Hello. I have several planting of Jack Frost Brunera and Heuchera (Coral Bells). For the past three or four years, something is eating the leaves. I do not see any signs of aphids on the plants. We think it may be slugs. We have put slug repellant around the plants, but it does not seem to be working. Any help you can provide about what the pest might be and how to control it would be most helpful. I have included a picture of the leaves from both plants. With thanks.
Thanks for getting in touch with Toronto Master Gardeners. It must be frustrating to have this happen year after year. Many bugs are more active during the night as opposed the day. If you don’t see any bugs on the plants during the day take a flashlight when it’s dark and collect any bugs you see. This is the first step to identification.
One insect that inflicts this type of damage on Heuchera plants in particular is black vine weevil (Otiorhynchus sulcatus). See image at:
Typically Jack Frost Brunnera plants are not bothered by pests so it would be worthwhile to take a flash light at night to look at the plant and see if it has black vine weevils on it or another type of bug. Black vine weevils are common insects that develop on the roots of many garden plants. They are active at night when they chew distinctive notches along the edges of leaves. The weevils emerge in mid to late spring. Most eggs are laid in late spring and early summer. The eggs hatch and become larva. During this time the larva start to feed on the roots of the plant and continue to do so throughout the winter. Larvae of black vine weevils are legless grubs, with a cream-colored body and a pale orange-brown head. In the early spring the larva transform into pupa in the soil. From the pupa the adult form emerges.
There are several environmentally friendly ways to control them:
- Shake the weevils onto a white cloth so they are visible and then destroy them in soapy water.
- Affix cardboard strips covered with a sticky substance to the stems and trunks of susceptible plants in early spring before adult weevils emerge.
- Weevils live in dead plants and ground litter. To prevent overwintering sites take all of the dead foliage of any infested plants and place it in the garbage (not the compost).
- To break their life cycle drench the soil around the plant with parasitic nematodes to destroy the larva. There are several possible times to do this: April, early June or as late mid-July and mid-September. Keep the soil of the treated area moist with frequent watering. You can easily find nematodes to buy online.
For more information, please review the following links:
http://cues.cfans.umn.edu/old/blackvw/blackve.html
https://www.mortonarb.org/trees-plants/tree-and-plant-advice/help-pests/black-vine-weevil