Help! My Knockout roses were lush and healthy until about the middle of May. Almost overnight, the leaves were devoured between the veins. Some of my bushes sported leaves so riddled with holes that it's a wonder they could photosynthesize!
I tried spraying with soapy water, but it did no good. Little worms (lime green to medium gray in color and 1/4th to 1/2 inch in length) continued to live on the underside of the leaves. I picked off what I could, but they were rampant. I finally resorted to a pesticide, but hate using anything with warnings longer than my income tax return. Any thoughts on what these little worms might be and how they might be routed without toxins?
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lynniegirl
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applestar
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Hmm... I'm afraid Bt will not work. I think what you have are sawfly larvae (otherwise known as "Rose Slugs"). They also eat strawberry leaves and raspberry/blackberry leaves. 
I usually pick them off also. Even if you don't actually squish or remove them, just knocking them off the leaves seem to help -- supposedly ants like to eat them -- maybe that's why. Sometimes the birds help -- especially finches and house wrens. This year, house wrens are nesting in a gourd house 2 feet from the rose bush, and a male wren has staked a claim on another birdhouse a few feet from the raspberries so if he manages to entice a female to join him, I'll have some really good help
I usually don't use sprays so I can't give you a good answer to that question.
I usually pick them off also. Even if you don't actually squish or remove them, just knocking them off the leaves seem to help -- supposedly ants like to eat them -- maybe that's why. Sometimes the birds help -- especially finches and house wrens. This year, house wrens are nesting in a gourd house 2 feet from the rose bush, and a male wren has staked a claim on another birdhouse a few feet from the raspberries so if he manages to entice a female to join him, I'll have some really good help
I usually don't use sprays so I can't give you a good answer to that question.