Promise of Smart Spraying for Weed Control in Apple Orchards

Weed-It Sprayer attached to an ATV ready for use

Attached here to an ATV, the Weed-It vision-guided sprayer detects weeds when blue light emitted from its sensor is absorbed by the chlorophyll of the weeds.
Photo by Sushila Chaudhari, Michigan State University

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As a weed scientist at Michigan State University, Sushila Chaudhari is always seeking improved technologies to manage problematic weeds. In 2022 she made headway while testing a chlorophyll fluorescence-sensing herbicide sprayer on three perennial crops, including apple.

Such a vision-guided sprayer (VSG) — whether categorized under precision, site-specific, or optical sprayer technology — can potentially benefit the grower in a variety of ways, according to Chaudhari:

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  • It reduces the overuse of herbicides, thus reducing cost.
  • It improves crop safety by reducing the off-target movement of the herbicides.
  • It increases the ability to target difficult-to-control and herbicide-resistant weeds with higher rates.
  • It increases the herbicide spectrum for a particular crop.

Speaking in February at the annual meeting of the International Fruit Tree Association in Grand Rapids, MI, Chaudhari detailed her results with the Weed-It Quadro (Agritech-America), one of several available precision sprayers that detects weeds through chlorophyll content. The brand and the WeedSeeker (Trimble Ag Solution) are less discriminating than other chlorophyll fluorescence-sensing products.

“They are going to detect the chlorophyll in the plant, and based on that, they are going to spray,” she says. “They don’t care if it’s the chlorophyll from the crop or the chlorophyll from the weed.”

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John Deere and Blue River Technology (which John Deere purchased in 2017) offer more advanced technologies in which deep learning algorithms distinguish the weeds from the crops based on their varying shapes.

With the Weed-It Quadro, a sensor emits a blue light that is absorbed by the weed’s chlorophyll. The chlorophyll emits near-infrared (NIR) in reaction to the blue light, and the NIR signal is received and analyzed by the sensor. A spray boom connected to the sensor sprays the weeds in one of three modes: spot spray, dual spray, or full coverage.

“This system can detect weeds that are very small — from 1 centimeter to 3 centimeters in size,” Chaudhari says. “One sensor can control four nozzles, and each nozzle can detect the weeds that are present in 25 centimeters of area; in total, 3.3 feet of width.”

Up close view of sensor and nozzle on Weed-It Sprayer

One Weed-It sensor can control four nozzles, each with a coverage area of 25 centimeters.
Photo by Sushila Chaudhari, Michigan State University

TWO PLUSSES, ONE QUESTION MARK

Chaudhari evaluated the effectiveness of the Weed-It Quadro in three perennial crops: apple (weed density: low), blueberry (weed density: moderate with black weed mat), and grape (weed density: high). Three to four differing herbicide programs (with each including a preemergent and postemergent treatment) were applied to the three cropping systems over the spring, summer, and fall.

In a head-to-head comparison with a CO2 backpack sprayer (BPS) that boasted a two-nozzle boom, Chaudhari’s VGS system fared better, or at least as well, in terms of crop injury and weed control:

Crop injury: In apple, there was no difference between the VGS and BPS regardless of herbicide program. With both blueberry and grape, there was less then 5% injury reported regardless of method of application and herbicide treatment.

Weed control: In apple, there was, for the most part, no difference between the VGS and BPS except at one trial site in which the VGS outperformed the BPS. With blueberry and grape, the VSG fared better at most sites.

On the downside, the VSG did not reduce the volume of herbicide used. At all but one of the apple, blueberry, and grape trial sites, the amount used by the VSG was 11% to 37% higher than that of the BPS. Chaudhari cites two primary reasons for this:

The VSG system boasts a range of sprayer settings from 1 to 5, with 1 detecting the smallest weeds and 5 the largest. Chaudhari had used level 3. “I’m thinking maybe our setting was more toward the sensitive side,” she says, “so most of the nozzles were spraying even if they were detecting a very minute amount of chlorophyll.”

Also, the detection zone of each nozzle, at 25 centimeters, was “very wide,” Chaudhari says. “That means if there is a small weed growing in that area, that nozzle will get activated. It could be that there are more systems out there that have smaller detection zones, and maybe we’ll get more savings on herbicides.”

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