Today there are a variety of sprayers ranging from small hand-held trigger sprayers to large capacity models that require a garden tractor to move about the yard. They make insect, disease and weed control easier. They are also useful for spraying liquid fertilizer on gardens and container plants as well. The size and type needed depends on the specific job, how often you'll be spraying, and how large or high an area you need to cover.
Here are some sprayers worth considering:
2 gallon: 4 gallon: 15 gallon: 25 gallon: