Northeast WI Forest Health

Diplodia Shoot Blight vs. Red Pine Shoot Moth

By Todd Lanigan, DNR Forest Health Specialist, Eau Claire, Todd.Lanigan@wisconsin.gov or 715-210-0150

Scattered damage to new red pine shoots has been observed across many counties this summer. With the intermittent rains during the summer, the first thought was that Diplodia shoot blight, a fungal disease, was causing the damage. Upon a closer look, some of the shoot mortality is caused by the red pine shoot moth. From a casual glance, these two problems will look the same, so you really need to take a closer look. 

If Diplodia causes the shoot mortality, the shoot usually forms a shepherd’s crook. And, in time, you will find the fungal fruiting bodies on the needles, especially if you look under the needle sheath (covering) at the base of the needles.

Shepherd’s crook caused by Diplodia shoot blight. Photo Credit: Elizabeth Bush, Virginia Polytechnic Institute and State University, Bugwood.org

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Redheaded Pine Sawfly Numbers Remain Elevated In Northeastern Wisconsin

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

For the third year in a row, colonies of redheaded pine sawfly have been noted on understory red pine in northern Wisconsin, with the most reports coming from Vilas and Oneida counties.

Redheaded pine sawfly larvae feeding on red pine needles. Note the needle stubs where they have eaten nearly to the base of the needle. Photo Credit: Wisconsin DNR

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White Pine Branch Tips Red And Wilting

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

White pine trees in many counties in northeast and northcentral Wisconsin have developed rusty-colored wilting needles on outer branch tips scattered throughout the tree’s crown. These dead branch tips are associated with the feeding by white pine bast scale. The scale is a tiny insect that inserts its straw-like mouthpart into the twig to suck sap from the outer layers of phloem called bast. Damage has been observed on trees over 20 feet tall this year. 

Branch tips on this white pine indicate a problem with bast scale and the disease Caliciopsis. Photo Credit: Wisconsin DNR

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Pear Slug Sawfly Defoliation: Treatment Tips

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

Pear slug sawflies (Caliroa cerasi) feed by scraping off the upper layer of the leaf, leaving the veins and the lower leaf surface. Severe defoliation has been observed and reported recently on crabapple, apple, mountain ash and serviceberry in Oneida, Forest and Oconto counties. The first generation occurs earlier in the summer, so the larvae and defoliation seen now are due to the second generation of the insect, which is larger than the first generation.

Pear slug sawfly larvae feed by scraping off the upper layers of the leaf. Photo Credit: Wisconsin DNR

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Oak Leaves Turning Brown? There Are Several Reasons This Year.

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

Oak wilt symptoms are active right now, but so are several other oak issues that may be mistaken for oak wilt symptoms. Issues including Tubakia leaf spot, Botryosphaeria canker, kermes scale damage and mite damage are all causing problems and may be mistaken for oak wilt.

Oak Wilt Leaf Symptoms

Trees in the red oak group (those with points on their leaves) that became infected with oak wilt in the spring will suddenly start to drop their leaves in July and August. Trees that were infected later in the high-risk period (April 15 – July 15 in northern Wisconsin) may start to drop their leaves later, in September or even into October.

Leaves dropping from oak wilt trees can be fully green, tan or a water-soaked, greenish color away from the petiole (leaf stem). There will often be an area that is still green near the petiole, even though the leaf has fallen to the ground. Wilting leaves typically start near the top of the tree and progresses downwards.

Recommended control measures depend on if you have just one tree actively wilting (and no others have died in past years) or if you are dealing with established pockets that have been present for more than a year. Contact your regional forest health specialist to discuss these control options if you think you have oak wilt.

Leaves dropping from trees dying from oak wilt often are brown or water-soaked on the outer portions of the leaf with green still found near the base of the leaf. Photo Credit: Wisconsin DNR

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Oak Wilt Symptoms Visible Now

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

Symptoms of oak wilt are showing up. Look for leaves that suddenly wilt and drop from the tree. Oak wilt is a non-curable, fungal disease specific to oaks. Trees in the red oak family will die quickly from this disease, while trees in the white oak family will die more slowly, with a branch or portion of the crown becoming infected. 

This tree is actively wilting from oak wilt infection and will drop most of its leaves within about 4-6 weeks.

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Oak Timberworm, Not Your Average Weevil

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

Oak timberworm, Arrhenodes minutus, is a primitive weevil that can cause defects and degrade in red and white oak timber. They can also infest elm, poplar and beech. Egg-laying females will seek out trees that are damaged, wounded, nearly dead or recently dead. After the eggs hatch, the larvae bore across the grain through the tree then “U-turn” back across the grain to the point of origin, taking two or three years to complete their life cycle and creating a lumber defect called a wormhole. When infested wood is split for firewood, the weevils may emerge in homes or garages if they had already pupated when the firewood was split. 

Male oak timberworm on a Northern red oak that was damaged in a storm.

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Lacebugs: Delicate But Damaging

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

Lacebugs are tiny, delicate-looking insects that can cause leaves to turn a little off-color. They are typically found feeding on the undersides of leaves, where they insert their mouthparts and suck the sap from the leaves. From the top of the leaves, these areas where the feeding damage occurs are stippled with small white or yellow specks, often in a generally circular pattern. Recently congregations of adult and nymph lacebugs were noted on the twigs of basswood, but it was unclear if they were feeding on the twigs or just resting there. 

Lacebug adults and nymphs have congregated on this basswood twig.

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Woolly Aphids Observed And Reported On Social Media

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

Have you noticed small, white fluffy things floating through the air? If you have a chance to look closely at these small bits of fluff, you’ll see that they’re actually insects; these are woolly aphids. They produce waxy filaments that help them avoid predators that don’t want to chew on their fluffy excretions.

Woolly alder aphid group is protected by the waxy filaments covering them.

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Emerald Ash Borer Identified In Iron County For The First Time

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

Emerald ash borer (EAB) has been detected for the first time in Iron County, in the Town of Oma. Many of the black ash at this site are already dead, with other trees still declining. EAB was first identified in Wisconsin in 2008 and has now been found in 60 of Wisconsin’s 72 counties.

Did you know that it takes fewer EAB larvae to attack and kill a black ash compared to a green ash or white ash? This means that black ash will have fewer galleries under the bark and consequently less woodpecker flecking than you would typically see with green ash or white ash. 

EAB was federally deregulated as of Jan. 14, 2021 and Wisconsin instituted a state-wide quarantine in 2018, so there are no regulatory changes due to this find. Emerald ash borer silviculture guidelines were created to help landowners make decisions about management in their woods. All forest sites are a bit different and it can be overwhelming to try to decide what management, if any, should be done in your stand and these guidelines are designed to help answer those questions.

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