Can you mix Roundup (glyphosate) with another weed killer such as 2,4 D?

Not a good idea. Read the labels on each. If you want to apply each then follow the application instructions for them and apply them separately. IDK if the two chemicals will be dangerous when combined but the ability of each to kill weeds is probably compromised.

Put it in a jar and shake it up. If it looks like it mixes and doesn't make precipitate in the jar.

But why would you. Roundup will kill almost everything and will get the root too. 24D will just kill the tops and not touch the grass.

Round up kills all. You don't need anything else. Use the 2-4-D where you want to preserve the grass, but kill the weeds.

If you don't get an answer here, try contacting Master Gardeners, or even your local nursery. Dr.S.

Stop using roundup its killing the bees and butterflies after that nothing not even the prettiest flower and veggies will grow..reasearch this please.

Yes.