Answer: Leafrollers are common pests and they knit leaves together with webbing, just as you've described. At this stage I'd recommend handpicking affected leaves and destroying them (along with the caterpillars). If it becomes a problem year after year you can spray trees and shrubs with horticultural oil in January and February before the buds open. Oil will suffocate the egg masses, and prevent a new generation from hatching. Bacillus thuringiensis (Bt) is effective against caterpillars and safe to use on your plants, if you opt to use a pesticide.
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