What's Killing our Oak Trees?

What'southward Killing our Oak Copse?

The mighty oak is an iconic tree family that populates forests and landscapes from coast to coast. Across their aesthetic beauty and related benefits to humans, oak trees offer important nutrient and shelter for many organisms from below-ground mycorrhizal fungi to insect larvae that feed on leaves, to birds and mammals that depend on acorns for wintertime nutrient. Only there is something incorrect. Oaks are dying at a high rate from a variety of causes that tin exist tricky to diagnose. This article reviews some common bug, offers help in identifying cause, and advises actions to minimize harm to damaged copse and neighboring survivors.

Red oak (A) White oak (B) Photo: Used with permission of Ohio State Univ. Extension

What type of oak tree is it?

There are virtually 90 different types of oak trees growing across the United states. Most are classified as either red or white oaks. Because susceptibility to many diseases varies by family unit, it is helpful to know whether your tree is a red or white oak variety. Leaf size and shape offering a quick indication. While leaf length is similar, crimson oak leaves are wider. Also, red oaks have more than angular, pointed lobes. White oak foliage lobes are rounded.

Oak refuse: Photo: David 50. Clement, Univ. of Md. Extension

A Description of Common Problems

Oak Turn down

Oak decline is a widespread issue for mature oaks, of both red and white oak families. It is characterized past progressive dieback of crowns, starting from outer limbs and moving in as the decline progresses, potentially over several years. Information technology is typically caused by a combination of biotic and abiotic factors. Abiotic contributors include maturity, site factors, weather extremes including tempest damage, extreme moisture periods, and droughts. In residential settings, structure activity may cause root damage that weakens trees, causing them to get susceptible to a variety of biotic factors. For example, defoliation from gypsy moths or tent caterpillars tin can accelerate decline of weakened copse. Borers such as the two-lined chestnut borer and fungal diseases like hypoxalon canker are two common contributors to oak decline.

Two-lined chestnut borer galleries. Photo: Phil Pellitteri, University of Wisconsin Insect Diagnostic Lab.

The two-lined chestnut borer is a damaging insect that is attracted to weakened or diseased trees of many varieties. The developed is a sparse, black beetle that is active from May to July. The developed lay eggs in bark crevices that hatch in one to two weeks. The larvae create winding tunnels chosen galleries as they feed on cambial tissues, cutting off food transport. They overwinter as larvae or pupae and emerge equally adults through D-shaped holes in the spring.

Damage symptoms include branch dieback with leafage wilt and sudden browning. Leaves typically remain attached to branches. Borers cause death of a tree when galleries girdle the torso, cut off nutrient passage to branches above the feeding level. Time to death tin be from i to v years.

All-time prevention practices are the usual skilful care techniques. Keep trees healthy by providing water during droughts, avoid soil compaction and root impairment from construction activity, protect bark integrity by fugitive injury by lawncare machinery, and manage defoliating insect infestations. If recognized early on, professionally applied imidacloprid injections can exist effective.

Hypoxylon herpes on oak tree. Photograph: Missouri Botanical Garden.

Hypoxylon canker on oak tree. Photo: Missouri Botanical Garden.

Hypoxalon canker is an opportunistic fungus that may attack any blazon of oak tree that is stressed or weakened from disease, environmental or other factors. It spreads by spores from diseased to healthy copse. Infection causes expressionless lesions on limbs, branches, or trunks equally it develops nether bawl. It causes sapwood decay, dissentious the structural integrity of the tree, and causing a potential safety hazard.

Symptoms include those typical of other oak tree wellness bug: yellowish or browning leaves, small leaves and reduced twig growth, thinning canopy, dead limbs and h2o sprouts on trunks and large branches. In later stages, bark falls off the tree exposing the fungus and white, stringy sapwood.

Avoid the canker by maintaining good tree health, allowing the tree's natural defenses to ward off infection. A costly but useful technique to try to salvage valued trees is vertical mulching. This involves drilling a grid of holes throughout the root zone, extending beyond the drip line. Holes should be a few inches in diameter and 18-24 inches deep. Fill them with a porous mixture of pea gravel or coarse sand and compost or other organic affair. This improves drainage during wet periods and conversely, infiltration and wet retention during droughts, while maintaining aeration.

If less than 15% of the canopy is affected, remedial pruning tin aid. Remove expressionless branches 8-12 inches below the infection, sanitizing the tool between each cutting with a x% bleach solution. If more than than xv% of the canopy is infected, the tree should be removed due to its likely structural damage. Because the mucus is already present in the surface area, destroying the woods is not likely a benefit. Even so stored forest should be located remotely from any remaining trees.

Sudden Oak Expiry

Sudden Oak Death. Photo: Richard Sniezko, USDA Forest Service.

