Pest

Hemlock Being Defoliated By Spruce Budworm

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Photo of spruce budworm eating hemlock needles.

Spruce budworm defoliation this spring on hemlock makes the trees look thin. Photo Credit: Linda Williams, Wisconsin DNR

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

Spruce budworm is finished feeding for the year, but the damage from the insects is still being observed.

Spruce budworm prefers to feed on balsam fir and spruce, but a previous newsletter article noted that tamarack had been observed as 100% defoliated by spruce budworm. More recently, stands of hemlock with moderate to severe defoliation were also identified.

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Basswood Thrips Causing Crumpled Leaves, Thin Crowns

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

Photo of basswood leaves damaged by basswood thrips.

Basswood leaves show damage after feeding of introduced basswood thrips. / Photo Credit: Wisconsin DNR.

For the second consecutive year, damage from introduced basswood thrips (Thrips calcaratus) is significant in some northeastern Wisconsin counties. Introduced basswood thrips are tiny, invasive insects that feed inside tree buds in early spring. Leaves are then deformed when they expand and can look like frost or wind has damaged them.

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Maple Petiole Borer Causes Leaves To Drop

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

Photo of maple leaf found on the ground with broken petiole (leafstalk).

A green maple leaf found on the ground with a broken petiole (leafstalk) due to damage by the maple petiole borer. / Photo Credit: Wisconsin DNR.

Some sugar maple trees in the northern half of Wisconsin experienced leaves dropping to the ground this spring.

These leaves were green and had no apparent areas of damage, but they covered the ground under some trees. A closer look showed these leaves had short petioles (leafstalks) that had been broken off when they fell, which indicates a tiny sawfly larva called maple petiole borer was to blame.

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Lecanium Scale Creating A Sticky Situation

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

Photo showing ladybug larva feeding on lecanium scale domes.

A ladybug larva feeds on lecanium scale domes on an oak twig. / Photo Credit: Wisconsin DNR.

Lecanium scale is infesting oak forests across Marinette, Oneida and Vilas counties. These scale insects insert their mouthparts into twigs and suck the tree sap. They release honeydew, which ants can collect, or coat leaves and anything located under infested trees (i.e., yard furniture or vehicles). Sooty mold can grow on that sticky material and turn things black, so homeowners may want to rinse off the honeydew from outdoor items regularly.

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Acorn Pip Galls, Woolly Catkin Galls All The Same

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

Photo of acorns showing small pip galls.

Pip galls are small, tongue-like protrusions emerging from under the caps of acorns. / Photo Credit: Linda Williams, Wisconsin DNR.

Gall wasp life cycles can be complex. Did you know that acorn pip galls, which I’ve written about several times, have another part of their life cycle that is entirely different? This stage is called the woolly catkin gall.

Both woolly catkin galls and acorn pip galls are caused by Callirhytis quercusoperator, a species of cynipid gall wasp. This gall wasp takes two years to complete development by going through the two parts of its life cycle. Both parts of the life cycle are completed on northern red oak in our area.

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Severe Spruce Budworm Defoliation Hits In Northwest

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

Photo taken through magnifying lens of spruce budworm caterpillars.

Spruce budworm overwinters as tiny caterpillars (yellow arrow) that migrate to the buds before they start to swell in the spring. A magnifying lens is needed to see them at this stage. / Photo Credit: Linda Williams, Wisconsin DNR.

For the 11th consecutive year in Wisconsin, spruce budworm has caused significant defoliation on spruce, balsam fir and tamarack in some areas of the state.

This year, areas with widespread severe defoliation include Oneida and Vilas counties, with Forest, Iron, and Langlade counties also showing significant defoliation.

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High Beech Scale Moving Beyond Door County

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By Bill McNee, DNR Forest Health Specialist, Oshkosh; bill.mcnee@wisconsin.gov or 920-360-0942;

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

Photos of white 'wool' coating on trees with beech scale.

Examples of white “wool” coating on trees heavily infested with beech scale at Kohler-Andrae State Park (left) and in the Town of Beecher in Marinette County (right). / Photo Credit: Bill McNee (left) and Linda Williams (right), Wisconsin DNR.

Fourteen years after first detecting beech scale (Cryptococcus fagisuga, a non-native insect) in Door County, sites with high populations of beech scale have been found in additional counties. Beech scale is believed to have spread through the range of American beech in Wisconsin’s eastern counties, but until now has only been seen at low levels outside of Door County.

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White Pine Weevil Damage And Management Options

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

Photo of a white pine tree showing weevil damage.

A dead terminal leader, resulting from an attack by white pine weevil. Photo: Linda Williams, Wisconsin DNR.

White pine weevil (Pissodes strobi) is a native insect that can kill the terminal leader of white pine, jack pine and spruce. Wisconsinites often refer to this insect as Tip Weevil.

The insects prefer to attack stout terminal leaders. When the terminal leader dies, lateral branches grow upward and compete to take over apical dominance. This can leave a noticeable crook for decades. If two or more lateral branches take over, forking can occur. New terminal leaders may be attacked in subsequent years, causing more crook or forking.

Spruce and jack pine tend to recover better from weevil damage than white pine because the lateral branch that takes over apical dominance often creates a less prominent crook.

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Diseases Take Aim At Spongy Moth

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Photo of tree showing caterpillars killed by virus and fungus

Caterpillars killed by nucleopolyhedrosis virus (NPV) hang in an inverted “V” orientation; caterpillars killed by the fungus Entomophaga maimaiga hang vertically. Photo: Wisconsin DNR.

By Bill McNee, DNR Forest Health Specialist, Oshkosh
bill.mcnee@wisconsin.gov or 920-360-0942

With this spring’s dry weather in Wisconsin came predictions of the largest spongy moth population in years.

When spongy moth populations are high, we often see heavy mortality of the larger caterpillars due to two pathogens. Heavy caterpillar mortality will reduce the severity of the following year’s outbreak and often causes a population crash during the current year. If a heavy die-off of caterpillars is observed, please let your local DNR Forest Health Specialist know about it.

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Spongy Moth Focus Of Video, Webcast

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Art Kabelowsky, DNR Forest Health outreach and communications specialist
Arthur.Kabelowsky@wisconsin.gov or 608-335-0167

Add “YouTube Influencer” to the long list of career accomplishments of Andrea Diss-Torrance, Ph.D.

With the spongy moth caterpillar population on the rise in many areas of Wisconsin this season, the Wisconsin Department of Natural Resources stepped into action last month.

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