What can be done about severe infestations of rose cheevers on my peonies? I’ve had issues with them for years . Picking them off is almost useless in dry June’s as our gardens have their favourite sandy soil.
Thank you for contacting Toronto Master Gardeners. Dealing with insect pests can be frustrating.
Traps are commercially available for rose chafer beetles. However, they are based on a lure or attractant (such as highly concentrated rose fragrance) and must be placed a significant distance, 20-25 feet (6-7.5 m), and downwind from your targeted plants. If your garden isn’t large enough for this amount of separation, you might risk attracting more beetles to your garden than you already have.
Some other strategies to control rose chafer beetles include:
Drenching the soil with a parasitic nematode to kill the larvae living in the soil;
Covering the plants with a physical barrier, such as cheesecloth or floating row cover, while the pests are active. The barriers should be placed when the rose chafers arrive in late May and then removed after they are done feeding (after June); and,
Applying pyrethrin (an organic control) when there is a severe infestation. Note that pyrethrin, while it may be organic, is a broad-spectrum insecticide that can harm beneficial insects as well as pests.
A novel suggestion for dealing with slow-moving insect pests such as rose chafers is simply to vacuum them from the plant.
For further information please refer to the links below. Note that any U.S.-based reference might suggest pesticides that are banned for cosmetic use in Ontario.
https://cedarcirclefarm.org/tips/entry/pest-rose-chafer
https://www.extension.umn.edu/garden/insects/find/rose-chafers/