Get one of the inexpensive hand pump or compression sprayers. These are what I use and they are work perfectly and are easy to use. And regardless of whether you are practicing organic methods or not, it is advised to have a sprayer dedicated to a specific purpose - insecticides in one, fungicides or fertilizers in separate sprayers, and if you use them at all, herbicides MUST have their own.

I have used these but would like something a little easier to carry around. I don't use any herbicides other than vinegar and usually I do that now with a handheld sprinkler.

Bought a backpack and returning before first use. Straps set for mens' shoulders ordered Smith 2 gallon contractor sprayer. Has a filter. Looks like decent reviews including for use with NEEM.