Author: Kirsten Held

Additional oak wilt found in several areas in Vilas County

A number of new oak wilt infections have been identified in Vilas County this summer.  I’m waiting on results for a few more samples, and have several more trees to go and collect samples from, so there will probably be additional reports to come.

Cloverland Township, Vilas County, had its first oak wilt identified this year.  Unfortunately, oak wilt was first introduced to this site last year when the harvest extended into the high risk period, and the storm damage that we had in May allowed oak wilt to infect many new trees at the site this spring.

In Arbor Vitae Township, northeast of Woodruff, there are a number of new sites where oak wilt has been identified; some of these are right on the southern border of Boulder Junction Township.  And several wilting trees have been identified along Nabish Lake Rd in Boulder Junction and Plum Lake Townships.

As I said, I’m still waiting on a few more results, as well as needing to collect from a few trees that were recently reported to me.  Oak wilt is generally not common in the northwoods so if you see wilting oaks in July or August, please report them.  To minimize new infections of oak wilt it’s important not to prune, wound, or harvest during the high risk period in the spring, April 15 – July 15 in the north.  For more information about minimizing the risk of overland spread of oak wilt, or for info on controlling oak wilt infections that are already present, check out the Wisconsin DNR oak wilt page.

Written by: Linda Williams, forest health specialist, Woodruff, (Linda.Williams@wisconsin.gov), 715-356-5211 x232.

Oak wilt vs. leaf diseases: Can you tell the difference?

Oak wilt symptoms are active right now, but so are several other oak leaf diseases.  Can you tell the difference?

Trees with oak wilt will suddenly start to drop their leaves in July and August.  These leaves will be either tan or a water-soaked greenish color away from the petiole (leaf stem).  Near the petiole there will often be an area that is still green, even though the leaf has fallen to the ground.  Symptoms typically start near the top of the tree and progress downwards.

Leaves dropped from a tree dying from oak wilt. Note the discoloration on the distal portions of the leaf, while the petiole area is still green.

Leaves dropped from a tree dying from oak wilt. Note the discoloration on the distal portions of the leaf, while the petiole area is still green.

Oak wilt leaves often drop from the top of the tree first.

Oak wilt leaves often drop from the top of the tree first.

Anthracnose is a fungal leaf disease that is quite common this year due to the wet weather that we’ve had.  Anthracnose is not fatal to the tree and the tree will hold these leaves throughout the season.  Irregular areas of the leaf will be dead, and if this infection occurred when the leaf was expanding the leaf will often end up misshapen or puckered.

Anthracnose causes irregular dead blotches on the leaf.

Anthracnose causes irregular dead blotches on the leaf.

Tubakia is another leaf disease that we will sometimes see.  Symptoms are typically worse in the lower canopy.  Leaves may drop from the tree but the pattern of mortality on the leaf will be different than what you see with oak wilt.

This oak is being affected by Tubakia, a fungal leaf disease. Symptoms are significantly worse in the lower canopy.

This oak is being affected by Tubakia, a fungal leaf disease. Symptoms are significantly worse in the lower canopy.

Written by: Linda Williams, forest health specialist, Woodruff, (Linda.Williams@wisconsin.gov), 715-356-5211 x232.

Dutch elm disease is prevalent this year

Dutch elm disease seems to be quite prevalent around the state this year, including the northwoods.  Symptoms, including whole tree yellowing and wilting have been occurring this summer, and will continue into this fall.  Dutch elm disease is an exotic fungal disease that is spread by the elm bark beetle and can spread underground through root grafts as well.  Since bark beetles are generally not attracted to smaller trees (sapling to small pole size) people often get their hopes up that their small elms have “escaped” and will survive and grow to maturity.  Unfortunately, as soon as the trees are large enough for the bark beetles to be interested in them the trees may become infected with Dutch elm disease.  The first symptom you will see is usually a single branch on which the leaves turn yellow and die.  The rest of the tree will die shortly after that.  Elm trees attempt to fight the fungus by walling off the portion of the tree where the fungus is located but this can lead the tree to self-induced water deprivation and death.  More info on Dutch elm disease, including useful pictures, can be found in the U.S. Forest Service document How To Identify and Manage Dutch Elm Disease.

Dutch elm disease is spread by elm bark beetles, which create artistic galleries under the bark of the tree.

Dutch elm disease is spread by elm bark beetles, which create artistic galleries under the bark of the tree.

Chemical injections can protect single trees, and some communities in North America still have large stately elms due to this strategy.  For new plantings, there are some disease resistant cultivars (those crossed with other elm species) and some disease “tolerant” cultivars of American elm which tolerate the disease without completely killing themselves.

Written by: Linda Williams, forest health specialist, Woodruff, (Linda.Williams@wisconsin.gov), 715-356-5211 x232.

