Pest

Widespread crown dieback and delayed leaf-out of bur oak

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by Paul Cigan, forest health specialist, Hayward, Paul.Cigan@wisconsin.gov. 715-416-4920 and Todd Lanigan, forest health specialist, Eau Claire, Todd.Lanigan@wisconsin.gov, 715-210-0150

Typical appearance of bur oak with crown dieback associated with cynipid gall wasp infestation in northwest WI during early summer, 2018.

Bur oak showing moderate crown dieback. Photo: Paul Cigan

Bur oak with heavy crown dieback and delayed leaf flushing in Polk County.

Bur oak with severe crown dieback. Photo: Paul Heimstead

Widespread dieback of twigs and branches and delayed leaf-out were present on bur oak trees this spring in Barron, Burnett, Chippewa, Eau Claire Polk, Rusk, and Sawyer counties, and in parts of central and east central Minnesota. Crown dieback of between 10 – 50% was observed in both mature and sapling-sized trees, although it was more common on open-grown trees and those along woodland edges. Tufted or “broomed” leaf shoots were apparent, a result of epicormic shoots developing below dead twigs and branches. Most impacted trees recovered well by early July as crowns filled in with leaves and epicormic shoots. Leaves in recovered trees appeared generally healthy and normal-sized.

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Defoliation of black cherry trees by cherry scallop shell moth

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

Caterpillars of cherry scallop shell moths (Rheumaptera prunivorata) are defoliating black cherry trees of all sizes in far southeastern Jefferson County and slightly into Walworth County. Many cherry trees have been completely defoliated. This is the third consecutive year of damage in this location. Defoliation by cherry scallop shell moth caterpillars has increased each year; hopefully natural enemies that typically cause the populations to crash show up soon and do their job as multiple years of defoliation is stressful to trees. In addition to cherry scallop shell moths, there is concern about possible attack on black cherry trees by peach bark beetles (Phloeotribus liminaris), but none have been reported yet.

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Fall webworms start making an appearance

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

A silken nest full of caterpillars, excrement and debris. Photo: Todd Lanigan

A silken nest full of caterpillars, excrement and debris. Photo: Todd Lanigan

Web-like nests of fall webworm (Hyphantrea cunea) caterpillars, a common native pest active from July through September, are beginning to appear in parts of the state. A common native pest throughout most of the U.S. and southern Canada, fall webworm caterpillars feed on leaves of almost all shade, fruit, and ornamental trees and shrubs, except for conifers. They typically form nests of loose webbing over the tips of tree branches.  Although populations of fall webworm caterpillars are rarely large enough to cause lasting damage to trees, the presence of nests and feeding damage from caterpillars can greatly affect trees’ aesthetic value. Typically, trees recover from feeding damage on their own, but defoliation for more than two or three years in a row could make trees more susceptible to diseases and pests.

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Rose chafer and Japanese beetle populations high in parts of state

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By Linda Williams, forest health specialist, Woodruff, (Linda.Williams@wisconsin.gov), 920-360-0665 and Todd Lanigan, forest health specialist, Eau Claire (Todd.Lanigan@wisconsin.gov), 715-210-0150

Rose chafer adults defoliate many different plants, shrubs, and trees. Photo: Linda Williams

So far this summer, only a few reports of significant defoliation and damage by rose chafers (Macrodactylus subspinosus) and Japanese beetles (Popillia japonica) have been submitted to the state’s DNR forest health specialists. Both of these leaf-skeletonizing beetles feed on foliage of many species of trees, shrubs and other plants. Although activity by Japanese beetles appears light this year, defoliation by rose chafers was reported in Marinette, Shawano, Waupaca, and Trempealeau counties.

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Defoliation by spruce budworm low to moderate in NE Wisconsin

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By Linda Williams, forest health specialist, Woodruff, Linda.Williams@wisconsin.gov, 920-360-0665 and Paul Cigan, forest health specialist, Hayward, Paul.Cigan@wisconsin.gov, 715-416-4920.

Severely defoliated balsam fir in Vilas County.

Severely defoliated balsam fir in Vilas County.

