Slug bugs (of the rose variety)

Once again I'm reminded that 'low maintenance' does not mean 'no maintenance.'

My Knock Out roses -- "the most maintenance-free rose in the world' -- have been attacked by rose slug worms (the larval stage of a sawfly). The skeletonized leaves tend to detract from the otherwise stunning floral display, so I did a search online to try to discover how to deal with the buggers.

Here's what I learned (courtesy of www.weidners.com):
The rose slug larvae turn into pupae and overwinter in the soil. It emerges in spring as a sawfly (a member of the wasp family) to lay eggs on your rose leaves. The eggs hatch out into these little green larvae that look a bit like a caterpillar. They cling to the undersides of your rose leaves, eat like crazy, and then disappear. Most varieties only have one cycle but they can do lots of damage in a short period of time. After the leaves are skeletonized and brown, it does no good to spray. That's like locking the barn door after the horse is gone! All the Bayer Rose products with cyfluethrin work really well. You can choose not to use an insecticide and hand pick and spray off the little slug worms with a strong spray of water. Horticultural oil used when they are first attacking will work and is a very safe alternative. Trichograma beneficial wasps won't help and BT will not work. Both of these are specific to caterpillars and this is a larvae not a caterpillar.

Well, I'll not be 'squishing' them by hand and they stick like glue to the undersides of those leaves, so I don't really think spraying them with water is going to be very effective. And, since my infestation is pretty advanced, horticultural oil doesn't sound like it's going to be an option either.

Am I really going to have to resort to chemicals on the "the most maintenance-free rose in the world?'