Forest Insect and Disease Newsletter - June 2019

New forest health specialists in the Northwest and Northeast Regions

My name is Megan O’Neil and I am excited to be one of the Minnesota DNR’s new forest health specialists. I grew up south of Detroit, Michigan on the island of Grosse Ile. I earned both my bachelor’s and master’s degrees from Michigan Technological University in the Upper Peninsula of Michigan. I grew fascinated with forest health issues as the impact of emerald ash borer became evident in the greater Detroit area.

I gained experience in forest health while working in a lab at Michigan Tech. I monitored emerald ash borer and other forest health concerns, such as hemlock woolly adelgid, across the Upper and Lower Peninsulas of Michigan. Besides my work in forest health, I was a Peace Corps volunteer in Ecuador and a forester for the Missouri Department of Conservation. I’m very happy to be part Minnesota’s forest health team and I look forward to working with you.

photo of Megan O'Neil

Hello, Forest Insect and Disease Newsletter readers. My name is Rachael Nicoll, and I am pleased to introduce myself as one of the DNR’s new forest health specialists. I am stationed in Brainerd and provide quarter-time support to the State Forest Nursery. Megan O’Neil and I share the Northwest Region; please feel free to contact both of us with questions in this area.

A Minnesota native, I was born and raised in Stearns County. Growing up in the woods instilled in me a passion for the outdoors as well as a desire to devote my career to making progress on the complex challenges of natural resources management. I earned a bachelor’s degree in forestry and master’s degree in forest entomology at the University of Minnesota where I studied the dispersal capacity of larval gypsy moth and analyzed perceptions of the gypsy moth invasion in Minnesota.

I have spent my career in Minnesota working at the University of Minnesota’s Forest Ecology Lab, the DNR Resource Assessment Unit, Itasca State Park, the Little Falls and Brainerd DNR offices, and for nearly five years as the Minnesota Forest Resources Council’s information specialist.

I look forward to providing you with interesting and timely information on tree and forest health issues. Please feel free to reach out to me with any questions. I am happy to be of service.

photo of Rachael Nicoll

I’m Eric Otto, the DNR’s new forest health specialist for northeast Minnesota. Growing up in Lester Prairie—about halfway between Waconia and Hutchinson—I developed a passion for nature by exploring the small woods outside our home. I built on that passion by earning a bachelor’s degree in forest resources from the University of Minnesota. Working in a forest pathology lab as an undergraduate stimulated my interest in forest health, as did working seasonal forestry positions in northern Minnesota, Wyoming, and Maine. From 2012 to 2014, I served as a Peace Corps volunteer in Ghana and worked in the agriculture sector. While there, I promoted the cultivation of moringa trees, often referred to as the miracle tree. When I returned home, I found myself back at the U of M. I entered graduate school to study Heterobasidion root disease in Minnesota and am currently a PhD candidate finishing my dissertation.

My position as forest health specialist will be challenging and rewarding. I’m excited to explore more of Minnesota’s forests and help protect them for future generations. Feel free to contact me with any questions. If you don’t find me working, you can find me running long distances in the woods or paddling down a stream.

photo of Eric Otto

Orange slime on birch and ironwood, and other weird stuff on tree bark

By Brian Schwingle, Central Region forest health specialist

Turkey hunters in Dakota County and a homeowner in Morrison County spotted some paper birch trees this spring that had orange slime oozing down the bark. Another homeowner noticed the same stuff on her ironwood in Washington County in early May. This orange gunk, coupled with white foam, occasionally appears on birch trees. It’s partly a result of orange-pigmented yeast growing on sap leaking from wounds, says Dr. Robert Blanchette, a tree pathologist with the University of Minnesota.

This orange yeast is just one of many microorganisms that grow on sap leaking from trees. Perhaps the most commonly seen organisms that grow on sap are sooty molds. Sooty molds are black fungi that feed on sugars in tree sap. Streaks of blackened bark colored by sooty mold often appear below tap holes in sugar bushes or below sapsucker holes drilled into sugar maples.

Additionally, there is a suite of organisms that feeds on dead outer tree bark or uses bark as a surface on which to grow. Several fungal species harmlessly feed on outer tree bark, creating a condition known as “smooth patch.” White and bur oaks frequently have smooth patch. Lichens, a combination of a fungus and either algae or a type of blue bacteria, also are harmless and common on tree bark.

With all of the above cases, the organisms you see are not harming the tree. In the cases of orange yeast on birch and ironwood trunks or sooty mold on tree trunks, they indicate the tree has some sort of injury. In most cases, that injury is minor and not concerning.

orange mold on birch trees

black mold on maple trees with sap tap buckets

Emerald ash borer update

By Brian Schwingle, Central Region forest health specialist

The latest community to discover emerald ash borer (EAB) is Sauk Centre in northwestern Stearns County. This comes six months after the discovery of EAB to the southeast, along Interstate 94 in Clearwater, Wright County. These EAB infestations so many miles apart probably were caused by people moving infested firewood or wood along the Interstate. Moving ash wood is ill-advised, not only for the homeowners and ash along the route and at the final destination, but also because moving wood is illegal in many cases. The Minnesota Department of Agriculture (MDA) regulates the movement of ash wood in Minnesota, so visit their quarantine webpage for information on moving ash wood.

