Japanese beetles are already starting to feed on the leaves of the earliest lilies that are out. I picked off seven. But they seem to be burrowed in the soil. What can I do?
Thankfully, there is only one generation of Japanese beetle per year – although it seems like there are many more! The best strategies for controlling the beetles is to kill them during the adult and larval stages:
- Adult beetles emerge in late June or early July. The adult insects are metallic green in colour with coppery brown wing covers. To prevent each female adult beetle from laying up to 60 eggs at the end of the summer, hand pick them from plants. Just knock them off the leaves of a plant, into a container of soapy water, and they will drown.
- Larvae. Eggs hatch after a couple of weeks, and larvae chow down on grass roots until the cold weather arrives. They resume feeding in the spring. To prevent next year’s infestation, treat the lawn and garden with beneficial nematodes that are specific to Japanese beetle larvae – apply these in late summer and water into the affected area.
For details, see an earlier post on this issue: Ask a Master Gardener. Insect ID – Japanese beetle.
One issue to consider – are your perhaps lilies being attacked by a different beetle? It has been a cool spring and is now the end of April – this is very early for Japanese beetles to appear in the garden. On the other hand, the brightly coloured scarlet red lily leaf beetle emerges in the early spring to start feasting on lilies (Lilium species) and fritillaria. See Ask a Master Gardener Lily beetles for information on control of these lovely, but nasty, critters. The main control strategies include hand picking and destroying both adult beetles and the larva (which are visible on the undersides of leaves) and to keep the lilies clear of debris underneath, to avoid encouraging the beetles from overwintering.
All the best in saving your lovely lilies!
Below are a couple of links to articles you might find helpful:
Government of Canada Japanese Beetle Fact Sheet. https://www.inspection.gc.ca/plant-health/plant-pests-invasive-species/insects/japanese-beetle/fact-sheet/eng/1328165101975/1328165185309
Sunset Nursery. Lily leaf beetle. http://sunsetnursery.on.ca/index.php?page=lily-leaf-beetle