Prairie Grains June99

Research that began at NDSU last year indicated that fungicide treatments need to be directed at wheat and barley heads to be effective. Also, that timing, size, type and angle of spray nozzles, ground speed and spray pressure are key factors that can influence the success of a fungicide application.

A greenhouse study over the winter expounds on these variables. The greenhouse, which is new and became fully operational last January, was built specifically to conduct fungicide evaluation research. It includes spraying equipment to simulate in-the-field ground spraying conditions. The new greenhouse was funded through federal dollars, attained in part by the legislative efforts of wheat and barley groups in the Northern Plains.

Over 40 different application treatment trials have been conducted in the greenhouse since application studies began at the end of February, 1999, says NDSU extension plant pathologist Marcia McMullen.

In the greenhouse experiments, a flu-orescent orange dye was applied with a track sprayer to determine percent head coverage. Fungicides were applied to determine efficacy against head scab, following inoculation and misting of plants to create a growth environment conducive for scab infection. Evaluations (using the spring wheat variety Russ, Munich durum, and Robust barley) included nozzle type, spray pressure, water gallons, and adjuvants. Some preliminary conclusions:

Nozzles and Spray Pressures
Optimum nozzle pressure varied among nozzle type and optimum nozzle varied across crops. Although the TwinJet TJ8002 nozzle was the least expensive nozzle arrangement tested, this nozzle generally did not provide as good of head coverage as the forward/backward orientation of the XR8001 flat fan nozzles or the forward/backward oriented TD01 turbo drop nozzles tested, regardless of sprayer pressure or water volume delivered.

Twin Jet

Cap with round nozzle opening

Twinjet nozzle

Threaded nozzle cap

1/4" pipe nipple

Double swivel nozzle body

Cap with round nozzle opening

8001--Flat Fan oriented forward and backward

Nozzles were tested at spray pressures of 30-90 psi in increments of 10 psi, across several water volumes. The optimum spray pressure for the turbo drop nozzles was 60 pounds per square inch (psi), for both head coverage and disease control. The optimum spray pressures for the flat fan nozzles were either 40 psi or 70-80 psi, while head coverage and disease control dropped at 50-60 psi with these flat fan nozzles.

The patented Turbodrop mixing/pulsation chamber provides large drift reducing drops over a large range of operating pressures.For the Robust barley tests, the XR8001 nozzles consistently performed better than the TD01 nozzles.

The pressure drop created by the venturi draws air in through the hole in the venturi.
The pattern tip forms large, drift resistant spray drops, filled with tiny air bubbles.

McMullen speculates that differences among nozzle performance can be related to droplet size, velocity of droplet movement, water volume, head shape and presence and compactness of awns.

Also tested was an experimental air-assist sprayer developed by Vern Hofman and Jim Moos, NDSU ag engineering researchers, with both downward orientation and forward/backward orientation of nozzles. Limited data from this sprayer suggests that having a forward/backward orientation of this sprayer increased head coverage by ten-fold over downward orientation.

Water volume
Generally, increasing water volume increased head coverage and decreased disease. This was most evident with Munich durum, when increasing water volume all the way up to 54 gallons per acre (gpa) increased head coverage, and increasing water volume up to 36 gpa decreased disease.

The spray results consistently showed that durum heads are tough to adequately cover without adequate water. Increasing water volume from 9 gpa to 18 gpa also increased disease control and head coverage on Russ spring wheat and Robust barley, but water volumes higher than 18 gpa did not significantly help.

"Increased head coverage and disease control with higher water volumes also has implications for aerial applications," says McMullen. "With aerial applications, spraying when dew is present to increase natural water volume, or spraying at 7.5 gpa instead of 5 gpa may improve control."

Treatment timing
For wheat, applying fungicides at grain flowering still appears to be optimum. However, the NDSU greenhouse research suggests application timing for barley is best soon after head emergence. "Disease did not develop when barley was inoculated with the scab fungus when awns were just showing, but did become severe when barley was inoculated after full head emergence," says McMullen. When a fungicide was applied to the fully emerged barley heads just before inoculation, however, the disease was effectively controlled.

More research this summer
McMullen says NDSU researchers are finalizing their greenhouse research results, and preparing fungicide application research that will continue at NDSU this summer. This will include plot efficacy studies, new product testing, refinement of application techniques, and further study on air-assist spraying. In addition, several aerial application studies are planned.

Jim Moos and Scott Halley, research technicians at North Dakota State University, are calibrating a greenhouse track sprayer used to analyze fungicide application effectiveness. The sprayer is capable of converting to various nozzles, pressures and speeds, and gallons of water. An orange dye is used to indicate percentage of wheat and barley head coverage from a test fungicide application in the greenhouse.

By Tracy Sayler