Forest Health News

Aspen blotch miner caterpillars

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

The tops of aspen leaves will appear off-colored when aspen blotch miner caterpillars feed within.

The tops of aspen leaves will appear off-colored when aspen blotch miner caterpillars feed within. Photo: Linda Williams

If you’ve noticed aspen trees seem a little pale lately, you are probably seeing damage from aspen blotch miner caterpillars. Typically, these leaf-mining insects only affect young aspen trees, but this year I’ve found uniform damage on bigger trees with large crowns. Symptoms include thinned crowns, off-color leaves with blisters on their undersides, and, later in the summer, curling and browning leaves. Tiny caterpillars spend their entire lives feeding within the leaf; they then pupate into the tunneled-out areas. Moths emerge in August and spend the winter in protected places.

I have reported this insect each year since 2012 in northeastern Wisconsin. This year, there were aspen leaf blotch miners in Marinette, Florence, Forest, Oneida, and Vilas counties, which is similar to where they were found last year. Although defoliation can be severe, aspen trees usually tolerate the situation well. Many affected aspen trees will send out new leaves after feeding by caterpillars ends. Although damage may appear severe, the effects on the trees’ overall health seems negligible.

 

Widespread crown dieback and delayed leaf-out of bur oak

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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Balsam fir mortality in many counties around the state

Counties shaded in blue are where balsam mortality has been reported, but the is even more widespread than this map indicates.

Counties shaded in blue are where balsam mortality has been reported, but it is even more widespread than this map indicates.

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

Reports of balsam fir suddenly turning rusty red to brown and dying have been coming in steadily this spring and summer. The accompanying map shows where this has been reported so far this year.

Spoiler alert! There are no insect or diseases involved. It appears the cause may be unusually severe winter drying or winter damage.

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Defoliation of black cherry trees by cherry scallop shell moth

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

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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Forest Health Program welcomes new forest invasive plant coordinator

By Jodie Ellis, communications specialist, Madison. Jodie.Ellis@wisconsin.gov; 608-843-3506

Michael Putnam

Michael Putnam, DNR Forestry’s new forest invasive plant coordinator.

The Forest Health Program is excited to welcome Mike Putnam as its new forest invasive plant coordinator. Mike has been working with the program as an LTE for more than four years in Madison; his new position is in Rhinelander. He’ll be focusing on invasive plants prevention and management with DNR foresters and partners, so please reach out to him with field work opportunities.

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Rose chafer and Japanese beetle populations high in parts of state

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

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.

White pine bast scale and fungus

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

Branches in the mid- and lower-crown of this white pine are being killed by white pine bast scale and a fungal disease.

Branches in the mid- and lower-crown of this white pine are being killed by white pine bast scale and a fungal disease. Photo: Linda Williams

White pine bast scale and canker fungus has been identified in two sites in Oneida County. This insect/fungus complex is a new issue in the state; those who work with white pine should be alert for signs and symptoms.

White pine bast scale, a native scale, is tiny, black, oval-shaped, and lacks both eyes and legs. It uses a long stylet to siphon sap from outer layers of phloem (bast) of twigs and branches. White pine bast scales live under lichens on white pine branches. Although lichens don’t directly harm trees, they provide shelter for scale insects.

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Sparse-leafed elms and maples

Heavy seed production by a red maple. The Ohio State University.

Heavy seed production by a red maple. The Ohio State University.

By Todd Lanigan, forest health specialist, Eau Claire. todd.lanigan@wisconsin.gov, 715-210-0150 and Paul Cigan, forest health specialist, Hayword. Paul.Cigan@wisconsin.gov, 715-416-4920

There have been reports that some elm and maple trees in the state have fewer leaves than normal this spring. The likely reason is that several elms and maples produced an unusually large amount of seed this year, which trees do periodically. During a heavy seed production years, the tree will produce fewer leaves, which may make it appear sparse. Continue reading “Sparse-leafed elms and maples”