Weed Suppression

with Cover Crops

Bob Hartzler

Meaghan Anderson

Department of Agronomy

2012 SARE Cover Crop Survey

Desired cover crop benefits

• Soil compaction 58%

• Soil erosion 56%

• Nitrogen scavenging 41%

• Weed control 40%

• Increase crop yields 36%

• Nitrogen source 36%

Cover crops and

weed management

• Mechanisms

– Physical barrier

– Allelopathy

– Enhanced seed predation

– Soil health

• Requirements

– Sufficient biomass

– Uniform distribution

Weed suppression experiments

• Cereal rye

– Mid-September and mid-October planting

– Seeding rates: 0.5 to 5 bu/A

– Terminated first week of May

• Waterhemp and common lambsquarter

seeded in fall after cover crop planting

October 7, 2013 (9 DBLP)

Rye at termination

May 5, 2014

Effect of rye planting date

and seeding rate on biomass

0 1000 2000 3000 4000

Oct14

Sept12

5

2.5

1.2

0.5

a

a

a

a

b

b

Bu/acre

Anderson. ISU. 2014.

Rye terminated on May 5.Feeke’s Stage 8-9 (flag leaf)

0

2

4

6

8

10

12

Control Oct Sept0

2

4

6

8

10

12

Control Oct Sept

Effect of rye planting date on

LQ and WH emergence

Lambsquarter Waterhemp

Rye planting date

% e

me

rgen

ce

Anderson. ISU. 2014.

0

200

400

600

800

0

200

400

600

800

Effect of rye cover crop on

waterhemp emergence patterns

Control Sept. Planting

Late

July

Early

July

Late

Jun

e

Early

June

Late

May

Early

May

Late

April

Anderson. ISU. 2014.

Late

July

Early

July

Late

Jun

e

Early

June

Late

May

Late

April

No

. wat

erh

emp

/ sq

m

Early

May

Time to 50% emergence delayedtwo weeks by rye

CC biomass vs weed suppression

0 1800 3600 5400 7100 8900 10700 12500 14300

Cover crop biomass (lb/A)

Webster et al. 2013. Crop Protection

% w

eed

co

ntr

ol

(6 w

eeks

aft

er p

lan

tin

g)

Rye levels observed inour research

Rye biomass accumulation

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

Rye

dry

wt

(lb

/A)

Kaspar. USDA/ARS. Ames, IAFeyereisen et al. MN. Trans. ASABE.

Approximately 170 lbs/day after initiation of stem elongation.

Weed suppression by cover cropsMoberly, MO. 2013.

0

20

40

60

80

100

120

Winter annuals Summer annuals

Hairy vetch

Tillage radish

Annual ryegrass

Cereal rye

Wheat

Kevin Bradley, Univ. Missouri.

Terminating cover crops

• Herbicide

– Rates, coverage

• Mechanical

– Timing: anthesis

– Mowing• Enhances breakdown

• Uneven distribution

– Crimper• Direction of operation

Summary

• Mulch effect primarily responsible for

weed suppression

– Large amount of biomass required

– Planting date critical

• Uniform establishment and distribution of

residue