Do chemicals loose potency after being mixed?

General Fruit Growing
1

I thought I remember reading something about certain chemicals loosing potency after being mixed with water, I.E, you shouldn’t use the half full tank from 2 weeks ago for your next spray. Is true and if so, what’s the “shelf life” of these chemicals after they are mixed:

Roundup
Imidan
Captan
Sulfur
Manzate

Thanks!

2

The pH of the water is critical to half life of a chemical mix. Some chemicals can lose potency in hours or even minutes. I’d never leave anything two weeks and expect it to be effective. A few things might be but many won’t.

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3

Thanks! Is it high ph or low that is the problem? Or does it depend on the chemical?

4

It’s best to have water with low ph.

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5

It totally depends on the chemical. Some chemicals are hydrolyzed (attacked by water) at low pH (acidic) and some are hydrolyzed at high pH (basic or alkaline). Though most common chemicals appear to be hydrolyzed more readily at high pH.

Here you go… this will give you an indication of how long many of those things you are looking at last.
https://extension.usu.edu/files/publications/factsheet/AG_Pesticides_14.pdf

Sulfur is a special case because it is an inorganic solid. It is fairly stable in water, but it will also settle out and form a dense cake at the bottom of your sprayer that will be hard to re-suspend. Bacteria are capable of oxidizing sulfur to sulfuric acid in the presence of oxygen so if you leave it sit long enough there is that possibility…

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