JD v. Kubota
Thanks to all for the replies.
I'll check out the Kubota range as well but the only smaller Kubotas I've seen here in NZ are the 16hp B7100 HST 4WD which don't have power steering and as a result are heavy to manoeuvre in tight spaces. They have a good range of dedicated mowers but they wouldn't be suitable for towing my sprayer and trailer.
Maybe the B7100 is now available with power steering... it's worth a look.
Failing that, the JD GT225 18hp looks suitable for my purposes.
Thanks again for your suggestions.