Disease

Updated forest health fact sheet – conifer bark beetle

Spruce beetle (Dendroctonus rufipennis)

Spruce beetle (Dendroctonus rufipennis). Photo: Edward H. Holsten, USDA FS, Bugwood.org

The Division of Forestry’s forest health team recently updated another forest health fact sheet about conifer bark beetles. Like the oak wilt and hickory dieback and mortality fact sheets revised earlier this year, the conifer bark beetle publication offers information about biology, impact, prevention and management of the insects. The conifer bark beetle fact sheet is available on the DNR’s forest health webpage.

Written by: Mike Hillstrom, forest health specialist, Wisconsin Dells. Michael.Hillstrom@Wisconsin.gov; 608-513-7690

Is it SNEED or wet soils and nutrient deficiency?

New needles are green (circled in red), and older needles are yellow (circled in blue) on this spruce. Spruce needles that are yellow, with no visible fruiting bodies on the needles, may be suffering from nutrient deficiency due to the constant wet soils this year, or they may have a disease called SNEED (spruce needle drop). Photo by Linda Williams, WI DNR.

New needles are green (circled in red), and older needles are yellow (circled in blue) on this spruce. Spruce needles that are yellow with no visible fruiting bodies on the needles may be suffering from nutrient deficiency due to constant wet soils this year, or they may have a fungal disease called SNEED (spruce needle drop). Photo by Linda Williams, WI DNR.

In late summer and early fall I had a few calls about younger spruce with yellow needles.  These trees were typically 8-20 years old and were a very yellow color, with new foliage emerging a green color but quickly fading to yellow.  There are two things that came to mind this year.  The first thought is that we’ve had a very wet year.  All year long roots were often in saturated or very moist soil. Consequently. the yellowing could be a sign of nutrient deficiency, specifically nitrogen, due to the saturated soils.  The second possibility is a disease called SNEED (an abbreviation for ‘spruce needle drop’), which I typically see on heavier soils. 

SNEED in spruce is thought to be caused by the fungus Setomalonomma holmii.  Pathogenicity of the fungus has not been proven, but it is the primary fungus present on trees with a particular suite of symptoms.  Spruce with SNEED have current year needles that are a nice green color, but older needles will be yellow or yellow/green in color.  Black fruiting bodies will look like pepper sprinkled generously on the twigs of the affected branches.  Old needles, although not showing any fruiting bodies, will drop from the tree prematurely, and repeated years of this will cause the tree to thin, decline, and can lead to mortality.  I’ve seen this primarily in plantations of white spruce on heavy soils, but have also seen it in blue spruce plantations; it’s reported in Norway spruce as well.  I don’t know of any sure-fire chemical options to prevent infection or to help the trees recover.  Management typically involves removing the most affected trees in the plantation, minimizing stress, and minimizing standing water or waterlogged soils where possible. 

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

Of historical interest…

Past reports from the 1992 and 1967 WI DNR Forest Health Annual Reports

25 years ago – 1992

European fruit lecanium (Parthenolecanium corni (Bouche))

Heavy infestations of this scale insect were reported on sugar maple twigs in Vilas and Price counties.

Jack pine budworm (Choristoneura pinus (Rohwer))         

The outbreak in the northwestern counties, which began in 1991, exploded this year (Figure 16). Over 114,000 acres of jack pine were heavily defoliated in Douglas, Bayfield, Washburn and Burnett counties. Egg mass surveys indicate extremely high numbers of jack pine budworm. The area of defoliation may increase in 1993. The present defoliation is not expected to cause significant mortality except in Highland Township, but another year of heavy defoliation in the same stands could cause 10-15 percent mortality. In Highland Township, Douglas County, extremely severe feeding produced significant. mortality and top dieback on several thousand acres of jack pine. Most of these stands are being harvested this winter. Moderate to heavy defoliation also occurred in Jackson, Juneau, Eau Claire, Marinette (1,650 acres), Vilas (2,960 acres) and Oconto counties. In Marinette County, 20 acres of 70-year-old jack pine were cut to release young jack pine and white pine. Jack pine budworm was causing severe top mortality. Evidence of budworm in the northern portion of the Monroe County Forest was observed on 35-40 year old jack pine (Sections 4, 9,16, T19N, R3W). DNR foresters have silvicultural guidelines available to manage budworm-prone jack pine stands.”

