Using the biology of weeds to leverage weed management

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Using the biology of weeds to leverage weed
management

• Chuck Mohler
• Cornell University

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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

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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

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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

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Wandering perennials

• Spread by thickened storage roots or by rhizomes
  (underground stems)

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Apical dominance in perennials
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Shoot above ground
Shoot below ground
New rhizomes
Old rhizome fragment
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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

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Choosing a tillage regimen for managing a weed
seed bank
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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

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Small seeded species only emerge if near the soil
surface
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Seed longevity
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Seeds survive better deep in the soil
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Death near the soil surface
                             
                                              
                                                  
                                                  
                     Dzier wlochaty (Harpalus
rufipes Dej.) w pelnym biegu.

• Seed predation
• Wetting and drying
• Freeze-thaw

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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.

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• 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 0.85x0.85x0.85x0.850.5
  2 so 50 will make it back into the
  safe-to-emerge zone before they die

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Species with small, long lived seeds?

• Lambsquarters
• Wild mustard

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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

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Manage Weeds on Your Farm a Guide to Ecological
StrategiesMohler 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

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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

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