1

Mechanical Weed Control in Organic Crops

Eric N. Johnson1 and Steven J. Shirtliffe1Agriculture and Agri-Food Canada, Scott, SK

2

EWRS

3

Hand weeding intra-row weeds:

200-500 hours per hectare in carrot and direct sown onion and leek

DIAS

4

Mechanical Weed Control Research in Saskatchewan

• Pre-seeding tillage• Pre-emergence tillage

– Rod-weeder, harrow, rotary hoe, small shovels on heavy harrow

• Post-emergence – Harrows, rotary hoe– Inter-row cultivation– Mowing, rolling, weed clipping– Alternative cropping study – long-term study

5 6

Pre-seeding tillage

2

7

Interaction of Seed Date and Flax Cultivar on Yield. Mean of 2 sites (Saskatoon, Scott). 2003

0200400600800

10001200140016001800

May 15 June 1 June 15

Seed Date

kg h

a-1

BethuneVimyNormandyLine 6Line 5

Seed Date X Cultivar interactionp < 0.01

8

Effect of seeding date and weed management on weed biomass in flax. Scott and Saskatoon, SK 2003-2005.

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

May 15 June 1 June 15

Seeding Date

g/sq

.m.

Pre-seed tillage Pre-seed burnoff Pre-seed burnoff + in-crop herbicide

9

0

200

400

600

800

1000

1200

1400

May 15 June 1 June 15

Seeding Date

kg/h

a

Pre-seed tillage Pre-seed burnoff Pre-seed burnoff + in-crop herbicide

Effect of seeding date and weed management on yield of flax. Scott and Saskatoon, SK 2003-2005.

~70%

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Post-seeding / Pre-emergenceTillage in field pea

MECHANICAL WEED CONTROL RESEARCH IN SASKATCHEWAN

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Questions

• Seed shallow and compete ??• Seed deep / pre-emerge till ??• Seed early?? Seed late ??

12

Interaction of Seeding Date, Seed Depth/Tillage System on Weed Biomass in Field Pea. Scott 1999-2001.

0100200300400500600700800900

1000

Wd

biom

ass

(g/m

2)

Check Harrow Rod Wd

Early May

HerbicideEarly

2.5 7.5 2.5 7.5 2.5 7.5Mid May Late May

3

13

Effect of Seeding Date, Seed Depth/Tillage System on Field Pea Yield. Scott 1999-2001.

0

500

1000

1500

2000

2500

3000

3500

Yiel

d (k

g/ha

)

Check Harrow Rod Wd

Early May2.5 7.5 2.5 7.5 2.5 7.5

Mid May Late May

HerbicideEarly

14

Field pea seeded May 4 3” depth - Herbicide

Field pea seeded May 18 3” depth - Pre-emergence rod-

weed

If timed properly, pre-emergence tillage can be effectivein large seeded crops

•The best seed date X seed depth/pre-emergence tillage combination resulted in 80% of the yield obtained with the best seed date/ seed depth/ herbicide combination.

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Maintenance ofCrop Residues

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17 18

Effect of rotary hoe passes on the maintenance of cereal stubble residue, Scott, SK. 2004 - 06.

No. of passes % surface residue0 641 612 584 615 566 55

LSD0.05 12CV 13

No Rotary Hoe

6 passes - Rotary Hoe

Rotary hoeing done after seedingbut prior to field pea emergence

4

19

Effect of number of passes from rotary hoeing on field pea and lentil density at two growth stages. Weed-free conditions. Scott 2004-06

0

20

40

60

80

100

Pre-emergence Ground-crack Pre-emergence Ground-crack

Plan

ts/m

2

0 1 2 3 4 5 6

Field Pea Lentil

20

Effect of number of passes from rotary hoeing on field pea and lentil density at two growth stages. Weed-free conditions. Scott 2004-06

0

10

20

30

40

50

Pre-emergence Ground-crack Pre-emergence Ground-crack

Yiel

d (b

u/ac

re)

0 1 2 3 4 5 6

Field Pea Lentil

21

Pre-emergence Rotary hoe

Check 1 pass 2 pass

4 pass3 pass 5 pass22

Heavy harrow shovel – Proof of Concept Study

23

Heavy Harrow / Small Shovels Proof of Concept

• Unreplicated strip trials in fallow and stubble• Stubble had moderate amounts of trash• Seeded to field pea• Treatments

– Untreated– Single Pass Till 5 DAS– Double Pass Till 5 DAS– Single Pass Till + Single Pass Rotary Hoe 5 DAS– Double Pass Rotary Hoe 5 DAS– Single Pass Till Ground Crack– Single Pass Till 3-node