Gypsy Moth Defoliation in Burnett County

An isolated outbreak of gypsy moth was documented on private property in southeastern Burnett County in July.  The origin of this population was most likely unintentional movement of outdoor items (e.g., R.V. campers) infested with gypsy moth life stages (e.g., egg masses) from an area where gypsy moth is established.  The severity of gypsy moth defoliation ranged from light to heavy across the 60 acre mixed species woodland.  Aspen was the most heavily defoliated species, with a 7 acre block of 15 year old aspen sustaining over 75% defoliation.  Surprisingly, adult gypsy moths were already flying, and younger caterpillars were still feeding. This was several weeks earlier in the season than normal moth flight would be expected in the state’s north, possibly owing to strong competition between caterpillars within this high population.  Burnett County is currently not quarantined for a gypsy moth and the pest is not considered established there.

Gypsy moth caterpillars seeking daytime protection from predators and sunlight on an aspen in the understory.

Gypsy moth caterpillars (Photo by Paul Cigan)

The Slow the Spread program is considering an aerial spray treatment of this property next year to control the population.  This isolated outbreak, several counties west of the contiguous quarantined area, provides a good reminder of the important role of human-assisted spread of gypsy moth to new areas – and a reminder of the opportunities to prevent such introductions.  Landowners and forestry professionals can help prevent gypsy moth spread by inspecting and cleaning outdoor items when traveling from quarantined to non-quarantined counties, keeping firewood local, and by following other gypsy moth quarantine regulations and reasonable precautions.  More information about gypsy moth can be found at gypsymoth.wi.gov.

Written by Paul Cigan, forest health specialist, Hayward (Paul.Cigan@Wisconsin.gov), 715-416-4920.

Elm sawfly with uncommon pink coloration

Elm sawfly is the largest sawfly found in North America and has the disturbing habit of falling out of trees when you walk under the tree.  They feed on willow and elm, although in Wisconsin I’ve only seen them causing noticeable defoliation on willow.  They may also feed on birch, aspen, basswood, and maple.  Most people don’t notice the damage until the larvae begin to migrate down and gather near the base of the tree.  Larvae will overwinter as pupae on the ground and emerge as adults the following year.

Pink form of the elm sawfly larvae crawls on the bark of a tree. Photo by Ricky Keller.

Elm sawfly larvae are typically yellow; it is uncommon to find the pink form. (Photo by Ricky Keller)

Larvae grow 1 ½ – 2 inches long and are usually a bright yellow color with a black strip down their back, although occasionally the pink form is found.  Adults are a large, dark brown sawfly that looks like a cross between a horse fly and a wasp.  Usually defoliation is localized to a single tree or group of trees.  Spraying a general insecticide or soapy water should kill these sawflies if you think control is warranted, but these late season defoliators rarely do serious damage to the trees that they defoliate.

HHere you can see how large elm sawfly larvae are, and there are some slight color differences in these. Photo by Chris Plzak.ere you can see how large elm sawfly larvae are, and there are some slight color differences in these.  (Photo by Chris Plzak)

 

 

 

 

Written by: Linda Williams, forest health specialist, Woodruff, (Linda.Williams@wisconsin.gov), 715-356-5211 x232.

Spruce needle rust

Spruce trees turn orangish or pinkish when spruce needle rust is sporulating.

In some areas of the northwoods, the blue spruce are turning pink or orange, and the black spruce and white spruce are turning pale yellow.  What is going on?  This is spruce needle rust, which infects the current year needles.  Problems were noted in northern counties in 2013, 2014, 2015, and now again this year (Forest, Oneida, Vilas Counties).  This fungus enjoys a moist spring, so this year it’s doing well.  As a rust it has an alternate host, probably a shrub in the heath family like Labrador Tea.  The infected needles will drop prematurely.  No treatment “cure” is available for the already infected needles.  Preventative fungicide treatments for yard trees could be done next spring and early summer to protect new emerging needles, but must be done before symptoms appear.  Repeated treatments are necessary as the fungicide must coat the needle to protect it and has to be reapplied after it washes off or weathers off.

Spore pustules of the spruce needle rust fungus erupt from spruce needles.

Spore pustules of the spruce needle rust fungus erupt from spruce needles.

 

Written by: Linda Williams, forest health specialist, Woodruff, (Linda.Williams@wisconsin.gov), 715-356-5211 x232.

Japanese Beetle Damage Extensive in 2017

Japanese beetles are abundant and causing extensive damage to many species of plants in 2017. Although many landowners in southern Wisconsin have experienced severe damage in the past, this is the first time many in central and northern Wisconsin have experienced an outbreak. The beetles are so common this year in part because populations have recovered after the droughts a few years ago. Many reports are also coming in from newly-invaded areas in northern Wisconsin.  Linda Williams noted heavy populations and significant defoliation to birch in the Minocqua/Woodruff area, and growing populations in the Rhinelander area.

