I had a 10 year old marmalade heuchera approx 4×4 feet in a sunny spot. It was thriving. Noticed flattening of stalks and shock to find plant had been disconnected from soil. Roots black and appeared bitten off in spots. No visible insects on roots. Suspect weevils. How do I treat soil in area in garden bed for future planting or how do I confirm problem. Heartbroken. Thanks for your help
Thank-you for contacting Toronto Master Gardeners with your question about your Heuchera plant. So disappointing to discover that a long-term, healthy perennial has fallen victim to a garden pest!
I suspect that you are correct in your suspicion that root weevils (likely black vine weevils) are the culprits here. The following link is to a previous TMG answer on the topic of weevils. The 2nd link is to a very useful article at the Missouri Botanical Gardens website. It will help you to make a positive identification and suggests remedies. The damage you are seeing occurs when the insect is in its larval stage and operating under ground. The adults are hard to identify as well because the feed at night and are dark in colour. They are usually discovered because of the characteristic notches they chew in the leaves of a a variety of plants. The larvae usually cause the most damage a little later in the summer, but the adults sometimes overwinter and begin a new generation by mid spring. This could certainly have occurred with the mild winter we just experienced.
Best of luck getting these pests under control!