Oak wilt: what the agencies record

This page reports what the official source says. It is not legal advice: ask the office named here. It lists what agencies record about oak wilt and does not diagnose any tree. The pruning months each agency gives are in the table on oak wilt by state and province, and the full list of diseases is on the tree diseases page.

At a glance

Item	What the sources say
Pathogen	The fungus Bretziella fagacearum, formerly named Ceratocystis fagacearum (Minnesota DNR, Forest Research)
Hosts	All oaks. Forest Research says all 58 North American native oak species are known to be susceptible to some degree, and that red oaks are the most susceptible.
United States	Forest Research says it has been reported from more than 25 eastern and mid-western states. New York DEC says it was first detected in that state in 2008.
Canada	The Canadian Food Inspection Agency names three Ontario locations: Niagara Falls (the first confirmed detection in Canada), the Township of Springwater and Niagara-on-the-Lake.
United Kingdom	Forest Research lists it as not present and notifiable.
Report to	See the report-a-pest guides for the United States, Canada and the United Kingdom.

How the sources say it spreads

Wisconsin DNR says the fungus grows through the water-conducting system of an infected oak. Sap-feeding beetles carry spores to fresh wounds. Spore-bearing mats form under the bark in the fall or spring after an infected tree dies, and the beetles are drawn to them. Once the fungus is in an area, the page says it moves to nearby oaks through grafted root systems, which makes an expanding pocket of dead oaks. It adds that a tree killed by oak wilt can hold spores for about one year, and that moving infected firewood can carry the disease long distances. Ontario's page and New York DEC describe the same two routes, above ground by beetles and below ground through roots. New York DEC adds that red oaks graft roots readily and white oaks much less so. Forest Research says bark beetles drawn to stressed oaks can also carry spores.

Symptoms by season as the sources state them

Spring. Iowa DNR says the first sign in red oaks is a subtle off-green shift in the upper crown, which may appear in mid to late spring or through the summer. The Canadian Food Inspection Agency says symptoms develop from May and continue through the growing season.
Summer. Wisconsin DNR says wilting is seen from June through September, most often in July and August. Leaves look dull green or bronze and water-soaked but partly green, and they drop while still partly green. New York DEC gives early July through the end of August for sudden wilting, with brown color starting at the leaf edge and moving to the midvein, and with dieback from the top of the canopy down. Ontario says leaves may drop in mid to late summer.
Fall and the following spring. Wisconsin DNR and New York DEC say spore mats form under the bark of red oaks after death. Forest Research says the mats are grey or tan, appear in late autumn or early spring, and stay visible for two or more weeks. Ontario says the mats may smell fruity and that bark can crack as they push outward.
White oaks. Iowa DNR says white oaks usually die slowly, one branch at a time, with yellow veins that turn brown. Minnesota DNR gives red oaks as dying about two months after infection, bur oaks between one and seven years, and white oaks from one to over 20 years.

Look-alikes the sources name

Wisconsin DNR says oak wilt symptoms are similar to those of other pest, disease and abiotic problems, and lists bur oak blight, anthracnose, leaf tatters, leaf and twig galls and two-lined chestnut borer among the other oak issues. The Canadian Food Inspection Agency lists frost damage, nutrient deficiency and natural leaf senescence, and says senescence differs because oak wilt symptoms begin in the upper canopy and do not curl the leaves. Minnesota DNR says other oak problems can easily be confused with oak wilt.

When the agencies say a lab is involved

Wisconsin DNR says a symptomatic tree "should be sampled and examined by a laboratory" for proper diagnosis, especially when active management is being considered, and points to the University of Wisconsin-Madison Plant Disease Diagnostics Clinic. Iowa DNR says experienced foresters, arborists or pathologists can often diagnose in the field from host species, symptoms and mortality patterns, and that sampling and culturing in a qualified laboratory may be needed in some cases. Minnesota DNR names the University of Minnesota Plant Disease Clinic as one way to send samples, and asks for a photo of the whole canopy in summer plus a close-up of fresh fallen or wilting leaves when photos are sent. New York DEC says its staff analyze report photos and then get in touch.

Legal status the agencies describe

In Canada, the Canadian Food Inspection Agency says it surveys affected areas and may issue a Notice of Prohibition of Movement or a Notice to Dispose, and that tree removal occurs where trees are suspected of oak wilt or sit near known infested oaks. In New York, the DEC says one active quarantine district exists, in the Finger Lakes region, and that its emergency order prohibits oak wood leaving the district unless chipped under one inch in two dimensions, tarped, and held on site for a minimum of seven days, with a separate heat treatment step for firewood. Forest Research lists the disease as notifiable in the United Kingdom. The report-a-pest guides above name the offices that take reports.

What the agencies list for management

The sources describe management in general terms. Wisconsin DNR says below-ground spread is controlled by breaking root connections, and that severing the roots with a vibratory plow or trencher has proven effective when the lines are placed correctly, with field trials of other methods under way. Ontario lists removing and chipping or burning infested trees including stumps, or burying logs, and breaking root connections to nearby oaks. Forest Research lists trenching and removal of infected trees, and says trunk injection is used as a preventive step for single high-value trees and is not usually practical for large numbers. Who may apply pesticides is covered in the guide to pesticide licences.

Credit

The Forest Research material was read under the Open Government Licence v3.0 and is restated here in our own words. Other agency pages are linked and restated, not copied.