I want to spray BAC (benzalkonium chloride) to kill a light growth of algae on concrete in a back yard. There's no moss.
Is it effective to apply the BAC on a hot day?
The algae looks dried out and may not absorb much chemical but is that actually needed for BAC to be effective?
In this heat the algae on there may already be dead, certainly dessicated and quite possibly dormant. Mosses do this too.
Save the treatment for a time when the stuff will have time to take effect. All weedkillers work better if the target is in active growth.
Get a used trigger pack, the sort used for kitchen sprays, etc.
Make sure it works.
The trigger part is usually a bayonet-type fitting, so twist and pull.
Make sure you can refit the top.
Rinse out the container part.
Add thick bleach to 25% of the pack's volume.
Add 2 drops of washing-up liquid.
Add cold water but leave 10% ullage.
Put top back on.
To mix the contents, don't shake but invert repeatedly until mixed.
Spray the affected area from close up. Don't get any on your clothes.
This cheap and cheerful method will kill moss, algae, black spot, brown spot, and white spot (but in the case of the latter it doesn't go away, but spraying twice a year will stop it forming)
Usual caveats apply..
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