Bur Oak - Quercus macrocarpa

Bur Oak - Quercus macrocarpa
Fagaceae -- Beech family
The Bur Oak grows to 100 feet, with a broad, rounded, open crown of stout, crooked, spreading branches. This tree has the largest acorns of all native oaks, sometimes to 2" diameter. The common name describes the cup of the acorn, superficially resembling the spiny bur of the Chestnut. Bur Oak is the northernmost growing of the New World Oaks. Also commonly called "blue oak" and "mossycup oak." [1]

This Bur Oak at The Morton Arboretum is over 300 years old. It is probably the oldest and largest Bur Oak in Northern Illinois. According to our sources at the arboretum, this tree is in excellent health, with no bark or limb damage and no disease -- it could live another 100-150 years.

Bur oak sheltered and inspired North American pioneers who settled the prairies. This bur oak or mossycup oak spotted the open spaces of the Great Plains and was noted for its thick "corky" bark that insulated the trunk and branches. The slow-growing, long-living oak could resist the fires that swept through mid-western prairies and forests. With roots that were nearly as expansive as the aboveground tree, the bur oak could withstand windstorms as well as droughts. These same pioneers found the tree to be excellent wood and waiting the necessary 20 to 30 years after planting was worth it for its shade and resistance to cold, drought and fire. [2][3]

Bur oak is widely distributed throughout the Eastern United States and the Great Plains. It ranges from southern New Brunswick, central Maine, Vermont, and southern Quebec, west through Ontario to southern Manitoba, and extreme southeastern Saskatchewan, south to North Dakota, extreme southeastern Montana, northeastern Wyoming, South Dakota, central Nebraska, western Oklahoma, and southeastern Texas, then northeast to Arkansas, central Tennessee, West Virginia, Maryland, Pennsylvania, and Connecticut. It also grows in Louisiana and Alabama. Bur oaks bear seed up to an age of 400 years, older than reported for any other American oak. The minimum seed-bearing age is about 35 years, and the optimum is 75 to 150 years. The acorns are disseminated by gravity, by squirrels, and to a limited extent by water. The Bur Oak is widely planted for shade, ornament and shelterbelts.

Bur Oak Foliage
New spring foliage

Bur Oak is a slow-growing bottom-land species, relatively intolerant of flooding. The tallest bur oaks reported from the Ohio River Valley were said to have reached 170 feet, and lived 300 years. A pioneer tree, bur oak is often succeeded by pin oak, black oak, white oak, and bitternut hickory.

Damaging Agents- Bur oak is attacked by several insects including the following defoliators: redhumped oakworm (Symmerista canicosta) in the Northeast, S. albifrons in the South, oak webworm (Archips fervidana), oak skeletonizer (Bucculatrix recognita), a leaf miner (Profenusa lucifex), variable oakleaf caterpillar (Heterocampa manteo), June beetles (Phyllophaga spp.), and oak lacebug (Corythucha arcuata). The latter species may heavily defoliate bur oaks in shelterbelt plantings, especially during dry weather. Attacks from bur oak kermes (Kermes pubescens) may distort leaves and kill twigs of bur oak.

Oak wilt (Ceratocystis fagacearum) is a less serious problem in bur oak than in members of the red oak group (5,10). Although spread of the disease from infected bur oak to adjacent oaks is infrequent, the disease sometimes spreads through root grafts, and entire groves have been killed by the gradual expansion of the disease from one center of infection.

Bur oak is susceptible to attack by the cotton root rot (Phymatotrichum omnivorum) and Strumella canker (Strumella coryneoidea). Half of the trees in a 20-year-old plantation in Pennsylvania became infected with the latter disease; and nearly a fourth of these died. Other fungi that have been isolated from diseased parts of bur oak include Dothiorella canker and dieback (Dothiorella quercina), Phoma canker (Phoma aposphaerioides), Coniothyrium dieback (Coniothyrium truncisedum), and shoestring root rot (Armillaria mellea).
-- USDA U.S. Forest Service Quercus macrocarpa Michx.

References:

NATIONAL AUDUBON SOCIETY, National Audubon Society Field Guide to North American Trees--E: Eastern Region, Chanticleer Press Ed (Knopf, 1980).
Howard A. Miller and Samuel Lamb, Oaks of North America (Naturegraph Publishers, 1984).
David Streeter and Richard Lewington, The Natural History of the Oak Tree: An Intricate Visual Exploration of the Oak and Its Environment, 1st American ed (DK ADULT, 1993).