Disease

Storm damage in May and June

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

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

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.

Rhizosphaera needlecast on balsam fir

Rhizosphaera needlecast of fir produces rows of round black fruiting bodies on the needles. Photo by Colton Meinecke.

Rhizosphaera needlecast of fir produces rows of round black fruiting bodies on the needles. Photo by Colton Meinecke.

Rhizosphaera needlecast was found on balsam fir in Shawano County, with additional reports from Todd Lanigan (West Central WI) and Paul Cigan (Northwest WI). It causes chlorosis in the needles which drop off prematurely, giving the tree a thin appearance. This disease is related to the Rhizosphaera needlecast of spruce which you may be more familiar with. Literature indicates that it is most common on fir trees in shaded damp areas, or on trees that are under stress from other issues. You will see small black fruiting bodies on the undersides of the needles, although what really stands out is the thin foliage or off-color needles compared to other unaffected trees. 

Needles from the previous year have turned brown and will drop off prematurely due to Rhizosphaera needlecast.

Needles from the previous year have turned brown and will drop off prematurely due to Rhizosphaera needlecast.

Additional info can be found in this pest alert from the Forest Service.  

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

Oak wilt and hickory mortality Forest Health Fact Sheets are available

The forest health program is in the process of updating some of our publications as Forest Health Fact Sheets. These publications offer biology, impact, prevention and management information about specific threats to forest health. Our new oak wilt fact sheet and hickory dieback and mortality fact sheet are currently available on the DNR’s forest health oak wilt and bark beetle webpages and will be available in the DNR’s online publications catalog  in the near future. Enjoy!

Written by: Mike Hillstrom, forest health specialist, Wisconsin Dells (Michael.Hillstrom@Wisconsin.gov), 715-459-1371.

Phomopsis galls on northern red oak

Phomopsis galls are woody, lumpy swellings on the branches and main stem of this northern red oak tree.

Northern red oak with many phomopsis galls on the branches and on the main stem.

Phomopsis galls are large, woody galls caused by a fungus and can be unsightly on the branches of trees (people often notice them in the winter when leaves are off). They occur in hickories, maples, oaks and a few other species. In northeastern Wisconsin, I find them most commonly on hickory, but in some areas northern red oaks can be heavily galled. Counties where I’ve seen these large galls on northern red oak include Oconto, Oneida, Shawano and Vilas. Continue reading “Phomopsis galls on northern red oak”

Eastern spruce dwarf mistletoe

Eastern spruce dwarf mistletoe (Arceuthobium pusillum), is a parasitic flowering plant that can be very damaging to black spruce, although it can also attack other spruces. Occasionally you’ll see it on other species growing amidst spruce such as tamarack, white pine, red pine, jack pine, or balsam fir. Continue reading “Eastern spruce dwarf mistletoe”

Invasive insects and disease awareness month

Vin Vasive is the spokesman for invasive insects at USDA APHIS. He is made up of invasive species. This USDA APHIS poster was designed by Deb Levy Creative.

Vin Vasive is the spokesman for invasive insects at USDA APHIS. He is made up of invasive species. This USDA APHIS poster was designed by Deb Levy Creative.

April is invasive plant pest and disease awareness month, and May 21-27 is EAB awareness week.

It’s spring, and a good time to remember that invasive species can be easily moved long distances by unsuspecting citizens; maybe even you! All it takes to potentially start a new infestation is to move things we often like to take with us, but don’t know are a problem:

  • firewood,
  • infected or infested plant material,
  • an infected or infested piece of fruit, or
  • even a decorative piece of northwoods style furniture that hasn’t been properly treated to kill pests hiding inside.

Take a moment to think about whether you are unknowingly moving items that could harbor pests. The Hungry Pests website lists things you can do to prevent the spread of invasive species, whether you’re a birdwatcher, gardener, hunter, logger, or anyone. Check it out! While you’re there check out some short videos of their “spokesman” Vin Vasive, who has gotten much creepier over the years. 

Help spread the word

Coming up, May 21-27 is emerald ash borer awareness week, which is right before the Memorial Day holiday, when lots of travelling, camping, and opening up of summer cabins occurs. The Don’t Move Firewood website has a nice video of how to identify an EAB infested tree. More detailed videos are also available at dnr.wi.gov, keyword “forest health.” If you would like some examples of outreach tools or publications you can use to promote EAB awareness, check out the Don’t Move Firewood website; there you’ll find games for kids, an EAB craft project, videos, press releases, and news articles from past years. 

Written by: Linda Williams, forest health specialist, Green Bay, (Linda.Williams@wisconsin.gov), 920-662-5172. Categories: FH, UF. Tags: Statewide FH, Insect, Pest