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Institute of Ag Professionals
Proceedings of the
2013 Crop Pest Management Shortcourse &
Minnesota Crop Production Retailers Association Trade Show
www.extension.umn.edu/AgProfessionals Do not reproduce or redistribute without the written consent of author(s).
Bob Hartzler Department of Agronomy
Iowa State University
Return of the seedbank: A long-term perspective towards weed management
Why worry about the seedbank?
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500
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33000 66000 132000 264000
1X 2X
Relationship between Palmer amaranth seedbank and preemergence herbicide rate
# Pa
lmer
/m
2
Palmer seed/m2
Sparks et al. 2003. Univ. Arkansas
Do we have realistic expectations for herbicide performance?
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33000 66000 132000 264000
1X 2X 4X %
con
trol
(e
xpre
ssed
as p
erce
nt o
f see
dban
k)
98%
One approach to seedbank management
Magnitude of weed seedbanks
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Morris Rosemount Iowa Illinois Nebraska
Lambsquarter Pigweed Foxtail
Forcella et al. 1992. Weed Sci.
Seedbank Dynamics
Dormant seedbank
Active seedbank
Decay Fatal germination
Seedlings
Predation
Seed rain Other seed sources
(wind, equipment, etc.)
Long distance dispersal
Dormancy
• Failure to germinate under favorable conditions
• Driving force for seedbank formation • Relieved by environmental signals
– Temperature fluctuations – Light exposure – Other factors
Seedbank behavior % germination
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70
Giant foxtail Waterhemp
Yr 1 Yr 2 Yr 3 Yr 4
% remaining
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60
70
Giant foxtail Waterhemp
Yr 1 Yr 2 Yr 3 Yr 4
Buhler and Hartzler. Iowa.
Seed accounted for
42% foxtail 24% waterhemp
Tillage influences on seedbank • Distribution of seed within profile • Burial of crop residue
– Temperature, moisture • Mixing of soil
– Exposure of seed to sunlight – Aeration
Effect of tillage on waterhemp emergence patterns
Leon and Owen. Iowa.
June 20 June 8 May 15
No-Till Chisel Plow Moldboard Plow
Influence of tillage on seedbank depletion
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2
4
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Lambsquarter Giant fox Redroot pig
No Till Tilled
Mulugeta and Stoltenberg. 1997. Univ. Wisconsin.
Decr
ease
in se
edba
nk (%
)
Reducing Seed Inputs • Control the damn weeds!! • Enhance the competitiveness of the crop
30” rows V2 15” rows V2
30” rows VE 15” rows VE
Marsden Farm Project Boone, IA
Reductions in off-farm inputs: (3 and 4 yr vs 2 yr) Synthetic N: 59 and 74% reduction Herbicide: 76 and 82% reduction
Weed population growth in 2- and 4-year rotations
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0 5 10 15 20
2-y rotation, lambda = 0.93
4-y rotation, lambda = 1.17
Liebman et al. Iowa State Univ.
Population growth in 4 yr rotation with and without seed predation
Liebman et al. Iowa State Univ.
Harrington Seed Destructor
Summary
• The seedbank is the weed problem • Seedbank is highly dynamic • Can be drawn down quickly by minimizing
seed inputs • But one bad year . . .
