Premiere Pulse Virtual Series

Weed Management in Peas

Shaun M. Sharpe

Research Scientist

Agriculture and Agri-Food Canada

Overview

• Soil Seedbank

• Physical Control Strategies

• Expectations from Soil Residuals

– Group 3 and 14

• Options in Organic (Cultural)

• Longer Term Rotations

SOIL SEEDBANK

Infestation Source

18 Year Rotation Study at Scott, SK

Benaragama D, Shirtliffe SJ, Gossen BD, Brandt SA, Lemke R, Johnson EN, Zentner RP, Olfert O, Leeson J, Moulin A,

Stevenson C. Long-term weed dynamics and crop yields under diverse crop rotations in organic and conventional cropping

systems in the Canadian prairies. Field Crops Research. 2016 Sep 1;196:357-67.

Canola, Fall Rye, Pea,

Barley, Flax, Wheat

Green Manure, Wheat, Pea

Barley, GM, Mustard

𝑹𝑹 = 𝑯𝒆𝒓𝒃𝒊𝒄𝒊𝒅𝒆 𝑨𝒑𝒑𝒍𝒊𝒄𝒂𝒕𝒊𝒐𝒏 𝑹𝒊𝒔𝒌 ∗𝑾𝒆𝒆𝒅 𝑷𝒐𝒑𝒖𝒍𝒂𝒕𝒊𝒐𝒏

Every Single Weed Exposed Has Resistance Risk!

Additive Effect!

(simplified form)

Resistance Risk (RR)

Norsworthy, J., Ward, S., Shaw, D., Llewellyn, R., Nichols, R., Webster, T., . . . Barrett,

M. (2012). Reducing the Risks of Herbicide Resistance: Best Management Practices

and Recommendations. Weed Science, 60(SP1), 31-62. doi:10.1614/WS-D-11-00155.1

Example Spray Threshold Framework

2020 Guide Crop Protection, Saskatchewan Ministry of Agriculture

Spray threshold

considerations are for

yield loss (shorter term)

Many post-emergence

herbicide use patterns

– early in crop

production only.

- Source of persistent issues,

buildup of seed within.

- Longer term considerations

- Ecology of our target

- Herbicide longevity

- Lowering the seedbank

- Reduces resistance risk

- Reduces input costs

Soil Seedbank

PHYSICAL WEED

MANAGEMENT

Reducing Seed Return to the Seedbank

Harvest Weed Seed Control

Harrington Seed Destructor

Tidemann, B., Hall, L., Harker, K., & Beckie, H. (2017). Factors Affecting Weed Seed Devitalization with the

Harrington Seed Destructor. Weed Science, 65(5), 650-658. doi:10.1017/wsc.2017.23

Mowing: Species Specific

• Patchy weeds.

• Mow earlier in the season if crop looks lost.

• Kochia can set seeds earlier.

• Harvest/postharvest mowing and tilling likely not effective.

SOIL RESIDUAL HERBICIDES

Setting Expectations

Group 3: Mitotic Inhibitors

• Absorbed in seedling roots

and shoots

• Essentially non-mobile in

soil.

• Low water solubility

• Immediate activity

• Most plants don’t emerge

• Does not control emerged

weeds

O2N NO2

N

H2C

CF3

CH3 CH2 C

CH3

CH2

N

CH2 CH2 CH3H2CCH2

CF3

O2N NO2

CH3

Ethafluralin

Trifluralin

Chemical formula by Bill Ahrens on WSSA.net

Soil Residuals: Group 3

• Ethafluralin (Edge) in no-till

• Fall or spring applied.

• Granular, requires harrowing,

same operation or same day.

• Zone of impact in the soil – 2.5

cm or less

• Pre-seed burn-down with

glyphosate is recommended.

Photo credits: Breanne Tidemann and Neil Harker

Ethafluralin Considerations

• Spring - Up to 10 days before

seeding.

• Fall – Oct 1 to before freeze.

• Persistence linked to moisture.

• Rotation – caution with wheat if

Group 3 used for 2 rotations.

