When spot-spraying came of age

For decades, researchers and entrepreneurs have been trying to offer farmers a system to reduce chemical application by targeting specific plants in the field.

Spot-spraying looked like it was coming our way in the early 1990s when Australian inventor Grant Yates visited Western Canada to demonstrate and sell his Southern Precision Weedseeker. He sold a handful of units, but it never caught on.

While Weedseeker may have had a fit in some situations, it depended on identifying a green plant standing against a background of black summer fallow. Weedseeker got confused looking at a background of Canadian prairie stubble. And with black fallow all but gone from the Prairies by then, Weedseeker didn’t gain much of a toehold.

Fast forward three decades and we see giant steps in technology allowing optical sensors and controllers to do things never before dreamed of.

There are now numerous devices that have been built upon the Weedseeker concept, but which have advanced systems for recognizing and quantifying chlorophyll in target plants.

One device now available to Canadian farmers is the Weed-it, which was developed in the Netherlands and is marketed by Jesper Voois at Croplands Equipment in Calgary. He explains how new technology has improved upon the basic Weedseeker principle.

Each sensor covers a 40-inch span on the boom and individually controls four solenoids when nozzle spacing is the standard 10 inches. Depending on options, Weed-it on a 120 foot Millennium boom adds about $150,000 to the price tag. | Weed-it photo

“We use a blue light of a well-known wave length. It’s independent of the sun or other light sources, or the weather. The sensor looks at the light reflectance to determine the level of chlorophyll in each plant,” Voois said.

“We scan for the wavelength of chlorophyll, and that tells us it’s a living plant. It’s basically a green and brown technology. We identify the plant against various background soil conditions, such as stubble or black soil.

“Here was the big breakthrough. We can tune the sensitivity to spot spray big weeds in a young crop. Or at harvest, we use it to spot spray only those plants that need desiccant.”

Voois explains how the tuning system lets Weed-it to be used in desiccation. His example is a field in which 80 percent of the crop has ripened off naturally, but there are patches remaining all over that need more time or maybe they could use a little squirt.

The operator can turn down the chlorophyll sensitivity and spray the entire field. The only plants to get sprayed are the ones that still have a higher level of chlorophyll, including weeds that have survived.

Because Weed-it seeks chlorophyll, the sensitivity can be tuned to spot spray big weeds in a young crop or all weeds in a burnoff. At harvest, it can find and spot spray only those slow-maturing plants that need a squirt. | Croplands photo

“It’s especially good in a young crop where the weeds have already gained an advantage over the plants. It’s another situation where we adjust the system for low sensitivity so it regards the young crop only as background. Then it identifies the big weeds whatever they are, and they get sprayed. It really cuts down on the amount of chemical and it means you can do this application with any crop regardless of its origins.

“In spring degraded stubble, at 15 miles per hour, we can detect a weed the size of your thumbnail and get it sprayed. It’s more difficult to detect the weeds if the stubble is high. So then we apply a background rate of 30 percent to take care of the small seedling weeds. Then when a sensor sees a big weed, it gives a full rate only on that weed. In fresh stubble, we get more random firings because it’s shiny and reflects into the sensor. That takes more chemical.

“We see a chemical reduction of 50 to 90 percent, depending on field conditions.”

Voois says he installs one detection sensor every three feet. That one sensor controls four nozzles when the nozzles are on 10-inch centres. Each nozzle had its own solenoid, and will only fire on the target weeds it’s told to hit.

Weed-it calibrates 40,000 times per second, compensating for dust, daylight conditions and stubble. It functions just as well at night, providing a wider window for application. Weeds are targeted accurately around tight corners, regardless of boom tip speed, because each sensor is fitted with a three-axis accelerometer for integrated speed correction.

Weed-It specialist Jesper Voois says the system targets a specific weed and fires a burst of herbicide at it. The selective spot spray system enables producers to attack the herbicide resistance problem. | Croplands Equipment photo

Voois says the system provides an opportunity to apply chemicals normally considered too expensive for blanket application. It lets a producer develop a long-term herbicide resistance strategy. It becomes economical to employ an aggressive early approach to weed management, targeting young weeds, thus driving down the overall weed bank.

Weed-it was introduced to Canada July 2019. He says Australian farmers have bought 14,000 of sensors. That number of sensors has equipped 600 sprayers.

Weed-it is working with Spec-ialty Enterprises to offer farmers a package deal that consists of a Weed-it system on a Millennium boom.

“This year we installed our system on a 120-foot Millennium boom. That worked very well. To install on a Millennium boom, there’s no grinding or welding. It fits on the cradles already built on the boom. The Weed-it option on that 120-foot boom will cost $180,000.

Beside chemical savings, there are other benefits:

  • It pays to spray higher doses or use more effective, more expensive chemicals to reduce the risk of weed resistance. Over time this will decrease seed banks in the soil.
  • There are savings in water and time on the number of refills of the sprayer.
  • The amount of chemical residue in the soil can be reduced, which can be beneficial for crops.
  • As the use of chemicals, especially glyphosate, is gaining more media attention, spot-spraying can be good for the reputation and image of farming.

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