Pest

White spotted sawyer

Our native pine sawyer has a “spot” between the elytra (yellow arrow) that Asian longhorned beetle does not have. They also will appear dusty or pitted.

Our native pine sawyer has a “spot” between the elytra (yellow arrow) that Asian longhorned beetle does not have. They also will appear dusty or pitted.

White spotted sawyer, sometimes called Pine Sawyer, is a native longhorn beetle. It is often mistaken for Asian Longhorned Beetle (ALB). How can you tell the difference between our native beetle and ALB?  First of all, size: ALB is a big burly beetle, while our native sawyer beetle looks slim in comparison. Second, ALB has a very smooth shiny appearance with distinct white spots on black wing covers, whereas our native sawyer beetle will appear pitted or dusty, and the white spots may be less distinct or absent. Finally, our native beetle will have a nice white dot “between its shoulders” where the wing covers meet, and ALB does not have this. 

Adult pine sawyer beetles feed on the bark of twigs which can cause branch tip mortality.

Adult pine sawyer beetles feed on the bark of twigs which can cause branch tip mortality.

Pine sawyer larvae develop in weakened, recently dead, or recently harvested conifers. Larvae first feed in the phloem layer then progress to inner wood. They will pupate within the tree and adults will chew their way out leaving large round exit holes. Adults feed on needles and the bark of twigs. Areas this year which will attract white spotted sawyers include areas of storm damaged pine, and areas of conifer decline due to high water levels, as well as any other areas where conifers are stressed. 

If you find a beetle and are unsure whether it’s ALB or our native sawyer, please take some photos to send for identification. 

Written by: Linda Williams, forest health specialist, Woodruff, (Linda.Williams@wisconsin.gov), 715-356-5211 x232.

Poplar vagabond aphid

Poplar vagabond aphid feeding on the buds of aspen or cottonwood cause the tree to form a fleshy, hollow gall around the insects.

Poplar vagabond aphid feeding on the buds of aspen or cottonwood cause the tree to form a fleshy, hollow gall around the insects.

Galls caused by poplar vagabond aphid form at the ends of aspen and cottonwood branches. The galls are caused by aphids feeding at the tips of twigs. This feeding causes the tree to grow an elaborate structure that the aphids can live inside. One of the galls in the photo is broken open so you can see the aphids inside. This damage does not usually kill the tree, but reduces branch growth because the formation kills the terminal buds. The aphids feed during the spring and early summer within the gall, and then leave to feed on an unknown second host plant. When the aphids leave the gall it will turn brown and woody, and will remain on the tree for several years before weathering off. Adult aphids return later in the fall and lay eggs on the woody gall or in crevices in the bark. Eggs will hatch the following spring and repeat the process. For control, prune the galls prior to egg hatch early in the spring. Because the aphids return to the same trees with the original galls it is common to see a single tree heavily infested while a nearby tree will have no galls at all. I have always seen this problem in trees that are open grown, either along the edge of a stand, along a roadway or fence row, or in a yard. I’m not sure how much of a problem it is in the interior of a stand.

Poplar vagabond aphids, which are covered in a white waxy material, are protected inside the large hollow galls formed by the tree. They suck the trees’ sap.

Poplar vagabond aphids, which are covered in a white waxy material, are protected inside the large hollow galls formed by the tree. They suck the trees’ sap.

Written by: Linda Williams, forest health specialist, Woodruff, (Linda.Williams@wisconsin.gov), 715-356-5211 x232.

Gypsy moth adults appearing now

Female gypsy moth lays an egg mass.

Female gypsy moth lays an egg mass.

As of mid-July, DNR forest health staff have received reports of adult gypsy moths present as far north as Burnett County. The brown-shelled pupae and white female moths can be crushed with a stick. The remaining caterpillars will also pupate soon, and where the caterpillars are a problem, they can be crushed, drowned in soapy water, or sprayed with insecticide or insecticidal soap. Continue reading “Gypsy moth adults appearing now”

Emerald ash borer new finds in Wisconsin

EAB emergence map as of July 10, 2017. Tan colors in the north are approaching peak emergence, light green is peak emergence, and olive is past peak emergence.

EAB emergence map as of July 10, 2017. Tan colors in the north are approaching peak emergence, light green is peak emergence, and olive is past peak emergence.

Much of Wisconsin has reached peak emergence of emerald ash borer adults.

EAB continues to be found in new areas. Wisconsin tracks EAB at the municipality or township level. Quarantine counties are shown in tan and infested areas are shown in green on the EAB Detections and Quarantine map below.

New county quarantines

  • none

New finds in counties already quarantined

  • Crawford County – city of Prairie de Chein
  • Grant/Iowa County — city of Muscoda
  • Milwaukee County — village of Whitefish Bay
  • Outagamie County — town of Grand Chute
  • Sauk County – village of West Baraboo
  • Waukesha County — village of Merton
EAB quarantine map. Counties shaded in tan are quarantined for EAB, and include much of the southern half of Wisconsin, as well as other counties. Areas shaded in green are the townships and municipalities where EAB has actually been identified, and show that not all counties that are quarantined are fully infested.

