Tree insects and diseases

Bark beetles are one of the biggest threats to forests across Northeast Michigan and the ice storm didn’t help pine trees brace for their return. Downed wood is a hotspot for these beetles to thrive and grow.

In larger populations, these beetles can move to healthier trees.

“Normally, they have two to three generations per year,” said Cheryl Nelson, a Forest Health Outreach Forester for Michigan’s Department of Natural Resources. “However, if there is a lot of extra debris on the ground, they can have more generations. They use that wood to lay eggs.”

Courtesy Photo from the Michigan Department of Natural Resources A bark beetle embeds itself into a tree. Bark beetles chew through the inside of trees, damaging the quality of timber.

Spring into early fall is when trees are at high risk from these wood-burrowing insects. Bark beetles can chew through tunnels through trees, damaging the quality of the timber.

Bark beetles aren’t the only beetles that may cause lasting damage to forests. During this time of year, Nitidulidae beetles, also known as sap beetles, can help transfer fungal diseases such as oak wilt.

“Those sap feeders can fly at least a mile and can arrive within minutes to a freshly wounded or pruned tree,” Nelson said. “Those wounds are viable or attractive to those Nitidulidae beetles for about three to four days.”

There was no risk of oak wilt during the time of the storm, so damaged limbs weren’t affected. However, pruning oak trees over the summer may increase the risk of the disease, according to Nelson.

Another way oak wilt, heterobasidion root disease (HRD) and other infections can get into trees is from stress due to harsh conditions such as ice storms.

Courtesy Photo from the Michigan Department of Natural Resources Autumn olive is an invasive shrub that can rapidly grow in open areas and outcompete native plants. It can be seen in areas like the sides of roads, the edge of forests.

“When they’ve been stressed from storm damage, droughts or multiple years of feeding by the spongy moth outbreaks that we’ve had, that can just allow them to get into a tree and take over where normally it wouldn’t be,” Nelson said.

Infected trees can show physical signs that they are fighting off these diseases:

Oak wilt: leaves may start to brown faster than usual.

HRD: Beginning stages of the fungus can look like white popcorn around the base of the tree. It can evolve into a more shell-like structure.

Armillaria root rot: Decaying bark, reduced growth in leaves. A key sign is a white fungal sponge sheet between the wood and bark.

Autumn olive: the aggressive, foreign shrub

Autumn olive is a tall deciduous shrub that is native to Asia and was introduced to the United States around the 1830s. The plant is able to aggressively outgrow native plants due to a small number of threats to it.

Chris Engle, a communications associate with the nonprofit conservation Huron Pines, said that the shrub is not disturbed by herbivores and can flourish in different regions across the state.

“It takes up the under story of a forest, it grows along wood lines and it just really disrupts our natural ecosystem,” Engle said.

Autumn olive can be identified by its small white flowers that bloom from April to June. The shrub can grow as tall as 20 feet. Often this plant can be found on the sides of roads, prairies or other open areas.

One concern that is being raised by foresters is the potential spread of this shrub while clearing damaged or downed trees, giving this plant more room to grow. The activity of machinery in a forest can also pose a risk of spreading autumn olive or other plants.

“When you clear out an area of forest, you’re bringing sunlight down to the ground,” Engle said. “You’re disturbing the soil, creating open exposed soil for seeds to take root. There’s a lot of elements that are all coming together at once to potentially boost the number of invasive species in these areas.”

He said that proper cleaning of forestry machinery is also important when transferring to a different site.

According to both Engle and Nelson, foresters use chemicals to treat the spread of invasive plants like autumn olive as well as diseases such as HRD.

“If you’re within five miles of a known location, it is recommended to have any of the stumps from tree removal treated with one of the approved chemicals in Michigan,” Nelson said.

A map of known HRD and oak wilt-infected areas and a list of regional foresters can be found at www.michigan.gov/dnr/managing-resources/forestry.

Blace Carpenter can be reached at bcarpenter@thealpenanews.com. This story was produced by the Michigan News Group Internship Program, a collaboration between WCMU Public Media and local newspapers in central and northern Michigan. The program’s mission is to train the next generation of journalists and combat the rise of rural news deserts.