Sudden Oak Death is caused by a fungal pathogen, actually a water mold, Phytophthora ramorum. It was transported into the Mid-Atlantic surface area on nursery stock from the West Coast, where the disease has caused widespread oak dieback in California and Oregon. It thrives in cool, moist environments, oftentimes infecting understory shrubbery, including rhododendron, laurel, azalea, and camellia. On the shrubs, leaves driblet but the plant usually survives. Spores on shrub leaves are air current-blown or pelting splashed onto the oak trunk. The fungus infects the living bawl layer. The infection then spreads around the tree circumference, cutting off nutrients passing from leaves to roots, killing the roots. The upper tree dies from lack of water. Red oaks are more susceptible than white oak varieties.

Leaf spotting and twig dieback are visible. Characteristic symptoms of sudden oak expiry are cankers and calluses on bark and wood, oftentimes seeping a blackness or reddish ooze. Tree death occurs in ii years or less, depending on general tree wellness when infected. There is currently no cure, although research at Virginia Tech has identified the pathogen's genome and holds promise for developing a cure. Until then, it is best to remove both shrubs and trees that are infected.

Oak Wilt Disease

Oak wilt. Photo past Joseph O'Brien, USDA Forest Service, Bugwood.org, CC Past 3.0

Oak wilt is another fungal disease that plugs water-conducting tissues with its mycelia and spores. Trees respond defensively to the invasion by plugging their own vessels and worsening the bear on.

Oak wilt affects all oaks with differing rates of decline. The red oak family including blackness, black jack, pin, red, scarlet, shingle and shumard oaks can die in weeks. The white oak group, including bur, chinquapin, swamp white and white oaks may survive for several years, showing decline symptoms.

The affliction is transmitted in ii ways. Above ground, sap feeding beetles pick up the fungus past feeding on an infected tree where there is a fresh wound from pruning, storm harm or bark openings, and send it to other newly wounded trees. Below ground, where root grafting between oak trees is common, the disease is transmitted straight from tree to tree.

Symptoms include withering of the upper canopy and browning of branches and crown portions. Red oaks show a yellowing and then browning of leafage margins or along veins, spreading outward. White oak symptoms are less distinct. Spring infections may crusade mid-late summertime wilting exacerbated by hot, dry out atmospheric condition and a resulting h2o deficit.

Scarlet oaks often prove dessicating bark cracked open by fungal mats disbursing the pathogen. In add-on, sapwood may bear witness brown streaks. Withal, conclusive diagnoses are difficult without lab piece of work to identify the fungus.

To minimize susceptibility, avoid wounding copse during the growing season when beetles are active. If growing season wounds are unavoidable, seal the wounds with a dressing.

To forbid spread from an infected tree, remove the tree afterwards severing root contact between neighboring trees by trenching around the root perimeter. Dig the trench prior to removing the tree to avert a water tension imbalance that could suck fungal material into good for you copse. Leave as short a stump as possible to minimize the fungal material left behind. Considering in that location will be fungal fabric beneath the bawl, logs should be removed and properly disposed of. The pathogen doesn't survive when subject to dessication and it is temperature sensitive. Chips are unlikely to spread the illness, but it is all-time non to employ them about salubrious oaks. Professional aid is strongly advised if oak wilt is suspected. While tree removal is generally recommended for red oaks, trees in the white oak family unit may be saved through propiconazole injections and pruning dead branches.

Armillaria Root Rot

Clusters of fruiting bodies at base of oak tree with armillaria root rot. Photograph: Robert L. Anderson, USDA Woods Service, Bugwood.org, CC By iii.0

Armillaria root rot, sometimes called oak root rot fungus, can survive for many years in wood debris or dead stumps and root systems. Information technology spreads to new trees of many species through root contact. It causes decay of roots and lower trunk eventually killing the tree and causing a toppling hazard.

Symptoms include poor growth, pocket-size yellowed leaves and dead branches in the upper awning.

A distinctive sign is the growth of dearest colored mushrooms at the trunk base in the fall. In addition, flat white fungal sheets grow between trunk and bark, and black fungal strands grow cyberspace-similar at the trunk base and surrounding soil.  Over time, the forest becomes soft and stringy from ground level to nigh half-dozen feet upwards the torso.  Young and stressed trees succumb quickly. Vigorous 15-20 yr old trees are more than tolerant.At this time there are no effective known chemic treatment strategies.

Lesser Threats

In add-on to the oak killers listed, there are a number of lesser diseases that may cause concern but are not by and large lethal to oaks.

Anthracnose on oak.  Photo: Joseph O'Brien, USDA Wood Service, CC By 3.0,

Anthracnose is a fungal disease that causes areas of browning on foliage margins and smaller necrotic spots on the leafage surface. It forms fruiting structures on the underside of leaves in necrotic areas, usually next to veins. It can infect twigs causing dieback prior to bud opening. The fungus likes cool, wet springs and tends to subside during hotter, drier summertime weather.  While unsightly, anthracnose is not usually seriously harmful to otherwise healthy oaks. Manage it with skilful hygiene. Remove dropped leaves, but don't prune trees until the fallow season to avoid subjecting the tree to other potentially more than serious diseases.

