Q. Looks like elm leaf beetle or
leaf miner damage in the picture I sent. What to do? Let the tree flush a new set of leaves after the
larval feeding frenzy? These are trees cared for by volunteers and found in
Spring Mountain Park near Blue Diamond. I would rather have the volunteers not
use any systemics. Any thoughts?
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| This is elm leaf beetle damage to Siberian elm. To my knowledge the elm leaf beetle only attacks Siberian elm. Siberian elm is different from Chinese elm. |
A. That’s elm leaf beetle (ELB)
damage on Siberian elm leaves. We used to see a lot of it when there were more
Siberian elms in our community. If you can catch them in the larval stage, they
are easy to control by spraying the leaves with any type of insecticide. Any
insecticide works including soap and water and salt sprays. You just need to
kill them.
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| That’s elm leaf beetle damage taken from a slide over fifty years ago in Colorado. |
The
problem is the act of spraying which means specialized equipment because the trees
can grow 40+ feet tall. Soap and water sprays kill on contact. They don’t have
any residual, so you must spray the leaves until the level of control you want
is achieved. Otherwise, you must use a systemic insecticide as a soil drench or
have it absorbed through the tree trunk.
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| Larvae of elm leaf beetle adults (don’t confuse them with adult cucumber beetles) taken from a slide over fifty years ago. They are ephemeral, meaning they last only a few weeks and they are gone. |
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| This is a nearly mature form of Chinese elm, maybe evergreen elm. Notice how tall Chinese elm can grow. Don’t confuse them with Siberian elm which is a trash tree. |
I
just ignore them and tell people not to plant Siberian elm when I see it. Recovery
of this tree from single feeding by ELB is not a problem. I have only seen ELB
eat the surface of Siberian elm leaves, not any of Chinese elm types including lacebark elm. Plus, ELB has only
one generation each year while other insects, like the great leaf skeletonizer,
is more destructive and mates multiple times each year.
I
consider Siberian elm a “trash” tree and ranks about 2 out of 10 in
desirability. Chinese elm, on the other hand, is a much better tree and I would
give it an 8 or 9 out of ten. By the way, Siberian elm is no longer sold as a
landscape tree. No great loss.
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| Siberian elm removed with a telehandler…aka forklift… at Aherns |