Features Fungicides Seed & Chemical
Ground versus aerial application

The divide over the best way to achieve an effective fungicide application is narrow.  

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.

February 15, 2007  By Potatoes in Canada