One of the things I was surprised to learn( too many years ago now) was how short-lived many pesticides were. This is particularly true if mixed in water that has low or high pH values (over/under 6.5-7.0)
The more alkaline or acidic the water you use, the shorter the shelf life or “tank life” of the mix is. The harder the water (different than acidity measurement) the worse the mixed-life. Some greenhouse material of those early days had a mixed life measure in half-hours (as in 30-45 minutes) before it was useless to spray.
So when you mix up a dose of “stuff” then use what you mix when you mix it.
Do not store mixed sprays around the house. One of the reasons we went to a full water treatment facility in the greenhouses was to adjust our water (not only for seedlings) but for tank-mixed spray applications.
I can hear you saying, “Well I only use organic sprays so that doesn’t apply to me”
It turns out there were several kinds of soaps being used in insecticidal soaps (different manufacturers) and some had an extremely short mixed-life when in alkaline waters (our problem). They would also precipitate out – form “scudsy balls” in the tank.
So we switched brands until we got our water treatment up and running.
If you’re having difficulties and wondering why your sprays aren’t working – this might be part of the problem.
What can you do at home?
- Only mix what you’re going to spray when you’re going to use it – don’t make a too-big batch and then save it.
- Go to a pool testing service, get your water tested and get the pool chemicals necessary to balance the water. They’ll tell you how to do it.
- Use this balanced water – it will make a difference to your spray program.