EAB quarantine map. Counties shaded in tan are quarantined for EAB, green areas are townships and municipalities where EAB has actually been identified.

Written by: Linda Williams, forest health specialist, Woodruff, (Linda.Williams@wisconsin.gov), 715-356-5211 x232.

Defoliation by rose chafers and Japanese beetles is showing up.

Rose chafers and Japanese beetles are starting to cause problems in some areas this summer. So far reports and damage are generally light for Japanese beetles, but in some areas rose chafer defoliation is noticeable. 

Rose chafers are beetles that can defoliate many plant species. They have fairly long legs, and are a dusty mustard color.

Rose chafers are beetles that can defoliate many plant species. They have fairly long legs, and are a dusty mustard color.

Rose chafer defoliation was reported from Florence, Marinette, Oconto, Vilas, and Waupaca counties this year. Rose chafers are more common in areas with sandy soil where they will lay their eggs. The eggs hatch into white grubs which live in the soil and feed on grass and weed roots. My books inform me that birds can die if they eat adult rose chafers because of a poison in the beetles that affects the heart of small, warm-blooded animals. For information on rose chafer control, check out UW Extension publication A3122.

The last significant defoliation that I noted from rose chafer was in 2012, and before that it was 2005. These beetles feed on a wide variety of plants and prefer blossoms, but they will skeletonize leaves as well. Control is difficult because the adults are good fliers and can easily fly in from neighboring areas to re-infest your freshly sprayed plants. 

Japanese beetle populations will emerge in southern Wisconsin first, typically by the first part of July. Some areas of the state have building populations while others, like the Madison area, may have populations that exploded in the past and are more stable now. These insects are occasionally mistaken for EAB because they have some metallic green coloring near their heads.  More commonly people will refer to the multicolored Asian ladybeetles as Japanese beetles, but the ladybugs are ladybugs and Japanese beetles are scarab beetles.

Japanese beetle adults feed on the flowers and leaves of over 300 plant species, including trees, shrubs, and herbaceous plants. They can cause significant defoliation. The larval stage of Japanese beetle is a white grub that lives in the soil and feeds on plant roots.  University of Wisconsin Extension has a Japanese beetle webpage including information on the damage caused by the adults, the damage caused by the white grubs, and control measures that are useful on the adults and the larvae. 

Written by: Linda Williams, forest health specialist, Woodruff, (Linda.Williams@wisconsin.gov), 715-356-5211 x232.

Spruce budworm defoliation is present

Spruce budworm defoliation is not as noticeable this year, although it is still present as you can see here with many needles missing.

Spruce budworm defoliation is not as noticeable this year, although it is still present as you can see here with many needles missing.

Spruce budworm damage is present this year but in many areas it is less noticeable than in past years. I believe this is due to a couple of things:

  1. The many storms we had this spring with heavy rainfall and strong winds may have washed some of the caterpillars out of the trees. They definitely washed budworm damaged needles off the tree. Damaged needles typically remain on the tree and turn a rusty brown, so not having these needles on the tree makes it less obvious where defoliation is present this year.
  2. Due to the constant rainfall this year, the growth on balsam fir and spruce seems to be quite good in general, which leads to additional green needles on the tree this year. This makes the trees look more green and less defoliated, but spruce budworm is still there.

Written by: Linda Williams, forest health specialist, Woodruff, (Linda.Williams@wisconsin.gov), 715-356-5211 x232.

Black canker and willow scab on willow

Black canker causes twig mortality and a sunken area on the branch. Photo by Mike Schuessler.

Black canker causes twig mortality and a sunken area on the branch. Photo by Mike Schuessler.

Do you have willow that is looking thin and sad this year?  In addition to some frost damage earlier this year, I’ve checked out several areas where black canker and willow scab are causing defoliation and fine branch mortality.  I’ve noticed this in Brown, Door, Kewaunee, Marinette, Oconto, and Waupaca counties.

Early in my career with the department I recall checking out a willow planting in Manitowoc County that had a lot of black canker killing the fine branches, but since then I haven’t run into it much.  Black canker starts by infecting a leaf but quickly moves into the petiole and into the twig where it causes a small sunken canker. This can cause the twig tip to wilt, shrivel, and die. Willow scab will also cause the twig tips to wilt, shrivel, and die. Willow scab and black canker can often be found affecting the same tree and are more common in years when we have a cool wet spring. 

New growth impacted by willow scab and black canker will shrivel and die.

New growth impacted by willow scab and black canker will shrivel and die.

Repeated defoliation of a tree due to black canker or willow scab can significantly impact growth and form because many branch tips will be killed. More information and pictures are available online by Cornell on black canker and willow scab

Written by: Linda Williams, forest health specialist, Woodruff, (Linda.Williams@wisconsin.gov), 715-356-5211 x232.

