Taking a Bite Out of Weeds

Using agronomic practices to manage weeds in puless

by Kim Waalderbos

Research at the University of Saskatchewan is identifying ways for growers to better manage weeds in pulse crops.

The multi-year, multi-project program has a team of professors and graduate students exploring various projects that together will build the tools available to growers to take the bite out of weeds, sustainably.

“We are aiming to manage weeds and herbicide resistance over the long term,” says Dr. Chris Willenborg, Associate Professor with the Department of Plant Sciences, leading some of the research. He says the growing resistance to Group 2 herbicides highlights the importance of looking at alternative practices for weed management.

Among the projects, the team has been working on discovering new herbicides, studying the effects of pairing herbicides, understanding varietal differences among pulses, and applying agronomic practices to manage weeds in season, he says. Already, grower recommendations are being developed.

Dr. Steve Shirtliffe and plant science graduate student Alex Alba have found cultural methods can provide effective weed management. The rotary hoe, tine harrowing, and inter-row tillage can “provide some benefit on their own, but are better when paired together,” says Shirtliffe.

Their research has found better than 80 per cent weed control — the standard used for registering new herbicides — by using a competitive seed rate (260 plants per metre squared - double the norm in lentils), along with two types of cultivation. Best results were obtained with the rotary hoe, followed by inter-row cultivation. The research also found tine harrowing plus inter-row cultivation can be effective. “We need to get in early when weeds are emerging,” Shirtliffe says.

Higher seeding rates, particularly with lentils, help to crowd out weed competition, says Shirtliffe, of his research findings to date.

In peas, the older-style leafed varieties with long vines have been shown to outcompete weeds better than newer pea varieties. However, the older-style varieties lodge. In continuing research, Willenborg says peas are being used as a model crop to understand how to make pulses more weed competitive.

“Peas do not produce true leaves to canopy, so we are looking at its ability to compete with a modified leaf,” Willenborg says. “Our research has shown there are differences among pea varieties for competitiveness, so we will try and pin down what underlies this mechanism.”

The Shirtliffe research team is looking at blending semi-leafless and leafed pea varieties to achieve some of the advantages of both.

In continuing research, Willenborg, along with graduate students Stefanie De Heij and Khaldoun Ali, is studying the impact of weed seed predators. In particular — the carabid beetle, which is the most abundant seed predator naturally occurring in
agri‑ecosystems.

“Weed seed predators offer a potential solution for managing weeds by destroying them in the seed bank, instead of waiting for the weed to develop above-ground where it has to be treated with a herbicide,” says Willenborg.

This first-of-its-kind research in Canadian pulses aims to identify what pulse crops better attract predation from carabids, and why. Willenborg and team are setting traps to sample catches of carabids to discern who is there and get a sense of their activity to better understand their biology. The team also lays out cards with seeds affixed that the carabids can eat to help estimate what they remove from the seed bank. 

Weed seeds can be an important food source for the carabid beetle. Eating the seeds makes them non-viable and unable to germinate — a benefit to pulse growers, Willenborg says. “It is free weed control, absolutely free, and it can be complimentary to herbicides and other management tools.” The team has two more years of field-level trials planned.

Above ground, Shirtliffe is studying the effect of clipping weeds at the flowering and seed-production stage, when they are extended above the lentil crop canopy. He says early results look promising. 

Shirtliffe and research officer Lena Syrovy are also exploring the benefits of weed wiping. That is, wiping the surface of weeds extending above the pulse crop canopy with a herbicide, in the hopes that the weed plant will absorb the product wiped selectively on its surface and translocate it down to the roots. Early results indicate some success with wiping glyphosate and 2,4-D, however there has been shown to be risk of damage to the underlying pulse crop from herbicide vapours.

This research is being conducted at field-level in the next few years to further understand the possibilities to these weed management tools, and their benefits on pulse quality and yields.

Ultimately, both Willenborg and Shirtliffe aim to develop tools through their research that will allow growers to use agronomy to help control weeds in pulse crops — and slow the evolution of herbicide resistance.

“Anything you rely on too much will eventually let you down,” Shirtliffe says. “Herbicides need to be reserved as the final nail in the coffin for weeds.”