As per the label:
Preventative rate; mix 2oz 1-2-3 NPP with 1 gal water to treat 1K. Apply every 14 days
Curative rate: mix 3oz 1-2-3 NPP with 1 gal water to treat 1K.
Do not irrigate for 4 hours if treating for tissue fungus.
Irrigate with 1/4" to 1/2" water after application if treating for soil borne fungus.
As Natty noted, follow up with a good soil inoculant and/or biologically active organic matter.
The nation that destroys its soil destroys itself.
Franklin D. Roosevelt