When is the best time to apply Munns Winter Grass Killer - regarding damp frosts and before or after rain?

Munns Professional Winter Grass Killer is absorbed by the roots. After application, we recommend to water the product in with 12-25 mm of irrigation (12 - 25 Litres of water per 1 metre square of lawn). 

The product can be applied before or after a frost, and, before or after rain. However, for especially heavy rain, reapplication may be required.