Oak wilt signs are showing up

Oak leaves from an oak wilt infected tree. The outer portions of the leaf will be brown or have a water-soaked appearance. Part of the leaf remains green even though the leaf has dropped off the tree.

Oak leaves from an oak wilt infected tree. The outer portions of the leaf will be brown or have a water-soaked appearance. Part of the leaf remains green even though the leaf has dropped off the tree.

Trees that were infected with the oak wilt fungus this spring, (whether from overland spread by beetles or underground spread by connected root systems) are beginning to drop their leaves. Leaves can drop anytime between July and September. This wilting and dropping of the leaves happens fairly quickly, and trees can go from looking nice and healthy to having lost most of their leaves within just a few weeks. This year I saw my first wilting oaks on June 28, although in areas further south the leaf drop may have begun earlier. Oak wilt is a non-curable, fungal disease specific to oaks. Once the fungus infects a tree it will begin to spread outward from the roots of the infected tree through grafted roots and into the roots of neighboring oaks, eventually killing the neighboring oaks. In this way pockets of dead oak will be created as each year more oaks die. For more information on oak wilt biology, prevention, and control check out the WI DNR’s oak wilt page

Firewood from trees that have died from oak wilt will remain infectious for 1 full year (12 months) after the tree has died. There are many areas of northern Wisconsin where oak wilt is not common. Please do not move firewood long distances because you could move oak wilt into a new area.

Many northern counties don’t have oak wilt or have only a few known infections. This map shows townships in the north where oak wilt has been identified. In the red counties oak wilt is considered to be scattered throughout the county, although it will not be found in every stand.

Many northern counties don’t have oak wilt or have only a few known infections. This map shows townships in the north where oak wilt has been identified. In the red counties oak wilt is considered to be scattered throughout the county, although it will not be found in every stand.

Written by: Linda Williams, forest health specialist, Woodruff, (Linda.Williams@wisconsin.gov), 715-356-5211 x232.

Wasp releases to fight emerald ash borer (EAB)

Tetrastichus wasp is one eighth inch in length and attacks emerald ash borer larvae beneath the bark of an ash tree.

Adult T. planipennisi wasp collected as a pupa in Ozaukee County, May 2017. This species attacks EAB larvae beneath the bark. Actual size is 1/8” in length.

This summer, DNR staff will continue to do introductions of three natural enemy wasps that attack emerald ash borer: Tetrastichus planipennisi, Spathius galinae and Oobius agrili. The Tetrastichus and Spathius wasps attack EAB larvae beneath the bark, and the Oobius wasps attack EAB eggs on the bark surface. The tiny wasps do not sting or bite, and the public is unlikely to know they are present.  Continue reading “Wasp releases to fight emerald ash borer (EAB)”

Oak wilt identified near Sayner in Plum Lake Township, Vilas County

Oak wilt fruiting body formed under the bark, shown here with the bark peeled away. The dark grey lump of stuff is the fruiting body which produces the spores.

Oak wilt fruiting body formed under the bark, shown here with the bark peeled away. The dark grey lump of stuff is the fruiting body which produces the spores.

I’ve identified oak wilt in Plum Lake Township, Vilas Co, west of Sayner. This is the first find of oak wilt in Plum Lake Township. The closest known oak wilt location is 6.7 miles from this new site. The tree rapidly dropped its leaves last July, and when it didn’t leaf out this spring the homeowner called me. Upon examining the tree I was able to find an oak wilt pressure pad, which is the fungal spore mat that forms under the bark and causes the bark to crack, which is how beetles can get access to the spores and move them to other oaks. 

Oak wilt is found throughout the counties shown in red. Where oak wilt is uncommon the townships where oak wilt has been identified are shaded in pink.

Oak wilt is found throughout the counties shown in red. Where oak wilt is uncommon the townships where oak wilt has been identified are shaded in pink.

The oak wilt map has been updated. Oak wilt is not common in our northern counties so the map highlights in pink the townships where oak wilt has been identified in the northern counties. The oak wilt guidelines for timber sales were updated about a year ago and list some exceptions and modifications for situations in which it is not necessary to implement the cutting restrictions during the high risk time period of the year (April 15 – July 15 in the north). 

Homeowners and those not doing timber sales should try to avoid pruning, wounding, or cutting oaks during the high risk time period of April 15 – July 15 in the north. This is the time of year when the beetles that can spread the spores overland will be attracted to fresh wounds on your trees; if you prune, wound, or cut your oaks during this period the beetles can introduce oak wilt to your tree. If it is necessary to prune, wound, or cut trees during that period, wound paint should be applied.

Oak wilt is always fatal to trees in the red oak group, which includes northern red oak, northern pin oak, and black oak. Trees that were infected with the oak wilt fungus this spring will begin rapidly dropping their leaves in July and August.

Written by: Linda Williams, forest health specialist, Woodruff, (Linda.Williams@wisconsin.gov), 715-356-5211 x232.