Forest Health News

Please report damage to white and bur oaks

By Mike Hillstrom, forest health specialist, Fitchburg, Michael.Hillstrom@wisconsin.gov, 608-513-7690; Alex Feltmeyer, forest health specialist, Plover, Alex.Feltmeyer@wisconsin.gov, 715-340-3810; and Paul Cigan, forest health specialist, Hayward, Paul.Cigan@wisconsin.gov, 715-416-4920

Forest health staff are again noticing health issues with white and bur oaks in 2019. A few trees with dieback in 2018 were recently resurveyed and were found to have recovered well. However, variable symptoms are appearing again in some areas. Forest health staff are conducting site visits to determine if the causal agents are the same as in 2018. Last year, leaf damage resulted from leaf fungal pathogens and twig damage was caused by Botryosphaeria fungi and gall wasps.

Please report any white or bur oak issues you notice to your local forest health specialist.

Same bur oak in June 2019 showing good recovery with only minor dieback.

Same bur oak in June 2019 showing good recovery with only minor dieback.

Bur oak with moderate crown dieback in June 2018.

Bur oak with moderate crown dieback in June 2018.

Fall webworm activity in July

By Todd Lanigan, forest health specialist, Eau Claire, Todd.Lanigan@wisconsin.gov, 715-210-0150

Fall webworm started showing up in early July. This native insect feeds on deciduous trees and shrubs and appears every year in yards and forests. Fall webworm forms loose webbing over branch tips. It can even completely cover a small tree with webbing. Inside the webbing you will find both live and dead caterpillars, partially eaten leaves and frass (caterpillar poop).

Fall webworm larvae in and on top of webbing spun around branch tip. Credit: Courtney Celley, USFWS.

Fall webworm larvae feed within webbed enclosures at branch tips. Credit: Courtney Celley, USFWS

Fall webworm is more of a cosmetic issue than a tree health problem, but if people are concerned, they can take some simple measures to remove them. Open up the webbing using a rake, fishing pole, long stick or another long tool.. This will allow predators to get at the caterpillars inside. Or people can use their tool to roll up the webbing, peel away from the branch and place the entire web in a container of soapy water for a couple of days.

Insecticides can also be used to control this insect. If you decide to go this route, make sure the insecticide is labeled for caterpillars/fall webworm and that it will penetrate inside the webbing. With all pesticides, the user needs to carefully read and follow label directions.

As a native insect, fall webworm defoliation is unlikely to cause any harm to healthy trees. Use a control method described above if you are concerned about the aesthetics of a defoliated tree. Do not prune off the branch or burn the nest. Burning will cause more harm to the tree than the caterpillars will. For more information about fall webworm, visit this page from Michigan State University Extension.

Professionally-designed HRD guidelines now available

Cover page of HRD guidelines documentThe professionally-designed version of the Heterobasidion root disease (HRD) stump treatment guidelines is now posted on the DNR’s HRD webpage. The revised stump treatment guidelines, developed to reduce the risk of introduction and spread of HRD in Wisconsin, were implemented January 1, 2019. The content is the same as the guidelines that were approved last year, but this document has a layout that is much more user-friendly. Explore the new look of the HRD guidelines.

 

Watch for signs of oak wilt

Linda Williams, forest health specialist, Woodruff, Linda.Williams@wisconsin.gov, 920-360-0665 

Trees in the red oak group (those with points on their leaves) that were infected with the oak wilt fungus this spring will rapidly drop their leaves from July to September and be dead by fall. This wilting and dropping of the green leaves happens quickly. Once it starts, the tree will drop most of its leaves within just a few weeks.

Tree dying from oak wilt with rapidly dropping leaves.

Tree dying from oak wilt with rapidly dropping leaves. The tree was injured in May, attracting the beetles that help spread the fungus, and the tree was dead by the end of the year. Photo was taken in August.

Red oak leaf from infected tree. Leaves are often green at the base, with the outer portions of the leaf appearing water-soaked or brownish.

Red oak leaf from infected tree. Leaves are often green at the base, with the outer portions of the leaf appearing water-soaked or brownish.

Continue reading “Watch for signs of oak wilt”

Ants, aphids and sooty mold on white pine

Linda Williams, forest health specialist, Woodruff, Linda.Williams@wisconsin.gov, 920-360-0665

Ants, aphids, and sooty mold can cause stunting and death of young white pines, but fortunately there are some steps you can take to protect your trees from these pests.

