Gardening & Living in Grand Style
Leaf beetles, caterpillars and cold damage…
by Michael Johnson
May 08, 2014 | 1578 views | 0 0 comments | 5 5 recommendations | email to a friend | print
Cottonwood leaf beetle
Cottonwood leaf beetle
It really has turned out to be a warm spring and for those who planted early and sheltered their warm-season plants on the few cold nights, you’ve gotten a good early start, assuming that the cold night we had last week didn’t get you. However, I believe those warmer conditions pushed some of our insect pests out of their warm winter beds earlier than usual.

I have seen and had calls on the cottonwood leaf beetles and tent caterpillars are now making an appearance. And it’s not all about insects, as I have seen examples of leaf damage that is likely due to the cold.

It really does seem early to be seeing cottonwood leaf beetles, especially in the numbers seen the last three to four weeks. I know some people have already taken some steps to control the beetles after the amazingly high numbers and damage we saw last year. I wrote an article on the beetles last year, now available on The Times Independent website,, at

Since that information is already available, I won’t go into a lot of detail. Just know that while there are beneficial insects that feed on the larvae, if the beetles get as numerous as last year those beneficials won’t be able to eat them all. The continual loss of leaves year after year due to beetles isn’t good for the tree.

Young larvae can be controlled with insecticidal soap or a summer horticultural oil. The older larvae can be managed with some organic controls, such as spinosad and the San Diego or tenebrionis strain of Bt – but not the tenebrionis Bt used for caterpillars. Of course, there are other, stronger non-organic controls.

Tent caterpillars, with their characteristic web nests, are one of those “oh here we go again” insects that are fairly common and seem to attack many of the same trees from year to year. In saying that, I don’t just mean the same tree species, but in many cases the exact same trees. There must be something really special about the taste of those leaves! While they generally aren’t considered a real threat to the tree since the leaves will grow back, you really don’t want yearly defoliation as it can weaken the tree.

The caterpillars seem to particularly like cottonwoods, willows and chokecherry but will attack many other trees, including fruit trees. When the nests are lower in the tree you can just take a pole or some other long item and break up the nest. If the larvae are still young and haven’t left the nest, this can be enough to end the problem. However, once the caterpillars are venturing out of the nest and eating the leaves then more control might be in order. Spinosad is recommended in such cases as is the Bt for caterpillars, which is the most often found Bt product in stores.

It’s not uncommon to have plants put out leaves early in the season that are then damaged by either cold temperatures or wind. With cold damage you can get some shriveling of the leaf, which initially might look like some kind of disease attack. These damaged parts will usually eventually brown up and fall away. With thicker leaves, the damage can be some bronzing or just general leaf discoloration. With wind damage the leaves are torn up and can look like something has been chewing on and eating them. This can take a bit more time to determine since you need to check which insect might cause the damage for that particular plant and then check the plant for that insect. So inspect the plant carefully and if unsure give it a little time and see what happens.

Thought for the day: “The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.” —William Arthur Ward

Previous articles can be found on The Times-Independent website, Have an idea you’d like Mike to consider writing about? Want more information about these topics? Call the Utah State University Extension Grand County office at 435-259-7558 or email Mike Johnson at

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