Adjustable nozzles, ease of mixing and efficiency ,make this a popular type of sprayer. Trombone Sprayers - are tubular and have a sliding. They are accurate, efficient and rather easy to operate. The spray is mixed into a container and then is carried to the spraying location. The weighted hose of the sprayer is lowered into or attached to the container.
Adjustable nozzles regulate distance and type of spray desired.
Mix and use as little or as much spray as you need. Keep one handy for that single rose bush, etc. Nozzles on some are adjustable and some are pressurized. Aerosols - many of the major companies now package insecticides and various other products in aerosol containers. These are especially handy for small spraying jobs.