Fungal pathogen

Apiognomonia quercina (Gleosporium asexual stage)

Area(s) affected

Leaves and twigs

Signs/Symptoms

Brown, irregular spots form on the leaves. These spots tend to follow the leaf veins and midrib causing only a portion of the leaf to turn brown. After drying, the spots will have a papery texture. Late in the growing season the fungus can be seen as dark pustules on the veins and midribs of infected leaves and dead twigs.

Photo credit: Joseph O’Brien, USDA Forest Service, Bugwood.org

Hosts

Black, California black, bur, cherrybark, chestnut, English, laurel, live, California live, Oregon, pin, northern pin, post, northern red, southern red, scarlet, Shumard, water, white, swamp white and willow oaks. White oaks are the most susceptible.

For more information

http://extension.psu.edu/pests/plant-diseases/all-fact-sheets/anthracnose-on-shade-trees

Fungal pathogen

Taphrina caerulescens

Area(s) affected

Leaves

Signs/Symptoms

Occurs on species in both the red oak and white oak groups. The fungus causes leaf cells to divide abnormally and enlarge. If you flip the leaf over you will observe light-green cup-like depressions. Yellow, blister-like bulges, corresponding with the lower leaf depressions, will be seen on the upper leaf surface. As the disease progresses, blisters coalesce and will cause the leaf to curl. The fungus can sometimes be seen in the depressions, first colorless then darkens after spores are released.

Photo credit: Andrew J. Boone, South Carolina Forestry Commission, Bugwood.org

For more information

http://extension.psu.edu/pests/plant-diseases/all-fact-sheets/oak-leaf-blister

Fungal pathogen

Actinopelte dryina

Area(s) affected

Leaves

Signs/Symptoms

This disease is most severe on members of the red oak group, but white oaks are also susceptible. Small, round spots form on the leaves. These spots are usually reddish-brown and tend to have a yellow halo around them. If the infection is severe, defoliation may occur.

Photo credit: Jason Sharman, Vitalitree, Bugwood.org

For more information

http://texasoakwilt.org/Documents/Diseases/Actinopelte.pdf

Fungal pathogen

Elsinoe quercus

Area(s) affected

Leaves

Signs/Symptoms

Tiny sunken blackish-brown spots will form on the upper surface of the leaf. Symptoms are first visible in early June and increase in number until the middle of August. By that time foliage is severely damaged and the tree is a pale yellow. When infection is severe, defoliation occurs.

For more information

Fungal pathogens

Microsphaera alni and Phyllactinia guttata

Area(s) affected

Leaves

Signs/Symptoms

Powdery mildew occurs on all groups of oaks. Infected leaves have a faint indistinct spot on the upper leaf surface and a white to off-white powdery growth on the lower surface. The fungus will most often be found along the veins and midribs of the leaf. In severe cases, infected leaves will be slightly disfigured.

Photo credit: Petr Kapitola, State Phytosanitary Administration, Bugwood.org

For more information

http://www.clemson.edu/extension/hgic/pests/plant_pests/flowers/hgic2049.html

Fungal pathogen

Cronartium strobilinum

Area(s) affected

Leaves

Signs/Symptoms

C. strobilinum infects pines in mid-winter. The telial stage is only produced on evergreen oaks, which are closely associated with live oaks. Yellow to orange pustules can be observed on the lower leaf surface of infected oak leaves.

For more information

http://www.fs.fed.us/r8/foresthealth/forestpests/diseases/socnrust.pdf

http://www.freshfromflorida.com/Divisions-Offices/Florida-Forest-Service/Our-Forests/Forest-Health/Forest-Health-Publications/Insects-and-Diseases/Southern-Cone-Rust

Fungal pathogens

Hypoxylon atropunctatum and other Hypoxylon spp.

Area(s) affected

Entire tree

Signs/Symptoms

Hypoxylon canker occurs primarily on trees which are or have been in stressed conditions. The fungus invades the tree through injured surfaces on its limbs and trunk. The disease is first evident as a dieback of one or more branches. The foliage of the diseased limbs turns yellow and dries. This dieback continues from branch to branch until the tree dies. The fungus infects the inner bark causing the outer bark to slough off. This exposes large masses of brown, dusty spores which disseminate. Left behind is a grayish surface covered with many black fruiting bodies. The fungus causes black to brown discoloration in the sapwood which can be observed in a cross-section of the wood.

