What is eating all the holes in the leaves of my roses?
Great question when you see rose leaves having either window pane type holes or complete holes in the leaves, but no bugs to be seen. Well, the reason the bugs aren’t being seen, is 1.) They’re very small and the same color of the leaf, and 2.) They’re feeding on the undersides of the leaves! Rose Slugs – The critter is called a rose slug, yet rose slugs are not slugs at all. They’re actually in the sawfly family, and there have been different types seen, ranging from 1 to multiple generations each year. They look like very small caterpillars (at the early stages are very hard to see), and typically feed on the underside of the leaves, causing the window pane effect from the younger rose slug larvae, to large leaf holes to total leaf skeletonization as the larva mature.
Control for Rose Slugs: 1.) Hand smashing the rose slugs as you can find them on the undersides of the leaves (look early morning). 2.) Repeated foliar sprays as needed, using Insecticidal Soaps or Horticultural Oils, but making sure to spray the undersides of the leaves where the rose slugs are feeding, not the tops of the leaves. 3.) Apply a systemic insecticide such as Bayer’s 3 in 1 Rose Care or Bonide’s (or Bayer’s) Tree and Shrub Insect Control, where the insecticide is taken up inside the plant and the sawfly larvae are killed as they feed on the leaves. Try to apply the systemic before damages are seen (at plant bud break), but can be applied later. Note: The foliar sprays are usually most effective for most immediate control, but a combination of systemic and foliar sprays work quite nicely. Remember, there may be several generations of the rose slug, so be persistent with the methods of control as you see the damages occur. And although the damages certainly make the rose plant’s leaves look bad, it rarely affects the overall health of the plant, especially those Knock Outs. They take a rose slug lickin’, but keep on tickin’.