Vapam, will stay under normal temperatures (< 30°C) some days actif in
the irrigation system or a spraying unit.
Abundant cleaning with water is the only solution.
All plants are sensitive to Vapam.
In order to control if there is still plant-toxic Vapam or other
toxic liquids, put some irrigation water on cotonwool and seed with
cress, after 3 days it will germ. If it germs and develops well,
everything is OK.
Did you check the pH of your irrigation water?