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Middle, Lower Canopy Penetration Is Key To Soy Rust Coverage

Soybean farmers, worried about Asian rust, now have a game plan for the best spraying tactics to fight this new disease.

According to field tests conducted in January by John Deere in Brazil, spraying at higher gallons-per-acre at higher pressures was a more effective way to treat the middle and bottom canopy, where Asian rust infections first begin to form.

Deere revealed results at a news conference held at Commodity Classic, Austin, Texas Feb. 23-26. Here's a rundown of results:

Higher GPA

Tests ranged from 5 to 20 gallons per acre. "As a rule of thumb, 15 gallons-per-acre (GPA) is the minimum," says Mike Miller, John Deere product planner. "With other variables being equal, coverage at the bottom of the canopy using 20 GPA was more than 17 times greater than using 5 GPA. At the middle and top of the canopy the difference was even greater, but when it comes to rust, you're more concerned with the lower part of the plant."

Higher pressure

Tests were conducted with pressures from 40 to 90 Psi. Higher pressures delivered better mid and low canopy coverage. "We had two times greater coverage in the lower canopy by increasing the pressure over 50 Psi," says Miller. There was only 1.5 times greater coverage at the higher pressure in the top canopy.

"Produce as much pressure as your sprayer can with the nozzle creating the proper droplet size," he recommends.

Field speed

Tests were conducted at speeds of 8, 12 and 18 miles per hour. Surprisingly, speed showed little effect on coverage, says Miller. "We are recommending to go as fast as possible while still maintaining good stability with your booms," he says.

That's critical if you need to cover a lot of acres within the two to three-day window after infection is first seen. "We wouldn't recommend a customer travel at 18 mph without good boom stability," Miller cautions. "With an older machine you might sacrifice control with booms flopping at high speeds."

Nozzles

Deere tested flat fan, hollow cone, extended range, low drift, ultra low drift, and a combined ultra low drift-twin cap nozzle that holds two standard spray tips at 30-degree angles (front and rear facing). TwinCaps fitted with Spraymaster Ultra Low Drift Nozzles provided 60% better coverage in the mid and lower canopy area compared to the other spray tips. Hollow cones performed the worst.

"We were extremely happy with the twin cap," Miller says. "Each soybean plant has its own umbrella with its leaves. If I come down from a 30-degree angle, such as with a twin cap, it's easier to get that bottom canopy covered."

Game plan

"Most equipment companies have been talking about increased carrier volumes, and this study confirms that," says Miller. "15 gallons per acre is definitely a starting point with your fungicide. The more gallons per acre you can go out with, the more coverage you can get and, in most cases, the better control you're going to get of any fungicide."

Deere first performed the field test in Iowa last summer, then repeated the same experiment in Brazil over the winter. Crop Systems Specialist Jeff Barnes, who developed the test, clipped 1.5-in x 3-in. cards to soybean plants at various heights, then sprayed plants using various sprayer settings. Nearly 2,500 cards were sprayed, collected and scanned. Soybeans were sprayed at growth stage R1, typical timing for fungicides.