Farm Table says:
This WA specific resource looks at how to reduce spray drift as well as outlines relevant WA legislation and regulation you need to be aware of.
As a rule of thumb, droplets with a mean diameter of 250µm (0.25mm) or larger do not normally drift. So, by aiming for large droplet sizes, drift is reduced.
Smaller droplets are, however, more economical. They give better coverage for a given volume of spray and provide better penetration of foliage and attachment to leaf surfaces.
Large droplets have other disadvantages; they give an uneven cover of the target plant surface and tend to bounce off leaves. They are also less likely than smaller droplets to stick to vertical surfaces and the underside of leaves.
The structure of the article is: