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What is causing large holes in my Rhubarb leaves?
Large and ragged holes in the leaves of rhubarb are caused by slugs. The conditions in which rhubarb thrives (moist and mulched) are ideal habitat for slugs. In the moist and temperate climate of southwest B.C. slugs may sometimes cause significant damage to rhubarb leaves but slug damage can be managed. Rhubarb should be watered in the morning to allow the soil surface to dry out during the day, which limits slug movement during night. Protecting and encouraging slug predators such as ground beetles, rove beetles, centipedes and garter snakes by avoiding use of pesticides and using cultural practices that encourage beneficial species (minimize soil disturbance and mulch). Slugs do not travel far so hand picking them off the plants at night or early morning can effectively manage local populations. Hand picking can be enhanced by laying down wood, paper or pieces of citrus peel near rhubarb plants then collecting the slugs that are hiding under these in the morning. Slug and snail baits containing ferric phosphate or ferric sodium are not toxic to pets or other animals. Small amounts of these may be spread over the area surrounding the rhubarb plants and will need to be reapplied periodically and especially after rain.
Sources:
Canadian Phytopathological Society, Diseases and Pests of Vegetable Crops in Canada, Chapter 17: Diseases and Pests of Vegetable Crops in Canada (phytopath.ca) (accessed September 23, 2023).
Gilkeson, Linda A., West Coast Gardening Natural Insect, Weed & Disease Control, Second Edition, 2013.
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