Spruce budworm defoliation showing up

By Linda Williams, forest health specialist, Woodruff,, 920-360-0665

Spruce budworm defoliation is becoming noticeable in northern and central Wisconsin counties as clipped host tree foliage stuck in the caterpillars’ webbing turns rusty red. The caterpillars should pupate soon, and moths will emerge a couple weeks later to mate and lay eggs. Spruce budworm is a native insect with periodic outbreaks that defoliates spruce and balsam fir in the Midwest.

Close-up of spruce budworm caterpillar near the silk web it spins around branch tips.

Spruce budworm caterpillar near the silk webbing it spins on branch tips.

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Pine tortoise scale can cause branch and tree mortality, sooty mold problems

By Linda Williams, forest health specialist, Woodruff,, 920-360-0665

Pine tortoise scales are sometimes found at very heavy densities on jack and scotch pine twigs. In Wisconsin they prefer young jack pine trees, inserting their straw-like mouthparts into twigs and sucking out the sap. When populations are high, pine tortoise scale can cause branch mortality and even whole tree decline.

Tiny pine tortoise scales clustered on a pine branch tip.

Pine tortoise scales are so plentiful on this twig that they are practically on top of one another.

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USDA seeks ash trees to battle EAB

Emerald ash borer (EAB) is an invasive insect from Asia that was first introduced into the United States in 2002. Since its discovery, EAB has caused the death and decline of tens of millions of ash trees. Today, the U.S. Department of Agriculture (USDA) is using ash trees against the pest to help preserve and protect the tree species. Staff in the USDA EAB biological control (biocontrol) program are asking Wisconsin landowners in Sheboygan, Fond du Lac and Door counties to help by donating infested ash trees for use in raising wasps that attack and kill EAB.

A square window of bark is removed from green ash to uncover EAB larvae underneath.

USDA staff cut a “bark window” in green ash to uncover signs of EAB.

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Two-lined chestnut borer in flooded oak stands

By Mike Hillstrom, forest health specialist, Fitchburg,, 608-513-7690

2019 was the wettest year ever recorded in Wisconsin. Four of Wisconsin’s top five wettest years have taken place in the last decade, three of them in the last five years: 2019, 2018 and 2016. Flooding can be stressful for trees, and with flooding occurring over the past few years in many parts of the state, forest health staff expect the impacts to forests to continue to escalate. Continue reading “Two-lined chestnut borer in flooded oak stands”

Gypsy moth spray program begins in May

The 2020 gypsy moth slow-the-spread program, operated by the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) is expected to begin aerial spraying in the second half of May to slow the westward spread of gypsy moth.

Map of counties to be sprayed in 2020.

Map of counties where slow-the-spread treatments will occur in 2020.

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Damage from heavy winter snow and ice

By Linda Williams, forest health specialist, Woodruff,, 920-360-0665

Heavy ice and snow loads can cause significant problems for trees. Branches can break under heavy loads, and entire tree tops loaded with snow can come crashing down in windy conditions. Trees that are repeatedly weighed down or tipped over by snow, only to have more snow pile up on them, can be further impacted.

Four images of winter damage to jack pine, including stem failure from gall damage, root failure due to Armillaria root disease.

Clockwise from top left: jack pine broken at site of gall on main stem; trees that break at their base due to heavy snow loads are not able to recover; previous attack from pine root collar weevil (yellow arrow) weakened this tree near its base; heavy snow load and a major root weakened by Armillaria caused this tree to break (yellow arrow) and tip over.

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Protect oak trees by pruning after July, not before

By Don Kissinger, urban forester, 715-348-5746, or Paul Cigan, plant pest and disease specialist, 715-416-4920,

Anyone with oak trees in their yards or on forested lands should avoid pruning or cutting them from April through July to protect them from oak wilt.

Sap-feeding beetle on diseased oak tree in Sawyer County.

Sap-feeding beetle on diseased oak tree in Sawyer County.

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Prepare for the return of gypsy moths in spring

By Bill McNee, DNR forest health specialist, Oshkosh,, 920-360-0942

Gypsy moth eggs are expected to start hatching as temperatures warm in the next few weeks. Now is a great time for homeowners to check their trees for egg masses and treat or remove any that are found. Removing the egg masses now will help protect trees from defoliation and reduce future caterpillar populations.

Gypsy moth larvae hatching from egg masses on an outdoor bowl.

Gypsy moth larvae hatching from egg masses on an outdoor bowl.

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Where are you, blue ash?

By Dan Buckler, DNR urban forestry assessment outreach specialist, Madison,, 608-445-4578

It is no secret that the emerald ash borer (EAB) has a voracious appetite. This pest has eradicated unprotected green and white ash in many communities in southern Wisconsin and can be expected to eventually impact all communities in the state. EAB is also damaging wetland and riverine forests by eliminating green and black ash from these woodlands, which had already become less diverse and resilient from the loss of American elm from Dutch elm disease.

While EAB can feed on all American ash species so far tested, some are less favored than others and thus take less damage from the pest.  Reduced feeding pressure may allow such species to persist in the presence of EAB.  Blue ash (Fraxinus quadrangulata) is one of these less preferred hosts of EAB.  This tree, a native of the Midwest and South, enjoys calcareous soils and has been found growing naturally in southeast Wisconsin. Even before EAB, it was considered a Threatened plant in the state, though it is common in states to the south of us.  It’s an unusual tree but some communities and individuals have planted blue ash across the state.

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Wisconsin DNR Forest Health 2019 Annual Report

The DNR Forest Health team recently completed the 2019 Forest Health Annual Report summarizing impacts from pests, diseases and weather on the health of Wisconsin’s forests. Highlights from 2019 include:

   •   Dramatically increased decline and mortality from EAB in southern WI

   •   New county and township detections of oak wilt

   •   Record-breaking precipitation and major storm damage

   •   Summary of state nursery studies

To read the report, follow this link.