My roses are developing spots and holes in the leaves. Any idea what this is? I don’t see any bugs.
Right now, we’re getting samples and questions about rose leaves having either window panes type holes or complete holes in the leaves, but no bugs to be seen. Well, chances are that’s the results of the rose slug. Rose slugs are 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 slugs, to skeletonization as well as the large holes as the larva mature. Control for the rose slugs includes 1.) Hand picking the infected leaves (with saw fly larvae on them) and destroying the leaves, 2. Repeated foliar sprays as needed, using Insecticidal Soaps or Horticultural Oils, and be sure to spray the undersides of the leaves, or 3.) By applying a systemic such as Bayer’s or Bonide’s 3 in 1 Rose Care. The foliar sprays are usually the most effective immediate control, but a combo of the above works quite nicely! (By the way, being they are saw flies, Bt is not an effective means of control.) Of course, these methods of control also work quite nicely with the aphids as well.
Should I deadhead my Knock Out roses?
It isn’t necessary as they are considered self cleaning, but if you’d like to get rid of those spent flowers, go right ahead. Simply clip out the spend flower just above a lower set of leaves. Knock Outs will go thru a brief delay period after the first set of flowers, but eventually fire back up and flower all summer long. Feel free to feed them with a rose food now as well.