Japanese beetles (Popillia japonica) are a very destructive landscape pest that has been present in the US since its accidental introduction in the early 20th century. While they have mostly been a problem for gardeners in the eastern United States, the populations are now spread more widely across the country. The beetle adult attacks the flowers and foliage of hundreds of plant species while the larvae eat away at grass roots. It is a heartbreak to see them feeding in large numbers on your roses.

The best long-term control of future populations is to target the grubs, which overwinter and spend most of the year about three inches deep in the soil, before emerging as adults in spring. Milky spore (a bacterium), applied to the lawn, causes a lethal disease specific to the Japanese beetle grubs. It does take a few years to become effective however.

The adult beetles produce a pheromone trail to your roses in their droppings so remove them as quickly as possible. It is not unreasonable to prune and dispose of heavily infested plant parts to discourage newcomers from finding their way to your plants. Hand pick the beetles and discard them in a pail of soapy water. They release easily when startled and may even fall off the plant into a bucket of water in an attempt to escape you.

Keep in mind that many birds such as cardinals, catbirds and grackles are the natural enemies of Japanese beetles and favor the grubs or beetles, or both, so support birds in your garden. Avoid the use of pheromone-emitting Japanese beetle traps. As satisfying as it is to remove a trap full of beetles, the attractant in the trap may be luring more beetles to your garden.

For more information on rose pests and other issues, see our Guide to Rose Problems.