Spray nozzle selection is one of the most important decisions to be made related to applying pesticides on vegetables, says Paul Sumner, University of Georgia Extension engineer.

The type of nozzle, he says, determines not only the amount of spray applied but also the uniformity of the applied spray, the coverage obtained on the sprayed surfaces and the amount of drift that might occur.

“Each nozzle type has specific characteristics and capabilities and is designed for use under certain application conditions,” says Sumner. “The types most commonly used for ground application of agricultural chemicals on vegetables include the fan and cone nozzles.”

The type of nozzle used for applying herbicides should be one that develops a large droplet and has no drift, he says. Nozzles used for broadcast applications include the extended range flat fan, drift reduction flat fan, turbo flat fan, flooding fan, turbo flooding fan, turbo flat fan and wide-angle cone nozzles.

“Operating pressures should be 20 to 30 psi for all except drift reduction and turbo drop flat fans, flooding and wide-angle cones. Spray pressure more than 40 psi will create significant drift with flat fan nozzles.

“Drift reduction and turbo drop nozzles should be operated at 40 psi. Flooding fan and wide-angle cone nozzles should be operated at 15 to 18 psi. These nozzles will achieve uniform application of the chemical if they are spaced uniformly along the boom. Flat fan nozzles should be overlapped 50 to 60 percent,” says Sumner.

Hollow cone nozzles are used primarily for penetrating plant foliage for effective insect and disease control, and for when drift isn't a major concern, says the engineer.

“At pressures of 60 to 200 psi, these nozzles produce small droplets that penetrate plant canopies and cover the underside of leaves more effectively than other nozzle types. The hollow cone nozzles produce a cone-shaped pattern with the spray concentrated in a ring around the outer edge of the pattern. Even fan and hollow cone nozzles can be used for banding insecticides or fungicides over the row,” he says.

Various types of nozzle bodies and caps - including color-coded versions and multiple nozzle bodies — are available, says Sumner. Nozzle tips are interchangeable and are available in a wide variety of materials, including hardened stainless steel, stainless steel, brass, ceramic and various types of plastic.

“Hardened stainless steel and ceramic are the most wear-resistant materials. Stainless steel tips with corrosive or abrasive materials have excellent wear resistance.”

Plastic polymer tips, he adds, are resistant to corrosion and abrasion and are proving to be very economical for applying pesticides. “Brass tips have been common but wear rapidly when used to apply abrasive materials such as wettable powders. Brass tips are economical for limited use, but other types should be considered for more extensive use.”

Growers who plan to use spray materials at the low water rates should follow all recommendations closely, advises Sumner.

“Use product label recommendations on water rates to achieve optimal performance. Plant size and condition influence the water rate applied per acre. When plants are small, use 25 to 30 gallons per acre. As the plant foliage becomes larger, increase the amount to 100 to 200 gallons per acre. A good indication is to examine the foliage behind the sprayer before the spray dries to determine if you have sufficient coverage.”