Symptoms: Wilt, defoliation and the premature drop of leaves help distinguish this vascular wilt from other causes of wilting.
Cause: Oak wilt is caused by a fungus carried by sap- feeding beetles and certain other insects that visit wounds in bark. The disease has caused serious losses in Midwestern states, including Illinois and Wisconsin and the Upper Peninsula of Michigan. Infected red oaks die within a few weeks, but white oaks may linger on for two to three years of decline. Studies in the Midwest have determined that infection occurs from mid-May through June. During this time, oaks should not be pruned, climbed with shoe irons or otherwise wounded. The disease can spread down a row of oaks as diseased roots infect healthy roots of nearby trees. Roots of trees belonging to one species often graft with one another, and this facilitates disease spread.
Control: Infected trees should be removed and wood, including stumps, should be debarked and split. Otherwise, the wood will bloom with the fungus beneath the bark and insects will seek the spores and carry them to healthy trees.
Closely planted trees should be treated to remove the chance of root grafting. This is best done by passing a root cutting blade 2 feet deep at the midpoint between the trees. This severs root connections between trees. Alternatively, a soil fumigant can be placed at an appropriate concentration in holes 2 feet deep and 8 inches apart along the midpoint between two trees to kill intermingling roots.
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|Oak wilt infested forest - 56K||Oak wilt leaf symptoms on red oak - 30K|
|Oak wilt mycelial pad under the bark - 36K||Root grafts - 33K|