I apologize for this delayed reply to your gardening question and hope it is still helpful to you.
Herbicides will not harm your beneficial insects. I suggest you use a product with glyphosate (Roundup is one brand and just apply it to the foliage of the plants you want to kill. If they are very woody and strong it may take more than one attempt. The glyphosate breaks down fairly rapidly and won't harm things you plant where it was used. If your pest is truly slugs the least toxic products are the bait Sluggo which is made of iron and phosphorus or Green Light's Bug and Snail Bait made from Orthoboric acid another ingredient considered among the least toxic.
Thanks for the question. Best wishes for a wonderful gardening season. Please stop in again soon!
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