Research shows a clear financial benefit to a two-pass weed control program in soybeans
Like corn, soybean is impacted by weed interference, and it is during the critical early season when they can be most affected by weed competition.
According to Dr. Peter Sikkema, Professor in Weed Management for Field Crops, University of Guelph, Ridgetown Campus, significant soybean yield loss from weed interference can occur if growers only rely on post-emergence only weed control programs.
There can be a dramatic yield and monetary loss from delayed herbicide application with post-emergence only weed control.
“Depending on the relative time of weed and crop emergence, weed species composition, and weed density, there can be a dramatic yield and monetary loss from delayed herbicide application with post-emergence only weed control programs in soybean,” says Dr. Sikkema. “If weeds are up and growing before you plant the crop, they will have a much bigger impact on soybean yield than a weed that emerges a month after the soybean has come up.”
As a member of the Weed Loss Committee of the Weed Science Society of America, he was asked to document the yield loss in various crops due to weed interference.
In 107 trials conducted from 2007 to 2021, he found that the average yield loss in soybean due to weed interference was 35 per cent.
“However, I want to stress that the actual yield loss in each individual field varies, and in our experiments, the yield loss varied anywhere from zero to 88 per cent.”
Soybean yield loss is going to be influenced by weed density. He says that if you have 100 weeds per square meter, that's going to result in a far greater yield loss than if you have one weed per square meter.
Weather during the growing season will influence the impact of weed interference on soybean yield.
“If you have extremely dry weather, there simply isn't enough moisture for both the crop and the weeds and yield loss would be greater in a dry environment compared to where you have really good growing conditions throughout the growing season.”
Start Clean, Stay Clean
Growers can minimize yield loss due to weed interference by starting clean and staying clean through the critical weed-free period.
“If your soybean field is kept perfectly clean from the time of emergence to the third or fourth trifoliate leaf stage, any weeds that come up after that point will have a minimal impact on a soybean yield.”
To ensure a clean field, he recommends farmers use a two-pass weed control program that starts with a broad-spectrum soil-applied herbicide that matches the weed species composition in each individual field. This may have to be adjusted based on soil characteristics and what crop is planned for that field the following year.
“After the application of the soil-applied herbicide, farmers need to scout their fields and manage the weed escapes,” he says. Growers will have to decide on a field-by-field basis whether or not it is worthwhile to apply a post-emergence herbicide, and the post-emergence herbicide they use will be determined by the weed species in each individual field.”
How to get a 344 ROI
Dr. Sikkema conducted an analysis of the value of a two-pass weed control program in soybean for the 2018/19/20 and 21 growing seasons. During that time, the average soybean yield in Ontario was 49.5 bushels per acre and the average selling price was $13.59 per bushel for a total value of $672 per acre.
There would be a 344 per cent return on investment in a two-pass weed control program in Ontario.
“Assuming a 35 per cent yield loss based on the 107 trials that we did in Ontario, there would be a loss of $236.60 per acre,” Sikkema says. “We calculated the cost of a two-pass weed control program to be $69 per acre. So based on those numbers, there would be a 344 per cent return on investment in a two-pass weed control program in Ontario.”
He emphasises that the timing of weed control is very important and also the need to start clean and stay clean through that critical weed free period.
If growers relied on a total post-emergence program in our trials, there is a loss of almost $45 per acre.
“In seven experiments that we did from 2017 to 2019, where we compared a total post-emergence program, the yield was 49 bushels per acre,” he says. “However, where we went with the two-pass program of a soil-applied residual herbicide followed by a post-emergence herbicide, there was a yield of 52 bushels per acre. And so, if growers relied on a total post-emergence program in our trials, there is a loss of almost $45 per acre.”
So, a perfectly clean field at harvest time does not equal optimal crop management. It is the time of weed control that's critically important to minimize any soybean yield loss due to weed interference.
Authority® brand herbicides from FMC are the cornerstone of an effective two-pass weed control program in both IP soybean* production as well as herbicide tolerant systems.
Authority® 480 herbicide is a flexible pre-emergent Group 14 herbicide that provides extended activity on challenging broadleaf weeds in soybeans. Whether applied alone or tank-mixed with glyphosate and other registered partners, the convenient concentrated formulation of Authority® 480 herbicide ensures ease of use and mixing.
Authority® Supreme herbicide delivers consistent, long-lasting pre-emergent control of grassy and broadleaf weeds. It also provides a high-impact tool for resistance management with Group 14 and 15 chemistries. The unique modes of action can also be tank-mixed with other residual and burndown products to control the weed spectrum growers have in their fields, including weeds resistant to groups 9 (glyphosate), 5 and 2 modes of action.
*Check with your IP soybean contractor / buyer about pyroxasulfone acceptability.
Click to listen to Dr. Peter Sikkema and Allison Hayward, Field Development Representative from FMC Canada, discuss these key research findings on the financial implications of weed interference in soybean.