Northwest WI Forest Health

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.

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.

Venturia shoot blight in northern Wisconsin

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.

Spruce budworm defoliation is present

Spruce budworm defoliation is not as noticeable this year, although it is still present as you can see here with many needles missing.

Spruce budworm defoliation is not as noticeable this year, although it is still present as you can see here with many needles missing.

Spruce budworm damage is present this year but in many areas it is less noticeable than in past years. I believe this is due to a couple of things:

  1. The many storms we had this spring with heavy rainfall and strong winds may have washed some of the caterpillars out of the trees. They definitely washed budworm damaged needles off the tree. Damaged needles typically remain on the tree and turn a rusty brown, so not having these needles on the tree makes it less obvious where defoliation is present this year.
  2. Due to the constant rainfall this year, the growth on balsam fir and spruce seems to be quite good in general, which leads to additional green needles on the tree this year. This makes the trees look more green and less defoliated, but spruce budworm is still there.

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

Woolly elm aphid feeding

Woolly elm aphid feeding of American elm causes leaves to curl inward, become bumpy, and develop necrotic brown and yellow blotches.

Woolly elm aphid damage on leaves.

Feeding by woolly elm aphids has become apparent this summer, with light to moderate, but non-threatening levels of foliar damage on American elm.  Woolly elm aphids are just one species among a specialized group of native aphids called woolly aphids.

Learn about the woolly alder aphid in this month’s northeast forest health article. 

Woolly aphids are sucking insects that feed on leaves, buds, twigs, bark, and roots, but rarely cause significant injury to mature trees.  Feeding causes leaves to curl inward, become bumpy, and develop necrotic brown and yellow blotches.  A cottony mass of pear-shaped aphids with waxy, white stands can be observed under damaged leaves.  Honeydew secretions from aphid sap feeding can promote sooty mold growth on leaves, but causes little injury.

A cottony mass of pear-shaped aphids with waxy, white stands under a damaged American elm leaf.

Woolly elm aphids on underside of leaf.

Woolly aphids produce a waxy white covering, giving them a “woolly” appearance and providing a protective barrier from predators.  Having a complex life cycle, most woolly aphids produce multiple clonal generations each year and use two different host plant species, which vary by the particular species of woolly aphid.  Woolly elm aphid uses American elm and serviceberry as its host species.  In early summer, after two generations of female-only clones are produced—each living and feeding for about 1 month—some winged females from the second generation fly to serviceberry where they produce yet another generation of female-only clones that then migrate down to the serviceberry roots to form a root colony.  In early fall, after two more clonal generations of females are produced, some fourth generation winged females emerge from the root colonies and fly back to elm, where they produce a blended generation of both male and females that then mate.  The mated females lay one overwintering egg in a bark crack and die, completing the life cycle.     

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

Oak wilt signs are showing up

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.

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”

Tornado whips across northwest Wisconsin at unprecedented scale

Approximate storm path and forest damage area.

Tornado path map. Map by Paul Cigan & Benjaman Garret.

An EF3 tornado swept through northwest Wisconsin from southeast Polk County to southwest Price County on May 16, leveling many structures and whole forest stands, in what the National Weather Service has declared the longest tornado path on state record. Continue reading “Tornado whips across northwest Wisconsin at unprecedented scale”

Tamarack defoliation by larch casebearer

A patch of brown tamarack trees defoliated by larch casebearer caterpillars photographed during aerial survey in early June.

Larch casebearer defoliation visible from an aerial survey on June 7, 2017. Photo by Josh Haberstroh.

Tamarack defoliation by larch casebearer is evident in northcentral and northeastern Wisconsin again in 2017. The most severe defoliation occurred in Lincoln and Langlade counties, while more moderate defoliation was noted in Waupaca, Shawano and Oneida counties. I saw extensive damage in northern Wisconsin by this insect in 2014 but damage was much more localized and less severe in 2015 and no damage was documented in 2016.

Larch casebearer, Coleophora laricella, overwinters as young caterpillars and is able to start feeding as soon as the weather warms up in the spring. The caterpillars mine out the needles of tamarack causing them to turn brown by late spring. Tamarack trees will typically produce new needles after moderate or severe damage. Caterpillars pupate on the tree in early summer and moths mate and lay eggs in summer. A second round of feeding, which causes additional stress to the trees, occurs by young larvae in summer before they overwinter. Repeated defoliation can weaken the tree, making it more susceptible to mortality from eastern larch beetle.

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.