Pest

Be On The Lookout For Forest Tent Caterpillar

Posted on by patricialindquist

By Paul Cigan, DNR Forest Health Specialist, Hayward, Paul.Cigan@wisconsin.gov or 715-416-4920; and Bill McNee, DNR Forest Health Specialist, Oshkosh, Bill.McNee@wisconsin.gov or 920-360-0942

Forest tent caterpillar (FTC) may be making its way back onto the radar of northern Wisconsin property owners in the coming years, as some confirmed reports of defoliation in northern counties have trickled in. A native defoliator with a preference for aspen, oak and birch, this species undergoes periodic population outbreaks every six to 16 years. Widespread outbreaks can last for several years, causing heavy defoliation, reduced growth and temporary stress on affected trees. The last widespread outbreak ended in 2002.

Many forest tent caterpillars gathered together on a tree.

Forest tent caterpillar larvae displaying gregarious behavior on tree stem. Photo credit: Dane Gravesen

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Spruce Budworm, Balsam Fir Sawfly, And Yellowheaded Spruce Sawfly

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

The spruce budworm outbreak continues this year, but the amount of visible defoliation is generally lower than last year. Some areas of the Northwoods have severe defoliation this year, but in many other areas, the amount of new, green foliage far exceeds the amount of defoliation.

In areas where the defoliation appears less severe, you can still find plenty of caterpillars, but the new foliage is less eaten than anticipated. The late spring frost/freeze may have killed some caterpillars, or the long cool spring may have delayed bud-break enough that the caterpillars did most of their feeding on older foliage before the new foliage expanded. 

The spruce budworm outbreak in Wisconsin started in 2012, and outbreaks typically last about 10 years.  Mortality of balsam fir trees started to show up last year following several years of significant defoliation. Even with new growth on the trees this year, they may continue to decline, and mortality could still occur. 

Spruce branches showing defoliation, older needles and new, bright green needles.

Defoliation is still present, but there is lots of new growth on balsam fir this year in many areas of northern Wisconsin.

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Aphids, Scales And Spittlebugs, Oh My!

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

This seems to be a good year for aphids, scales, spittlebugs and other insects that suck the sap of trees. 

Large conifer aphids have been observed on white pine, jack pine and balsam fir. These large, dark colored aphids insert their mouthparts into the twig and suck the sap. They are often guarded fiercely by ants because aphids excrete a waste product called honeydew that ants collect as food. Sooty mold can grow on honeydew so when it covers the twigs and needles of the trees it makes them look darker than normal. Sooty mold is a problem because it limits the ability of those needles to photosynthesize, which can put the tree under stress if it occurs over multiple years. 

If you have just a few colonies of these aphids, there is no control necessary as tree health shouldn’t be affected. If more than 30% of the branches have ant colonies present, or you’re noticing a buildup of sooty mold, you can spray the aphids with a pesticide or a soapy water mixture. Natural enemies, including ladybugs and lacewings, can be very effective at reducing aphid populations. But if ants are guarding the aphids, it can be difficult for natural enemies to work effectively, so controlling the ants may be necessary.

Aphids on balsam fir. There are several ants in this photo that are tending the aphids.

Aphids on balsam fir. There are several ants in this photo that are tending the aphids.

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Oak Shot Hole Leafminer And Spiny Oak Sawfly

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

Two very different insects are creating holes in oak leaves this spring, the oak shothole leafminer and the spiny oak sawfly. 

Oak shothole leafminer

In 2019 and 2020, many eastern U.S. states noted damage from this insect. While this is mostly a cosmetic issue for the tree, it can cause concern for homeowners and landowners when it appears that their trees are defoliated. The good news is that this damage rarely has an impact on the health of larger trees. 

Small holes in the leaf, often with similar holes on the both sides of the main vein, indicate damage from oak shothole leafminer adults.

Small holes in the leaf, often with similar holes on the both sides of the main vein, indicate damage from oak shothole leafminer adults.

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Pine Bark Adelgid Causes Needle Stunting

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

Pine bark adelgids are tiny insects that suck the sap of white pines. Once they insert their mouthparts into the tree, they won’t move any more during their lifetime, so for protection, they grow a white, woolly covering around themselves. A young, white pine plantation in Vilas County is suffering severely stunted needles from the 2020 growing season due to very high populations of pine bark adelgid. 

All branch tips on this white pine sapling have needles that were stunted by heavy populations of pine bark adelgid.

All branch tips on this white pine sapling have needles that were stunted by heavy populations of pine bark adelgid.

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The Dangers And Costs Of Infested Ash Trees

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Credit: Joseph O’Brien, USDA Forest Service, Bugwood.org

The emerald ash borer (EAB) will kill nearly all of Wisconsin’s ash trees that are not protected by insecticides. To help the public understand why it’s important to act against EAB, the DNR created a publication aimed at homeowners that addresses the dangers and costs of infested ash trees. Urban forestry professionals may wish to share this flyer with those who ask questions on these topics.

The key message of the publication is this: It’s crucial to decide ASAP whether to protect your ash trees with insecticides or have them removed. Either way, time is of the essence. If you delay in treating your ash trees, the treatment may be less effective. And if you wait to remove them, removal costs will be greater and safety hazards will only get worse.

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

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By Andrea Diss Torrance, Invasive Insects Program Coordinator, andrea.disstorrance@wisconsin.gov, 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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New Factsheets And Webpage Now Available

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By Elly Voigt, DNR Forest Health Lab Technician. Eleanor.voigt@wisconsin.gov

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

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By Bill McNee, DNR Forest Health Specialist, Oshkosh. Bill.Mcnee@wisconsin.gov 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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Keep An Eye Out For Beech Leaf Disease

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By Elly Voigt, DNR Forest Health Lab Assistant, Fitchburg

Beech leaf disease (BLD) is a destructive disease affecting beech trees in the U.S. The disease has not yet been observed in Wisconsin, but it could become an issue in the future in the eastern third of the state, which is the edge of the American beech’s native range.

Figure 1. Symptomatic banding on beech foliage, as well as asymptomatic leaves. Photo: Ohio State University Extension

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