Insects and Diseases
Urban environments cause lots of stress on trees, making them vulnerable to diseases and insect attacks. The Fort Collins Forestry Division actively monitors and manages these threats to our urban forest, but there are several ways you can also help to protect our trees.
Emerald Ash Borer (EAB) is a highly destructive, non-native insect that infests and kills all North American true ash species. EAB was detected several years ago north of Fort Collins and is now within city limits.
To mitigate the impacts of EAB, the City of Fort Collins has developed an Emerald Ash Borer Response Plan that outlines a phased treatment approach for all strategically selected, City-owned ash trees.
The City maintains about 10% of the 70,000 ash trees in Fort Collins. The remaining are privately-owned, making it important for community members to make their own ash management plan.
Find an Ash Tree
All City-owned trees and species are tracked in TreeKeeper. This is a useful tool to identify whether the trees near you fall under the City management plan or should be handled privately.
Treatment Phases
The Forestry Division has strategically selected 2,100 City-owned ash trees to be treated in a three-year rotation between 2024 and 2026. Anyone interested in self-funding additional treatment of trees in the public right-of-way should contact forestry@fortcollins.gov to receive a permit prior to starting independent treatments. Permits will be issued only after a tree evaluation to assess if it is worth treating.
Evaluation criteria for self-funded ash treatment:
- Size: Tree is 8 inches in diameter or greater (diameter measured at 4.5’ above ground)
- Tree Condition: Tree is in fair to good condition
- Canopy: Tree has a healthy and full canopy
- Structure: The tree has good overall structure
- Health: Is the tree diseased? Is there evidence of insect damage? Are there trunk wounds present?
Symptoms
EAB signs and symptoms include thinning canopy, loss of leaves, new sprouts on lower trunk or lower branches, vertical splits in bark, D-shaped exit holes about 1/8-inch wide, S-shaped tunnels produced by larvae under the bark, and increased woodpecker activity.
For more information on finding ash trees on your property, view Colorado State University’s tips on identifying ash trees.
Treatment Plans
If you determine you have an ash tree in your yard, please call a City of Fort Collins licensed arborist to evaluate your tree.
Consider the benefits that your ash tree(s) provide to your property:
- Do they shade your house?
- Are they large, healthy trees?
- Do the benefits of treating the ash tree long term outweigh the costs?
- Or, should the ash tree be removed and replaced?
Next, develop a plan for removal and replacement or treatment of your ash tree(s) by working with a local licensed arborist.
If you decide to treat your ash tree(s) with an insecticide, keep up with the treatments. Water, water, water! This will keep your tree healthy and help with better pesticide uptake once you start treating.
If you decide to not treat your ash tree(s), it is safer to remove the tree before it is killed by EAB. Make sure that you are replacing them with a suitable species for this area. If you are planting multiple trees, make sure that you diversify so that when the next pest moves in, you are prepared.
Slow the Spread
EAB has never been eradicated out of a community. The best thing to do now is slow the spread in Fort Collins and prevent the spread to other communities.
Here are some ways you can help slow the spread of EAB:
- Become educated and stay vigilant.
- Report suspect ash trees or beetles to the Forestry Division.
- Remove and replace low-value ash trees with a diverse palette of tree species that are capable of becoming large shade trees at maturity.
- Never move firewood, ash nursery stock, or raw ash material, except when moving to a proper disposal site. The number-one cause of the arrival of EAB in a community is humans!
- Keep all ash material local in order to prevent the spread of EAB to other communities.
- If you’d like to help Forestry Plan(t) for the Future and diversify our urban forest, visit CityGive.
Frequently Asked Questions
How did EAB get here?
Adult beetles are strong flyers, but they typically fly less than half a mile once they emerge from their host tree. This means that the pest most likely arrived in our area via human transport of infested ash wood, such as firewood or other raw ash material.
Why is EAB such a big problem?
EAB has never been eradicated from an area or community since its detection within the United States in 2002.
Leading entomologists suggest that EAB has the potential to bring about the extinction of North American ash species if the pest is not managed.
How can I help slow the spread of EAB?
- Become educated and stay vigilant
- Report suspect ash trees or beetles to the Forestry Division
- Remove and replace low-value ash trees with a diverse palette of tree species that are capable of becoming large shade trees at maturity.
