Every year about this time (actually, slightly earlier) my neighbors know that I am an organic gardener because although I may have lovely rose blooms, my leaves look like those above.
Why? First of all, I’m not growing all Knockout roses, which don’t seem to get bothered.
But that’s not the answer you’re really looking for. If you look at the second leaflet on the lower right, you can barely see a tiny caterpillar-like insect. I have better photos from my post on the topic last year.
This is the larva of something called the rose sawfly.
Since it’s not a caterpillar, bt (bacillus thuringencis) doesn’t work.
The non-organic folks can use systemics to solve for this–but many of the rose systemics have the same neonicontinoids that may be implicated in bee deaths. So if you are non-organic, please reconsider this.
On occasion, and this year was one of those, I sprayed an OMRI certified herbal oil for this–just because the population seemed inordinately high. Insecticidal soap will also work–but again, spray at sunset so as to disturb as few beneficials as possible. Remember, these “good organics” don’t discriminate between good bugs and bad bugs–they just kill everything they land on–rose sawfly larva, spiders, bees–so try to spray when as few “good bugs” are around as possible.
I also had a caterpillar–a genuine one–eating my rose buds. That I really didn’t want. So I sprayed–at sunset, on an extremely cool day, when it was least likely that any beneficials might be around.
This is probably the first time I’ve sprayed the roses in 6 or 8 years. I really hate to do it–but when I do it, I try to do it responsibly!