If you are seeing smooth-edged, curved holes cut in your rose leaves, that may be the work of leafcutter bees.We hesitate to call leafcutter bees a pest. The bees are not feeding on the leaves, they are using the cuttings to line their nests, usually in rotting wood, and their activity is brief.

These bees are important native pollinators and many rose gardeners choose to leave them alone. That is what we recommend. Any product that you attempt to apply to them will equally affect beneficial insects.

Less tidy damage is often created by Japanese beetles (Popillia japonica), a very destructive landscape pest that has been present in the US since their accidental introduction in the early 20th century. The beetle adult attacks the flowers and foliage of hundreds of plant species while the larvae eat away at grass roots.

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.

Windowpane, skeletonized leaf damage is likely to be caused by roseslugs.These yellow-green, olive green or black, slug-like pests are the larvae of several varieties of sawflies, non-stinging wasp family insects. They are frequently mistaken for caterpillars. These damaging larvae are active mostly at night and leave behind windows of papery, translucent damage on your rose leaves that later turns brown. Their feeding damage is rarely a threat to the health of the rose though the results are not pretty. Occasionally, a heavy infestation can defoliate a plant to the point of serious decline.

Begin looking for these pests on the underside of leaves in early spring. Larvae actively feed on plants for a period of about a month before dropping to the ground. The larvae cannot return to a rose leaf once they have fallen to the ground so spraying with a hose or brushing them off the plant is very effective. Some types of rose slugs may have multiple generations in a year so keep an eye on your roses for a reappearance later in the season.

You have many natural allies who will happily consume these insects. Birds, beneficial insects and even small mammals will help to control rose slugs if you make them welcome in your garden and limit the use of chemicals that can cause them harm. More gentle chemical approaches, like neem oil, horticultural oil and horticultural soap will all be effective in controlling rose slugs if applied to the insects while they are active.

For more information on "rose slugs" and keeping roses problems free,  see our guide Rose Problems.

See our Companion Planting FAQ for more information on deterring "bad" bugs.

For tips on a variety of gardening topics, see our Plant Information Guides.
- Courtesy of NYBG Plant Information Service