
Rising spot-spraying technology promises significant savings on chemical inputs and increased accuracy at targeting just the weeds. While the cost savings are enticing, Marcelo Zimmer, a weed science program specialist at Purdue University, says that folks should not get too far ahead of themselves when it comes to cutting inputs.
“We cannot compromise weed control in the long run for short-term savings,” Zimmer says. Rather, he shares that there are seven main factors that affect spot-spraying efficiency. If you monitor and adjust these factors, they could help you make the most of your spot-spraying technology without simply cutting herbicide rates.
Here are the key factors:
Weed pressure. “We’re going to see the most benefit of this technology in fields that have very low weed pressure,” Zimmer says. If you head into a field with heavy weed pressure historically, then you probably will not notice the savings that this technology promises.
Herbicide program and timing. If your program relies on one post-emergence application, then this technology will not be a benefit to you. In that situation, you would likely need to make several post-applications to ensure that you catch all the weeds. This technology works best following a preemergence broadcast application. Zimmer recommends implementing a two-pass program where you use a full amount of the herbicide when you make a preemergence broadcast application and follow that with a targeted post-application.
Cover crops. Using cover crops in your cropping system can help suppress weeds, lowering weed pressure. By implementing cover crops, your spot-spraying technology could be more effective with less weed pressure.
Model sensitivity. You have the option to tweak the sensitivity settings in your spot-spraying technology. Lower sensitivity settings could generate more savings with less herbicide being used, but there is the potential for missing weeds if they are not detected at the threshold you set.
Nozzle factors. The nozzle type, spacing and angle are all components that determine the size and scope of the area being sprayed. For example, wider nozzles spaced further apart would mean more herbicide being sprayed, Zimmer says. This would lead to less savings on inputs.
Buffers. The latitudinal and longitudinal buffers of your spot-spraying technology determine which nozzles turn on and how long they run when a weed is detected. Toggling those buffers to different parameters will affect how much product is sprayed. “If you don’t care about missing some weeds, you might use narrower buffers,” Zimmer says. “But if you really want to make sure you get all the weeds, you’re going to have wider buffers, and that’s going to increase your spray volume.”
Additional conditions. Factors such as travel speed, topography of the field and dust all can affect when the spot-spraying technology is triggered. If the conditions are pushing the technology beyond what it is set to deliver, then it will default to a broadcast application. “Every time the system is not confident if there is a weed or not, it’s going to go back to broadcast mode, and you’re going to be spraying parts of the field you didn’t need to spray just because you’re running it too fast,” Zimmer says. “If the topography is a little bit challenging as well, we have a lot of boom sway. The camera is not going to be as good at capturing the weeds in the field.”
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