Musk thistle and thistle head weevil: noxious weed and biological control

Musk thistle along a Pemiscot County roadway

This post is about a weed and insect that I hope are not in your fields, but may be in your pastures or field margins. Recently I have been observing the thistle head weevil throughout the Bootheel on musk thistle. Musk thistle is a Missouri listed noxious weed that seems to thrive in disturbed areas in the Bootheel. Noxious is a legal status and Missouri actually has a musk thistle statute and control is legally mandated. As such, the help of an introduced biological control agent is somewhat comforting. Ben Puttler et al. wrote an article in Weed Science (1978) about the introduction of thistle head weevils into Missouri and a useful fact sheet about musk thistle control. However, the weevil’s host range has expanded to include native thistles with ecological impacts causing this weevil to fall out of favor as a biological control in many places.

Based on the 1978 article it appears that musk thistle acreage has expanded in the Bootheel and the weevil has followed the thistles. I do not know if intentional introductions were made in the Bootheel (if any readers know please comment). Regardless, I have found the adult weevils in most of the thistle patches I have examined. If you have musk thistles on your land, you may want to scout for weevils and the damaged flower heads they cause. As the fact sheetshows an IPM approach can provide good control. At the very least you will get to see a beautiful (yet noxious and introduced) plant and an interesting (also introduced) biological control insect that has persisted in Missouri 30 years after initial introduction.

 


Categories: Insects

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  1. Mecinus janthinus | biologistsoup

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