I did not find it but the usual rate of application is 9:1. That is 9 parts water to one part ammonia. Most do a drench in fall after the plants have gone dormant and then again in spring for a bad infestation.

There are multiple threads. Here are a couple:

https://www.gardenweb.com/discussions/1961439/the-ammonia-slug-solution#n=7

https://www.gardenweb.com/discussions/2022665/ammonia-for-slugs#n=10

https://www.gardenweb.com/discussions/1980764/the-ammonia-bath-and-slugs-snails-it-worked#n=7

Seems the consensus is a 10 to 1 solution.

its discussed ad nauseum in the hosta forum ... 10% .. 9 to 1.. 10 to one.. no diff ..

the same for vinegar ... imo.. whichever is cheaper ..

try using the search bar in hosta forum ...

some peeps.. after full dormancy.. use it to drench the mulch ... to kill the eggs ... others just use a spray tank to spray the leaves.. tops and under ... and let it run down the stalks into the crown ...

its really a year round battle to win ... full fall cleanup ... drench soil/mulch ... and start as soon as the leaves mature in spring ... and dont stop until next fall clean up ... in my MI with the cold soil and air temps.. it usually takes the slugs so time in spring to get real active ... thats why we can wait until leaf out... the warmer the zone.. the sooner you should get at it]

get this.. one slug is both momma and daddy ... whats that all about ... lol ... and if you can kill them in fall or winter ... then consider that wil be 100 less slugs next summer .. or more ...

i know you PNW peeps do slugs to the extreme ... my experience is just the midwest hordes .. but it cant be that much different ...

finally .. keep in mind.. vinegar is in teh pickling aisle at the grocer .. in large containers.. which usually make it cheaper in the long run ... and no.. you cont need ACV .. nor balsamic.. nor any hoity toity type.. lol ... even if you can convince yourself they are escargot ... lol...

ken

oh.. as to your title.. this is a contact kill ... it is not a prophylactic ... you cant spray just the plant.. and hope that it will kill later... once dry.. its useless ...

ken