Holes in Knock-out rose bush leaves but no Japanese beetle in sight!

Asked June 14, 2017, 11:30 AM EDT

Every year we have a beetle battle. This year the knock-out roses bloomed as usual but the leaves were being attacked. There is no sign that beetles are eating the leaves or blooms but something is going on!

Baltimore County Maryland

3 Responses

Based on your description it sounds like you may be dealing with rose slugs. There are several species and there may be several generations in a season.
You will have to look for them as the damage may have already been done.

Check the upper and lower leaf surfaces for greenish yellow larvae. Mature larvae are about 1/2 inch. If the infestation is light, pick off and destroy the larvae. To control heavy infestations, use horticultural oil or spray with spinosad. Follow label directions and do not spray in the heat.
See our website for more information http://extension.umd.edu/hgic/rose-slugs-shrubs

I don't think that's it. There are no bugs, larvae, spiders or tiny white mites. All I see are leaves that are dried up with a these holes in them!

This does look like heavy damage from rose slugs.
They can be hard to find, but this could also be old damage too, as the new growth on the top of your plant looks good.
Follow the link above.
They scrape, or "windowpane" the leaf surface, which then turns tan and falls out.
There are three different kinds, some with multiple generations per season.
If you begin to see any tan windowpanes on the healthy new leaves, check for them, then squish them and/or treat.