Sprayer Drone Use and Utilization in Louisiana Agriculture
The Louisiana sugarcane industry has persevered for more than 225 years, even though it is a tropical crop is growing in a temperate environment. Growers regularly face a challenging climate, which includes the threat of early winter freezes before the crop is harvested. An early freeze can kill the sugarcane plant and cause the sugar (sucrose) inside of the stalk to deteriorate. Another challenge is the short seven-to-10-month growing season. Due to limited daily processing capacity at Louisiana’s 11 raw sugar factories, sugarcane harvest typically begins in mid-September. At the start of the harvest season, sugarcane has low sugar content; thus, growers utilize sub-lethal doses of glyphosate or glyphosate in combination with trinexapac-ethyl to hasten sugar accumulation in the stalk.
By Randy Price and Albert Orgeron
Drones were initially utilized primarily by hobbyists, but more recently have become employed in numerous fields of work, especially agriculture. The incorporation of cameras and sensors on drones has led to novel uses and has aided in crop scouting. Recently, commercial production of spray drones has presented the agricultural community with a possible new tool to aid in crop management. Sugarcane ripener has typically been applied by airplane or helicopter. In 2020, LSU AgCenter scientists first investigated the possibility of applying ripener to sugarcane with a spray drone. Drone-treated plots averaged 30 more pounds of sugar per ton of sugarcane after six weeks compared to untreated plots. The increase in sugar per ton of cane is similar to ripener applications by airplane or helicopter.
For those looking to purchase a sprayer drone, the current most popular and well-regarded brands are DJI, Hylio and XAG and come in tank sizes that hold from 10 to 50 liters (2.6 to 13.2 gallons). A typical spray drone setup composed of one drone, one to three batteries and a charger will cost from $20,000 to $60,000 depending upon brand. Extra equipment is also needed, such as a trailer, extra batteries (at least three), water tank, pumps, chemical storage, hoses, nozzles, quick-fill caps, generator and possibly a cooling system, as some drone batteries need cooling to charge quickly. This extra equipment can add another $10,000 to $20,000. For continuous nonstop spraying, two drones may be necessary.
While the operation of spray drone aircraft is not difficult, operators must be aware of several factors that influence the effectiveness and limitations of a spray drone. Just like spraying with a tractor, spray nozzles can impact pesticide drift and effectiveness for targeting a potential pest. It is important to conduct pattern testing prior to pesticide application to evaluate the effective spray width of the spray drone, which varies from model to model; application height; application rate per acre; nozzle type; and weather conditions. Some drones have rotary or centrifugal nozzles that spin a serrated disc below a liquid outlet and create an adjustable droplet size depending upon rotation speed of the disc and the disc design, such as the “double cutter.” These nozzles have more concise, smaller droplet sizes than standard nozzles — less than 300 micrometers (um) — but may require higher flying altitudes of 10 to 15 feet above the crop surface to create uniform coverage. It is recommended to fly cross-wind if possible to preserve application patterns.
Long-distance drift of 300 feet seems to be negligible with drones, but they can have quite significant side drift (20 to 50 feet) dependent upon wind conditions and nozzle type. Lowering the travel speed around borders can help reduce this effect.
A limitation of spray drones is the battery life. Batteries typically last for 10 to 12 minutes per flight before needing to be recharged. Extra batteries and a generator that is appropriately sized to recharge the batteries is important. To gain maximum efficiency with spray drones, spray the longest possible distance at the fastest speed allowed by the manufacturer. Research has also shown that faster speeds also create wider swath widths. Refill the tank and replace the spray drone battery by driving to the drone on the turnrow, as opposed to having the drone fly to a distant refilling location. Chargers will need 220 to 240 volts at 30 to 50 amps to provide fast 10-minute charging. For sugarcane, corn and other tall crops, an elevated platform may be necessary to visually observe the drone during use. The elevated platform can also be used for landing and takeoff, which saves energy to climb up and over the crop. Every turn or unnecessary flight movement decreases the amount of time the aircraft can fly.
The LSU AgCenter has pattern-testing equipment and offers testing through the Operation Self-regulating Application and Flight Efficiency (S.A.F.E.) program certified by the National Agricultural Aviation Association.
Randy Price is an associate professor at the AgCenter Dean Lee Research Station and Extension Center in Alexandria, and Albert Orgeron is an associate professor at the AgCenter Sugar Research Station in St. Gabriel.
This article appears in the winter 2024 issue of Louisiana Agriculture.
Spray Drone Regulations
Spray drones are regulated by the Federal Aviation Administration (FAA) and primarily fall under two categories. Spray drones that weigh less than 55 pounds when fully loaded operate under 14 Code of Federal Regulations (CFR) Part 107, Small Unmanned Aircraft Systems whereas, drones weighing more than 55 pounds operate under Part 91, General Operating and Flight Rules or via a Special Airworthiness Certificate. Operating larger drones is like any agricultural pilot that flies airplanes or helicopters to apply pesticides and governed under 14 CFR Part 137. Drone pilots must also petition the FAA to be exempted from specific portions of regulations of 14 CFR Part 61, 91 and 137. Additionally, a commercial pesticide certification for aerial application must be obtained from the Louisiana Department of Agriculture and Forestry. Insurance is also needed to cover any damage to adjacent fields from drift, which occurs when droplets or vapor from herbicides travel to other crops that are not the target of the herbicide application.
A spraying drone applies a ripening agent to a sugarcane field. Photo by Al Orgeron
Large drones used for spraying crops are now being used to spray ripening agents on sugarcane, a job once reserved for crop dusters and helicopters. Photo by Randy Price
Randy Price, an agricultural engineer, works on spray pattern testing equipment prior to pattern testing a spray drone. Photo by Al Orgeron.