Japanese beetles are pests both as larvae and adults. Larvae feed on roots of turf and ornamentals causing pale, dead patches that eventually combine.  Adult beetles feed on foliage and flowers of many plant species including trees, fruits, vegetables and weeds.  Linden, birch, crabapple, mountain ash, Norway maple and Japanese maple are favorite host trees.  Adults eat between the veins causing leaves to look lace-like.  Trees severely damaged turn brown and become partially defoliated.

Adult Japanese beetles feed on a wide-variety of plants causing leaves to have a lace-like appearance.

Adult Japanese beetles feed on a wide-variety of plants causing leaves to have a lace-like appearance.

 

Many treatment options are available, but in outbreak years landowners may be resigned to limiting damage to their favorite plants.

Control options include:

  • Remove beetles by hand and squish or put in soapy water.
  • Spray beetles with an insecticide labelled for Japanese beetle control.
  • Do not irrigate during peak adult flight to make the soil less attractive for egg laying.
  • Apply carbaryl (Sevin), clothiandin (Arena) or trichlorfon to the soil in early to mid-August to kill larvae.
  • Apply imidacloprid, chorantraniliprole, clothianidin and thiamethoxam to soil from May to early July to kill larvae.

Some common control options are not recommended. Traps are typically ineffective as they attract more beetles to the area. Biological control of grubs using milky spore disease or others biologicals is often inconsistent.

For more information see UW-Extension’s fact sheet.

Written by Mike Hillstrom, forest health specialist, Fitchburg (Michael.Hillstrom@Wisconsin.gov), 608-513-7690.

Heavy Diplodia shoot blight following hail storm in Polk and St. Croix Counties

Stand of mature red pine with heavy crown browning from Diplodia shoot blight following a hail storm in June.

Hail-induced Diplodia shoot blight. (Photo by Paul Cigan)

Red pine stands in a localized area of southwestern Polk and northwestern St. Croix counties are displaying heavy crown browning, shoot blight, and tree mortality following a June hail storm that left many red pine injured in local plantations.  In many stands, the entire crown on most overstory trees has turned brown, leaving behind a stark illustration of just how damaging the fungal pathogen, Diplodia pinea, can be to red pine following hail storms.  Bark-breaking hail wounds on red pine of all ages serve as entry points for wind- and rain-dispersed spores of the disease.  Wet and warm spring and summer weather, similar to conditions observed this year, can promote spore production and intensify infections.  Cankers soon develop at infected wound sites, enlarge, and may cause death of branches and terminal shoots within weeks.  Landowners affected by hail and Diplodia damage should contact their local DNR forester to evaluate the extent and severity of damage, discuss management options, and identify contacts in wood-utilizing industries to coordinate salvage operations on smaller acreages.

Bleeding canker caused by Diplodia at the site of a hail wound on red pine branch.

Bleeding Diplodia canker

Generally, salvage and pre-salvage harvest efforts should prioritize the removal of pine with greater than 50% crown browning and those with at least 3 feet of terminal leader dieback.  Trees with less damage should be monitored for bark beetle attack for two years after thinning and be promptly removed if crowns begin browning due to bark beetle attack.  To reduce bark beetle attack during harvesting March through August, remove all material greater than 2 inches in diameter within three weeks of harvest.

 

Written by Paul Cigan, forest health specialist, Hayward (Paul.Cigan@Wisconsin.gov), 715-416-4920.

Collect seeds in Wisconsin for us

Are you looking for a fun activity for yourself or your family this fall? Why not spend some time helping the Wisconsin reforestation team fill our seed coffers.

The Wisconsin state nurseries have been producing seedlings since 1911. In that time, there have been many changes in personnel, growing techniques and distribution methods. However, something that has remained constant is the source of those seedlings: Wisconsin seeds. The vast majority of seedlings produced at the Wisconsin state nurseries originate from seed collected from native trees. From the tiny, pepper-like seed of aspen to the large, husky black walnut, the reforestation staff at the nurseries collects, cleans and stores hundreds of pounds of more than 30 varieties of native tree and shrub seed every year.

While we are able to satisfy some of our needs, we rely heavily on members of the public to collect for us as well. For those interested in becoming seed collectors, we publish a newsletter every fall. Information on seed collection and the 2017 Seed Collector’s Newsletter can be found on the DNR website. Our staff is always available to answer questions about seed collection or any other reforestation topic.

Head outdoors this fall. You will be amazed at how much fun it is to crawl around in the woods for a few hours picking up acorns or walnuts!

Written by Jeremiah Auer, Wisconsin DNR forest regeneration specialist, (715) 459-1999, Jeremiah.Auer@wisconsin.gov

Preparing your site for tree planting

Now is a great time to start planning for tree planting next spring and site preparation is a critical component of that planning. During the end of the growing season, while the landscape is in full bloom and lush, landowners are better able to visualize opportunities to develop wildlife habitat, provide visual barriers, and improve aesthetic qualities on their property. These timely observations and some research will provide the necessary information to determine how newly-established trees will impact their property. Continue reading “Preparing your site for tree planting”