Photo credits: Breanne Tidemann and Neil Harker

Group 3: Ethafluralin

• Interesting reported efficacy

spectra:

– Control of foxtails*, kochia,

lambsquarters, redroot

pigweed, wild buckwheat.

– Suppresses wild oats.

– Known weeds with resistance.

*Will not control trifluralin resistant green foxtail!

Soil Residuals: Group 3

0

10

20

30

40

50

60

70

80

90

100

Wild Oat (n=3) Kochia (n=1) Buckwheat (n=2) Green Foxtail (n=2)

% Weed Control

Data supplied by Gowan Agro Canada

Group 14: PPO Inhibitors

• Soil applied, taken up by

roots then moves to seedling

leaves and shoots.

• Disrupt light harvesting.

• Moderate water solubility,

requires water activation.

• Strong broadleaf control.

• Tank-mix with pyroxasulfone

(Group 15)

Flumioxazin

Sulfentrazone

N

O

O F

N

O

OCH2CHC

N

N

N

Cl

O

H3C

HF2C

Cl

NH S

O

O

CH3

Chemical formula by Bill Ahrens on WSSA.net

Flumioxazin Considerations

• Length of residual control depends on rate

applied and temperature.

• One application

• Moisture is necessary to activate.

– ½ to 1 cm of irrigation water.

• Control reduced by mechanical incorporation.

• Apply prior to planting to 3 days after

planting, before peas emerge.

Weed Spectra

• Flumioxazin Alone

– Control: Redroot pigweed, lambsquarters,

kochia, waterhemp.

– Suppresses: Green foxtail, volunteer canola.

• Flumioxazin + Pyroxasulfone

– Control: Redroot pigweed, lambsquarters,

waterhemp, green foxtail, wild buckwheat, wild

mustard, kochia, annual sowthistle, cleavers.

– Suppresses: Volunteer canola, wild oats, bromes.

Sulfentrazone Considerations

• Requires rainfall / irrigation for activation

(1 to 2 cm)

• Don’t use flood irrigation to activate.

• Shallow incorporation (

OPTIONS FOR ORGANIC

PRODUCTION

Physical, and Cultural Methods

Delayed Seeding + Rod Weeder

• Delay seeding until some

weeds emerge (mid-May)

• Seed at 7.5-cm depth

• Two sequential rod-weeding

passes prior to crop

emergence.

• Field pea emergence = 10 to

14 days after seeding

Johnson, E. N. and Holm, F. A. 2010. Pre-

emergence mechanical weed control in field

pea (Pisum sativum L.). Can. J. Plant Sci. 90:

133138.Photo credits: Breanne Tidemann and

Neil Harker

Pea Genetics

For Italian genotypes

• Yield associated strongly with weed densities.

Taller plants and larger seeds were dominant factors for competitiveness.

Pecetti Luciano, Marcotrigiano Angelo R., Russi Luigi,

Romani Massimo, Annicchiarico Paolo (2019)

Adaptation of field pea varieties to organic farming

across different environments of Italy. Crop and

Pasture Science 70, 327-333.

https://doi.org/10.1071/CP18216

Photo credits: Breanne

Tidemann and Neil Harker

Seeding Rates

200 seeds / m2, plant densities of 120 plants / m2.

Vs 75 to 85 plants / m2 for conventional.

Baird, J. M., Walley, F. L. and Shirtliffe, S. J. 2009. Optimal seeding rate for organic

production of field pea in the northern Great Plains. Can. J. Plant Sci. 89: 455464.

Long-term Rotation Insights

Benaragama D, Shirtliffe SJ, Gossen BD, Brandt SA, Lemke R, Johnson EN, Zentner RP, Olfert O, Leeson J, Moulin A,

Stevenson C. Long-term weed dynamics and crop yields under diverse crop rotations in organic and conventional cropping

systems in the Canadian prairies. Field Crops Research. 2016 Sep 1;196:357-67.

Canola, Fall Rye, Pea,

Barley, Flax, Wheat

Green Manure, Wheat, Pea

Barley, GM, Mustard

Conclusions

Physical methods to prevent seeds return.

Soil residual chemistry to control emerging weeds.

Cultural techniques to compliment residual herbicides and provide canopy closure and weed suppression.