I like weevils. Weevils are funny little beetles with silly
looking “snouts” and they have a name begging to be made into puns. It’s too
bad that some of them are also annoying pests that chew on the roots and leaves
of a variety of garden plants. Perhaps some might even call them weevil (sorry,
but you knew it was coming).
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| Weevil. Photo by Stephen Luk, bugguide.net |
In Colorado some of the more common root weevils include
strawberry root weevil (Otiorhynchus ovatus), rough strawberry root weevil
(Otiorhynchus rugostriatus), black vine weevil (Otiorhynchus sulcatus) and
lilac root weevil (Otiorhynchus meridionalis). Lilac, privet, peony, euonymus,
heuchera, hosta, rose, strawberry, raspberry, white clover, dandelion, dahlia,
and mint are few examples of plants that can be fed upon by one or more of
these root weevil species.
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| Lilac root weevil on peony. Photo by Whitney Cranshaw |
Root weevil larvae are legless, cream-colored grubs with
orange-brown heads that can be found in the soil in winter. Starting around
late-winter through early-spring the grubs pupate in the soil before emerging
as adults mid- to late-spring. The adults cannot fly, so they will likely feed
on the same plant it developed on as a larva.
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| Black vine weevil larva. Photo by Peggy Greb, bugwood.org |
Grubs feed on roots, which may cause decline or dieback in
plants if the feeding is extensive, but this is quite uncommon in landscape
plantings. Adults feed on leaves at night and cause leaf notching. It’s likely
that a gardener will not notice the damage until the daytime, but just because
one sees no weevil does not mean weevil is not there…. Fortunately, adult root
weevil damage is typically only aesthetic and the plant will tolerate a bit of
herbivory. If you think you need to manage the pest, check out Dr. Whitney
Cranshaw’s Root Weevil Fact Sheet for control methods.
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| Circular shaped cuts from leafcutter bee. Photo by Whitney Cranshaw |
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| Adult root weevil U-shaped feeding damage. Photo by Whitney Cranshaw |
Sometimes adult root weevil damage is mistaken for
leafcutter bee damage, or vice versa. Leaf notching caused by root weevils
tends to be jagged and U-shaped, while leafcutter bee damage is smooth and
shaped like a half-moon. If you’re still having a hard time identifying the
insect or the damage contact your local Extension office. Weevil help you!
This was really fun and interesting to read!
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