Evergreens, Maples, Oaks and more struggling this summer
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| Arborvitae killed by winter drying. Photo: DNR |
One of the big headlines for gardeners and home owners this
year is all about trees. Trees appearing to turn brown, trees turning yellow or
not leafing out at all; conifers with multiple dead limbs particularly among
the lower branches, even dying outright. So what’s happening?
The DNR forest health team tracks what’s happening statewide
and in each region so they can help address problems both for the trees in our forests
and at home. Here’s a summary of their Summer 2018 findings to date:
Evergreens: Winter winds prove fatal
In this summer’s “Forest Insect and Disease Newsletter,” the
team said since May, it has fielded reports from Anoka, Fillmore, Freeborn,
Goodhue, Hennepin, Houston, Rice and Winona counties about dead evergreens—in particular
black hills spruce, white cedar (arborvitae) and white pine.
DNR Forest Health Specialist Brian Schwingle says the dry
and windy weather in April caused these trees to die. “This happened because in late
April we had warm, very windy days with low relative humidity, causing needles
to lose moisture," he writes. "Frozen soil in the root zones of these trees prevented water
from moving back into the needles to replace the lost moisture.”
Recommendation: Schwingle suggests immediately removing any conifer with more than half
of its branches killed by winter drying to avoid an attack by bark beetles.
Oaks: Trouble leafing out
From Brainerd and Sauk Rapids to Hinckley and even Chanhassen,
reports came into the DNR about bur and white oaks that barely leafed out this
spring. The team says it hasn’t “solved this puzzle” yet as to why this severe
dieback happened, but suspect it may have something to do with cynipid wasps.
Recommendation: The DNR recommends the following: “homeowners [should] leave affected
oaks in place and allow them the opportunity to recover. Many of the affected oaks are already
recovering and will survive.”
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| Masting on a west metro maple tree. Photo: Mary Meyer, UMN Extension |
Maples: Are the leaves brown or is it seeds?
Extension Horticulturist Mary Meyer wrote this spring about
the large number of seeds being seen on maples and Siberian elms (”Brown
foliage on your maple trees & American elm? Look closely…it may be seeds!”).
The production of abundant seeds is called a mast year or masting, which current
research says happens every 2-5 years. The DNR says: “every now and then
this happens across a large area, and it usually does not hurt the tree.”
Recommendation: Sometimes the outer branches on maples that produce these
bumper crops of seeds can die, but trees recover over time. Meyer also recommends that you examine your trees
for any signs of stress (or distress) which can also cause excessive seeds to pinpoint other possible causes.
Spruce: Losing needles on lower branches
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| Black hills spruce with stigmina needle cast. Photo: DNR |
Have the needles on the lower branches of your spruce tree
died? The DNR says it’s a common tree health concern. Spruce trees planted in a
row are susceptible to a needle cast disease caused by a fungus.
Stigmina needle cast disease appears when there’s lots of
rain, and moist conditions around your tree(s).
They are particularly susceptible if planted in a low-lying area. If
your tree is growing by itself in the sun and away from other trees with good
air circulation, it will rarely be affected.
Recommendation: To minimize spruce needle cast diseases, here are some DNR tips:
- Plant spruce in full sunlight by themselves.
- Alternate spruce with different trees.
- Remove every other spruce if you do have a row of them and their branches are in contact with each other.
- Don’t spray water on needles or up into the tree.
- And prune lower canopy branches.
White cedars: Yellowing leaves a sign of trouble
If you live in northern Minnesota, you may have noticed
northern white cedars (Thuja
occidentalis) with yellow leaves or yellow foliage tips on the ends of the branches. The DNR forest health team says two causes are possible: winter injury or a pest called arborvitae leafminer:
- The team determined a regional outbreak of a pest called arborvitae leafminer has caused some of the yellowing, or yellow tips. These small silvery moths lay their eggs on arborvitaes in June and July. The larvae tunnel into the foliage, feed into the fall, then overwinter in the tree.
- Those yellow leaves may also be a sign of winter injury, which often appears on the south and southwest sides of the tree where the sun shines.
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| 1. Northern white cedar near Hill City showing yellowing shoots from arborvitae leafminer infestation. 2. Black arrow pointing to an exit hole created by the arborvitae leafminer (magnified 40x).3. Red pine showing symptoms of winter burn on the south side of the tree. Photo: DNR |
Ultimately, the DNR says here’s how to tell the difference: ”Remove
and inspect the brown tips. Frass (insect feces) in hollow, brown tips is a
characteristic of insect activity. If brown tips are not hollow or filled with
frass, the cause may be winter injury.”
Recommendation:
Water, fertilize and
prune your trees. This is the best way to prevent damage. Otherwise, unless a
tree is severely infested, there’s no need to control cedar leafminers. You can
try to destroy the caterpillars in the spring by picking them off. Check your trees in March and
April, and prune the infested twigs from the tree.
More information
For more information on all of the tree health issues mentioned above,
click on the following link: https://www.dnr.state.mn.us/treecare/forest_health/fid/summer-2018-articles.html
Article written by: Gail Hudson, Extension Communications Specialist
