Answer: Without knowing exactly what the pests are, it is difficult to make a recommendation. If they are aphids (which I suspect), you can kill them off with Insecticidal Soap. I use Safer's and it is quite effective. However, you may have to treat several times to rid the plants of the pests. Spraying 50 shrubs might be quite labor intensive, but worth the results in the end.
Good luck with your project!
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