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Oak wilt detected in Sheboygan County; additional finds in northern WI

Alt text: Oak leaf from the first oak wilt detection site in Sheboygan County, showing bronzing coloration characteristic of oak wilt infection. Photo: William McKnee, WI DNR

Oak leaf from the first oak wilt detection site in Sheboygan County, showing bronzing coloration characteristic of oak wilt infection. Photo: William McKnee, WI DNR

Oak wilt, a deadly fungal disease affecting the red oak group, was recently detected in Sheboygan County for the first time. Wood samples were collected from adjacent symptomatic oak trees on the Kettle Moraine State Forest – Northern Unit in the Town of Mitchell after the trees were spotted by DNR Forestry staff. The presence of Ceratocystis fagacearum, the fungus causing oak wilt, was confirmed through a DNA test done at the DNR Forest Health Lab and DNA sequencing done at the UW-Madison Biotechnology Center. On-the-ground control options are currently being examined.

Oak wilt is a common disease in the southern two-thirds of the state, but has been

Map of counties where oak wilt has been detected, with the recent Sheboygan County confirmation shown in orange.

Map of counties where oak wilt has been detected, with the recent Sheboygan County confirmation shown in orange.

increasingly found in the northern counties. DNR staff have recently reported first community detections in these northern counties already known to have the disease:

  • Langlade County – Town of Langlade
  • Sawyer County – Town of Edgewater
  • Washburn County – Town of Stone Lake

Oak wilt has been found in all Wisconsin counties except Ashland, Bayfield, Calumet, Door, Douglas, Forest, Iron, Kewaunee, Manitowoc and Taylor.

Additional information about oak wilt can be found at the DNR Forest Health website.

Written by Bill McNee, DNR Forest Health Specialist, Oshkosh.  Bill.McNee@wisconsin.gov; 920-360-0942

 

Oak wilt continues to be found in the north

In this photo two oak trees have died from oak wilt (yellow dots). One tree is currently wilting and dropping its leaves (purple dot).

In this photo two oak trees have died from oak wilt (yellow dots). One tree is currently wilting and dropping its leaves (purple dot).

In August, I reported that we’d found oak wilt in Cloverland Township in Vilas County, in Arbor Vitae Township northeast of Woodruff, (on the southern border of Boulder Junction Township), and along Nabish Lake Road in Boulder Junction and Plum Lake Townships.

So, what’s new since then? Another tree killed by oak wilt was identified on the western side of Plum Lake in Plum Lake Township in Vilas County; another tree died in Washington Township just north of the city of Eagle River. I’m still waiting on results from a suspicious tree in northern Three Lakes Township in Oneida County. In many cases spring storms, which occurred during the high-risk period for overland transmission of oak wilt, were to blame for new oak wilt infections. But in some cases, disease was due to logging or pruning that occurred during the high-risk period for overland transmission of oak wilt. It’s important to know where oak wilt is and to minimize your risk.

For more information, visit the DNR oak wilt web page.

 

Continue reading “Oak wilt continues to be found in the north”

Oak leaves dropping, but it’s not oak wilt!

This oak tree near Pelican Lake dropped leaves due to Cylindrosporium both in 2011 and again this year. This will not cause mortality of the tree.

This oak tree near Pelican Lake dropped leaves due to Cylindrosporium both in 2011 and again this year. This will not cause mortality of the tree.

The small round leaf spots characteristic of infection by Cylindrosporium fungi

The small round leaf spots characteristic of infection by Cylindrosporium fungi.

In September and October, I visited several northern red oaks that were dropping leaves, but none of them looked like they had oak wilt. The dropped leaves were still green but had many perfectly round tan dots on their surface. I collected some leaves and sent them into the lab to verify the causal agent. One of these trees had shown similar symptoms in 2011. At that time, Brian Schwingle (who has since taken his forest health skills to the Minnesota DNR) looked at it and diagnosed Cylindrosporium leaf spot. I suspect the same this year. I’ve found trees of all ages with similar leaf spots in Marinette, Oconto, Oneida, Vilas, and Waupaca counties. Impacted trees often dropped some of the infected leaves, although a lot of green leaves (with additional leaf spots) remained on the tree. These trees should leaf out normally next year.

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

What is causing hardwood species to appear off-color?

Numerous issues are causing various hardwood species to become off-color this summer.  Below I’ve listed a few issues that I’m seeing.  Most of these issues do not require any control or any mitigation if your trees are showing these symptoms.

Anthracnose causes irregular dead areas on ash leaflets.

 

Anthracnose – irregular dead brown blotches on oak leaves and ash leaflets, caused by the fungal leaf disease anthracnose, is making some oaks and ash appear to be browning.  Phone calls with concerns about dying trees have been coming in.  Symptoms are typically worse in the lower crowns, and the ash I’ve seen with this issue in Marinette, Oconto, and Vilas Counties have very thin looking crowns.

 

Browning areas on this aspen leaf are caused by aspen blotch miner.

Browning areas on this aspen leaf are caused by aspen blotch miner.