Photo credit: USDA Forest Service – Region 8 – Southern Archive, USDA Forest Service, Bugwood.org

Photo credit: Molly Giesbrecht, Texas A&M AgriLife Extension Service, Bugwood.org

For more information

http://txforestservice.tamu.edu/main/article.aspx?id=1262

http://www.fs.fed.us/r8/foresthealth/publications/r8_pr_29.pdf

Fungal pathogen

Physalospora glandicola (syn. Botryosphaeria quercuum)

Area(s) affected

Twigs and branches

Signs/Symptoms

The fungus enters the tree through wounded twigs. Brown streaks can be observed in the sapwood of infected twigs and branches. Bark lesions that resemble pimple-like swellings will also develop. Infected twigs and branches die and the attached leaves will turn brown. Affected trees will look like they have been attacked by cicada.

For more information

Sinclair, Wayne A., Howard H. Lyon, and Warren T. Johnson. “Diseases of oak caused by Botryosphaeria quercuum and related fungi.” Diseases of Trees and Shrubs. Ithaca, NY: Comstock Pub. Associates, 1987. 178-79. Print.

Fungal pathogen

Endothia parasitica and Endothia gyrosa

Area(s) affected

Branches and trunks

Signs/Symptoms

Post oaks and red oaks are particularly susceptible. It has been associated with pruning cuts or limb breakage. Removal of cankers by pruning and increased tree vigor helps reduce losses.

For more information

http://harris.agrilife.org/files/2011/05/oakdisease.pdf

Fungal pathogens

Irpex mollis, Polyporus hispidus and Poria spiculosa

Area(s) affected

Branches and trunks

Signs/Symptoms

For more information

http://www.na.fs.fed.us/spfo/pubs/fidls/canker-rots/fidl-cr.htm

Fungal pathogen

Phomopsis spp.

Area(s) affected

Branches and trunks

Signs/Symptoms

Burls can occur on both oaks and hickories. The fungus causes large tumor-like swellings on the branches and trunk of the tree. There are some swellings which occur on white oaks that aren’t caused by a fungus, but rather by the wood naturally growing over young buds and forming burl-like swellings.

Photo credit: Robert Anderson, Bugwood.org

For more information

http://forest.mtu.edu/research/hwbuck/hardwood_defects/burls.html

Fungal pathogen

Ceratocystis fagacearum

Area(s) affected

Entire tree

Signs/Symptoms

This is an important disease of all oaks. Members of the white oak group die very slowly after infection occurs and can carry the fungus in the vascular system without showing any symptoms. Red oaks die rapidly after infection occurs. Symptoms show up on red oaks in early May as a bronzing of the leaves. On live oak, the leaf symptoms are variable. The most common symptom is brown necrosis of the leaf veins. The remainder of the leaf may remain green or turn slightly yellow. Severe leaf drop occurs while the leaves are still green. Cuts made through the wood may show discoloration in the last annual ring. Symptom development usually begins on one limb or branch and in time spreads rapidly to the remainder of the tree.

The fungus may be carried from tree to tree by various insects and through root grafts. Sap feeding beetles are important in the short range spread. Red oaks which wilt in the late summer or early fall develop spore mats under their bark during the next spring. As the mats develop, the bark sloughs off or ruptures exposing the fungus. Insects are attracted to the mats. If the insects move from mats to healthy trees which have open wounds the fungus can then enter the healthy tree and move into the water conducting tissue.

Photo credit: Joseph O’Brien, USDA Forest Service, Bugwood.org

Photo credit: Paul A. Mistretta, USDA Forest Service, Bugwood.org

Photo credit: Ronald F. Billings, Texas Forest Service, Bugwood.org

Photo credit: Ronald F. Billings, Texas Forest Service, Bugwood.org

For more information

http://texasoakwilt.org/oakwilt/oak-wilt-identification/

Causal agents

Combination of abiotic stress factors, fungal pathogens, and insects

Area(s) affected

Entire tree

Signs/Symptoms

Trees affected by the fungus first show signs of thinning out and twig dieback in their upper canopy. The dieback will generally increase each year. As dieback reaches the larger limbs, which comprise the main canopy, sucker growth becomes evident on the main scaffold limbs. As the disease continues to progress, only the main scaffold limbs remain alive, however, they will eventually die. This may take from five to ten years on live oaks, but less on other oaks after the first visual symptoms are observed. Live oak, post oak, water oak, Texas red oak, willow oak, sycamore, persimmon, winged elm, hackberry, American elm and western soapberry are reported to be hosts for Oak Decline.

Photo credit: Joseph O’Brien, USDA Forest Service, Bugwood.org

For more information

http://www.na.fs.fed.us/spfo/pubs/fidls/oakdecline/oakdecline.htm

http://www.uky.edu/Ag/Forestry/extension/pub/pdf/for99.pdf