Disease

Dutch elm disease is prevalent this year

Posted on by Kirsten Held

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.

Spruce needle rust

Posted on by Kirsten Held

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.

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

Posted on by Kirsten Held
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.

Venturia shoot blight in northern Wisconsin

Posted on by colleenrobinson
Sapling aspen with withered, drooping shoot killed by Venturia shoot blight.

Venturia shoot blighted aspen shoot. Photo by Gerred Carothers.

Venturia shoot blight has been observed throughout northern Wisconsin this summer. Venturia shoot blight is one of the most common fungal diseases of aspen and is favored by cool, wet spring weather. 

The pathogen rapidly kills expanding terminal and lateral shoots, causing shoots to wither and droop. It also causes leaf necrosis, appearing as black circles of varying sizes, necrotic curling at the margins, or complete leaf death. The disease is most damaging to seedling and sapling aspen, where it can reduce height growth and cause temporary stem crooking as lateral shoots are released and compete for apical dominance.  Disease control is unnecessary in a forest setting.

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

Black canker and willow scab on willow

Posted on by colleenrobinson
Black canker causes twig mortality and a sunken area on the branch. Photo by Mike Schuessler.

Black canker causes twig mortality and a sunken area on the branch. Photo by Mike Schuessler.

Do you have willow that is looking thin and sad this year?  In addition to some frost damage earlier this year, I’ve checked out several areas where black canker and willow scab are causing defoliation and fine branch mortality.  I’ve noticed this in Brown, Door, Kewaunee, Marinette, Oconto, and Waupaca counties.

Early in my career with the department I recall checking out a willow planting in Manitowoc County that had a lot of black canker killing the fine branches, but since then I haven’t run into it much.  Black canker starts by infecting a leaf but quickly moves into the petiole and into the twig where it causes a small sunken canker. This can cause the twig tip to wilt, shrivel, and die. Willow scab will also cause the twig tips to wilt, shrivel, and die. Willow scab and black canker can often be found affecting the same tree and are more common in years when we have a cool wet spring. 

New growth impacted by willow scab and black canker will shrivel and die.

New growth impacted by willow scab and black canker will shrivel and die.

Repeated defoliation of a tree due to black canker or willow scab can significantly impact growth and form because many branch tips will be killed. More information and pictures are available online by Cornell on black canker and willow scab. 

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

Oak wilt signs are showing up

Posted on by colleenrobinson
Oak leaves from an oak wilt infected tree. The outer portions of the leaf will be brown or have a water-soaked appearance. Part of the leaf remains green even though the leaf has dropped off the tree.

Oak leaves from an oak wilt infected tree. The outer portions of the leaf will be brown or have a water-soaked appearance. Part of the leaf remains green even though the leaf has dropped off the tree.

Trees that were infected with the oak wilt fungus this spring, (whether from overland spread by beetles or underground spread by connected root systems) are beginning to drop their leaves. Leaves can drop anytime between July and September. This wilting and dropping of the leaves happens fairly quickly, and trees can go from looking nice and healthy to having lost most of their leaves within just a few weeks. This year I saw my first wilting oaks on June 28, although in areas further south the leaf drop may have begun earlier. Oak wilt is a non-curable, fungal disease specific to oaks. Once the fungus infects a tree it will begin to spread outward from the roots of the infected tree through grafted roots and into the roots of neighboring oaks, eventually killing the neighboring oaks. In this way pockets of dead oak will be created as each year more oaks die. For more information on oak wilt biology, prevention, and control check out the WI DNR’s oak wilt page. 

Firewood from trees that have died from oak wilt will remain infectious for 1 full year (12 months) after the tree has died. There are many areas of northern Wisconsin where oak wilt is not common. Please do not move firewood long distances because you could move oak wilt into a new area.

Many northern counties don’t have oak wilt or have only a few known infections. This map shows townships in the north where oak wilt has been identified. In the red counties oak wilt is considered to be scattered throughout the county, although it will not be found in every stand.

Many northern counties don’t have oak wilt or have only a few known infections. This map shows townships in the north where oak wilt has been identified. In the red counties oak wilt is considered to be scattered throughout the county, although it will not be found in every stand.

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

Oak wilt identified near Sayner in Plum Lake Township, Vilas County

Posted on by colleenrobinson
Oak wilt fruiting body formed under the bark, shown here with the bark peeled away. The dark grey lump of stuff is the fruiting body which produces the spores.

Oak wilt fruiting body formed under the bark, shown here with the bark peeled away. The dark grey lump of stuff is the fruiting body which produces the spores.

I’ve identified oak wilt in Plum Lake Township, Vilas Co, west of Sayner. This is the first find of oak wilt in Plum Lake Township. The closest known oak wilt location is 6.7 miles from this new site. The tree rapidly dropped its leaves last July, and when it didn’t leaf out this spring the homeowner called me. Upon examining the tree I was able to find an oak wilt pressure pad, which is the fungal spore mat that forms under the bark and causes the bark to crack, which is how beetles can get access to the spores and move them to other oaks. 

Oak wilt is found throughout the counties shown in red. Where oak wilt is uncommon the townships where oak wilt has been identified are shaded in pink.