24

Pre-emergence Tillage With Small Shovels – Field Pea Density Scott 2008

0102030405060708090

100

Unt

reat

ed

SP T

ill 5

DA

S

DP

Till

5 D

AS

SP T

ill, S

P R

. Hoe

5 D

AS

DP

R. H

oe 5

DA

S

SP T

ill G

. Cra

ck

SP T

ill 3

Nod

e

Plan

ts/m

2

Stubble

0102030405060708090

100

Unt

reat

ed

SP T

ill 5

DA

S

DP

Till

5 D

AS

SP T

ill, S

P R

. Hoe

5 D

AS

DP

R. H

oe 5

DA

S

SP T

ill G

. Cra

ck

SP T

ill 3

Nod

e

Fallow

5

25

Pre-emergence Tillage With Small Shovels – Field Pea Yield Scott 2008

010203040506070

Unt

reat

ed

SP T

ill 5

DA

S

DP

Till

5 D

AS

SP T

ill, S

P R

. Hoe

5 D

AS

DP

R. H

oe 5

DA

S

SP T

ill G

. Cra

ck

SP T

ill 3

Nod

e

bus/

acre

Stubble Fallow

010203040506070

Unt

reat

ed

SP T

ill 5

DA

S

DP

Till

5 D

AS

SP T

ill, S

P R

. Hoe

5 D

AS

DP

R. H

oe 5

DA

S

SP T

ill G

. Cra

ck

SP T

ill 3

Nod

e

26

Pre-emergence Tillage With Small Shovels – Field Pea Yield Scott 2008

0

10

20

30

40

50

Unt

reat

ed

SP T

ill 5

DA

S

DP

Till

5 D

AS

SP T

ill, S

P R

. Hoe

5 D

AS

DP

R. H

oe 5

DA

S

SP T

ill G

. Cra

ck

SP T

ill 3

Nod

e

% d

ocka

ge

Stubble Fallow

0

10

20

30

40

50

Unt

reat

ed

SP T

ill 5

DA

S

DP

Till

5 D

AS

SP T

ill, S

P R

. Hoe

5 D

AS

DP

R. H

oe 5

DA

S

SP T

ill G

. Cra

ck

SP T

ill 3

Nod

e

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Tilling at 3-node stage

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Post-emergence Tillage

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Selectivity of Harrow Types

Tine Rotary

Flex-Tine Lely

Flex-Tine Einbock

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Mechanical In-Crop Weed Control Selectivity

• Selectivity

– differential tolerance in plant species.

– Ratio between weed control and crop damage

• Selectivity dependent on:

– How closely weeds resemble the crop

– length of seed germination period

– ineffective - perennial weeds

6

31

Relationship between crop burial and yield of field pea from post-emergence harrowing at 3 above-ground node stage. Weedy conditions. Scott 2004 & 2006.

y = -3.8378x3 + 4.6535x2 - 0.7566x + 1.0213R2 = 0.6236

0%

20%

40%

60%

80%

100%

120%

140%

160%

180%

0% 20% 40% 60% 80% 100% 120%

Crop burial (%)

Fiel

d pe

a yi

eld

(% o

f che

ck)

32

1999

Harrow Type / SettingTine low Tine high Rot. low Rot. high

0

20

40

60

80

100

..................................................................................................................................

single harrow double harrow

Fie l

d p e

a de

n sity

(pl

ants

m-2

)

Untreated

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Effect of harrow type and disturbance level on wild oat fresh weight (g m-2), Scott, 1999

0100200300400500600

Tine Low Tine High Rotary Low RotaryHigh

Untreated

Harrow Type

g m

-2

10° back

High45° back

Low

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Crop Tolerance to Post-Emergence Harrowing

• Crop tolerance is composed of two factors:

– Resistance: the ability of the crop to resist soil covering;

– Recovery: the ability of the crop to recover from soil covering.

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Crop burial of barley, oat and wheat (from left to right) after four passes at the two leaf stage. Averaged over all treatments, crop burial of wheat (57%) was significantly greater (P<0.05) than barley (44%) and oat (38%).

Oat and barley had higher resistance to crop burial

than wheat

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Effect of timing of post-emergence harrowing on crop burial – mean of oats, barley, and wheat. Scott/ Saskatoon

y = 5.8834x + 59.129R2 = 0.9318

y = 6.4145x + 17.746R2 = 0.9989

y = 2.1129x + 5.8R2 = 0.8764

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6 7

Number of Harrow Passes

Estim

ated

Cro

p B

uria

l (%

)

2 4 6

Leaf stage

y = 5.8834x + 59.129R2 = 0.9318

y = 6.4145x + 17.746R2 = 0.9989

y = 2.1129x + 5.8R2 = 0.8764

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6 7

Number of Harrow Passes

Estim

ated

Cro

p B

uria

l (%

)

2 4 6

Leaf stage

Later growth stages had higher resistance to crop

burial

7

37

Effect of post-emergence harrowing on yields of oats, barley, and wheat relative to untreated checks. Weed-free conditions.

