Statewide Forest Health

Fall Webworm Is Active

Written By: Todd Lanigan, DNR Forest Health Specialist, Eau Claire, or 715-210-0150

As we head into September, fall webworm is starting to make its presence known. This native insect feeds on deciduous trees and shrubs and appears every year in yards and forests. Fall webworm forms loose webbing over branch tips and can completely cover a small tree with webbing. You will find both live and dead caterpillars, partially eaten leaves and frass (caterpillar poop) inside the webbing.

Fall webworm larvae inside webbing. Photo Credit: Wisconsin DNR

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Heterobasidion Root Disease (HRD) Found In Fond Du Lac And Racine Counties

By Bill McNee, DNR Forest Health Specialist, Oshkosh, or 920-360-0942

Heterobasidion root disease (HRD), formerly known as annosum root rot, was recently found in Fond du Lac and Racine counties for the first time. Thinned pine stands were surveyed by DNR forestry staff in four eastern counties where the disease had not been previously found (Fond du Lac, Manitowoc, Racine and Winnebago counties).

Counties where Heterobasidion root disease (HRD) has been found as of August 2021 are shown in green.

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Wild Cucumber Will Catch Your Attention

Plants that are pokey, viney or spread quickly across the landscape sometimes seem alarming when you discover them in your backyard or woods or when they’re spotted along the highway. Wild cucumber has all these characteristics but is not as ominous as it seems.

Wild cucumber (Echinocystis lobata) is a vine native across the U.S. and found throughout Wisconsin. It has maple-like star-shaped leaves and has pale greenish-white flowers from July through September. A single plant is self-fertile but can also be pollinated by bees, wasps and flies. It produces a pod-like fruit with spikes resembling a cucumber which is unsafe to eat. Each pod produces four seeds that fall to the ground when the pod is ripe. The pods may persist into the winter and become thin brown shells.

Star-shaped leaves, pale flowers, and cucumber fruit of wild cucumber. Photo: Bugwood

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What is growing on that oak tree?

By Todd Lanigan, DNR Forest Health Specialist, Eau Claire, or 715-210-0150

This time of year, you may be noticing some large growths on oak leaves. You are either seeing oak apple gall and/or wool sower gall. These galls are formed by a small, stingless wasp, known as a Cynipid Wasp. 

For the oak apple gall, when the female lays her egg, she injects a growth regulator that causes the leaf tissue to form around the egg. When the larvae begin to feed for the wool sower gall, this causes the gall to form. The galls in both cases protect the developing wasps from the elements and predators. 

Oak apple galls are round and initially are green in color. Eventually, the gall turns brown as the wasp larva matures inside.

Oak apple gall growing on the underside of a leaf.

An oak apple gall

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Oaks Hit Hard By Frost/Freeze Prior To Memorial Day

Written by: Linda Williams, DNR Forest Health Specialist, Woodruff, or 920-360-0665. 

A frost/freeze on the night of May 28 strongly impacted our oaks in areas of central and northern Wisconsin. Some leaves were completely killed while others had portions of the leaf that were impacted. Those leaves with some dead spots have continued to expand and grow but the dead parts of the leaf are causing them to curl and pucker. 

Oak leaves killed by the frost are brown, curled and puckered.

Oak leaves killed by the frost.

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Giant Hogweed: Rare But Harmful

By Bernie Williams, DNR Invasive Plant Specialist. or 608-444-6948. 

Giant hogweed is a non-native, invasive plant that has gradually gained a foothold in the northeastern U.S. Once popular for its massive size and white umbrella-like flowers, it was introduced as an ornamental as early as 1917. Now known for its harmful blisters, it is recognized as a public health hazard and controlled wherever possible.

Characteristic purple blotches and white hairs on green stem of giant hogweed. Photo credit: Herkulesstaude_Fritz Geller-Grimm

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Eau Claire And Richland Counties Now Added To The Gypsy Moth Quarantine

By Andrea Diss Torrance, Invasive Insects Program Coordinator,, 608-516-2223

Gypsy moth has moved slowly across Wisconsin in the last 30 years since gaining a foothold in the counties along Lake Michigan. This month, the Animal and Plant Health Inspection Service and the Department of Agriculture, Trade and Consumer Protection (DATCP) determined that the invasive pest has become established in Eau Claire and Richland counties and have extended the quarantined area to include them.  This is the first time since 2015 that new counties have been added to the quarantine. Fifty-two of Wisconsin’s 72 counties are now quarantined for gypsy moth.

Wisconsin Gypsy Moth Quarantined Counties

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Oak Wilt Seasonal Harvesting Opportunities Web Map

By Paul Cigan, DNR Forest Health Specialist

The Forest Health Team has just launched an interactive web map showing areas where seasonal oak harvesting opportunities and restrictions exist within the state. The map provides users with general geographical information on the presence and seasonality of oak wilt restrictions to support decisions concerning the application of the Oak Harvesting Guidelines [PDF] during timber management planning and establishment. As a highlight, areas that favor flexibility in the application of the seasonal harvesting restrictions — based on the nearest known detection of oak wilt — are displayed on the map. If you have any questions about this map, please contact your regional Forest Health specialist.

Oak Wilt Seasonal Harvesting Opportunities Web Map

New Factsheets And Webpage Now Available

By Elly Voigt, DNR Forest Health Lab Technician.

The Wisconsin DNR’s Forest Health Team has recently released four new factsheets and a new webpage. The new factsheets are on the following topics:

Armillaria root disease

Beech bark disease

Peach bark beetle and cherry scallop shell moth

Hemlock woolly adelgid

Hemlock Woolly Adelgid Forest Health Factsheet

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Updated Emerald Ash Borer Treatment Guides Now Available

By Bill McNee, DNR Forest Health Specialist, Oshkosh. or 920-360-0942

The University of Wisconsin-Madison Extension has recently updated two insecticide guides for those interested in treating high-value ash trees against emerald ash borer (EAB). One guide lists options for homeowners and the other lists options for tree-care professionals. Download the guides here.

First page of the homeowner guide to EAB insecticide treatments.

First page of the homeowner guide to EAB insecticide treatments.

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