Weed management with peas and lentils

A closer look at herbicides in your rotation

Written by: Allison Friesen

Increasing diversity by incorporating pulses in your rotation has a number of well-established benefits in terms of disease management, soil conservation and weed control. When including crops like peas or lentils, it is important to carefully consider your available herbicides and how those choices can be best integrated with the bigger picture of weed management. Both crops are relatively non-competitive, especially in their early stages just after emergence. A plan that ensures weed control through their critical periods of early development is essential for preserving early gains in yield potential. Herbicide choices both before and after the pulse crop also need to be considered in terms of resistance management and crop safety. So how do you put it all together?

Critical period of weed control in peas.

Critical period of weed control in lentils.

Herbicide application options for pulses

A good first step is to understand the differences between pre-seed, pre-emergent, and in-crop herbicide applications.

  • Pre-seed applications are made on weeds that are actively growing before the field is seeded
  • Pre-emergent applications are made after seeding but before the crop has emerged
  • Both pre-seed and pre-emergent applications can have burndown and residual activity to control emerged weeds and prevent others from germinating, before the crop appears
  • In-crop applications are made after the crop has emerged to control later germinating weeds during the crop’s early development

For early weed control, pre-seed applications are generally recognized as the most ideal option for pulses as there several modes of action available. If you are unable to make a pre-seed application, pre-emergent herbicide applications are still an option, however it is important to refer to the label for any restrictions to avoid possible injury to the emerging plants.

A tank mix of glyphosate with a Group 14, applied pre-seed or pre-emergence is a great option to control actively growing weeds through two modes of action. This is especially important for resistance management on weeds like kochia, wild mustard and volunteer canola.

In-crop herbicide options

Following the pre-seed application with an in-crop application of a multiple-mode-of-action herbicide registered for peas (e.g. Groups 2,6) helps to clean up any later germinating weeds. This helps keep the crop weed-free until it is well established and also reduces the weed seed pressure for the next season. The Group 6 also provides another mode of action for the resistance management plan.

Conventional lentils are very sensitive to most herbicides. Post-emergent options are typically limited to Groups 5 and 1 herbicides applied when the plants are small. If you are growing a herbicide-tolerant crop like Clearfield® lentils, in-crop applications are open to alternative Group 2 chemistries, as well as the Group 1 and 5.

Fall herbicide choices

Pulse crops can be sensitive to herbicide residues, especially in drier years. To avoid crop injury, it is important to be careful when planning the sequence of crops and the herbicides used two or three years prior to growing peas or lentils. Keep a record of the previous herbicides used in that field and be sure there are no restrictions for seeding your pulse crop when the time comes.

Reducing the risk of resistance

With the extensive use of glyphosate in production, there is a risk that several weeds could develop resistance to its Group 9 chemistry. To help preserve glyphosate’s future utility, it is recommended that it be tank-mixed with alternative modes of action when using it for pre-seed or per-emergent applications.

Repeated use of herbicides using the same group chemistry will eventually select for weeds that are resistant to those herbicides. It is therefore important to plan rotations that include as much diversity in the herbicide group chemistries as possible. Weeds such as cleavers, kochia, wild mustard and wild oat have populations that are resistant to Group 2 herbicides (wild oat has been found to be resistant to Group 1 as well). The recommendation is to use herbicides other than Group 1 and 2, especially in years where other crops, like cereals, are in the rotation. BASF recommends using Group 2 herbicides no more than twice in a 4-year period and never twice in the same year.

Herbicide-resistant weeds in Western Canada

Weed Herbicide group resistance
Ball mustard 2
Chickweed 2
Cleavers 2,4
Combinations of 2 & 4
Cow cockle 2
Green foxtail 1,2,3
Combinations of 1 & 3
Hemp-nettle 2,4
Kochia 2,4,9
Combinations of 2 & 9
Combinations of 2 & 4
Lamb's quarters 2
Narrow-leaved hawk's beard 2
Persian darnel 2
Powell amaranth 2
Redroot pigweed 2
Russian thistle 2
Shepherd's purse 2
Smartweed 2
Spiny sowthistle 2
Stinkweek 2
Wild buckwheat 2
Wild mustard 2,4,5
Wild oat 1,2,4,8,14,15,25
Combinations of 1 & 2
Combinations of 1 & 8
Combinations of 2 & 8
Combinations of 1 & 2 & 8
Combinations of 1, 2 & 25
Combinations of 1, 2, 8 & 25
Combinations of 1, 2, 8, 14 & 15

Source: heap. I. The international Survey of Herbicide Resistant Weeds. Online. 1993. 2016 WeedScience.org

There are a lot of good reasons to include a pulse, like peas or lentils, in your rotation plans. In addition to other benefits, it’s also a good opportunity to gain perspective on herbicide use and how your choices can be optimized for the best results in weed management.

Always read and follow label directions.
Clearfield is a registered trade-mark of BASF Agro B.V.; all used with permission by BASF Canada Inc. © 2017 BASF Canada Inc.

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