Spraying more efficiently

Many changes are taking place with pest control products. New materials are available that are highly target-specific and effective at low rates. As products have changed, so has the cost of a treatment. With some products costing several hundred dollars per gallon and application rates at less than an ounce per acre, application efficiency is more important than ever.

Off-target drift is a major source of inefficiency. If drift is occurring during application, not all the product is reaching the intended target. These off-target deposits can injure desirable vegetation, damage wildlife, contaminate water and harm people. Although you cannot completely eliminate drift, using proper nozzles and spraying techniques will help keep drift within acceptable limits.

The application equipment available today is more sophisticated and often more expensive than those from years ago. Regardless of the cost of the spray machine, one important but inexpensive component of the sprayer is the nozzle.

Choosing a nozzle Select a nozzle for its orifice size to control the spray volume in gallons per acre (gpa) or per 1,000 square feet. (Nozzle flow rate is calculated by using the gallons per minute (gpm) formula. (See table on page 54.)

Position the nozzle on the spray boom at a spacing, height and orientation so you can achieve pattern uniformity on the turf.

The nozzle type will have a major effect on drift potential. A fine line exists between minimizing drift and choosing the right size of spray droplet needed for adequate control of the targeted pests. Turf professionals should have a broad base of knowledge about products, nozzles and droplet sizes to help them find the right balance.

How the product works, or its 'mode of action,' influences the sprayer setup for each application. For example, systemic or translocated products move through the plant from the point of uptake. Contact products remain on the surface. Therefore, for materials that require good surface coverage, you need to apply smaller droplets, while a systemic material may function adequately if you use larger droplets that do not require as thorough a coverage.

Drifting off-target There are two ways that sprayed products can move off-target to cause damage: particle and vapor drift. Vapor drift occurs when a volatile pesticide evaporates and the vapor moves off the application site. This may occur regardless of how carefully you apply the product. Particle drift is the off-target movement of spray particles (droplets) formed during application.

The amount of particle drift depends mainly on the number of small "driftable" particles produced by the nozzle. Although you can achieve excellent coverage with extremely small droplets, decreased deposition and increased drift potential limit the minimum droplet size.

Spray droplet size The effects of droplet size and the relationship between droplet size and target coverage are complex and may lead to several common misconceptions. For example, it is generally believed that applying small droplets at high spray pressures will provide increased coverage. Research data, as well as a study of particle dynamics, does not substantiate this theory. It is true that atomizing a known amount of spray solution into smaller droplets will increase the coverage that is theoretically possible, but you must also consider evaporation, drift potential, canopy penetration and deposition characteristics, all of which may be adversely affected by droplets that are too small.

Selecting nozzles for improved efficiency Many nozzle types are available for applying pesticides, but some manufacturers have developed nozzles with spray drift in mind. For example, Delevan developed the RA Raindrop nozzle specifically for drift control in turf applications. When operated within a pressure range from 20 to 50 psi, this nozzle delivers a wide-angle, hollow-cone spray pattern.

At the time of its development the RA Raindrop nozzle produced fewer smaller driftable drops than other nozzle types. However, one drawback with this nozzle has been its streaky pattern on turf. To achieve a more uniform spray pattern, you should space nozzles no more than 30 to 40 inches apart on the boom and rotate them 30 to 45 degrees from the vertical axis. The rotation improves target uniformity, but will lead to increased drift when spraying in windy conditions. Although these nozzles produce large droplets, the overall droplet spectrum still contains finer droplets that are blown out of the pattern and off-target in windy conditions.

Low-drift nozzle technology In recent years, nozzle manufacturers have worked to design "low-drift" nozzles that will effectively reduce the development of driftable fines in the spray pattern. One emphasis in design has been the "pre-orifice" concept. A pre-orifice on the entrance side of the nozzle effectively creates a flow restriction without flow rate reductions, resulting in lower exit spray pressures and larger spray droplets.

A more recent design improvement incorporates the pre-orifice concept with an internal turbulation or impingement chamber. This not only creates larger droplets, but also improves the uniformity of the spray pattern. Turbulation-chamber nozzles were first designed for agricultural applications, but have since been manufactured in an orifice size appropriate for turf applications.

The original Turbo Flood nozzle, designed by the Spraying Systems Company (TeeJet), combines the precision and uniformity of flat spray tips with the clog-resistance and wide-angle patterns of flooding and Raindrop nozzles. A new design of the Turbo Flood has been developed for the turf industry.

This new design, the Turbo Turf Flood (TTF), not only increases droplet size but also provides an improved pattern to the turf. Recommended operating pressures for this nozzle are 20 to 50 psi. With the reduction of the number of driftable size droplets in the spray pattern, the TTF nozzle is suitable for drift-sensitive applications. The orifice size options with this nozzle allow it to be exchanged with the Raindrop nozzle without changing the operating parameters of pressure, speed and application volume.

Improved pattern performance Because of the improved pattern uniformity, you can spray the TTF nozzle in a "straight down" orientation. For best results use at least a 50-percent overlap (25-percent on each edge) to obtain proper application uniformity (see figure, page 52.)

A good way to see the benefits of the TTF nozzle is to compare it with the Raindrop nozzle while spraying on a parking lot surface. Observe the streaking with the RA Raindrop nozzles (see photo, page 52). Also, in a windy setting you will notice less drift coming from the boom section while using the TTF. Because of the improved pattern quality and the ability to spray straight down, the TTF nozzle is even less likely to drift when spraying in windy conditions.

Other factors Many other factors influence application efficiency. Use as many approved application techniques as possible. This can only improve the performance of your spray materials. The improvements in spray efficiency will benefit the environment as well as give you better results for your application dollar.

Dr. Robert E. Wolf is an assistant professor and an extension specialist in application technology in the Biological and Agricultural Engineering Department at Kansas State University (Manhattan, Kan.).

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