Oak leaf blister on pivot oak.  Photo: Missouri Botanical Garden

Oak leaf blister is another fungal affliction that commonly affects the ruddy oak family during cool wet springs. Information technology causes circular raised chocolate-brown sections up to about 2 inches in diameter over the leafage surface. Information technology may cause leaves to fall to the ground prematurely. If leafage drop happens early on, second leafout may occur. If defoliation occurs belatedly in the season, a single occurrence normally has piffling health outcome on the tree. Consecutive infections can affect tree health.

Treatment includes maintaining good hygiene and watering during drought periods. Information technology is possible to take an arborist apply a fungicide in early leap to protect at-risk trees.

Good Hygiene Minimizes Risk

Reviewing the affliction summaries higher up shows a clear pattern. Good hygiene promotes oak tree health and will help them fight off disease. Key advice includes:

  • Provide skilful drainage to avoid oxygen deprivation during wet periods
  • Water during dry spells and droughts
  • Mulch under the canopy to promote soil health. Get out a gap around the trunk base.
  • Take intendance non to wound bark with lawn or other equipment.
  • Remove damaged limbs and use a wound sealant during the growing season.
  • Perform normal pruning during dormancy
  • Avert compaction and have care to prevent root damage during construction projects.
  • Remove diseased debris when trees are removed to prevent spread to healthy neighbors.

Whether you are trying to protect valued oaks or are concerned about specimens showing signs of weakness, I hope this data is helpful in keeping your copse healthy.

References:

https://extension.psu.edu/oak-diseases (Oak Diseases)

https://naswc.org/docs/oak_tree_diseases.pdf   (Oak Tree Diseases)

https://marylandgrows.umd.edu/2019/10/01/why-are-so-many-oak-trees-dying-this-year/ (Why are then many oak copse dying this year?)

https://climate-woodlands.extension.org/oak-decline/   (Oak Turn down)

https://forestupdate.frec.vt.edu/content/dam/forestupdate_frec_vt_edu/newsletter/archives/2018/32_2/Chamberlin.pdf   (Oak Pass up)

http://www.pilotonline.com/news/environs/vp-nw-oak-bloodshed-20191220-kkkafwo5trgqzbyv24bs6fjvhu-story.html   (Virginia Seeing Surge in Deaths of Oak Trees)

https://extension.psu.edu/stay-warning-for-oak-wilt   (Stay Alert for Oak Wilt)

https://www.fs.fed.united states of america/research/invasive-species/plant-pathogens/oak-wilt.php   (Oak Wilt)

https://dnr.wi.gov/topic/ForestHealth/OakWilt.html   (Oak Wilt)

https://extension.umd.edu/hgic/topics/oak-wilt   (Oak Wilt)

https://ohioline.osu.edu/factsheet/plpath-tree-02   (Oak Wilt)

https://forestry.ca.uky.edu/oak_wilt (Oak Wilt)

https://vtnews.vt.edu/articles/2004/06/2004-264.html   (Virginia Tech Advances Fight Against Sudden Oak Death)

https://www.fs.usda.gov/naspf/sites/default/files/publications/06_na-pr-02-02_pest_alert_sudden_oak_death_eastern_508c.pdf   (Sudden Oak Decease)

https://www.fs.usda.gov/naspf/sites/default/files/publications/pest_alert_sudden_oak_death_west.pdf   (Sudden Oak Death caused by a new Pest)

http://www.suddenoakdeath.org/diagnosis-and-direction/hosts-and-symptoms/   (Sudden Oak Death)

Univ.Ga.Ext./Key to Diseases of Oaks in the Landscape

Univ.Maryland Ext./Is Information technology Oak Wilt?/UMD Plant Diagnostic Laboratory

Tex.A&Thou AgriLifeExtension/hypoxylon-canker-of-oaks (Hypoxylon Herpes of Oaks)

MissouriBotanicalGarden.org/advice-tips-resources/pests-and-bug/armillaria   (Armillaria Root Rot)

http://hyg.ipm.illinois.edu/article.php?id=648   (Red Oak Borers)

https://hort.extension.wisc.edu/articles/two-lined-chestnut-borer/   (Two lined Chestnut Borer)

https://plantpathology.ca.uky.edu/files/ppfs-or-w-12.pdf (Bacterial leaf scorch)

https://www.pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/3001/3001-1433/SPES-83NP.pdf   (Bacterial Leaf Scorch)

https://www.pubs.ext.vt.edu/430/430-456/430-456.html (Guide to Successful Pruning)

Featured photo:  White oak tree past Pat Chadwick