Switching gears, the memory of our winter is probably fading now (finally). Yes, it got cold and, yes, many overwintering EABs died from prolonged sub-zero exposure (somewhere between 40 and 99 percent died, according to a survey that MDA conducted). Keep in mind, though, that many EABs survived, and winters like this past one only slightly delay the wreckage EAB will bring to many woodlots and communities. For forests consisting mostly of ash, now is the time to plant other tree species so that EAB won’t convert your wet forest to a wet meadow or a buckthorn swamp. The DNR is showcasing online some examples of preparing for EAB in our state forests. Also, the Great Lakes Silviculture Library summarizes an impressive Chippewa National Forest effort. If you are a small woodland owner, you may be eligible for financial assistance from the DNR to prepare your woods for EAB. Check out the DNR’s Forest Stewardship webpage for details.

For communities with lots of ash along streets and in parks, EAB brings an overwhelming financial burden as it kills trees. The earlier communities start to prepare for EAB, the better. A combination of preemptive healthy ash tree removal, replacement with other tree species, and protective tree injections will help slow the movement of EAB and spread out the financial burden over time. The good news is that the 2019 legislative session produced $1 million in funding for communities to begin managing EAB.Grant applications will be released later this summer through the DNR.

Leaf disease on ash and oak

By Brian Schwingle, Central Region forest health specialist

I began noticing green ash leaflets falling on May 29 in Dakota County. Ash leaflet drop was reported in Isanti County and was probably happening elsewhere, too. Looking closely at the leaves, I saw they were subtly deformed. This is a telltale sign of the fungal disease anthracnose.

Anthracnose is a general term for a group of diseases that strikes many plants, causing dark spots on the leaves. It starts in the inner and lower canopies of trees in spring, and causes blotches on leaves, leaf deformity, and leaf loss.

Anthracnose is just one of many types of fungal leaf diseases that broadleaf trees get during wet growing seasons. All of the rain southern Minnesota received from April 1 to early June occurred during leaf emergence, providing the perfect growing environment for anthracnose fungi.

Besides anthracnose on green ash, I also noticed anthracnose developing in the lower canopies of white oaks in Dakota County. Anthracnose also is likely deforming some sugar maple leaves in certain parts of southern Minnesota, too. Although anthracnose looks bad, it does not pose any serious health problem for the tree.

ash leaves with anthracnose

Other fungal diseases to watch for

Crabapples are starting to show indications that they will develop severe apple scab later this summer. Brian predicts that bur oak blight, a fungal leaf disease that shows up in late summer, will be common this year, too.

photo with apples and leaf showing sings of apple scab

Photo: Penn State University,

leaf showing signs of BOB

Winter drying injury on evergreens in northern Minnesota

By Megan O’Neil, Northwest Region forest health specialist

When the snow finally started to melt after this year’s long winter, many northern Minnesota residents noticed their evergreens showed signs of winter drying injury. Symptoms included needles that turned brown or looked bleached. We received many reports of white pines with brown needles on one side or just the upper portion of the tree.

Winter drying injury happens when water evaporates through openings in the needles. The water loss occurs because the tree’s roots are in frozen ground and unable to replenish the needles with water. Needle browning typically occurs from the tip downward to the base. Although it’s more of a problem on recently transplanted trees, winter drying injury also will affect established trees. Browning usually occurs on exposed upper branches, while lower branches protected by snow cover remain green.

Winter drying usually does not kill trees. As long as the buds are alive, the tree will produce new needles to replace the ones that have died.

If you have a yard tree that has signs of winter drying, you can prune out the dead tissue. To determine whether a limb is dead, simply use your thumbnail to scratch the bark and check for green tissue below. You also can check the buds for green living tissue.

white pine with brown needles

Witches’-broom on red pine

By Eric Otto, Northeast Region forest health specialist

Sometimes people forget to look upward when walking through a forest. If they do, they might see a witches’-broom. A witches’-broom is generally a deformity of the tree in which a dense mass of shoots grows from a single point. The exact cause of most witches’-brooms is unknown, but could be due to stress in the tree. Fungi, mites, aphids, and phytoplasmas (bacterial parasites) are some things that can cause this stress. A disruption of the normal functioning of the plant’s hormones also can cause a witches’-broom. This disruption can occur when there is an increase in a plant hormone that promotes branching and a blockage in a plant hormone responsible for normal cell expansion and growth. Finally, it’s also possible that the broom is caused by eastern dwarf mistletoe, a parasitic plant.

In Minnesota, witches’-brooms can be seen more commonly in balsam fir and black spruce than in red pine. Fir-broom rust, a fungal disease, causes brooms on balsam fir while Eastern dwarf mistletoe can cause them on black spruce—the latter can be a problematic and prevalent forest health threat to black spruce production. This same species of mistletoe also can attack red pine, but this is less commonly seen.

We don’t know the cause of the witches’-broom in this photograph, but it could be due to one of the factors already mentioned. A forester in the Hibbing area discovered the witches’-broom in this red pine. So, the next time you find yourself wandering through a red pine stand or mixed coniferous forest, look up. What you see may surprise you.

red pine with large witches' broom