June 1998
Apply fungicides more effectively to control scab…
Direct spray at heads for better success, says NDSU
By Tracy Sayler
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Prairie Grains is the
official publication of
the Minnesota
Association of
Wheat Growers,
North Dakota Grain
Growers Association,
South Dakota Wheat,
Inc., and the
Minnesota Barley
Growers Association.
"For controlling head diseases like scab, spraying fungicides like herbicides won't do the job. The treatment has to be directed at the heads to be effective," says Terry Gregoire, NDSU extension agronomist, Devils Lake, ND.
Gregoire and NDSU plant pathologist Ron Stover conducted several experiments last summer at the NDSU Research Center in Langdon, ND, to evaluate different application techniques optimal for scab suppression. They used red food color dye applied to a wheat crop to evaluate the deposition of spray on heads, to simulate applying a fungicide during anthesis for scab control.
They found that spray coverage can be affected by several factors:
Nozzle angle
Nozzles angled forward to deposit spray on the sides of the heads consistently performed better than nozzles pointed downward. Backward-directed nozzles didn't work as well as nozzles pointed forward, depositing less spray on the sides of wheat heads than forward-angled nozzles.
Double swivel nozzle body
An adapter called a "double swivel nozzle body" is sold by some chemical dealers and nozzle equipment suppliers to allow spraying at different angles, which will enhance fungicide applications for scab control.
About two inches long, two inches deep, and shaped like a goal post, one end of the adapter attaches to the boom where the nozzle would usually sit. The other end is two-pronged, with uprights where the nozzles are placed. The adapter allows the nozzles to be adjusted forward and backward, then locked into place at the desired angle.
NDSU extension agricultural engineer Vern Hofman says the adapter is available in nylon or brass. Expect the brass version to be stronger, but also more expensive. "Either will work," he says.
Nozzle size
Smaller nozzles seemed to work better than larger nozzles. "Cones don't seem to work as well as flat-fanned nozzles. Vertical-mounted nozzles give little coverage, because they're not directed at the heads. Twin jets and using 8001 or 8002 directed nozzles worked well," says Gregoire.
Spray pressure
Optimum pressure appears to be affected by different variables. In general, the 40 pounds per square inch (psi) treatments were better than either 30 or 60 psi. At 30 psi, the solution is sprayed less forcefully toward the sides of the heads, so that a greater amount of spray may fall downward by gravity past the heads into the canopy.
However, in one experiment using 0.067 gallons-per-minute nozzles applied with water at 20 gallons per acre (gpa), the 30 psi treatment was superior to the 40 psi. This may be due to greater spray uniformity occurring when a lower ground speed was used.
With 10 gpa applied, the 60 psi treatment was apparently less satisfactory than 40 psi, but both pressures were the same when 20 gpa were applied. Using 0.067 nozzles, 60 psi was superior to 30 and 40 psi treatments, although nozzle leakage was sometimes a problem with 60 psi pressures on the sprayer used.
Nozzle plugging can also be a problem with wettable powders when using 0.067 nozzles. Hofman notes that 0.067 nozzles, described by some suppliers as 80067 or LF .67, 80 degree nozzles, are not as commonly used as other nozzles.
It appears that 8001 and 8002 flat fan nozzles or 8002 twin jet nozzles at 50-60 psi and around 15 gallons per acre water volume give adequate head coverage when the spray pattern is directed at the heads, says Gregoire.
Ground speed
Smaller nozzles and lower spray pressures require a slower ground speed to maintain the same gallons per acre, while larger nozzles and higher spray pressures require a faster ground speed. NDSU's experiments suggest that a steady, slower ground speed may provide more uniform coverage than faster ground speeds.
Gallons per acre
Application volumes of 15 and 20 gpa worked better than 5-10 gpa and improved the uniformity of coverage, though a desired field application volume may be 10 gpa. But with this coverage, the selection of nozzle size and spray pressure is more crucial.
Multiple applications
Optimizing spray coverage from one pass is preferable, but a second application from another direction may improve spray uniformity and provide coverage for heads that may be hidden in the canopy during a single application.
NDSU researchers are testing fungicide application methods again this summer. Hofman is giving further attention to evaluating fungicides applied at different spray angles and pressures.
At Langdon, researchers will conduct several application experiments on winter wheat, barley, and bearded and beardless spring wheat varieties. They also will look at the effect of surfactants and adjuvants, as well as the effect of newer spray technologies such as electrostatic and air-assisted spray. A dye that fluoresces under a black light will be used in the experiments. The dye coverage can be analyzed by computer to measure spray deposition and uniformity under different application methods.
"What we've done in the past hasn't done the job. Much of it just wet the leaves," says Gregoire. "Now we're recognizing that application can make a difference. The key is to optimize all of the factors involved in applying fungicides to control scab."n