Scott/ Saskatoon

Wheat had poorer recovery than oat and barley

(as well as resistance)Later growth stages had

better resistance but poorer recovery

(oats and barley) 38

Post-emergence rotary hoeing

39

2- year study at Scott

• Field pea• Treatments

– Untreated– Single Pass – Ground Crack stage (1)– Double Pass – Ground Crack stage (2)– Triple Pass – Group Crack stage (3)– Single Pass – Ground Crack + 3-node stage (2)– Double Pass – Ground Crack + 3-node stage (4)– Triple Pass – Ground Crack + 3-node stage (6)– Single Pass – Ground-Crack + 3-node + 5-node stage (3)– Double Pass – Ground-Crack + 3-node + 5-node stage (6)– Triple Pass – Ground-Crack + 3-node + 5-node stage (9)

( ) Total passes

40

Rotary Hoe – Effect on Field Pea Density Scott 2007 + 2008

0102030405060708090

100

0 1 2 3 4Number of Passes

Plan

ts (#

/m2)

Ground CrackGround Crack + 3 NodeGround Crack + 3 Node + 5 Node

41

Rotary Hoeing – Effect on Weed Biomass

0

100

200

300

400

500

600

700

0 1 2 3 4Number of Passes

Wee

d Fr

esh

Wei

ght (

g/m

2)

Ground CrackGround Crack + 3 NodeGround Crack + 3 Node + 5 Node

Herbicide

42

Rotary Hoeing – Effect on Field Pea Yield

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

0 1 2 3 4Number of Passes with Rotary Hoe

Yie

ld (b

u/ac

re)

Ground CrackGround Crack + 3 NodeGround Crack + 3 Node + 5 Node

Herbicide Treatment

8

43

Rotary Hoeing

• 4 – 6 passes is a lot!• Only done by crazy

scientists!

Pre-emerge

+

Post-emerge

= ??

44

Inter-row Cultivation

45

Inter-row cultivation - benefits limited by in-row weed competition

46

Integration of Mechanical Weed Control MethodsPre-emerge rod-weed X post-emerge harrow X inter-row cultivation

Untreated

Pre-emerge rod-weed, cross-harrow and inter-row cultivate

47

Yield Response from Pre-Emergence Rod-Weed, Post-emergence Harrow, and Inter-row Cultivation. Mean of 3 years, Scott (2000, 2001 and 2003)

NSInter-row Cultivation

2.0Post-Emergence Harrowing

5.9Pre-Emergence Rod- Weed

Bu/acre

48

Interaction of Pre-Emergence Rod-Weed and Inter-row Cultivation on Yield of Field Pea, Scott, Mean of 3 years (2000, 2001, 2003)

0

5

10

15

20

25

30

No PE Rod Wd PE Rod Wd

bu a

cre-1

0 Harrow 1 IR Cult 2 IR Cult

9

49

Weed Clipping

50

05

1015202530354045

Wee

dy

Her

bici

de 400

550

700

Con

tinuo

us

Wild

oat

see

dlin

gs /

m2

GDD0.05

Effect of clipping on wild oat seedling recruitment. Mean of 2 years. Scott 2007

No weed clipping Weed clipping

52

0

20

40

60

80

100

Check Tine Lely-Low Lely-Mod Lely-High

plan

ts m

-2

1 2 3 4

* * * * * * *

* Statistically lower than the herbicide check at P<0.05

Harrow Type

53

Effect of harrow passes on weed biomass. Mean of 4 harrow settings. Scott. 1999-2001

0100200300400500600700800900

Check 1 2 3 4

No of Passses

Wee

d bi

omas

s (g

/m2) 0.47 0.32

0.060.03

Numbers represent p values for contrasts vs. check

54

Effect of harrow passes on weed biomass. Mean of 4 harrow settings. Scott. 1999-2001

00.5

11.5

22.5

33.5

Untreated Herbicide Tine Lely-Low Lely-Mod Lely-High

Yiel

d (t

/ha)

1 2 3 4

* * * * **

10

55

Rotary Harrow – Soil Disturbance Settings

45°

45°Harrow

High15°

Harrow

Low

15°

56

Untreated Single Harrow 3Xemg, 3 & 5 lf

Double Harrow 3Xemg, 3 & 5 lf

Herbicide