In many areas this summer, damage from spruce budworm (Choristoneura spp.), a native insect, is less noticeable than in past years. Although heavy defoliation is evident north of St. Germain in Vilas County and at a site in Shawano County, only light to moderate defoliation has been seen in other areas. Light defoliation was observed in Bayfield, Florence, Forest, Marinette, Oneida, Shawano, and Vilas counties. Defoliation was less predominant last year as well, probably because of unusually heavy rainfall in spring 2017 which led to an increase in tree growth. This year’s spring was also unusually wet, resulting in increased tree growth.

Spruce budworm outbreaks typically last about 10 years; the current outbreak began in 2012. The last two years of exceptionally robust tree growth may help some of the damaged trees to at least partially recover. Since 2012, some areas of northeastern Wisconsin experienced three or four years of heavy defoliation; affected trees are either dead or declining despite good growing conditions.

Defoliation by June beetles

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

June beetles defoliating an oak sapling at night.

June beetles defoliating an oak sapling at night.

June beetles (also called May beetles) are defoliating oak, aspen and birch trees in several parts of Wisconsin this spring. These beetles are unusual in that they feed on foliage at night – look for defoliation during daytime hours although no insects are present. Although the highest densities of June beetles have been found in Crawford and Grant counties in southwest Wisconsin, forest health staff has also received reports of the insect from northeast and west central Wisconsin. Continue reading “Defoliation by June beetles” →

Forestry partners take lead in 2018 EAB trapping

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By Paul Cigan, forest health specialist, Hayward. Paul.Cigan@wisconsin.gov; 715-416-4920

As summer approaches, adult emerald ash borer (EAB) beetles are beginning to emerge to feed and reproduce.

Areas of possible initial EAB emergence.

USDA APHIS EAB emergence map. Map credit: USDA Cooperative Emerald Ash Borer Project

Due to the recent statewide quarantine for emerald ash borer and workload considerations, USDA’s Animal and Plant Health Inspection Service, Plant Protection and Quarantine (APHIS PPQ), the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP), and the Wisconsin DNR Forest Health Program have discontinued trapping programs for adult beetles in Wisconsin. Continue reading “Forestry partners take lead in 2018 EAB trapping” →

Eastern tent caterpillar and control options

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By Linda Williams, forest health specialist, Woodruff. Linda.Williams@wisconsin.gov; 715-356-5211 x232

Young eastern tent caterpillars on their web nest. Photo: Linda Williams

Young eastern tent caterpillars on their web nest. Photo: Linda Williams

Winter is finally over and eastern tent caterpillars are hatching and building their web nests! In northern Wisconsin, the caterpillars began hatching in early to mid-May, but they emerged earlier in southern Wisconsin. Webs will become larger as the caterpillars feed and grow. Continue reading “Eastern tent caterpillar and control options” →

Forest tent caterpillar: surveys, prediction, and history

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By Paul Cigan, forest health specialist, Hayward. Paul.Cigan@wisconsin.gov; 715-416-4920

Areas in northern Wisconsin with forest tent caterpillar defoliation during the peak year of most recent regionwide outbreak, from 1999 – 2002

Forest tent caterpillar larvae feeding on ash foliage. Photo: Paul Cigan

Late-winter surveys in northern Wisconsin for egg masses of forest tent caterpillars (FTC) suggest that numbers will remain low through 2018, continuing a 15-year trend, one of the longest documented intervals between FTC outbreaks in the state. Continue reading “Forest tent caterpillar: surveys, prediction, and history” →

Trapping for non-native beetles

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

A Lindgren funnel trap hung to collect beetles near Green Bay, WI. Photo: Mike Hillstrom

Scott Schumacher, an insect trapper for the Wisconsin DNR’s forest health team, will spend this summer hunting for non-native beetles using funds provided by the U.S. Forest Service. The survey is particularly focused on non-native bark and ambrosia beetles, which are potentially harmful to Wisconsin forests. In early May, Schumacher hung Lindgren funnel traps at 12 sites in Wisconsin which he will be checking throughout the season. Traps were placed at high-risk sites in wooded areas near large commercial port entries on Lake Michigan and near pallet and other waste-packaging recycling companies. Although preventing the arrival of non-native species is always top priority, early detection and rapid response (EDRR) to newly-detected infestations is an important strategy to protect forests from damaging invaders.