Minnesota Tree Care Advisors

Characteristics
Disease Management

Bur Oak: native tree, a member of the white oak family which in Minnesota includes white oak (Quercus alba) and swamp white oak (Quercus bicolor). This group of oaks can survive oak wilt.

Large tree height:		50-80'

Canopy spreads:		40-80', Rounded crown

Drought Tolerance:		Tolerant

Shade Tolerance:		Intermediate

Soil pH Tolerance:		Intolerant to high pH

Poor Soil Drainage:		Intolerant to flooding

Salt Tolerance:		Sensitive to salt spray and intermediate in tolerance to soil salts.

Alternately branched tree with rough, deeply fissured bark - often the bark has lost a layer, become smooth, due to a saprophytic fungi commonly known as smooth patch. Foliage is dark green in summer and becomes yellow to brown in the fall. Flowers, monoecious, or catkins are green and fruit is an acorn with a fringed over cup. Look for smooth to ridged, corky twigs.

Bur oak and white oak are "tap" rooters and are difficult to transplant. However, bur oak is a good tree for tough urban sites.

Did you know
Bur oak can be a very long lived tree putting three to four hundred years into its branches. This species has been in a long battle with the grasslands of the prairie states where it invades to form large expanses of oak savanah.

DISEASE		SYMPTOMS	MANAGEMENT
Anthracnose, Apiognomonia quercinia	Fungi	Starts as small brown leaf spots in the inner and lower portion of the canopy during spring rains. Spots develop into large brown to tan blotches often along the large veins. Foliage may shrivel or appear deformed. Defoliation may occur. New foliage often develops following severe infections. Fungus also infects twigs causing small cankers and twig dieback. Most prevalent on white and bur oak. Contrast symptoms with those of oak wilt below.	Rake and destroy fallen leaves. Keep irrigation water out of the tree canopy. Prune out dead and diseased branches. Keep trees vigorous. CHEMICAL: Preventative fungicides should be applied beginning at bud break. Thiophanate-methyl (Warning: tank mix or alternate this with sprays of different fungicides), Bordeaux, chlorothalonil or mancozeb.
Armillaria root rot, Armillaria spp.	Fungi	Check declining trees for white felt-like masses of fungus at the base of the trunk between the bark and the wood. Black shoestring-like strands of the fungus, called rhizomorphs, are also present there and in the soil. Honey-colored mushrooms of the fungus may form at the base of the tree in the fall.	Keep trees healthy. Deep water if dry; avoid wetting trunk/root area. Surface watering during warm months softens the main roots in the crown area which favors progress of the fungus. Replant with resistant species such as Scots pine, catalpa, mock orange and sumac. CHEMICAL: None.
Oak heart rot, Laetiporus sulfureus	Fungi	Fungus invades the roots, trunk and butt of tree through wounds causing a brown cubical rot. First evidence may be the production of a fleshy, yellow shelf fungus on the trunk. However, presence of the fungus suggests considerable rot within and possibility of a hazard tree should be investigated.	Keep trees healthy and avoid wounds. Prune properly. CHEMICAL: None.
Oak leaf blister, Taphrina caerulescens	Fungi	New growth develops yellow green flecks which develop into a puckered or raised area on the leaf surface. Area is hollow or empty beneath. The blister may have a reddish cast.	Mostly a curiosity in wet years. No control usually needed. CHEMICAL: Spray once in spring before bud swell with chlorothalonil or mancozeb.
Oak wilt, Ceratocystis fagacearum	Fungi	Wilting and scorching of leaf margins in the upper crown of the tree. May occur first on one limb. Leaves completely brown and remain attached. Oaks in the red oak group may completely wilt and die in two weeks following the first symptoms. Infection in white oaks is slow to progress. REFERENCE: Oak Wilt, MI-3174(MN).	DO NOT prune oak trees between April 15 and July 1. If damage occurs during that period, immediately cover exposed areas with a tree wound dressing. Do not transport or store oak from recently wilted trees. Use a vibratory plow to sever root grafts before removing infected trees. Consult a professional arborist.
Smooth patch, Aleurodiscus sp.	Fungi	The outer rough bark of white and bur oak trees sloughs off exposing the lighter-colored smooth inner bark.	The fungus does not attack living plant parts. No control is necessary.