Top Crop Manager

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Controlling fusarium:

Target the wheat head when spraying.


November 16, 2007
By Top Crop Manager

Topics

8aSuccessful spraying to control Fusarium Head Blight (FHB) depends on good coverage
of the wheat heads at the appropriate timing for the fungicide. That differs
from spraying weeds, where canopy penetration is more critical. Wheat heads
present vertical targets that are cylindrical in nature; weeds, that present
a more horizontal target, are closer to the ground where spray deposition is
aided by gravity.

"When applying a fungicide for fusarium control, it is a much more complicated
system. Complete coverage of the wheat head is critical," says Tom Wolf,
a researcher with Agriculture and Agri-Food Canada's Saskatoon Research Centre.

Previous information in the US indicated that a double nozzle system worked
the best. One tip was pointed frontward and the other rearward, both pointing
60 degrees from the vertical. They operated using a fine spray and low travel
speed. However, since the spray window for fusarium is extremely small (as little
as two days for ideal control) and fine sprays are prone to drift, Wolf wanted
to investigate whether there were other nozzle tips that could be used in either
a single or double nozzle configuration that would allow faster spraying while
minimizing drift.

In a laboratory setting, Wolf compared various nozzles in different orientations.
He used vertical plastic drinking straws to simulate wheat heads. Three different
experiments using 7.6km/hr or 15.2km/hr sprayer speeds, single or double nozzles,
and air induced versus conventional nozzle tips were compared. Wolf measured
the amount of spray deposited on the front and the back of the simulated wheat
head.

The combination of double nozzles, air-induced sprays and faster travel speed
increased spray retention on the simulated wheat heads by more than 100 percent.
Setting the nozzle tips with a separation of 60 degrees from vertical rather
than 30 degrees also increased deposition, but more for coarse sprays than fine
sprays. The wider angles also increased deposition on the backside of the vertical
target. These findings are important for spraying fusarium, because any spray
solution that misses the head is essentially wasted product. Put another way
– any part of the wheat head that is not sprayed is vulnerable to infection
by FHB.

The double nozzle system works best with coarse spray patterns. Conventional
nozzles with fine spray droplets do not have the velocity to coat the wheat
head. The fine spray loses its velocity a few inches from the nozzle tip and
will drift on the wind, coating the side of the wheat head facing the wind.
Some turbulence created by a conventional nozzle may help with the coverage,
but the potential for complete coverage is not predictable due to varying wind
directions and speed.

"Clearly, in the double nozzle system there is an advantage with the air-induced
coarse sprays over a conventional single nozzle system," says Wolf.

While the faster 15km/hr speed provided better coverage, Wolf says he is not
a fan of higher speeds. "I would draw the line at 15 kilometres per hour
because of the potential for drift. I know, though, that everyone has to make
a decision based on need, and sometimes the timeliness of the spray operation
has an impact."

Double nozzle systems can be easily set up, with a double nozzle adapter such
as the Lurmark Twin Cap matched with one of many air-induction nozzles. Low
pressure air-induction nozzles, such as the Air Bubble Jet, Greenleaf AirMix,
Lechler IDK and Hypro Ultra Lo-Drift, are common. High-pressure air-induction
nozzles may include Greenleaf TurboDrop XL, Albuz AVI, TeeJet AI, and the Lechler
ID/Hardi InJet.

Another type of nozzle has captured Wolf's interest, the Albuz AVI-Twin. It
is an air-induction model but has two, 110 degree flat fan patterns coming out
of the one nozzle head. By orienting the spray patterns forwards and backwards,
it can mimic a double nozzle system.

Turbo FloodJet nozzle may be practical choice
At Ridgetown, Ontario, Bayer CropScience sponsors the Sprayer Rodeo that helps
scientists and farmers evaluate the best sprayer set up for fungicide applications
to control fusarium. The Sprayer Rodeo has been a nozzle show-down since 2002
when six sprayers hit a 100 acre wheat field to determine which nozzle offered
the best coverage. Coverage is a key to success with many products, but especially
with Folicur, Bayer CropScience's fungicide for fusarium head blight.

In 2004, the Sprayer Rodeo sparked renewed interest in the familiar Turbo FloodJet
nozzle in trials that are part of serious research conducted by Helmut Spieser,
Ontario Ministry of Agriculture and Food engineer, and Dr. Art Schaafsma, researcher
with the University of Guelph. They also compared double nozzle systems with
conventional and air-induction nozzles in various configurations.

Turbo FloodJet's consistent performance was impressive. They were set up on
20 inch centres alternating forward and backward across the spray boom. "We
put the Turbo FloodJet nozzle onto a standard sprayer," Spieser says. "When
it's clipped into the nozzle body, it's either going to spray forward or back.
It's almost tailor-made."

He points out that Turbo FloodJet is doing much the same job as the double
nozzle assembly but at much less cost. "It is very compact, very convenient,
does a good job at six and at 12mph and is not prone to being shifted if it
sweeps into the wheat heads," Spieser says. Researchers used the nozzles
on 20 inch spacing and 40psi for the 6mph run, and at 71psi for the 12mph run.

Although the Turbo FloodJet nozzles wowed the crowd in 2004, when tested at
the 2003 rodeo they gave inconsistent results. That year the double nozzle assembly
came out on top. But the double nozzle assembly, Spieser points out, is somewhat
cumbersome, costly and has an annoying tendency to adjust itself as it goes
through the canopy, or can even snap off. Double nozzle assemblies can cost
upwards of $30 each while single nozzles come in around $10 for many conventional
types.

Luc Bourgeois, Bayer CropScience manager for research and development in Guelph,
Ontario, says, "We are definitely going to promote the use of Turbo FloodJet
nozzles. It can only help Folicur work better for farmers." Researchers
hope to test air-assist and electrostatic spraying systems in the next year
or two.

What about aerial application?
Ridgetown College and OMAF have also tested aerial application with helicopters
and airplanes. Spieser says that in general, the aerial applications had similar
coverage as the conventional ground application, but not as good as a double
nozzle ground application. "Visually, the water sensitive papers from the
aerial didn't look as good as the conventional ground applications. However,
when we analyzed the water sensitive papers for levels of powdered copper tracer,
the aerial application methods came out equal to conventional ground application
systems," he says.

Whether aerial is an option is debatable, and its use also hinges around time
management. "What I like about aerial is the ability to be timely with
the application. A properly applied fungicide at the wrong time isn't very valuable.
With aerial, you are always trying to balance drift and coverage. You might
get better coverage with a double nozzle ground application, but the question
is whether you can cover all your acres in time," says Wolf.

For ground applications, Wolf has not been able to prove that the improved
coverage delivers better fusarium control. Out in the field where so many biological
factors mix together, including weather conditions, disease development and
fungicide applications, the advantages from the better coverage under simulated
conditions did not demonstrate significant effects on FHB severity, wheat yield
or seed quality.

"I think the key thing, though, is that if your application method presents
a greater dose in a more uniform fashion, it can position you for increased
fungicide performance when external variables permit improved disease control,"
says Wolf. -30-