What’s eating your trees?

If you’re the lucky person who gets to sit under that one spot of shade at the longest red light in town, you might give thanks for the tree that kept you cool.   

Except in these moments, trees are often the unsung heroes we forget to appreciate.   They just stand there making shade and cleaning the air and producing oxygen.  They don’t turn brown in 20 seconds like the grass does when it gets hot, either.  This is all the more reason we should look after them – especially when there are insects lurking to do them harm.

If you have evergreen trees or elm trees, now is the time to heed two threats:  ips beetle and elm leaf beetle.  This is their active time along the Front Range.

Ips beetle
Some experts say this pest is as prevalent in some urban areas as the Mountain Pine Beetle is in the high country.  It attacks the gamut of evergreens – ponderosa, Austrian pines, spruce.  It bores under the bark and creates girdling tunnels that cause the tree to die back or die altogether.

The good news is that it rarely attacks healthy trees.  The bad news is that dry conditions are its friend.  When trees become drought stressed with lack of water and good nutrition (fertilizer), their immune systems, so to speak, are compromised.  This is when pests pounce.  Newly planted trees are also a target.

The best defense against ips beetle – and most pests and disease – is making sure trees have adequate water and fertilizer on a consistent basis.  Staying healthy makes them most resistant to attack.  For newly planted trees and stressed trees, preventive insecticide treatments may be needed to control the pest until the tree regains its good health.  They should be applied by a properly licensed tree care expert who knows the proper timing for the application.    

Elm leaf beetle
As the name suggests, elm trees are the target for this pest.  In 2012 the Front Range saw one of the worst outbreaks of elm leaf beetle in 30 years – and this season is expected to have similar activity.  The beetle attacks elm leaves and causes them to turn brown and fall off the tree.  Without leaves to photosynthesize, the tree loses its ability to take in and store nutrients.  Repeated injury weakens the trees and makes branches prone to die back and wind injury.  Infestation can also kill the tree.

According to CSU experts, there are few natural enemies to the elm leaf beetle.   So using natural predators as an Integrated Pest Management strategy to control them is not an option.  Common treatments are to spray the leaves with an insecticide – or to inject a product into the tree or soil.  Experts recommend treatment in late July/early August for Front Range trees.

For plants, as with people, good health is the best defense.  And when the health threat is serious, consulting with an expert to get the right treatment at the right time is usually the best course of action.  

Learn more about Responsible Approaches to Pest and Weed Management from the Green Industries of Colorado.

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