Spruce Budworm, Balsam Fir Sawfly, And Yellowheaded Spruce Sawfly

Linda Williams, DNR Forest Health Specialist, Woodruff, Linda.Williams@wisconsin.gov or 920-360-0665. 

The spruce budworm outbreak continues this year, but the amount of visible defoliation is generally lower than last year. Some areas of the Northwoods have severe defoliation this year, but in many other areas, the amount of new, green foliage far exceeds the amount of defoliation.

In areas where the defoliation appears less severe, you can still find plenty of caterpillars, but the new foliage is less eaten than anticipated. The late spring frost/freeze may have killed some caterpillars, or the long cool spring may have delayed bud-break enough that the caterpillars did most of their feeding on older foliage before the new foliage expanded. 

The spruce budworm outbreak in Wisconsin started in 2012, and outbreaks typically last about 10 years.  Mortality of balsam fir trees started to show up last year following several years of significant defoliation. Even with new growth on the trees this year, they may continue to decline, and mortality could still occur. 

Spruce branches showing defoliation, older needles and new, bright green needles.

Defoliation is still present, but there is lots of new growth on balsam fir this year in many areas of northern Wisconsin.

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Aphids, Scales And Spittlebugs, Oh My!

Linda Williams, DNR Forest Health Specialist, Woodruff, Linda.Williams@wisconsin.gov or 920-360-0665. 

This seems to be a good year for aphids, scales, spittlebugs and other insects that suck the sap of trees. 

Large conifer aphids have been observed on white pine, jack pine and balsam fir. These large, dark colored aphids insert their mouthparts into the twig and suck the sap. They are often guarded fiercely by ants because aphids excrete a waste product called honeydew that ants collect as food. Sooty mold can grow on honeydew so when it covers the twigs and needles of the trees it makes them look darker than normal. Sooty mold is a problem because it limits the ability of those needles to photosynthesize, which can put the tree under stress if it occurs over multiple years. 

If you have just a few colonies of these aphids, there is no control necessary as tree health shouldn’t be affected. If more than 30% of the branches have ant colonies present, or you’re noticing a buildup of sooty mold, you can spray the aphids with a pesticide or a soapy water mixture. Natural enemies, including ladybugs and lacewings, can be very effective at reducing aphid populations. But if ants are guarding the aphids, it can be difficult for natural enemies to work effectively, so controlling the ants may be necessary.

Aphids on balsam fir. There are several ants in this photo that are tending the aphids.

Aphids on balsam fir. There are several ants in this photo that are tending the aphids.

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What is growing on that oak tree?

By Todd Lanigan, DNR Forest Health Specialist, Eau Claire, todd.lanigan@wisconsin.gov or 715-210-0150

This time of year, you may be noticing some large growths on oak leaves. You are either seeing oak apple gall and/or wool sower gall. These galls are formed by a small, stingless wasp, known as a Cynipid Wasp. 

For the oak apple gall, when the female lays her egg, she injects a growth regulator that causes the leaf tissue to form around the egg. When the larvae begin to feed for the wool sower gall, this causes the gall to form. The galls in both cases protect the developing wasps from the elements and predators. 

Oak apple galls are round and initially are green in color. Eventually, the gall turns brown as the wasp larva matures inside.

Oak apple gall growing on the underside of a leaf.

An oak apple gall

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Oak Shot Hole Leafminer And Spiny Oak Sawfly

By Linda Williams, DNR Forest Health Specialist, Woodruff, Linda.Williams@wisconsin.gov or  920-360-0665. 

Two very different insects are creating holes in oak leaves this spring, the oak shothole leafminer and the spiny oak sawfly. 

Oak shothole leafminer

In 2019 and 2020, many eastern U.S. states noted damage from this insect. While this is mostly a cosmetic issue for the tree, it can cause concern for homeowners and landowners when it appears that their trees are defoliated. The good news is that this damage rarely has an impact on the health of larger trees. 

Small holes in the leaf, often with similar holes on the both sides of the main vein, indicate damage from oak shothole leafminer adults.

