Infrared will find weeds that hide

The rising cost of tank mixes is generating interest in weed detection technology

WEEDit has created a big social media buzz over the past year with videos of its infrared spraying technology shared and discussed on Twitter.

The technology, which can be installed on existing production sprayers, can detect and treat individual weeds using red lights, sensors and a nozzle control system installed along the boom.

Instead of blanket spraying an entire field with herbicides, the nozzles are activated only when a weed is detected, which the Dutch company claims will save up to 90 percent of chemical inputs on some fields.

It has been able to deploy its technology on a significant number of Australian acres, said Adam Hutton, who is a product manager in Australia. He said the company is selling 120 sprayers a year in that country.

“The science behind it is called fluorescents,” Hutton said.

“They shine a red light on the plant, and then the wavelength of that light gets shifted in the chlorophyll of the plant and a little tiny amount of it gets beamed back out of the plant as near infrared.”

The high energy LED lights illuminates weeds with a leaf diameter as small as 25 millimetres.

Each sensor monitors a one-metre section of the infrared light that is bounced off the ground ahead of the sprayer’s boom.

The sensor divides the one metre length that it’s responsible for into five lanes, and each of these 20 centimetre lanes have a nozzle dedicated to spraying any of the weeds detected within the lane.

“Each sensor is it’s own computer,” Hutton said.

“Each sensor head is its own brain, and all it does is report its activity back to the council, but the council doesn’t say when to fire. It’s the sensor on the boom that is the boss.”

Reporting the sensor’s activity to the council in the cab allows its firing frequency to be compared to other sensors on the boom.

The council in the cab also monitors boom pressure, flow rate, voltage on the system and the number of acres sprayed.

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The sensor’s quick processing time allows for high travel speeds.

“The sensor samples the ground 40,000 times per second and can achieve speeds of approximately 25 km-h,” Hutton said.

“They can go up to 30 km-h, but there is no way that we can see that you can get chemical to the ground going that fast.”

The sensors sample the ground for an increase of near infrared light that is reflected back by a plant, but it also calibrates itself 50 times per second to adjust for changing levels of infrared light in the natural environment, he said.

Spray expert Tom Wolf said a 20 cm fan width is relatively narrow, which helps the WEEDit technology efficiently target small areas.

“They’ve done a good job of minimizing the dosage,” he said.

“Usually a nozzle on that height, they are talking about a metre boom height, will spray a much wider swath. So they can get good savings by subdividing the field of view into these 20 cm sections, so kudos to them for that.”

The idea of identifying and spraying individual plants has been around on the Prairies since the early 1990s, when Concord Manufacturing’s detect sprayer was developed and Trimble bought WeedSeeker and turned it into GreenSeeker.

Wolf said the previous weed detection technologies were not more widely used on the Prairies because they were introduced at a time when glyphosate was becoming cheaper and growers could easily afford to blanket spray their fields.

However, tank mixes are becoming more expensive as producers combat herbicide resistant weeds, and the opportunity for savings is much greater than it was in the past.

“It might make it worthwhile to go to a more expensive tank mix that you were reluctant to use before,” Wolf said.

“It could make resistant management cost effective now.”

Rotational restrictions on residual products will still limit tank mix options.

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The WEEDit system will be marketed in Canada for preseed burnoff, chemfallow and postharvest applications, said Andreas Mellema, who is the company’s im-porter in Canada.

Prairie producers will get a chance this summer to see WEEDit up close and working in the field at PAMI research stations.

“We will be bringing in a demo unit to some farm days in Saskatchewan,” Mellema said.

“Right now, we have appointments to go into Scott research station on July 13 and Indian Head on July 19.”

He said the price in Canada is still being established as the company works out import duties, but in Europe it retails for around $4,400 per metre.

Wolf said these kinds of technologies are powerful public relations tools for agriculture because they are easy to describe to the public.

“It will become difficult to imagine doing a broadcast spray over a whole field when there are only a few weeds on a field. The savings that are possible are mind boggling,” Wolf said.

For more information, contact Mellema at mellema@bell.net.

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