How long will mixed pesticides sustain potency?

I had just mixed about 20 gallons of a tank mix of captan, rally, avuant, tactic and a TBS of citric acid when the sprayer motor blew. I won’t get the chance to spray it before it has sat for 18 hrs. Anyone have any idea if it will lose potency in that time?

I don’t know but my thought is that if the water were distilled it will help. I think it came up once before and someone (@scottsmith?) suggested there might be a 24 hour window.

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It’s going to be dependent on the pH of the spray mix and you would want to check the pH of your mix. Take a look at this list of spray chemicals that has the stability information at different pH levels.

Captan and Avaunt are on the list. Avaunt is pretty stable. Rally isn’t on the list but I suspect Rally is pretty stable since it’s a water based formulation. I am not familiar with Tactic I assume that is your sticker.

Looking at the list Captan has the shortest half life. At a pH of 5 the half life of Captan is 32hrs. In other words 1/2 the Captan is gone at 32hrs. So after setting 16 hrs in the tank you will have lost 25% of the Captan in the tank. At 18 hrs you would lose a bit more.

I think you could do any of the following:

  1. Spray the mix as is and accept the Captan level is going to be low.

  2. Add more Captan to compensate for the lost Captan if you not at the max legal rate. If you at the max rate already I not sure of the legality of adding more…I am not a licensed applicator. Adding more would be the right thing to do chemically but the legality is a different matter.

  3. Add a different fungicide not already in the tank to compensate for the lost Captan.


I found a second stability list and it has Myclobutanil (Rally) as being stable for the pH range of 5-9

Here is the second list.


similar question. my pump died last year and i stored 12 gallons of clethodim in buckets. is it still usable?

You could still apply it as you normally would. But I’d expect greatly reduced efficacy.


I am not familiar with the herbicide clethodim. It’s not listed on the references I linked above. You might want to look at the label you have for it and see if it has any contact info on it. If it does you could ask them what the stability of clethodim is in the tank mix you used.

From a practical point of view you may want to go ahead and use even if the efficacy is reduced. I would expect if you would have to pay disposal costs for 12 gallons it might be more than you would want to pay.

Thanks. I will go ahead and mix with 5 gallons of fresh and spray it. It is for clover on my backwoods food plot so doesn’t need to be perfect.