Tree Insect & Disease Management

Two lethal and contagious vascular diseases threaten our community’s elms () and red/northern pin ( wilt). Both diseases are spread via connections between trees and boring insects, but are host-specific (i.e. Dutch elm disease only occurs on elms). Oaks of the white oak group (bur, white and swamp white) are more resistant to oak wilt than the red oak group and are not actively managed as part of the City’s oak wilt control program. Oaks in the red oak group that contract oak wilt most often always wilt within 2-6 weeks. All elms are susceptible to Dutch elm disease but the exotic Siberian elm is relatively resistant.

Once an elm or red/northern pin oak has been diagnosed due to characteristic wilting in the canopy or stained sapwood, the tree needs to be removed and the properly disposed of. In cases of early diagnosis, therapeutic treatments (removal of symptomatic wood combined with an injection of a systemic ) may be pursued on elm trees.

Movement of infected elm or oak wood is often how Dutch elm disease and oak wilt spreads to new areas. Even after a diseased tree is cut down any remaining wood with intact bark is still a disease risk. Elm wood with intact bark will attract and serve as a breeding site for elm bark beetles that spread Dutch elm disease. Diseased oak wood will often produce spore mats (mushrooms) under the bark which attract picnic beetles who then spread the disease to healthy oak trees. If wood from a diseased oak is desired to be kept as firewood the wood must be stacked and completely covered by a thick plastic tarp anchored at ground level for at least a year. This prevents contact between beetles and spore mats.

The Robbinsdale City Code directs Forestry staff manage these diseases on both public and private property. Public diseased trees are promptly removed by the City. When a dying or diseased elm or red/northern pin oak is located on private property a notice will be sent to the property owner, identifying the tree(s) in question and explaining removal options and procedures. The notice also specifies the completion deadline, which for elms is twenty days during the growing season (excluding Sundays and holidays). For diseased oaks the deadline will normally be prior to the next year’s growing season since spore mats normally form in the spring following tree death.

Information about the is covered in the Treatment of Public Ash Trees link directly below the link to this document. For more information about Dutch elm disease, oak wilt and various other forestry topics please visit http://www.myminnesotawoods.umn.edu/.