Features Agronomy Soybeans
Spraying technique, nozzles not a complex issue

Sometime in the future, the call will come that soybean rust has arrived in
Ontario. At the urging of extension personnel and agronomists, more growers
may scout their fields, but concerns will remain over the application of fungicides.
Four different chemistries are currently approved and available to growers in
Ontario, but are there other issues to consider prior to the arrival of soybean
rust?

There are a few minor but nonetheless important factors to note, says Helmut
Spieser, an engineer dealing with spray application technology for the Ontario
Ministry of Agriculture and Food at Ridgetown. There are differences between
spraying herbicides to control weeds and spraying fungicides for disease control.
With herbicides, timing is the key and using the right product for the right
weed is essential. "With soybean rust, just because we get the fungicide
there doesn't mean the disease is controlled," reminds Spieser. "If
you miss covering a percentage of the leaves with the fungicide, those are the
spots that will become infected or stay infected and possibly give you something
to spray later on down the road."

Establish an order of importance
Before spraying, Spieser urges growers to familiarize themselves with all aspects
of soybean rust: understand how it spreads, how to identify it, the weather
conditions under which the disease thrives and its impact on crop health. "Then
understand the fungicide products that are available, look at the timing as
to when they need to go on," he says.

"If we're looking at coverage, then water is the key," says Spieser,
stressing growers should refer to the label for specific volumes, but noting
15 to 20 gallons per acre is a good starting point. "With the application
of fungicides, more water gives us better coverage. We've got a lot of foliage
that we have to cover, and water is cheap."

In trials using the same nozzles with different water volumes, the difference
in spray coverage levels from 12 to 20 to 30 gallons per acre was evident with
the greatest coverage at 30gal/ac.

In terms of nozzle choice, the key is actually the droplet size. "You
want to shoot for a medium spray quality," he says. That can be accomplished
using flat fan nozzles, TwinJet nozzles and double nozzle holders using some
type of flat fan nozzle and even some air induction nozzles. Spieser adds that
most growers are likely to have suitable nozzles to do the job, but early planning
to make sure would avoid the cost and anxiety of missing a spray application
while awaiting a special order.

Designed for rust
Spraying Systems was one of the first out of the gate with a nozzle designed
specifically to provide thorough plant coverage for effective treatment
of Asian soybean rust. Featuring a dual flat spray pattern, the Turbo TeeJet
Duo (TT Duo) provides better canopy penetration and leaf coverage than single
flat spray nozzles and produces larger droplets. -30-


Choosing the right pressure and height
As for pressure, Spieser cites a range of anywhere from 40psi to 100psi, not
out of the realm for most pumps and sprayers. On boom height, he emphasizes
the importance of maintaining proper nozzle-to-target distance. "In most
cases, when we have a boom with nozzles on 20 inch (or 50 centimetre) centres,
we need about 20 inches or half a metre from the nozzle tip to the target, and
that distance should be to the top of the canopy," says Spieser. Any closer
than that risks interfering with the spray pattern before it has a chance to
fully develop. "So we'll get tiger striping, heavy applications, light
applications, whether under the nozzle or between the nozzles. It's not much
different than if we're spraying a cereal, but the boom may be higher."

Spieser concedes that changing boom height may be easier for some growers than
others. On newer sprayer models, height can be adjusted with the flick of a
lever or a switch.

Another factor in the accuracy with which application can be made, and the
speed of application, is the type of sprayer: whether it's a self-propelled
or pull-type unit on large diameter tires or an older model with smaller tires.
As well, the boom suspension system may limit or extend the capability of the
sprayer.

Nozzle configuration is the last of the concerns and will depend on the stage
of the crop when soybean rust strikes. "If we have a full canopy with no
definable rows, and it's filled in, the straight boom is as good as any, and
if we've got some row middles that we can actually see, there might be an advantage
to a multiple nozzle over the row arrangement," says Spieser. He acknowledges
that growers do not typically favour that approach because of its extra hardware
and costs.