Small holes in the leaf, often with similar holes on the both sides of the main vein, indicate damage from oak shothole leafminer adults.

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Oaks Hit Hard By Frost/Freeze Prior To Memorial Day

Written by: Linda Williams, DNR Forest Health Specialist, Woodruff, Linda.Williams@wisconsin.gov or 920-360-0665. 

A frost/freeze on the night of May 28 strongly impacted our oaks in areas of central and northern Wisconsin. Some leaves were completely killed while others had portions of the leaf that were impacted. Those leaves with some dead spots have continued to expand and grow but the dead parts of the leaf are causing them to curl and pucker. 

Oak leaves killed by the frost are brown, curled and puckered.

Oak leaves killed by the frost.

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Balsam Fir Needle Rust

By Linda Williams, DNR Forest Health Specialist, Woodruff, Linda.Williams@wisconsin.gov or 920-360-0665. 

Balsam fir needle rust is infecting current year needles on balsam fir trees in north-central Wisconsin. Balsam fir needle rust has white pustules that emerge from the lower surface of infected needles. Infected needles will turn yellow and the combination of white pustules and yellow needles gives the trees a pale, ghostly appearance from a distance.

Bright yellow needles are infected with balsam fir needle rust.

Bright yellow needles are infected with balsam fir needle rust.

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Pine Bark Adelgid Causes Needle Stunting

Linda Williams, DNR Forest Health Specialist, Woodruff, Linda.Williams@wisconsin.gov or 920-360-0665. 

Pine bark adelgids are tiny insects that suck the sap of white pines. Once they insert their mouthparts into the tree, they won’t move any more during their lifetime, so for protection, they grow a white, woolly covering around themselves. A young, white pine plantation in Vilas County is suffering severely stunted needles from the 2020 growing season due to very high populations of pine bark adelgid. 

All branch tips on this white pine sapling have needles that were stunted by heavy populations of pine bark adelgid.

All branch tips on this white pine sapling have needles that were stunted by heavy populations of pine bark adelgid.

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Giant Hogweed: Rare But Harmful

By Bernie Williams, DNR Invasive Plant Specialist. Bernadette.Williams@wisconsin.gov or 608-444-6948. 

Giant hogweed is a non-native, invasive plant that has gradually gained a foothold in the northeastern U.S. Once popular for its massive size and white umbrella-like flowers, it was introduced as an ornamental as early as 1917. Now known for its harmful blisters, it is recognized as a public health hazard and controlled wherever possible.

Characteristic purple blotches and white hairs on green stem of giant hogweed. Photo credit: Herkulesstaude_Fritz Geller-Grimm

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Watering Trees In A Drought

By Olivia Witthun, DNR Urban Forestry Coordinator, Plymouth, olivia.witthun@wisconsin.gov, 414-750-8744 

Photo credit: City of Minneapolis Forestry Division

Things just keep getting drier and it seems like there is no end in sight. The trees are thirsty, and they need your help!

Watering Newly Planted Trees

Newly planted trees need extra watering until they are established. The amount of water depends on tree size and on your soil type (sandy versus clay).

  • 1-2 weeks after planting: water daily.
  • 3-12 weeks after planting: water every 2 to 3 days.
  • After 12 weeks, water weekly until roots are established.

Watering Tips

  • Deep watering is best. Try to get the soil wet to a depth of at least 6 inches.

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Public Awareness Ideas For Watering Trees In A Drought

By Olivia Witthun, DNR Urban Forestry Coordinator, Plymouth, olivia.witthun@wisconsin.gov, 414-750-8744 

Most of you are doing your best to keep things watered, but you could always use some help. Below are a few ideas for public awareness and pleas to get homeowner assistance in watering trees. As always, contact your DNR Urban Forestry staff if you’d like more specific examples.  

  • Social media is a great avenue to get these types of messages out. Use your community’s Facebook, Twitter and other social platforms to your advantage.
  • Consider dropping off a doorhanger reminding folks to water trees. Perhaps work it into your watering schedule; each address you stop at gets a doorhanger.

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