Balsam fir needles infected with needle rust turn bright yellow. / Photo Credit: Wisconsin DNR
Although this summer has been dry in north-central Wisconsin, there was enough moisture this spring to promote some needle rusts. Needle rusts are fungi that infect needles of various conifers. Most rusts require two hosts to complete their life cycle.
A look at common types of needle rust:
A pitch “glob”, with oozing pitch running down the trunk of a young white pine infected with pitch mass borer. / Photo Credit: Wisconsin DNR
By Linda Williams, Forest Health Specialist, Woodruff
Linda.Williams@wisconsin.gov, 920-360-0665
Have you seen big globs of gooey pitch on the main stems of eastern white pine trees? Or maybe you’ve seen them on spruce?
For those with an adventurous side, grab a stick and scrape off some of that gooey glob. You might be rewarded with the sight of large larvae feeding beneath all of that goo. This is the larvae of our native pitch mass borer. Adults are clearwing moths that look a bit like wasps.
Using a stick to pry away some of the gooey pitch on a tree exposes a pitch mass borer larva underneath. / Photo Credit: Wisconsin DNR
Adults lay eggs on the bark. When eggs hatch, the tiny larvae chew into the bark and begin feeding on the inner bark. They feed enough to irritate the tree, causing more sap and pitch to be produced, which the larvae feed on.
Pitch mass borer can take two to three years to complete development, remaining in that same location throughout their life and continuously irritating the inner bark to promote continued pitch production. Pupation occurs under the glob of pitch and adults then chew their way out. Old pitch globs will harden and darken over time, remaining on the tree for a year or more before finally weathering off.
Hosts include pines (eastern white, jack, scotch and Austrian) and spruces (blue and Norway).
Management on forest trees is not necessary. Severely damaged and deformed trees can be removed during the first thinning. Management on yard trees includes maintaining healthy trees (which are less attractive to the adults), watering during droughts, avoiding pruning during mid-summer (which can attract adults to lay eggs near the fresh wounds), destroying any larvae under the globs of pitch and removing and disposing of severely infested trees.
Scraping more pitch off a tree’s main stem shows a pitch mass borer larva on the end of the stick. / Photo Credit: Wisconsin DNR
Pitch mass borer larvae can be shades of white to pink, depending on the host. / Photo Credit: Wisconsin DNR
Linda Williams, DNR Forest Health specialist for Northeast Wisconsin, inspects a tree during a training session. / Photo Credit: Wisconsin DNR
By Art Kabelowsky, DNR Forest Health Communications, Fitchburg;
Arthur.Kabelowsky@wisconsin.gov or 608-335-0167
Linda Williams, Wisconsin Department of Natural Resources Forest Health specialist for Northeast Wisconsin, will speak at multiple “Learn About Your Land” teaching events scheduled in September.
Continue reading “Forest Health Staffers Plan Public Appearances”
Young larvae of aspen leaf beetle feed on the undersides of aspen leaves. The arrow points to the cluster of eggs that produced the larvae. / Photo Credit: Wisconsin DNR
By Linda Williams, Forest Health Specialist, Woodruff;
Linda.Williams@wisconsin.gov, 920-360-0665.
Aspen leaf beetles have recently been spotted defoliating young quaking aspen trees in Vilas and Oneida counties.
Both adults and larvae will feed on aspen leaves. The defoliation level detected was light to moderate.
Continue reading “Aspen Leaf Beetle Defoliation Found In North”
Messy webbing filled with frass (droppings) and pieces of needles are signs of pine false webworm feeding on this young white pine. The arrow points to a pine false webworm larvae. / Photo Credit: Wisconsin DNR
By Linda Williams, Forest Health Specialist, Woodruff;
Linda.Williams@wisconsin.gov, 920-360-0665
Pine false webworm (Acantholyda erythrocephala) is not a very common insect in Wisconsin, though it is present. They prefer to feed on white pine in Wisconsin, though reference materials say they will also feed on red pine, jack pine and Scotch pine.
Damage was reported as “minor” in the central part of the state from 1953 to 1961. Later, in 1995, 1997, 2002, 2004 and 2006, it was once again observed as a minor pest feeding on red or white pine in the central part of the state, particularly Portage, Waupaca and Waushara counties. In 2024 and again this year, a few scattered young white pine were observed being significantly defoliated in Oneida and Vilas counties.
Japanese beetles defoliating a basswood leaf. / Photo Credit: Wisconsin DNR
By Linda Williams, Forest Health Specialist, Woodruff;
Linda.Williams@wisconsin.gov, 920-360-0665
The Japanese beetle (Popillia japonica) is an invasive insect that feeds on many plant species. The adult beetles “skeletonize” leaves by eating the material between the veins.
Adult Japanese beetles feed on the flowers and leaves of more than 300 plant species, including trees, shrubs and herbaceous plants. Forest trees can be defoliated, with open-grown or edge trees suffering the highest defoliation rates.
Continue reading “Japanese Beetle Populations Still Building In The North”
Hemlock branches show missing needles, and needles with feeding damage, as the result of spruce budworm infestation. / Photo Credit: Wisconsin DNR
By Linda Williams, Forest Health Specialist, Woodruff
Linda.Williams@wisconsin.gov, 920-360-0665
Spruce budworms are finished feeding for the year, but the damage is still being noticed. That’s especially true in areas where defoliation was severe, such as northeastern Oneida County and southeastern Vilas County.
Spruce budworm prefers to feed on balsam fir and spruce, but in areas with very high populations and severe defoliation, they will also feed on hemlock and tamarack.
Tamarack trees showing the effect of larch casebearer defoliation. / Photo Credit: Wisconsin DNR
By Linda Williams, Forest Health Specialist, Woodruff;
Linda.Williams@wisconsin.gov, 920-360-0665
Earlier this spring, scattered areas of tamarack in North Central and Northeastern Wisconsin showed tan or light brown foliage. Sometimes that is due to frost, but this year it was the work of an insect called larch casebearer.
As the foliage started to expand this spring, the larch casebearer became active and began to feed. The tiny caterpillars mine out the needles of tamarack and use them as “cases” to protect themselves, thus their name.
Continue reading “Tamaracks Busy Refoliating After Larch Casebearer Defoliation”
Pale swallow-wort flowers along the stem at the leaf axils. / Photo Credit: Chris Evans, University of Illinois, Bugwood.org
By Mackenzie Manicki, DNR Natural Resources Research Scientist
The Wisconsin Department of Natural Resources has confirmed that the state’s first populations of the invasive vine pale swallow-wort (Vincetoxicum rossicum) have been found.
The populations were first detected in Oconto and Shawano counties, within the outskirts of Krakow along the shared county line.
These are the first known populations in the state, making rapid response efforts critical in preventing the establishment of this species in Wisconsin.
Continue reading “First Populations Of Invasive Pale Swallow-wort Confirmed In Wisconsin”
Mike Hillstrom and Linda Williams of the Wisconsin Department of Natural Resources Forest Health team look over a tree during a walking tour put on by the Cambridge Tree Project on July 10, 2025. / Photo Credit: Wisconsin DNR
By Art Kabelowsky, DNR Outreach and Communications, Fitchburg
Arthur.Kabelowsky@wisconsin.gov or 608-335-0167
Mike Hillstrom, Invasive Forest Pest Coordinator for the Wisconsin DNR Forest Health Team, will make a presentation on forest health to the Heartland National Christmas Tree Organizations Convention, scheduled for Friday, Aug. 7, at Hann’s Christmas Farm, 848 Tipperary Road, Oregon, WI 53575.
