Weeding between the rows, finding control of pests

Sprayer systems with the technology to provide mechanical selection between crops and everything else in the field

Spraying a non-selective herbicide between crop rows isn’t a common practice in broad-acre grain and oilseed production, even though there are a few sprayers available in foreign equipment markets that can perform such a pass.

“Garford makes one in Australia called the Crop Stalker. They have been around for a few years, but they are not widely used here that I’m aware of,” said Eric Johnson of the College of Agriculture and Bioresources at the University of Saskatchewan.

“I assume they’re probably used more in high-value horticultural crops and not in larger areas.”

But with the rise of herbicide-resistant weeds in prairie crops and significant improvements in spraying and sensing equipment, it’s likely only a matter of time until Canadian farmers pull out their cheque books for sprayers that give them more chemical options for weeds located in between the rows of their crops.

To test the feasibility of inter-row spraying in western Canadian crop production Johnson and Christian Willenborg built a plot sprayer in Willenborg’s lab that uses Garford shields.

“Our work goes back probably four or five years where the idea sort of came from,” said Willenborg.

“At that time we were trying to spray in between rows of lentils using glyphosate for control of most of the weeds that you’re dealing with, but in lentils we were looking at some of the herbicide-resistant weeds, in particular some of the Group 2 resistant weeds.”

But the inter-row sprayer had problems staying within the row and off of the edge of the crop, which challenged the analysis of some of the plots it was used on.

Johnson has since taken the design further and mounted specialized nozzles lower down on a steerable frame that is better at staying within the rows.

Restrictions due to the COVID-19 pandemic actually helped with the project because the number of trials many researchers are able to run has been cut back, which gave Johnson more time to tinker with the plot sprayer.

“I think now we are at a point where we can do some good research with it,” Johnson said.

He said the project is a proof of concept so they didn’t spend lots of money on a vision-guided system that could keep the plot sprayer within the rows.

Instead, he mounted the spray shrouds on a steerable cultivator that’s used for inter-row cultivation research for organic systems and operators manually steer it away from the crop rows.

“We weren’t satisfied with the weed control that we were getting and part of the problem was we were just using a normal flat fan nozzle, an 80-degree flat fan nozzle and turned it sideways. So we weren’t really getting that good of a pattern in terms of spraying,” Johnson said.

“This year I changed that. We installed what are called Teejet Even nozzles and they tend to be more uniform across the whole spray pattern. I also lowered the nozzles so they are only five inches above the target and they make a really nice eight-inch band.”

Johnson has funding from the Saskatchewan and Alberta Wheat Commissions to examine a system that targets herbicide-resistant wild oats, where a soil active herbicide like Avadex or a pyroxasulfone like Focus or Zidua is applied and then an inter-row application of a non-selective herbicide like glyphosate or glufosinate is used to take out the inter-row wild oat survivors.

He said the soil-applied products are reasonably effective, but they usually don’t control resistant wild oat populations into the 90 to 100 percent efficacy range.

“We’ll pick up some of those residual weed misses from the soil applied herbicide and try to get the numbers into the 90s to 100 percent control, and also maybe reduce seed production and things like that,” Johnson said.

“Based on some of my early observations, I don’t think inter-row spraying is going to be a stand-alone, because you still have weeds within the crop row and you’re only spraying, in our situation 70 percent of the area at most,”

Another drawback of inter-row spraying is the crop rows have to be fairly well established in order to do it properly.

For instance, he said in wheat the crop has to be in the five- or six-leaf stage before an inter-row spray pass should be attempted.

Another project that Willenborg is running uses the inter-row sprayer to target wild oats with Liberty that are growing in between the rows of a tame oat crop.

Liberty, a non-selective herbicide, has been applied between the rows of this oat crop. | Eric Johnson photo

“The theory would be that you could control the wild oat in between those rows, and then use a weed wick to go over top of that crop canopy and any of the wild oat that may have emerged before would in theory be taller and be hit with that weed wick that contains glyphosate,” Willenborg said.

He said the weed wick hasn’t worked out as well as they had hoped because of little height separation between the oats and the wild oats when the inter-row spray application is done.

However, he said there is nothing stopping researchers from coming back into the plots with a wick application once the wild oats get ahead of the crop.

Johnson said they would not likely be exploring this technology if herbicide-resistant weeds hadn’t become such a problem, but he also sees other uses for the inter-row sprayer.

“In the case of some of the specialty crops, pulses and maybe even mustard and some of these other crops where you have really limited herbicide options, this may be an option for them as well,” Johnson said.

He said inter-row spraying may have a good fit with the Weed-It spraying system, which has optical sensors that detect green spots and then precisely controlled nozzles blast the detected weed.

Inter-row spraying may also work with automated platforms like the DOT, because time isn’t as important as precision for this growing technique, he said.

Johnson said they are two or three years away from having good data on inter-row spraying in Canada, so when sprayers capable of hitting weeds in between the rows with a non-selective herbicide become more widely available for growers here, they expect to have data on whether they are worth the investment.

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