Country of Origin: Australia
Cost: $549 for full version. A free version gives full functionality minus some reporting aspects.
Spray, an iOS app by EziApps is the most comprehensive app I have seen for recording agricultural chemical operations. While it is not the prettiest app out there and takes a lot of sliding back and forth between screens to get to where you want to it is more than made up for by the range of things you can record for every spray application. Multiple weather readings, detailed equipment settings, chemical lists, operator equipment and so on.
A free lite version gives almost full functionality in order to be able to see what the app offers. To be able to export reports however (essential for record keeping) you need the full version which costs $549.99