Post on 16-Jul-2015
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