Diversifying Weed Control Strategies for Pulse Growers - PulsePoint
December 17, 2018
Herbicide layering, tank-mix options, and beneficial insects offer increased chances of success with weeds
by Trudy Kelly Forsythe
Pulses tend to be weak competitors when it comes to weed pressure. This makes strong weed control with an integrated weed management strategy essential. Fortunately, there are several options available to producers to help them diversify their strategies.
The go-to option for growers is often herbicides, and within this there are some best management practices that will optimize weed control, as well as lessen the impact on the growing problem of herbicide resistance.
Choosing Your Herbicide
Clark Brenzil, Provincial Specialist, Weed Control with the Saskatchewan Ministry of Agriculture, says because pulses are so varied in their tolerance to the various herbicides on the market today, pulse growers should choose ones that are registered and proven to work on their
particular pulse crop.
“Pulse producers have had a history of innovation, conducting field-scale research back when pulse crops were new and had few herbicide options that often did not have great tolerance on the crop or adequate weed spectrums,” says Brenzil. “This, 20 years ago, was out of necessity, but the risks of doing this today are twofold.”
“One, not having a solid foundation of research behind a product puts your crop at undue risk of injury, and two, there is heightened vigilance from the buyers of pulses to the presence of unregistered pesticides in shipments of grain,” he adds. “Buyers today have access to technology that can detect these with ever greater sensitivity and at lower cost, meaning they check more often and have better odds of finding something amiss. Local grain buyers also hold back samples from deliveries in case a problem arises and they need to take legal action.” Pulse growers should be aware of possible marketing restrictions that may arise from using certain crop protection products improperly.
As for choosing products proven to work, Brenzil explains that because many of the herbicides for pulses are not particularly diverse when it comes to herbicide groups, pulse crops have challenges with herbicideresistant weeds that, without alternative herbicide options, go untreated and compete with the crop.
Strategies such as diversifying tank-mix products, herbicide layering, and herbicide rotation can help control weeds and slow the development of herbicide‑resistant weeds.
Since pulse crops have few herbicide options, this also means tank-mix options allowing producers to combine multiple herbicide groups, or modes of action, are limited. Herbicide layering gives producers another way to apply pressure to the weeds, at different stages or timings, using as many different modes of action or herbicide groups as is economical.
“While there are still few foliar herbicide tank mixes, there are more options becoming available as soil-active herbicides that can be used in herbicide-layering programs,” says Brenzil, adding that research has found that rotation alone was not providing the
level of protection against resistance that scientists originally believed it would, but merely delayed its development.
“Mixing or layering two modes of action that control the same weed species, creates a multiplier effect on the risk of finding resistance, whereas rotating herbicides is only an additive buffer against resistance.”
It is important that herbicide group mixes have overlapping activity on the same target weed prone to resistance, and to always apply them at the recommended rates and proper time.
A Biological Option
Given the challenges of herbicide use with pulse crops, researchers are looking at how the use of beneficial insects and seed predation fit into the overall spectrum of weed control for pulses.
Dr. Christian Willenborg, Associate Professor in the Department of Plant Sciences at the University of Saskatchewan’s College of Agriculture and Bioresources, says promoting the abundance of invertebrate species, such as insects, is critical to managing weed seeds that are dispersed into the soils seedbank, because they represent formidable agents of biological weed control.
He stresses that there are few published reports in the literature that examine weed seed predation in pulse crops, which is why they are now assessing the importance of weed seed predators to weed seed consumption within pulse crops. Specifically, they are looking at how much eed predation occurs in various pulse crops, which species contribute to the predation, and whether seed predation in different pulse crops differs between some of the more problematic weed species, such as wild mustard, volunteer canola, and kochia.
“Weed seed predation is one of the only free weed control measures growers have at their disposal, but creating an ecosystem that favours the seed predators is key,” says Willenborg. “Herbicide resistance is becoming an increasing problem, and even weed seed destructors are not capable of controlling all weed seeds. Ensuring we have seed predation occurring in fields is critical to managing weed populations and especially, weed escapes, over the long term.”
Research has discovered that of all invertebrate predators, carabid beetles are the most abundant in the agroecosystem, and have the greatest effect on seed consumption. Weed seed predation along with herbicide layering and diversifying tank mix options are all part of Willenborg’s larger weed research program, funded by Saskatchewan Pulse Growers, tasked with finding a robust strategy for long-term weed management.
These weed management options, when partnered with other non-herbicide options, including tillage, harrowing, and higher seeding rates, can provide pulse producers with more options to help their crops compete against weeds.
