms native to Wisconsin forests. The goal of the project is to identify and propagate survivor American elms, especially from the colder hardiness zones 3-4, and develop a series of clone banks. Selections would eventually be screened for tolerance to DED. Ultimately, the goal is to make DED-tolerant American elm available for reforestation in northern areas, particularly as a component on sites currently forested by black ash.

If you live in hardiness zones 3 and 4, please look for evidence of surviving elms and report them to the US Forest Service.

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Forest tent caterpillar populations high in small localized areas

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Linda Williams, forest health specialist, Woodruff, Linda.Williams@wisconsin.gov, 920-360-0665

Forest tent caterpillar (FTC) is a native insect with periodic outbreaks. Reports of high populations have been coming in this spring from the towns of Nokomis, Three Lakes and Sugar Camp in Oneida County. There is some defoliation in these areas, but the geographic extent of damage is still limited. When looking for caterpillars in northeastern Wisconsin, it was not difficult to find at least one or two of them, which is an increase from past years when it was difficult to find any caterpillars at all.

Close-up photo of forest tent caterpillar shows the insect's unique "footprint" design that runs along the top of its back.

Forest tent caterpillars go through several instars, or growth stages. Colors vary between stages but all have the cream-colored “boot prints” down their backs.

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Reddish oak leaves not a cause for concern

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Linda Williams, forest health specialist, Woodruff, Linda.Williams@wisconsin.gov, 920-360-0665 

Have you noticed any oaks looking kind of red this spring? Or maybe you’ve noticed that the leaves at the tips of the branches are looking red or maroon? 

Some oak leaves look red from a distance, likely due to a prolonged cool spring.

From a distance some oaks have a red hue, probably due to a prolonged and cool spring.

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Basswood leaves defoliated and trees looking thin

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Linda Williams, forest health specialist, Woodruff, Linda.Williams@wisconsin.gov, 920-360-0665 

Basswood trees in Forest, Marinette and Oconto counties are looking very poor this year. The leaves are damaged, misshapen or completely missing. Several things seem to be happening, but the worst offenders seem to be a late frost/freeze and a suspected infestation by introduced basswood thrips.

Evidence of basswood thrips on a single leaf; some defoliation and dieback.

Evidence of suspected basswood thrips infestation in early spring.

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Updated emerald ash borer silviculture guidelines now available

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

The Division of Forestry has completed a revision of the emerald ash borer silviculture guidelines to help foresters prepare for and respond to the arrival of emerald ash borer (EAB) in a forest stand.

Cover page of new guidelines. Continue reading “Updated emerald ash borer silviculture guidelines now available” →

New insect and disease factsheets available

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By Mike Hillstrom, forest health specialist, Fitchburg, Michael.Hillstrom@wisconsin.gov, 608-513-7690

The forest health team has produced four new factsheets since the start of 2020. These resources are designed to be informative, 2-page documents for a wide audience that includes landowners, foresters and natural resource professionals, educators, and more. The new factsheets of 2020 are linked below, and more will be announced as they are finalized:

Please check them out and our other recently updated factsheets about Heterobasidion root disease, oak wilt, conifer bark beetles, and hickory decline and mortality. You can find all of these and more forest health publications in the publications catalogue and on the DNR forest health webpage.

The Tick App! ‘Your Tick Expert On-The-Go!’

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By Bieneke Bron, Midwest Center of Excellence for Vector-Borne Diseases, UW-Madison

Do you ever wonder why you are always finding ticks on yourself or around you, but your friends never do? Researchers at the University of Wisconsin – Madison have developed a mobile application that allows users to share their experiences with ticks to help prevent future tick bites.

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