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Fungicides require different nozzles

Agriculture.com Staff 07/06/2010 @ 5:21pm

"The most important factor to control when spraying for soybean rust will be spray droplet size," says Scott Bretthauer, an application technology specialist with University of Illinois Extension. "Small spray droplets provide better coverage and tend to deposit well on the target. But if droplets are too small, they will be unable to penetrate and deposit in the canopy, or they may drift off target."

He notes that large droplets will not deposit as well because they have a tendency to bounce or run off the plant, and there will be fewer droplets, which reduces coverage. "The key is to create the droplet size that gives a good balance of coverage, penetration, and deposition."

Fungicides require more volume than many farmers use for herbicides. Most labels call for 10 to 20 gallons per acre (gpa). The high side of that range seems to be preferred. "For the best performance, applications by ground rigs should be made in a minimum of 15 gpa of water, and 20 gpa may be preferred," says Boerboom.

Hypro, a manufacturer of nozzles and pumps, gives this procedure for selecting a spray tip:

Select size and pressure needed for the tip to achieve the desired gpm.

Check the spray quality it will produce at the selected pressure.

If the spray quality (droplet size) is too coarse or too fine, select a different tip.

Flat-fan nozzles head most people's list of favorites. Ozkan says, "Nozzles producing a cone pattern may work for soybean rust, but since they produce a higher portion of extremely small (less than 100 micron) droplets than flat-fan nozzles, the flat-fan pattern nozzles are still the best choice as long as the (droplets) are fine to medium (200 to 300 microns). A flat-fan nozzle set up with two spray patterns seems to provide a better coverage of plants with full canopies."

New tips and old standbys

Spraying Systems added two new nozzles to their TeeJet line in January. One of the new nozzles is a DG TwinJet; the other is the Turbo TeeJet Duo (TT Duo). According to the company, the TT Duo provides better canopy penetration and coverage than single flat-spray nozzles and produces larger droplets than other dual-spray nozzles for greater drift control. The DG TwinJet produces finer droplets than the TT duo but larger droplets than standard twin-spray nozzles to help minimize drift. The regular TwinJet nozzle can also be used.

Greenleaf says their TurboDrop nozzle was designed specifically for high-pressure canopy penetration. More recently, they have found that the TurboDrop Venturi with a dual flat-spray outlet can provide even better chemical efficacy where canopy penetration is important. They also have an AirMix TwinFan configuration for lower pressures of 50 to 70 psi.

The Hypro Guardian is a new tip this spring that can produce a medium droplet. Hypro says the slightly air- enhanced design creates fewer fine droplets yet keeps the spray from becoming too coarse. Hypro also has a TwinCap that holds two tips. One sprays forward at 30 degrees; the other sprays backward at 30 degrees.

Hardi says the best compromise for fungicides is a medium-size spray. They say that goal is best met with a standard flat-fan nozzle. Or for some higher spraying speeds, using a pre-orifice low-drift nozzle is best.

Do you have an agronomy question? Email cheryl.rainford@meredith.com. We'll send some of the most common questions to professionals in the industry and see what they say. Look for answers in upcoming Agro-Connect Ask the Experts columns.

"The most important factor to control when spraying for soybean rust will be spray droplet size," says Scott Bretthauer, an application technology specialist with University of Illinois Extension. "Small spray droplets provide better coverage and tend to deposit well on the target. But if droplets are too small, they will be unable to penetrate and deposit in the canopy, or they may drift off target."

While nozzle selection for herbicides is often based on drift control, nozzle selection for fungicides is based primarily on coverage and penetration.

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