What attacks oak: pests and diseases the sources name
A register of seven things that university, state and forestry-body sources tie to oak: oak wilt, bur oak blight, acute oak decline, sudden oak death, oak processionary moth, spongy moth and oak galls, with the oaks each source names, where it is recorded and the season it mentions.
Checked against the sources at the bottom of this page on October 9, 2026. Rules, fees and pay change: the source has the last word.
This page reports what the named sources say. It is not a diagnosis of any tree and does not say what should be done with one. Each row names its source, all read on October 9, 2026. Where this site has a full profile, the row links it, and the regulated status tables are on the linked pages and are not repeated here. Oak species are covered one by one in tree species in the agency records, including white oak, northern red oak, bur oak and pin oak.
Diseases
| Agent | What the sources record |
|---|---|
| Oak wilt, Bretziella fagacearum (fungus). Full profile | Oaks named: The Wisconsin Department of Natural Resources calls it a particularly serious problem for the red oak group, naming northern red, northern pin and black oaks, whose infected trees lose most leaves and die within approximately one month of wilting showing. Bur and swamp white oaks show moderate tolerance, and white oaks progress slower and may survive. Where and status: Widespread in southern Wisconsin, and in much of northern Wisconsin a new and uncommon disease, as mapped to January 21, 2026. The page names no federal regulated status. Season: Wilting from June through September, most commonly July and August. The page gives April through July as the greatest risk of transmission by spore-carrying beetles. |
| Bur oak blight, Tubakia iowensis (fungus). Full profile | Oaks named: Iowa State University Extension says it is known to infect only bur oaks. Where and status: Observed in Iowa since the mid 2000s, with severity increasing across much of the western two-thirds of the state. The page names no regulated status. Season: Spores are produced in May and infect new shoots and leaves in rainy weather. Dramatic leaf symptoms do not become evident until July and worsen in August and September. |
| Acute oak decline (several agents, especially bacteria). Full profile | Oaks named: Forest Research says it mainly affects the two native oaks of the United Kingdom, pedunculate and sessile oak, and lists cases on Turkey, red, scarlet, pin, water, holm and other oaks. Where and status: Present in the United Kingdom and reportable. Mostly in south-eastern, central and eastern England and the Welsh Borders and South-East Wales, and not reported in Scotland or Northern Ireland as of 2020. Season: No season given for onset. Forest Research says trees can die within four to six years of the first symptoms, and symptoms can develop rapidly over 18 months. |
| Sudden oak death, Phytophthora ramorum. Full profile | Oaks named: The California Oak Mortality Task Force site says only oaks in the red or intermediate groups have been found infected and white group oaks are not susceptible. It says tanoak is the most susceptible known host and that on oaks only trees larger than 10 cm in diameter show symptoms. Where and status: The site says USDA APHIS keeps an official host list as part of the federal quarantine. The disease is on more than 100 plant species, and on most of them it causes only leaf spots and shoot dieback. Season: No season given. The site says death usually follows an infection estimated at more than two years. |
Insects and galls
| Agent | What the sources record |
|---|---|
| Oak processionary moth, Thaumetopoea processionea. Full profile | Oaks named: Forest Research says the caterpillars are pests of oak, the genus Quercus. Where and status: Present in the United Kingdom and notifiable. Forest Research says it is established across London and surrounding areas, and the rest of the country is designated free from the pest. Season: Caterpillars are seen from mid to late spring and early summer, May to July, moving in nose-to-tail processions. |
| Spongy moth, Lymantria dispar. Full profile | Oaks named: The Morton Arboretum says oaks are the preferred host when numbers are low, and lists beech, maple, pine, spruce and others as showing some resistance. The Wisconsin Department of Natural Resources says the caterpillars feed on more than 300 species of deciduous and evergreen trees. Where and status: The Wisconsin page says it has defoliated millions of acres in at least 20 states and the Washington, D.C., area. Regulated areas are on the linked profile. Season: The Arboretum says eggs hatch in spring, usually in May in northern Illinois, and full-grown caterpillars stop feeding by mid-June. Wisconsin says caterpillars rest on trunks and buildings in June and July. |
| Oak galls. Full profile | Oaks named: The University of Arizona says the makers on its oaks are most commonly small cynipid wasps, and that Arizona white oak is one of five native oak species it names there. Where and status: The page covers north central Arizona and gives no regulated status. It says most insect galls on Arizona oaks are not harmful, with little more than cosmetic damage to leaves and occasional twig death, and that on eastern oaks twig galls reportedly cause significant damage to pin and willow oaks. Season: Leaf galls generally start around bud break in spring, or early summer on evergreen oaks. |
What the register shows
The sources split oaks by group when they speak about hosts. Wisconsin and the California task force both separate the red oak group from the white oak group, and they point the same way for two diseases: oak wilt is serious in the red group, and sudden oak death has been found only in red or intermediate oaks. Bur oak blight is the one named for a single species, bur oak, which sits in the white group. Forest Research does the same for the United Kingdom, naming pedunculate and sessile oak for acute oak decline.
Several rows are cautious about what a symptom proves. Forest Research says a stem bleed alone does not necessarily indicate acute oak decline, because trees weep from bark attack by other agents such as Phytophthora species. The Wisconsin Department of Natural Resources says oak wilt symptoms resemble those of other pests, diseases and non-living causes and that a lab should examine a symptomatic tree. The California task force says only a lab can confirm sudden oak death.
Who the sources say to report to
Forest Research asks that acute oak decline and oak processionary moth in Great Britain be reported through TreeAlert, and in Northern Ireland acute oak decline through TreeCheck, both of which need clear close-up photographs. For oak wilt, the Wisconsin page points urban tree owners to a local urban forestry consultant or arborist or a sample to the University of Wisconsin-Madison Plant Disease Diagnostics Clinic, and forest owners to a local forester or regional forest health specialist. The Iowa State page offers its own diagnostic clinic. The reporting offices for each country are on the report a pest in the United States and report a pest in the United Kingdom pages.
Sources
- Wisconsin Department of Natural Resources, oak wilt page, read October 9, 2026
- Iowa State University Extension and Outreach, Bur oak blight (last reviewed January 2022), read October 9, 2026
- Forest Research, acute oak decline page, read October 9, 2026
- California Oak Mortality Task Force, Sudden Oak Death hosts and symptoms, read October 9, 2026
- Forest Research, oak processionary moth page, read October 9, 2026
- The Morton Arboretum, spongy moth, read October 9, 2026
- Wisconsin Department of Natural Resources, spongy moth page, read October 9, 2026
- University of Arizona Cooperative Extension, Backyard Gardener 61, Oak galls (January 16, 2023), read October 9, 2026