I have only one sprayer and am always paranoid that I'm going to kill the grass the use after glyphosate. I haven't had a problem yet, though. Just clean extra well. Maybe use some soap.

I wouldn't be too concerned as long as you rinsed the sprayer well. Dilute glyphosate does not kill and at most will act as a plant growth regulator which was it's initial application.

This little reno is a learning experience for me and the learning is easier and much less stressful with all your help. Thanks !

As above, just rinse well. And pump out the wand thoroughly with fresh water.

Even if you only rinse out 99% of the glyphosate, you're doing pretty well. A mix that thin would be a growth inhibitor at worst, for a short time before it resumes normally--and a 99% rinse is a pretty poor job!

I must be kind of lazy! I don't use very much glyphosate - mostly at my elderly neighbor's at her request. I have a separate sprayer. The other sprayer I use for everything else.

I worked in the laboratory for years and a working rule when washing dishes was that about three rinses would dilute any material to the point it would not interfere with subsequent analysis.

Assume you have a 10% solution in the sprayer, and you leave 25 milliliters of active ingredient in the spray when you have finished spraying. If you have a 4 liter sprayer, Filling a gallo sprayer with water would dilute the pesticide to about 0.6%. With the next fill with water, the concentration would be 2 ppms. The third time would be .5 ppbs.

25 mllliliters used above would mean you were leaving about about a cup of 10% solution in the sprayer when you were done. I never leave that much.

5 parts per billion is below the threshold limit of most poison and pesticides.

Still are not sure fill it for the fourth and fifty time.

But people never fill a jar to the top and then dump it out. They put some water in, swirl it around and then dump it out. Then do that several times. Does the three rinse rule cover that scenario as well? Of course there is also a potential for some of the active ingredient to become absorbed into the plastic container to be leached out over time. Glass containers are not often used for lawn care. Maybe not significant, but this is one reason they say not to use your irrigation system to dispense chemicals.

It's not the same with plastic, or with swirl and dump, but doing that several times is more than adequate (as years of doing so around here proves!)

So I'd say krnuttle's general rule is a very good one--even a bit overkill, which is always a good thing.

I have 3 separate sprayers. One is only for glyphosate, a second one is strictly for selective herbicides like 2,4d & sulfentrazone, then a third is used for liquid fertilizers like fish emulsion. Probably overkill, but whatever they're only 10 or 15 bucks apiece

It is good to have dedicated sprayers. But the problem is storing all these after use! Unless you have a large outdoor shed or something similar. Right now all the lawn care/yard stuff that I have, 2 riding lawn mowers, 1 walk behind lawn mower, 1 blower, 1 snow thrower, 1 yard vacuum, 1 hedge trimmer, 1 tiller, 1 edger, 1 tow behind sprayer etc. etc. has completely filled up my two car garage. Cars are perennially parked outside! LOL.