Insect Identification – Slugs eating my dahlias and peony leaves


My flower leaves are being eaten by a white insect in shape of Slug. Please let me know what pesticide should I use.
I live in Toronto, the location is partly sunny. I recently used Mulch and landscape fabric. I am not sure if that creates the insects. I have peonies and dahlias.


From your photos, the culprit appears to be a garden slug, with your close-up photo clearly showing the slug tentacles.  However, your note mentions an “insect” that looks like a slug.  If you feel that this is not a slug, please tell us why.

Slugs prefer soft, fleshy leaves, and find dahlias especially tasty.  However, slugs generally stay away from peonies, which are often listed among the plants that slugs don’t like!

Master Gardeners do not recommend the use of pesticides.

It takes some work to get rid of slugs – hand-picking them off the plants in the early evening is one of the best ways to do so.  Other methods of preventing slugs from accessing your plants include placing barriers around the plants – e.g., wide copper strips (which will give the slug an electric shock) or sharp materials like crushed eggshells, and sharp sand – to physically deter them from getting to your plants.  Some people have success with eggshells while others say they are not effective. Slugs lose a lot of moisture through the mucous they produce, and do not like moving across dry material.   When these physical barriers other than copper become wet (even when you water the plants!), they can lose their deterrent effects.

Mulch (e.g., grass clippings, straw, bark) can provide the ideal moist environment for slugs to lay their eggs, so this could have contributed to the problem.  Keep the area around your plants clean of debris, to discourage slugs from visiting.  I doubt that the landscape fabric is contributing to the slug problem.

Our website has several previous postings that respond to your question.  In particular, the following provides many details:

  • Toronto Master Gardeners. Ask a Master Gardener. Solutions for slugs. A couple of the links are no longer available (first paragraph – Earth Day present, relating to pesticides – this is no longer on-line), and Integrated Pest Management (I’ve updated this link here)  .

Finally, if you continue to have slug problems, some experts suggest planting a “trap” or “sacrificial” crop that you know is especially attractive to the slugs – this will draw them away from your peonies and dahlias.  However, this would not get rid of the slugs, so is not likely an option for most people! Slugs would gather on these plants, and you could then pick off the slugs or simply pull up the plants. See  Laid back gardener. Trap plants for slugs.