Gardening & Living in Grand Style
Insects, both troublesome and not…
by Michael Johnson
May 22, 2014 | 715 views | 0 0 comments | 3 3 recommendations | email to a friend | print
The leaves of this lilac plant show notches caused by root weevils. Courtesy photo
The leaves of this lilac plant show notches caused by root weevils. Courtesy photo
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As part of my professional work with USU Extension I provide research-based information on gardening topics including insect pests. However, having been personally involved in the gardening industry in various ways for decades now, I have come to a more live-and-let-live approach to many insects. Still, there are some instances where instect control should at least be considered for the sake of a plant’s long-term health.

In the case of insects, there are also those that, while they may annoy some people, just don’t need to be killed. Rather, the person should take a chill-pill and just enjoy the wonders of nature.

Root weevils

A troublesome pest that could, over time, eventually damage and weaken a plant is the root weevil. The two more common root weevils here in Utah are the lilac root weevil (Otiorhynchus meridionalis) and the strawberry root weevil (Otiorhynchus ovatus). The adults of both are somewhat shiny, brownish black and approximately one-quarter-inch long.

The damage the adult does is somewhat noticeable in that it eats notches out of the edges of leaves of woody ornamentals such as lilacs, but can also feed on a wide host of plant materials if left unchecked. Adults climb plants at night to feed and will drop to the ground if disturbed and hide in debris. They hide in the soil surface during the day. However, the adult isn’t the real problem since notching along the edges of the leaves seems to be its main occupation. The larvae, which live in the soil, feed on roots and can weaken plants over time, especially if weevil populations reach high levels and the plants aren’t large.

Larvae might be controlled through the use of parasitic nematodes, however, that has shown to have mixed success. On ornamental plants such as lilacs, the larvae and adults can be controlled with the systemic imidacloprid and with various pyrethroid insecticides.

Inchworms

Another pest that I periodically see but is likely around most years is the cankerworm or inchworm. When fully grown these can be an inch long and vary in color from greenish to brownish to blackish. This coloration can help camouflage the worms. They feed on the leaves of a variety of tree species, eating the tissue between the veins.

There is a spring and a fall cankerworm, and it’s generally thought the fall cankerworm is the most common. However, this spring I am fairly sure I saw a cankerworm on a tree where the leaves had been chewed quite a bit. The owner noticed the damage but didn’t see any insects, and as I have mentioned before, sometimes our winds can damage leaves to the point that they look as if they have been chewed on by some type of pest. However, while inspecting the tree I saw a small caterpillar, which moved with a looping motion where the midsection of the body bows or loops after the cankerworm extends its body and then the back legs catch up. While the inchworm is not considered a serious pest, if the foliage of a tree is eaten time and again over a few years it can weaken the tree.

Leafcutter bee

An insect that is good, but often annoys people, is the leafcutter bee. This is another of our local native bees that is a good pollinator but likes to cut circular-shaped sections out of leaves to use when building its nest cells. These bees also like to nest in soft, rotting wood and in plant stems. While the root weevil just takes a notch out of a leaf, this bee takes out a large section that often is almost totally round.

While I understand the interest in honeybees in our community, my favorite bees are the natives since they provide a lot of help but require little care beyond us growing plants they like, and limiting the spraying of insecticides. We can also easily offer space for them to have their young and should be tolerant of the need for a little of our greenery as used by the leafcutter bee.

Thought for the day: “We hope that, when the insects take over the world, they will remember with gratitude how we took them along on all our picnics.” —Bill Vaughan.

Previous gardening columns 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 mike.johnson@usu.edu.

Copyright 2013 The Times-Independent. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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