Picking the perfect sprayer

Soap and oil sprays, weed killers, insecticides and fungicides must be applied with the right tool to be effective.

The best types of garden sprayer are those that can be pressurized to apply a fine spray mist. It's the fine mist that provides the best and most uniform leaf coverage and thus the best control of insects, weeds and disease.

For small jobs, like the spraying of houseplants and small patio plants, a quart-size misting bottle works just fine. The pressure is applied by pumping the trigger, and the nozzle can be adjusted to provide a fine mist. This is the least expensive type of sprayer.

Small, nonaerosol plastic pump sprayers are best for spraying larger potted plants, flowers, vegetables and small shrubs. They're pumped up to build pressure and operated by pressing down on a thumb trigger to release the spray. They're light enough (even when filled) to hold and operate with one hand. Small pump sprayers hold up to two quarts of spray material, with adjustable spray nozzles for settings from coarse to fine.

Large pump sprayers for home use range in size from one-half to three gallons' spray capacity. They're best for spraying medium to large shrubs and small trees up to 15 feet high. Pressurized sprayers have a spray wand with adjustable nozzle connected to a tank pressurized with a hand pump. You can purchase replacement parts for the more expensive models, should the need arise.

Whatever the size, I recommend sprayers made of plastic. They're less expensive, lighter and more durable than metal sprayers. And because they're relatively inexpensive, you can purchase separate ones dedicated to applying a specific type of pesticide.

It's important to note that sprayers used to apply weed killers should not be used to apply other types of sprays. For instance, if you mix an insecticide in a sprayer formerly used to apply weed killer, any residual herbicide in the tank, no matter how slight, can harm desirable plants.

So, dedicate one sprayer for the task of weed control and mark it in bold print with a permanent marker: "Weed Control Only." If you apply both post-emergent (contact) weed controls, such as Roundup, and pre-emergent (preventative) materials such as Surflan, it's best to have a separate sprayer for each.

To keep your sprayer working its best, rinse it out after each use. Operate the sprayer with clear water to rinse the tank supply tube and nozzle of all soap, oil or pesticide.

To reduce wasted spray material, first spray all or a portion of the plants or area to be sprayed with clear water. This will give you a good idea of the amount of spray material needed to be mixed to do the job.

Adjust the nozzle of your sprayer to deliver a fine mist when applying soaps, oils and insecticides. This will be more effective in covering both the top and the underside of plant leaves, which is important in controlling insect pests. Use a slightly coarser spray when applying contact herbicides such as Roundup. These products are most effective when enough spray is applied to thoroughly wet the leaf surface of the weeds.

Coarse, solid-stream sprays, with the nozzle turned wide open, should be used only when a longer spray stream is needed to reach up into small and medium-size trees.

● John P. Begeman is the urban horticulture agent for the University of Arizona-Pima County Cooperative Extension. If you have questions, call 626-5161 to reach a master gardener.

Gardening

Advice by John P. Begeman

» gardening class

"Pruning Trees and Shrubs" will be the topic for this week's garden demonstrations. They will be at 9 a.m. Wednesday at the Pima County Extension Center, 4210 N. Campbell Ave; 1 p.m. Wednesday at the Wilmot Library, 530 N. Wilmot Road; and 1 p.m. Friday at the Oro Valley Public Library, 1305 W. Naranja Drive.