By Osakis Review staff
Is your maple tree looking a little sickly lately?
You’re not alone.
Maple trees in Douglas County and across Minnesota are struggling now, according to experts, and the exact reason why remains a mystery.
Across Minnesota, tree experts are hearing from homeowners whose cheery emblems of fall are in trouble. Instead of producing full, vibrant branches, some maple trees appear to be on their way to an early grave.
“Our native maples … as well as the introduced Norway maple and amur maple have been tanking all over the state for several years, but the past two have been particularly hard on them,” said Gary Johnson, a professor who specializes in urban and community forestry for the University of Minnesota’s Urban Forestry Outreach, Research and Extension office.
A scan of news headlines over the past year report maple problems in other states, including Michigan, Washington and Virginia. However, tree experts say those problems could be completely unrelated to what is happening in Minnesota.
“I have received zero reports of maples declining in our natural forests,” said Brian Schwingle, a tree insect and disease specialist for the state. “I think that is highly noteworthy. Having said that, sometimes ornamental tree health concerns are the canary in the coal mine for forest problems.”
He added that he was not convinced that is the case in Minnesota.
If maple problems are isolated to yards, they could well be caused by the hard winter last year, southern seed stock not equipped for northern climates and urban stress, he said.
The issue does warrant further investigation, Schwingle said.
Douglas County Master Gardener Robin Trott pointed out challenges facing maple trees in her weekly column.
Trott recommended homeowners to take a peek outside and check their maples for these signs and symptoms:
Reduced twig growth. Yearly twig growth varies considerably between trees and even within the canopies of individual trees. If the distance from bud scar to bud scar is less than or equal to five centimeters on a non-shaded twig, the tree may be in trouble.
Reduced foliage growth. Keep in mind the normal, healthy appearance of the particular maple species' foliage. Foliage that is sparse, light green and/or scorched signals that the tree may be declining. Scorching may also be due to water stress, exposure to de-icing salts, or infection by a bacterium.
Early fall coloration. Maples normally begin showing fall color after the first frost or in early-to-mid-September. When fall color develops earlier than normal, in late July or early August, the maple may be suffering from decline.
Where individual larger branches exhibit premature fall color, and leaves are noted to be small, that may be evidence of verticillium wilt. Analysis of symptomatic branch tissue by a diagnostic lab may be required however to confirm that diagnosis. (Plant Disease Clinic: pdc.umn.edu)
Dead branches in upper canopy. Small dead branches seen in tree tops in late spring or early summer are indicative of decline. Over time, larger, more visible branches and limbs will die back. The more numerous the dead twigs or branches are, the more severe the decline condition.
Poor root condition. If roots can be examined, look for reduced occurrence of small feeder rootlets and/or brittle roots. Also examine the lower stem and buttress roots for any evidence of wounding or decay. Wounds to buttress roots may help open up weak trees to colonization by wood decay organisms.
Trott pointed out that once a tree is in a severe state of decline, it might be incurable.
However, providing good cultural care may help prolong its life long enough to plant a replacement tree. In this way the newly-planted tree will have a few years to grow prior to the removal of the declining maple.
Trott advised to plant young maple trees away from roads to avoid future de-icing salt problems.
For newly-planted trees and trees in decline:
Be certain to provide adequate water during dry periods
Provide adequate nutrition.
Remove dead wood
Protect the tree from de-icing salt.
As defoliation can be a triggering factor in decline, pay close attention to developing insect issues on your trees. Although forest tent caterpillar populations may not be high every year, severe defoliation by these or other pests may trigger decline or result in the death of an already weakened tree. In years when pest issues may be high, an insecticide treatment may help.
The success of treatment to declining maples depends primarily on early detection of maple decline, the health of the tree prior to treatment, and/or its ability to respond to treatment, Trott noted. Positive diagnosis will often depend on examination or the amount of information provided by the person submitting a sample.
However, the prescribed treatments of fertilizing, watering and pruning will not damage healthy trees, and may also benefit trees suffering from other issues such as verticillium wilt.