Post on 30-Jan-2016
description
Using the biology of weeds to leverage weed management
• Chuck Mohler
• Cornell University
Weeds are plants that thrive in disturbed environments
• For example, in a farm field
• Our crops are mostly annual plants - they live for one season
• We kill off natural vegetation & disturb the soil to make conditions suitable for crops
• But this also creates habitats for weeds
Many ways to be a weed
• Annuals– Summer annuals– Winter annuals
• Perennials– Stationary perennials
• Taproots• Fibrous roots
– Wandering perennials• Bulbs & tubers• Rhizomes or storage roots
Outline
• Two general examples
• Managing perennials through exhaustion of roots and rhizomes
• Choosing an appropriate tillage regimen for depleting a weed seed bank
• A specific example – your choice
Wandering perennials
• Spread by thickened storage roots or by rhizomes (underground stems)
Apical dominance in perennials
Tillage
Shoot above ground
Shoot below ground
New rhizomes
Old rhizome fragment
Management of perennials
• Key is exhaustion of reserves.
• Time shoot removal relative to growth stage
• Shallow roots & rhizomes – chop & bury,
• Deep roots & rhizomes – hit them often
• Competitive crops, frequently cultivated crops, short season crops
Choosing a tillage regimen for managing a weed seed bank
Seeds of most weeds are tiny – why?
• Disturbed environments are risky
• Tiny seeds spread the risk over many offspring
• Seedlings can be small because in a recently disturbed environment they have little competition.
• Seedlings have limited resources
Small seeded species only
emerge if near the soil surface
0
0.2
0.4 Velvetleaf
0
0.2
0.4
Lambsquarters
0
0.02
0.04
0 2 4 6 8Depth (cm)
Redroot pigweed
Seed longevity
Loss per year (%)
Species Cultivated Uncultivated
Lambsquarters 31 8
Annual bluegrass 26 22
Common chickweed 54 32
Common groundsel High 45
Seeds survive better deep in the soil
Depth in soil (inches)
0 2 4 6 8 10
See
d s
urv
ival
(%
)
0.0
0.2
0.4
0.6
0.8
1.0
Velvetleaf
Pigweed
Death near the soil surface
• Seed predation• Wetting and
drying• Freeze-thaw
Dzier włochaty (Harpalus rufipes Dej.) w pełnym biegu.
Plowing vs. minimum tillage?
• Small seeded species with short lived seeds plow them under– Most will die before they find their way to surface
again– Example: hairy galinsoga– Needs to be in the top ¼” to emerge– So if mixed into 8” of soil, the average return time
will be 32 years– But few live longer than 2 or 3 years.
• Large seeded species with long lived seeds keep them near the surface– Their mortality will be greater at the surface– And most that are tilled under will come back to
bother you later– Example: velvetleaf– Emerges well from the top 2” of soil– So if mixed into 8” of soil, the average return time
to the emergence zone is 4 years– 80-90% survival below 4” –
0.85x0.85x0.85x0.85=0.52 so 50+% will make it back into the safe-to-emerge zone before they die
– <20% survival near the surface
Species with small, long lived seeds?
• Lambsquarters
• Wild mustard
Many other examples
• Germination cues – Cultivated fallows – Mulches– Stale seedbed
• Relative size of crop and weed seeds– Management of crop competition
• Plant size distributions– Reduction of weed seed production
“Manage Weeds on Your Farm: a Guide to Ecological Strategies”
Mohler and DiTommaso, SAN
• Ecology of weeds
• Cultural control methods
• Physical control methods
• Farm case studies
• Identification, ecology and management of the 75 worst agricultural weeds in the United States
A specific example
• Most farms have many weeds, but only one or two really problem weeds
• Often need to focus on those
• http://www.css.cornell.edu/weedeco
• http://www.organic.cornell.edu/ocs/index.html