I don't know about the efficacy of garlic spray for slugs, but you ought to visit the Hosta forum -- many of the members use an ammonia drench to combat slugs which are soooo attracted to hostas. I have not tried that myself, just having read about it, but it apparently works well.

Check out cutworm damage on hosta to see if it matches. Otherwise my go to slug control has always been the 10 percent ammonia and water. Yes it is a contact killer but it will kill those hiding in the soil. If I see damage but no slugs I’ll pour a little down the petioles.

tj

I had such bad slug damage last year on so many hostas I was just sick about it. I was told that once you see damage in the spring you’ve lost the battle. Anyway the 10% either vinegar or ammonia drench was recommended. I was told to do it in fall and in spring again just as the pips come out. I did it and my hostas are looking perfect. It’s not that late in the year, I would try the drench. What have ya got to lose??? Good luck!

I don't know about garlic, but my MIL had many hostas and she used the good ole' beer traps. I think she used a pie tin with beer. It was quite disgusting to see all the slugs dead in the beer each day, but satisfying at the same time.........she used to get A LOT that way. FWIW.

In the Pacific Northwest , I think you would need a keg of beer to get those whopper slugs and snails. Have you tried Sluggo Plus to get the other chewing critters? It gets those other leaf munchers like earwigs and cutworms. What does the damage look like? Weevils notch the edges around here, whereas tiny TINY little green caterpillars eat holes. Way too may hours of turning over leaves to find critters. Must be something better to do these days....

-Babka