Issue: July 18, 2001

Elm leaf beetles

Question:

I am in Las Vegas on a piece of property surrounded by about 10 elm trees, 1 pine, 3 maple and 2 chinquapin oaks. Our elms are under siege! First, we got these little beetles about 3/8" long with yellow and green stripes and yellow insides (yes, we squish them when we can!), then we got these guys that look like ladybug larvae—4 legs up front, soft body, lengthwise stripes of black and yellowish-green. Next we got little yellow pupal sacks with yellow insides again (they got washed out of the trees in one horrendous rain I think). Now we're back to the beetles again. The leaves on our trees are eaten down to the veins—all of the green is gone! It doesn't seem to matter whether the trees have been radically pruned in the last few years or are all old growth, and it doesn't look like other elm trees in this town are getting devastated like ours. A sideline—we can't even sit outside without beetles dropping into our coffee, food, etc.

HELP! I've tried leaving messages with a lot of people. I'm afraid that without the leaves, we will lose all of our 70-year-old elms, and the trees are a major part of the charm of this property. As such, we have been planting other trees (fruit, honey locust, etc.) amongst the elms, but.... Do you have any suggestions? —Linda K., Las Vegas, NM

Answer:

You have described elm leaf beetles in their adult (beetle) phase, as well as juvenile and pupal stages. They make elms look bad but rarely kill the trees outright unless the trees are unhealthy for other reasons (such as last year's drought). There are several approaches to try—several chemical sprays are effective, also a biological insecticidal spray of Bacillus thuringiensis var. San Diego can be helpful. Since the trees are pretty well defoliated, you may not have much success this year. The insects will probably return next year (to neighboring trees as well).

They may try to overwinter in your attic (or the void between ceiling and roof in flat roofed houses). In late winter as their hiding place warms, they may begin emerging and accidentally enter you home - the vacuum is the best means of managing them at this time. Remember to empty the vacuum bag outside—don't just put the vacuum in the closet after vacuuming.

Next year when you notice their return, the sprays may be employed to control the first generation in May. As the larvae crawl down the trunk to pupate at the base of the tree, they may often be trapped in burlap wrapped around the trunk. This may then be removed and burned. If you choose to use a spray product, you will probably need to hire someone with the equipment to reach the top of the trees.

Remember, however, that elms are really tough trees and will often survive the beetles for years.

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