- Never move firewood, ash nursery stock, or raw ash material:
- From one community to the next
- From one spot within our community to another, except when moving to a proper disposal site
What does EAB look like?
An adult EAB is an emerald green metallic beetle that is about ½-inch long and is bullet-shaped. The area under the wing covers of an adult beetle is coppery red. The larva is off-white and flat with bell-shaped segments and can grow up to be about 1-inch long.
How does EAB kill my tree?
EAB larvae damage trees by tunneling under the bark, producing girdling wounds that interfere with the movement of water and nutrients. Infested trees gradually die over a period of 2 to 4 years.
How do I know I have an ash tree?
All true ash trees (Fraxinus spp.) have the following characteristics:
- Leaves are compound, which means multiple leaflets occur on a common stalk, and typically have five to nine leaflets. The one exception is single-leaf ash which may have simple or compound leaves, with up to five leaflets.
- Leaflets are smooth or finely toothed along the edges.
- Seeds on female trees are paddle-shaped.
- Branches and buds grow in pairs, directly opposite from each other.
- Mature bark displays diamond-shaped ridges.
The following App is a handy tool to help you identify what type of trees you may have on your property: search for EAB/Ash Tree ID. Not an App/smartphone user? Send pictures to forestry@fortcollins.gov or contact a Licensed Certified Arborist.
What are the signs a tree has been affected by EAB?
The presence of EAB in a tree typically goes undetected until more than a year after initial infestation. Symptoms of infested trees may include:
- Thinning of upper branches and twigs
- Loss of leaves
- S-shaped tunnels produced by larvae under the bark
- D-shaped exit holes about 1/8-inch wide
- New sprouts on the lower trunk or lower branches
- Vertical splits in the bark
- Increased woodpecker activity
Should I treat my ash tree?
At this time, the Forestry Division is advising Fort Collins residents to act now and start implementing their own EAB management plans. Residents should first determine if their property has any ash trees, and if so, evaluate the condition of each tree, with continued monitoring throughout the year. Residents should also decide whether to have infected ash trees treated, or removed and replaced. City Forestry staff urge residents to weigh the benefits and costs associated with ash removal and replacement, versus ongoing insecticide treatments.
Should I get rid of my ash trees?
If the ash tree is in poor health or is smaller than 11-inches in diameter, Forestry recommends either planting another tree near-by (shadow planting) or removing and replacing the ash with a suitable species for the Front Range.
During the summer of 2022, Fort Collins saw a dramatic increase in spruce tree deaths caused by the ips beetle. The spruce ips beetle, Ips hunteri, initially causes mortality in the top of an infested tree, then moves downward, killing the entire tree relatively quickly.
The spruce ips beetle is an indigenous beetle to Colorado and typically attacks trees that are experiencing some form of stress. Here are some primary preventative measure tree owners can take to protect their trees:
- Water your spruce trees when the temperature is above 40 degrees.
- For optimal tree health, the general guideline for watering trees in Fort Collins is to provide 10 gallons of water per diameter inch, every week from May through October, and twice a month if weather allows from November through April.
- Other preventative spruce treatments can be applied by arborists with the proper State pesticide applicators licenses.
Once a spruce is infested with the ips beetle, there is no effective control for the insect. The wood of infested spruce trees must be carefully disposed of to prevent beetle spread. Infested wood must be immediately chipped, recycled at Ewing Landscape Materials, milled (remove and dispose of all bark), or taken to the landfill for proper disposal after removal. Ips infested wood should not be used for firewood.
There are several steps you can take to help keep our urban forest healthy, resilient and resistant to pests like these.
- Don't move firewood.
Moving firewood spreads insects and disease from one area to another. EAB and IPS Beetle can be brought into Fort Collins from infested wood found in our local mountains.
- Routinely monitor your trees throughout the growing season.
If you notice anything that looks out of the ordinary, contact a licensed, certified arborist. Learn more about the signs and symptoms of an infestation.
- Take good care of your trees.
Insects and diseases typically only attack trees that are under severe stress. Planting drought tolerant and/or native species and following proper planting, mulching, watering and pruning techniques will help ensure that your tree remains healthy.