Oak wilt is found throughout the counties shown in red. Where oak wilt is uncommon the townships where oak wilt has been identified are shaded in pink.

The oak wilt map has been updated. Oak wilt is not common in our northern counties so the map highlights in pink the townships where oak wilt has been identified in the northern counties. The oak wilt guidelines for timber sales were updated about a year ago and list some exceptions and modifications for situations in which it is not necessary to implement the cutting restrictions during the high risk time period of the year (April 15 – July 15 in the north). 

Homeowners and those not doing timber sales should try to avoid pruning, wounding, or cutting oaks during the high risk time period of April 15 – July 15 in the north. This is the time of year when the beetles that can spread the spores overland will be attracted to fresh wounds on your trees; if you prune, wound, or cut your oaks during this period the beetles can introduce oak wilt to your tree. If it is necessary to prune, wound, or cut trees during that period, wound paint should be applied.

Oak wilt is always fatal to trees in the red oak group, which includes northern red oak, northern pin oak, and black oak. Trees that were infected with the oak wilt fungus this spring will begin rapidly dropping their leaves in July and August.

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

Storm damage in May and June

Posted on by colleenrobinson
Young trees and branches that are whipped by strong winds may have splitting bark on their branches or trunks. Although the trees will eventually grow over these wounds, the wounds will dry out and probably open up a bit more.

Young trees whipped by winds may have splitting bark on their branches or trunks. The trees will eventually grow over these, but first the wounds will dry out and open up a bit more.

Storms, storms, and more storms! It seems like we’ve had a lot of storms that brought severe weather this year. Storm damage to oaks at this time of year creates the risk of oak wilt introduction in new areas as the beetles that can spread oak wilt are attracted to the fresh wounds from the storm damage. Pine that is damaged by the storm can be infested by bark beetles, or blue stain can enter the wood via hail wounds, or Diplodia can kill branches that were damaged by wind or hail. When blowdown or tornado damage occurs it presents some additional forest health concerns with staining and decay. We have some information available online regarding storm damage, which currently highlights the May 16 tornado but applies to all tornado/wind damage to your trees.

Some of the storms during the past month are highlighted below.
Continue reading “Storm damage in May and June” →

Deciduous tree leaf loss

Posted on by colleenrobinson
Black, dead areas of leaf tissue on maple leaves caused by anthracnose.

Anthracnose on maple leaves. Photo by Joleen Stinson.

As anticipated, anthracnose is common on a number of deciduous tree species statewide this spring, especially maple and ash. Many of the maple samples we’ve seen also have tar spot. The cool, wet, humid conditions this spring were ideal for fungal leaf diseases. Anthracnose symptoms appear as patches of brown or black, dead leaf tissue which may cause leaves to curl or shrivel up as damage progresses. Trees may drop the infected leaves but will send out new leaves within a few weeks.

An aspen tree with less than half the leaves it should have because frost damage.

Aspen with thin crowns caused by frost damage. Photo by Bob DeBruyckere.

Damage to other species, including aspen, cottonwood and willow appears to have been caused by frost damage. These tree species likely became active and had the buds swell during the early warm up in February, then suffered damage to the buds and twigs from the cold weather thereafter. Although the damage was severe in some cases it seems that the trees produced new buds and are working on sending out additional leaves.

Significant dieback was noted in many locations around the state, including on some hybrid poplar in Shawano County, on trembling aspen in central and northern Oconto County, and on big toothed aspen in western Vilas County. We had reports of impacted aspen, cottonwood and willow from south central, southwest, central, west central and northcentral Wisconsin. Forest health specialists in Minnesota report similar damage.

Keep impacted trees healthy by watering (where possible) during hot and dry periods to help the trees recover.

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

White pine blister rust infections

Posted on by colleenrobinson
Spore-producing structure formed on edge of white pine blister rust canker in spring.

White pine blister rust fruit body.

White pine blister rust (Cronartium ribicola; WPBR), a naturalized pine rust disease, has been infecting white pine saplings in several northwest Wisconsin counties this spring. Although WPBR is common in the Lake States and can in some cases cause significant losses in white pine, taking several steps can help prevent infections before they start and manage them before damage occurs.

Like many foliar diseases, WPBR infections are promoted by moist and cool spring weather that results in persistent wetness on foliage; specifically, at least 2 days of wetness while air temperatures are under 68oF. Maintaining dense stocking (6×6) reduces incidence of infection by increasing the mortality of lower branches, most susceptible to infection. Similarly, successive pruning of lower branches beginning at age 5 to a minimum branch height of 9 ft. prevents leaf contact with moist surface vegetation and can increase airflow, hastening foliar drying. If caught early enough, infections can be stopped before reaching the main stem by pruning out flagging twigs and branches to at least 4 inches past the interior-most wilting needles; if the main stem is closer than 4 inches from the interior-most canker or wilted foliage, unmanageable stem infection may already have occurred and the tree cannot be saved. 

White pine sapling with significant blister rust infection causing resinous, sunken canker, and main stem girdling.

White pine sapling infected with blister rust. Photo by Kyle Young.

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