Disease

Sign Up For Oak Wilt Vector Emergence Estimate Daily Email Notification

By Kyoko Scanlon, Forest Pathologist, Fitchburg, Kyoko.Scanlon@wisconsin.gov or 608-235-7532

Oak wilt is a serious disease that occurs when insects carrying oak wilt fungal spores land on a healthy oak tree’s fresh wound. To prevent oak wilt infections, it is important to avoid pruning, wounding and harvesting oaks when these insects are abundant, generally from April through July. Predicting exactly when these insects start to emerge in the spring can be difficult as their emergence is highly weather-dependent, and spring weather varies significantly from year to year.

In 2021, the Oak Wilt Vectors Emergence Thermal Model tool, a unique estimation tool, was developed as a collaborative project between the University of Wisconsin-Madison and the Wisconsin DNR to help with these predictions. This online tool offers localized recommendations about the emergence status of the two most important insects that transmit oak wilt in Wisconsin. The interface uses a degree-day model (Jagemann et al., 2018) constructed from insect trapping data and actual weather data, which helps refine the beginning of the periods when you should avoid pruning, wounding or harvesting oaks.

A screen shot of the oak wilt vector emergence homepage where the location and date data is entered to model growing degree days.

UW Extension’s Oak Wilt Vectors Emergence Thermal Model can help predict when oak wilt vectors may be coming. Photo Credit: UW Extension

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Bur Oak Blight Confirmed In Fond du Lac County

By Bill McNee, DNR Forest Health Specialist, Oshkosh, bill.mcnee@wisconsin.gov

Recent lab examination has confirmed bur oak blight in Fond du Lac County. The disease affects only bur oaks and is caused by the fungus, Tubakia iowensis.

Map of Wisconsin counties where bur oak blight has been confirmed.

Map of counties where bur oak blight has been confirmed. Map credit: Wisconsin DNR.

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Moving Firewood Can Spread Invasive Species

An image of an insect walking away from burning firewood in a forest with the caption, “Buy it where you burn it.”

Don’t Move Firewood, The Nature Conservancy

October is Firewood Month! Help prevent the spread of invasive insects and diseases by buying firewood where you burn it.

Firewood Scout can help you find local firewood for sale.

See the DNR website for more information on invasive species and forest health. Continue reading “Moving Firewood Can Spread Invasive Species”

Check Conifer Trees For Severe Root Disease

By Michael Hillstrom, DNR Forest Health Specialist, Fitchburg, michael.hillstrom@wisconsin.gov

Considered one of the most destructive diseases of conifers in the northern hemisphere, Heterobasidion root disease (HRD) is very difficult to control once established in a forest. Infestation of a conifer stand may significantly impact stand management, making early detection essential.

A pine stump with a Heterobasidion root disease fruit body with old brown growth in the center and new, bright white growth along the edges.

A Heterobasidion root disease (HRD) fruit body with new white growth observed in the fall. Photo: Wisconsin DNR

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Aspen Leaf Diseases Responsible For Thin Crowns

By Linda Williams, Forest Health Specialist, Woodruff, Linda.Williams@wisconsin.gov or 920-360-0665

Northeastern Wisconsin saw thin and defoliated aspen trees in early summer this year due to a few diseases. A sample from Marinette County turned up Alternaria leaf and stem blight, Venturia leaf and shoot blight and Phyllosticta leaf spot. Venturia was also noted in central Wisconsin, causing shoot blight, which kills the terminal leaders (growth buds) of young aspen.

Aspen trees with leaves damaged by leaf disease..

Aspen crowns were thin due to multiple leaf diseases. Photo: Wisconsin DNR

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Eyes On Beech Leaf Disease

By Ethan Wachendorf, Forest Health Lab Technician, Fitchburg, ethan.wachendorf@wisconsin.gov or 608-273-6276

Forest owners and land managers should be on the lookout for beech leaf disease (BLD), a destructive disease of beech trees. The disease is primarily found on American beech (Fagus grandifolia) but can also be found on ornamental species like European, Oriental and Chinese beech (F. sylvatica, F. orientalis and F. engleriana).

Multiple symptomatic beech leaves showing dark striping between lateral veins on the underside of the canopy.

Symptomatic striping seen from under the canopy. This photo was taken in Ohio. Photo: Wisconsin DNR

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Troubled White Pines: Disease And Thinning

By Linda Williams, DNR Forest Health Specialist, Woodruff, Linda.Williams@wisconsin.gov or 920-360-0665

Scattered white pine in Oneida and Vilas counties had significant amounts of needles that turned light tan or pale yellow this spring. Those needles have mostly dropped from trees, leaving them quite thin.

Some white pine needles are tan colored due to Lophodermium infection.

Tan-colored needles infected with Lophodermium. Photo: Wisconsin DNR

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Tubakia Leaf Disease Mimicking Oak Wilt

By Linda Williams, DNR Forest Health Specialist, Woodruff, Linda.Williams@wisconsin.gov or 920-360-0665

Tubakia leaf spot (Tubakia dryina) is a leaf disease that typically affects the lower canopy of oaks. It caused some issues in 2021 and is affecting red oak trees in north-central Wisconsin this year as well.

Oak leaves with abnormally-shaped brown blotches.

Tubakia creates abnormal blotches and spots on oak leaves that can coalesce. Photo: Wisconsin DNR

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Lecanium Scale: A Sticky Situation

By Linda Williams, DNR Forest Health Specialist, Woodruff, Linda.Williams@wisconsin.gov or 920-360-0665

Lecanium scale is popping up in a few areas of Oneida and Vilas counties. These scale insects insert their mouthparts into twigs and suck the sap of the tree. They release honeydew, which can be collected by ants or may coat leaves and anything located under infested trees (i.e., yard furniture or vehicles). Sooty mold can grow on that sticky material and turn things black, so homeowners may want to rinse off the honeydew from outdoor items on a regular basis.

Brown lumps on a twig.

The brown lumps on this stem are lecanium scales. Photo: Wisconsin DNR

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On The Lookout For Oak Wilt Fruiting Bodies

By Linda Williams, DNR Forest Health Specialist, Woodruff
Linda.Williams@wisconsin.gov, 920-360-0665

Have you ever seen an oak wilt fruiting body? Oak wilt is a fungal disease that kills trees in the red oak group (northern red oak, northern pin oak, black oak and other oaks with points on their leaves). Trees in the white oak group (white oak, burr oak, swamp white oak and other oaks with rounded leaves) are more resistant to the disease, but branches or branch tips can still be killed.

A small crack in tree bark that indicates an oak wilt pressure pad is underneath.

Oak wilt pressure pads can create a crack in the bark, allowing beetles to get into the spores. Photo: Wisconsin DNR

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