Aspen blotch miner – all ages of trembling aspen are being impacted by aspen blotch miner this year.  Aspen crowns appear thin, leaves appear off-color from a distance, “blisters” form on the underside of the leaf, and eventually the leaves curl and brown of the leaves.  This is the 4th year in a row that I’ve noticed defoliation by this insect.  This year, similar to past years, I’ve seen it in Oconto, Marinette, Florence, Forest, Oneida, and Vilas Counties.  Tiny larvae spend their entire life feeding within the leaf and pupate within the area that they mined out.  Moths emerge in August and spend the winter in a protected place.

The winding galleries of aspen leafminer make the tree appear grey from a distance.

The winding galleries of aspen leafminer make the tree appear grey from a distance.

 

 

Aspen leaf miner – for those leaves that aren’t heavily infested with aspen blotchminer, they are often infested with aspen leaf miner.  Aspen leafminer is another tiny larvae that spends its life feeding within the leaf, but they create picturesque winding trails that give the leaves a pale appearance.

 

Balsam poplar browning – a couple of things are going on with the Balsam poplar in Brown and Oconto Counties, including a leaf disease and aspen blotch miner.  The trees are thinnest in the lower crowns, but the upper portions don’t look too hot either.

This birch leaf shows both the feeding of Japanese beetles (which don’t eat the veins of the leaf), and a brown blotch where birch leafminer was feeding.

This birch leaf shows both the feeding of Japanese beetles (which don’t eat the veins of the leaf), and a brown blotch where birch leafminer was feeding.

Birch dropping leaves – every year about this time birch will drop a portion of their leaves.  Many of those leaves don’t appear to have much damage on them.  But there is certainly leaf damage if you look closely at birch.  The primary issue that I’ve been seeing this year in Brown, Oconto, Oneida, Shawano and Vilas Counties is from birch leafminer.  Dead blotches on the leaves may make you think anthracnose, but holding the leaves up to the light you will discover you can see through them and see signs of insect activity inside the leaves.

Birch look brown – defoliation from Japanese beetle in Minocqua/Woodruff area is causing the birch to appear tan.  Defoliation is more significant in the lower canopy, but some trees are heavily defoliated top to bottom.  Japanese beetle is something that you may want to do some treatments for.  There are many options for treatments, whether excluding them with netting, or using insecticides against the adults, using traps for the adults, or using insecticides or fungal biocontrol against the larvae.           UW Extension has a great document with more info on Japanese beetle control.

A young black cherry turns red. While some are being defoliated by lacebugs (causing them to turn red), others like this one have very little defoliation.

A young black cherry turns red. While some are being defoliated by lacebugs (causing them to turn red), others like this one have very little defoliation.

Cherry lacewing and cherry turning red – I’m not quite sure what’s going on with all of the cherry.  Some of them are turning reddish in color because they are being defoliated by Cherry Lacebug (Oconto County), but others don’t seem to have any damage that I see (Marinette and Oconto Counties), so I’m not sure why they’re turning red.

Maple early fall color – check out Todd Lanigan’s article  which highlights the high water levels that are causing stress to lowland trees.  Many maples growing in these lowlands are already turning a rich shade of red due to water stress.

Brown blotches on these oak leaves are not anthracnose. The tiny oak leafminer lives within the leaf, feeding on the leaf material. The damaged area eventually turns brown.

Brown blotches on these oak leaves are not anthracnose. The tiny oak leafminer lives within the leaf, feeding on the leaf material. The damaged area eventually turns brown.

 

Oak leafminer – in Minocqua/Woodruff area I was noticing some oaks were looking a bit brown, which I assumed was probably anthracnose.  Always good to double check these things!  Once I stopped to check it out I discovered activity from oak leafminer was to blame, causing dead brown areas where the insects feed within the leaf.

 

Defoliation by oak skeletonizer will leave a layer of cells, which appear like parchment paper if you hold the leaf up to the light.

Defoliation by oak skeletonizer will leave a layer of cells, which appear like parchment paper if you hold the leaf up to the light.

 

 

 

Oak skeletonizer – scattered light levels of defoliation have been seen in nearly every county in Northeast and East Central Wisconsin.  Oak skeletonizer defoliates oak leaves by scraping off a single layer of the leaf, leaving a parchment-like layer on the leaf which turns pale tan.  Holding these leaves up to the light makes it clear that they’re defoliated.

A willow leaf is brown where willow flea weevil larvae have been feeding inside the leaves.

A willow leaf is brown where willow flea weevil larvae have been feeding inside the leaves.

 

Willow browning – although we started this spring with some willow scab that caused significant defoliation, the current issue is the leafmining action of the larvae of willow flea weevil.  This is the fourth consecutive year that Brown, Calumet, Marinette, Shawano, and Oconto Counties have experienced significant defoliation of willow from this insect.  I’ve also noted this in a few willow in Florence and Langlade Counties this year.

 

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

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.