Ants guard aphids from predators as they feed. In exchange, the ants collect the sweet honeydew excreted by the aphids.

Ants (upper right) guard aphids from predators as they feed. In exchange, the ants collect the sweet honeydew excreted by the aphids.

Continue reading “Ants, aphids and sooty mold on white pine”

Watch for cherry scallop shell moth defoliation

Mike Hillstrom, forest health specialist, Fitchburg, Michael.Hillstrom@wisconsin.gov, 608-513-7690

Cherry scallop shell moth, a native defoliator, is back again in Jefferson and Walworth counties. Several residents recently reported large numbers of moths in areas that have experienced multiple years of defoliation by this insect.

Eggs laid by those moths are expected to hatch soon, and the emerging caterpillars will begin feeding on cherry tree foliage. Hopefully, populations of egg-parasitizing natural enemies will be high enough this year to provide relief to stressed trees.

Early instar caterpillars on cherry leaf.

Early instar caterpillars on cherry leaf.

Continue reading “Watch for cherry scallop shell moth defoliation”

Heavy seed crop leads to sparse-looking trees

Todd Lanigan, forest health specialist, Eau Claire, Todd.Lanigan@wisconsin.gov, 715-839-1632

You may have noticed some of the elms and maples had a lot of brown in them at the end of May and early June. Some elms and maples produced a lot of seed this spring, which reduced the amount of energy available for producing leaves. With fewer leaves and more of the brown, papery seeds, the trees can take on a thin, brown appearance.

Heavy seed years can occur for many reasons. It happens naturally from time to time and it can also be stimulated by environmental stressors. A couple of examples of environmental stressors are: excessive moisture, winter injury and frost damage to roots.

The cause of this year’s heavy seed production is anyone’s guess. There does not appear to be a common pattern between the affected trees to indicate whether it was simply a normal heavy seed year or related to an environmental factor.

 

Browning on tamarack needles

Linda Williams, forest health specialist, Woodruff, Linda.Williams@wisconsin.gov, 920-360-0665

Defoliation from larch casebearer (Coleophora laricella) is showing up in some areas of northeast and northcentral Wisconsin. The defoliation is patchy and of moderate intensity, resulting in trees with various degrees of browning due to the insect’s feeding habits. Some appear pale yellow or brown throughout the crown while others only have partial browning.

Defoliated larch needles turn yellow then brown.

Defoliation by larch casebearer will cause needles to turn yellow then brown. Trees will usually send out more needles and be green again by mid-summer.

Continue reading “Browning on tamarack needles”

Branch flagging caused by jack pine resin midge

Paul Cigan, forest health specialist, Hayward, Paul.Cigan@wisconsin.gov, 715-416-4920

Jack pine shoots are flagging over a large area of northern and west central Wisconsin this summer due to feeding injury from the jack pine resin midge. Symptoms include scattered dead branch tips and pitch masses on terminal buds and on twigs where larvae feed.  

Jack pine with dead branch tips caused by jack pine resin midge. Photo: Paul Cigan.

Jack pine with dead branch tips. Photo: Paul Cigan.

Continue reading “Branch flagging caused by jack pine resin midge”

Native caterpillars not a major concern for trees

Mike Hillstrom, forest health specialist, Fitchburg, Michael.Hillstrom@wisconsin.gov, 608-513-7690

Eastern tent caterpillars (ETC) are hatching and beginning to feed on host trees, including cherry, apple and crabapple. Landowners and homeowners may notice the white silken tents forming in branch forks. Although they form unsightly tents, ETC is a native insect so management is not typically necessary. Even completely defoliated trees will put out new leaves within a few weeks.

A group of eastern tent caterpillars warm themselves on white silk tent before leaving to feed on black cherry leaves.

If landowners want to remove the tents the best time to do so is early morning or evening when the caterpillars are inside. Unless it is raining, eastern tent caterpillars leave their tents each morning to feed throughout the day before returning at night. Caterpillars can be removed either by hand if they are within reach or with a rake if they are high in the tree. They can then be killed by soaking them in soapy water or sealing them in a trash bag. Insecticides are rarely necessary but should penetrate inside the tent if used. Do not prune branches, burn tents or soak them with WD-40. These methods are more harmful to the tree than ETC defoliation and are not recommended.

For more information on eastern tent caterpillar, read this factsheet from UW-Madison Division of Extension.