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Pests and Diseases
The Asian Longhorned Beetle (Anopliphora glabripennis) is a large insect native to Southeast Asia that was first discovered in the United States in the mid 1990’s in New York. The Asian Longhorned Beetle (ALB) has no known natural predators and poses a threat to hardwood forests. This invasive beetle is not a species-specific pest, but targets many different species of trees.
The Federal government is working in conjunction with local governments and professional arborists to combat it. ALB was successfully eradicated in Illinois and parts of New Jersey, and is currently being controlled in New York and Massachusetts.
Signs of Asian Longhorned Beetle infestation include perfectly round exit holes (about 3/8 to 1/2 inch in diameter) made by adult beetles when they emerge from trees; pockmarks on tree trunks and branches where female deposit eggs; frass (wood shavings and saw dust) produced by larval feeding and tunneling; early fall coloration of leaves or dead branches; and running sap produced by the tree at the egg laying sites, or in response to larval tunneling. Infested trees may also snap or break during high winds due to the wood being weakened by tunneling.
The Emerald Ash Borer (Agrilus planipennis) is native to Eastern Asia, first seen in the United States near Detroit in 2002. The Emerald Ash Borer (EAB) has no native predators and has spread throughout most of Iowa and much of the eastern United States. The insect matures just beneath the bark of ash trees, eating vascular tissue of the tree which ultimately leads to the tree’s death. All species of ash are affected and mortality rate nears 100%. Adults are usually 1/2" long and 1/8" wide, while eggs are extremely small at about 1/25". Females usually lay eggs after adults emerge in mid-to late spring. Larvae will bore into the Ash Tree and feed under the bark, which disrupts the tree’s ability to transport water and nutrients. Trees that have been affected will present with bark splitting, thinning of ash tree crowns, suckers seen at the base of the tree, D-shaped exit holes, and tunneling under the bark.
Things you can do to help manage this pest:
- Do not move firewood from your property or take to another location
- Burn any remaining firewood supply on your property before spring to prevent any pest spreading to live trees
- Call our forestry division for advice on how to manage or what to do if you suspect an infestation
Iowa DNR Information and Map
Iowa Department of Agriculture and Land Stewardship Information
EAB Information Network
Oak Wilt is a vascular fungal disease that harms many oak species and is caused by the fungus Ceratocystis fagaceous. Trees from the Red Oak family (Red, Scarlet, Black, Pin, etc.) are very susceptible and can cause the affected tree to die within 4-6 weeks.
Infection Methods and Identification
Oak Wilt Disease is spread by three different methods:
- Root Grafts from a diseased tree to a healthy tree
- By a Sap Beetle that has fungus on it
- From arborist tools that have fungus on them
Trees that are infected will try to protect themselves by producing a gummy material called tyloses which then can clog the water conducting vessels. This prevents water from moving to the canopy so leaves begin to wilt, turn brown at the edges and fall off.
The best times to work on Oaks is outside of the growing season, between the months of October and March. If there is work required during the growing season, precautions can be taken to prevent to protect your Oak tree.
- Clean all tools with a bleach solution of 1 part bleach to 9 parts water after working in a tree.
- Spray wounds on non-infected trees with a transpiration product like Shellac.
- Remove all wood material to a safe location that will reduce the likelihood of spreading the disease.
There are three basic options for treatment and to stop the spread of Oak Wilt; mechanical, chemical and transportation.
- Clean tools correctly and thoroughly after each tree
- Root trenching: Sever the root connections to block the spread of this disease
- Injecting a fungicide into healthy trees to prevent contraction of the disease
- Injecting a fungicide into infected trees to help stop the spread of the disease throughout the trees vascular system
- Properly dispose of all woody material to a safe location.
Oak Wilt Resources
Texas A&M Eight Step Management Program
ISU: How to determine if your tree has Oak Wilt
Thousand Cankers Disease (TCD) primarily affects black walnut trees, as well as other species of walnut, and is caused by fungus (Geosmithia sp.) transported by the walnut twig beetle (Pityophthorus juglandis) - a type of bark beetle. Discovered in Colorado in 2003, TCD has caused the widespread death of black walnuts in many western states over the last decade.
Signs and symptoms of TCD include thinning crowns, yellowing or wilted leaves in the crown, and limbs that died recently. The fungus causes distinctive circular to oblong cankers in the phloem under the bark. The bark surface may have no symptoms, or dark amber to black stain or cracking of the bark may occur directly above the canker. Numerous tiny bark beetle entrance and exit holes are visible on dead and dying branches.