Answer: It sounds as though your cotoneaster is playing host to sucking insects which are producing honeydew (a sticky, sweet substance), which in turn is attracting wasps and yellowjackets. You'll need to get rid of the aphids, scales or mealybugs to stop the development of honeydew which will keep your plants from attracting wasps and bees. You might start by hosing the plants off with a strong stream of water from the hose to dislodge some of the honeydew. Then you'll want to closely inspect the plants for signs of insects. I'd check the plants in the early evening or early morning when the wasps are not as active. Once you've determined which insect is causing the problem you can treat it with an insecticide specific to that pest. When you've eliminated the honeydew producing pests, the wasps won't be quite so interested in your hedge.
Stunted growth could be due to insect feeding. After you've gotten the pests under control you may want to prune your plants back to encourage healthy new growth.
Best wishes with your landscape!
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