Ground versus aerial application
The divide over the best way to achieve an effective fungicide application is narrow.
November 14, 2007 By Top Crop Manager
For many years it was assumed that aerial spraying cost more than ground applications.
That may have been true when the industry was in its infancy and ground spraying
equipment was less sophisticated and, therefore, cost less. But, times have
changed and research shows old assumptions may not be valid and the advancement
of spray technology and production styles have made the ground versus aerial
debate more about what method is most suitable for each farm.
The debate can be most intense in western Canada where aerial spraying, extensive
irrigation systems, high clearance sprayers and large fields offer many more
options than are available to eastern Canadian growers who contend with smaller
fields often hemmed in by trees or bordered by other hazards. While having more
options to deliver fungicide to a valuable potato crop might appeal to many
growers in Canada, in western Canada, where fields can be a mile long with few
hazards, the choices can be a source of debate.
As the potato growing areas in western Canada increase and the knowledge and
expertise of growers expands, anecdotal evidence over the effectiveness of each
delivery prompted the commissioning of studies to prove one was better than
the other. In truth, while air application may have nudged ground application
aside on some fronts, experts agree that ground applications are just as effective.
It seems the best way for growers to make a decision is to weigh the pros and
cons of both and make decisions based on the needs of individual operations.
In 2003, Blair Geisel of Gaia Consulting Limited near Portage La Prairie, Manitoba,
conducted research evaluating the yield loss resulting from soil compaction
and damage to foliage caused by the ground sprayer wheels. Where anecdotal evidence
indicated that yield losses occurred in the wheel tracks following repeated
sprayer passes, Geisel's research proved those suspicions to be true although
losses were less costly than suspected.
"There are positives and negatives for both ground and aerial application,"
comments Geisel. "There is soil compaction and damage to foliage in the
wheel tracks of a ground application, but aerial doesn't offer the exactness
of ground application. In my experience, growers in western Canada use a blend
of the two methods depending on their operations." He says many growers
start with ground applications of fungicide until the plants get larger and
then a switch is made to aerial application. As well, weather and time constraints
may make one method more desirable than the other.
It could be a six of one/half dozen of another debate raging over the two methods.
An agricultural engineer from the University of Arkansas with many years experience
in potato research in Canada and the US and himself an aerial applicator, agrees
that a combination may be a sensible option. Dennis Gardisser says that aerial
application does not get in the corners effectively and, as a result, some growers
do not plant in the corners. However, this could balance the loss of yield caused
by tracks from the ground sprayer, so yield loss may not be enough of a reason
to choose air over ground.
"Aerial application doesn't take very long and ground can take several
hours which can cause issues with irrigation," Gardisser explains. He adds
that aerial application may not always give complete coverage of the plant,
but this can also be true with a ground sprayer if it is not calibrated properly.
Gardisser says there are concerns about the amount of water required, but he
believes droplet size is more important than volume. "Three hundred to
350 microns, on average, per spray hitting the plant is the most effective application
no matter how it is accomplished," he says.
"It is true that ground sprayers tend to be more on target with less drift,
causing fewer problems with wildlife and adjoining fields," adds Geisel.
"Aerial sprayers are farther from the canopy making it difficult to target
specific areas. However, air is more time effective, but the newer, larger ground
sprayers can cover larger areas with their wider booms, which also means the
impact of compaction is reduced because fewer passes across the field are required."
If there is one area that cannot be argued, it is the chance that ground sprayers
can increase the spread of disease by carrying it through the crop on the sprayer
after it brushes by diseased plants. Gardisser adds that changing the direction
in which spraying is accomplished also adds to the effectiveness of the operation,
but this is not possible with ground, which gives aerial the edge in this situation.
In both cases, the effectiveness of the application can also be enhanced by
properly calibrated equipment and the experience and skill of the operator.
"Growers tell me that compaction can be more of an issue at harvest than
concerns over loss of yield," says Geisel. He says that the compacted tracks
make digging the potatoes more difficult and also result in large clods of soil
being taken up with the tubers.
"Sometimes terrain, weather or timing may dictate the most effective method
to spray a field," adds Gardisser. "Growers have to make the determination
for each field and for their own operation."
Cost wise, aerial versus ground is less than a dollar difference, so the decision
has to be made on other fronts: loss of yield due to compaction or unplanted
areas, effectiveness of the spray pattern, harvest problems, concerns about
disease spread, and the time it takes to get either application completed, plus
the expertise of the operator. There is no complete study to determine which
is the most cost effective and disease controlling.
Geisel says that to mount this research would be difficult because it is nearly
impossible to maintain the same conditions for both the aerial and ground sprayed
plots. For some growers, the difference may be so minute that it is not worth
the effort to make the comparisons and they will continue to use the method
that suits their operations the best. -30-