CO-Horts Blog

Monday, March 4, 2019

The Lesser of Two Weevils

Posted by Jessica Wong, CSU Department of Bioagricultural Sciences and Pest Management

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).

Weevil - Amalus scortillum
Weevil. Photo by Stephen Luk,
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.

Image result for lilac root weevil on peonyImage result for lilac root weevil on peony
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. 

Image result for root weevil larvae
Black vine weevil larva. Photo by Peggy Greb,
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. 

Image result for leaf cutter bee damage
Circular shaped cuts from leafcutter bee. Photo by Whitney Cranshaw
Image result for root weevil damage colorado
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!

1 comment: