What are you putting it on? Days to harvest varies with the plant, if I recall correctly. I certainly would not eat leafy greens still visibly sporting Sevin.

Lots of things - that does not matter. What I am curious about is when does the "clock" start? From when you apply it OR when it is no longer visible?

The clock always starts from date of application. Visibility - or lack of it - has nothing to do with the time interval.

I sure wouldn't eat anything that still has the dust on it no matter how long it's been.

I have some Sevin liquid but the only time I've used it on edibles in the last decade is to eradicate asparagus beetles and Japanese beetles from my asparagus post harvest and that was only when I was out of pyrethrin.

Sevin is somewhat soluble in water, so when it rains, two things happen. One is that some of it gets washed off. The other is that some dissolves and disappears on the foliage. So every time it rains, there will be less Sevin on your crops, but just because you can't see the dust doesn't mean some isn't still there. The amount that is left depends on how hard it rained. The insecticidal effect starts when you put it on, and stops when it is completely gone.

Note that as of this year, Sevin isn't what it used to be - carbaryl. The brand name was recently bought, and the composition changed. It is now zeta-cypermethrin, another pyrethrin. I understand that cats are a lot more sensitive to zeta-cypermethrin than to carbaryl. I think people used to kill fleas on cats by dusting them with Sevin. Wouldn't do that with zeta-cypermethrin. Have not looked at the MSDS for the stuff, but I'd use with care.

This is just a reminder that brand names can't necessarily be trusted to have the same composition. Look at the labels. A given brand name may have totally different usage instructions as the composition changes. I've seen this happen in several products, but never in an insecticide. It's like if Ford bought the Porsche name, and started selling their cars with the name Porsche because, well, it's their name now.

This seems odd to me. Many veggies take only 3 days to "clear" of sevin. However you can still see it on there 4 days later..................

The product oxidizes, the sun makes the product inert.

Ahhh thanks! That makes sense.

Just to add, be aware that zeta-cypermethrin is stable with regard to sunlight. It's just slowly oxidized. On foliage, the half-life is about two weeks. In soil, the breakdown is much faster because of microbial action. I think the same is true with carbaryl. That's why these are not particularly useful soil insecticides. But yes, thorough washing of treated produce before consumption is smart. Should make no difference whether you see it on the produce or not. If you applied Sevin, wash before eating.