Weed resistance is changing more than just which herbicides to use. The need for a consistent spray pattern that ensures complete coverage is vital. Nobody wants to see weeds develop resistance to the new herbicide technologies. Killing weeds completely and thoroughly both in the field and at the edges and corners is the best way to prevent this, and that means more attention must be paid to all aspects of application: pressure, speed, boom height, nozzles, and droplet size.
“Consistent spray pattern is so important to preventing weed resistance,” says Gary Esselink, Precision Ag Specialist for Raven. “If weeds are only partially damaged, but not killed, eventually a population will develop resistance. Getting the correct rate of the herbicide onto the plant is key to killing it completely. The right nozzle directly affects the coverage.”
One of the most significant changes is that the labels of the new dicamba products all have specific nozzle requirements.
“Drift is a significant concern with the dicamba technologies,” says Esselink. “Droplet size is an important factor, and nozzles that provide a coarse spray are required.”
Right Nozzle + Right Pressure = Right Droplet Size
Esselink explains that droplet size is measured in microns; the diameter of a human hair is about 100 microns. Droplets in medium to coarse spray are 400 to 600 microns, and in fine spray they are 150 to 200 microns.
“Of course, fine droplets drift more easily,” Esselink says. “They also may be so light they don’t adhere to the leaves, which means the correct rate of herbicide does not reach the plant. The goal is to get complete coverage with the product and have it stick to the foliage of the weeds. If the droplets are too big, say up to 800 microns or more, they may hit the leaf and bounce off. The goal for most dicamba herbicides is recommended to be about 600-700 microns.”
In a flow-based system, speed and pressure directly affect droplet size. The faster the speed, the higher the pressure through the boom and the finer the droplet. The slower the speed, pressure is lower and droplet size larger. If the speed and pressure are too low, the herbicide may not even reach the end of the boom, meaning weeds will be missed. Rough spots in the field can cause an operator to slow down and thus, produce an uneven spray pattern.
“With glyphosate, everything was easy— in the beginning, you could apply a reduced rate and not worry if just a few drops reached the weed, because it would still kill it,” Esselink says. “But that is not the case anymore, now correct and consistent spray patterns are so much more important, with all the many different herbicides that are out there. It’s like Farmers and operators have to go to school all over again—Spraying 101.
”Pulse-Width Modulator Valves Ensure Consistent Pressure
Another factor is the larger sizes of booms being used today, Esselink says.
“Farmers and applicators used to have boom sizes of 60 feet, or maybe 80 or 90 feet. However, there are a lot of 120-foot booms being used now, and the longer length magnifies any loss of pressure because the herbicide has to travel farther.”
A solution to this problem is pulse-width modulated valve technology, or PWM. The PWM valve is attached to the nozzle body and controls the rate electronically, so the pressure doesn’t change according to the speed of the sprayer. The valves work in an on/off duty cycle.
The variability is managed by the PWM valve, Esselink says. If you are driving faster, the duty cycle is on more, allowing flow to go through faster but still maintaining the same consistent pressure. If you drive slower, the valve is more in the off mode than the on mode. The pressure doesn’t change, so the droplet size doesn’t change.
Esselink says the PWM technology is not brand new, but several factors are leading people to look at it more seriously.
“The longer booms are one of the major reason why PWM technology is gaining traction,” he says. “Concern about correct droplet size and consistent spray pattern as it relates to application management is another. Killing weeds completely and reducing the likelihood of herbicide resistance is a third factor. But over it all is the increased importance of getting the right rate of herbicide on the weeds, and that means a consistent spray pattern is more important than ever before.”
Hawkeye Nozzle Control System Provides Consistent Spray Application
Raven’s Hawkeye Nozzle Control system incorporates PWM technology. It also has turn compensation; when going around a curve, the system detects the boom is going faster on the outside, it will put more spray on that part of the boom and less on the inside. “Again, it’s about consistent spray pattern,” Esselink says. “Often you will see a lot of weeds at the corners of a field that are damaged, but not killed because the herbicide was under-applied as the sprayer goes around the corner. Conversely, you run the risk of crop dam¬age if the spray is over-applied on the inside of a curve.
Raven’s AutoBoom is also important in maintaining a consistent spray pattern. Correct and even boom height play a large part in a desired spray pattern, especially with the larger booms. Without correct boom height control, if the end of the boom is allowed to go too high, you may experience spray drift, if it goes too low, you will diminish the size of the spray pattern. Sensors measure the boom’s height from the ground, making adjustments to keep it level.
Esselink says there are sprayer nozzles labeled for dicamba technologies that work with the Hawkeye system. And he stresses that worn nozzles can negate the benefits of the best technology.
“Correct nozzles are everything,” he says. “Applicators or farmers can spend more than $250,000 on a sprayer but if they neglect good nozzle maintenance or properly functioning sprayer nozzles that cost $5,000 to $6,000, then the whole sprayer can become ineffective. That’s why proper application is so important to us at Raven. We’re not in the nozzle business, but we want customers to have optimum results.”