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Understanding weed biology. Chuck Mohler Cornell University. Outline. Intro - what is a weed, types of weeds Perennial weeds Types of perennial weeds Cutting up perennials Weed seeds Germination cues Season of germination Seed longevity in the soil Seed size Seed production

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understanding weed biology
Understanding weed biology
  • Chuck Mohler
  • Cornell University
outline
Outline
  • Intro - what is a weed, types of weeds
  • Perennial weeds
    • Types of perennial weeds
    • Cutting up perennials
  • Weed seeds
    • Germination cues
    • Season of germination
    • Seed longevity in the soil
    • Seed size
    • Seed production
    • Seed dispersal
  • Conclusions
weeds are plants that thrive in disturbed environments
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
understanding the biology of weeds is a key to their control
Understanding the biology of weeds is a key to their control
  • Killing the weeds without harming your crops depends on the biological differences between the weeds and crops.
types of perennial weeds
Types of perennial weeds
  • Stationary
    • Taprooted -- dandelion
    • Fibrous rooted -- plantain
  • Wandering
    • Bulb -- nutsedge
    • Shallow storage organ -- quackgrass
    • Deep storage organ -- bindweeds
slide6

Common bindweed

Broadleaf plantain

Yellow nutsedge

stationary perennials
Stationary perennials
  • Mostly a problem of hay fields and pastures
  • Usually not competitive the first year
  • “Easily” eliminated by tillage
  • Establish from seed
  • Control in adjacent habitats
wandering perennials
Wandering perennials
  • Spread by thickened storage roots or by rhizomes (underground stems)
annual weeds
Annual weeds
  • Live less than one year
  • Establish from seed each year
  • Seeds/seedlings are critical stages
seeds of most weeds are tiny
Seeds of most weeds are tiny

• The plant has limited resources

• Disturbed environments are risky

• Tiny seeds spread the risk over many offspring

• Seedlings can be small because in a recently disturbed environment, competition is limited.

germination cues
Germination cues
  • Seedlings compete poorly with established plants
  • So weed seeds need to know when other plants are absent
  • Respond to cues associated with
    • absence of plants
    • Near-surface conditions
    • soil disturbance
slide15

Common purslane

Redroot pigweed

slide18

Curly dock

Common chickweed

response to chemical environment
Response to chemical environment
  • Absence of volatiles (like ethanol and acetone)
    • velvetleaf
  • Presence of nitrate
    • Lambsquarters
slide20

Lambsquarters

Velvetleaf

consequences
Consequences
  • Can use tillage to flush seeds out of the soil
  • But deep tillage will bring new seeds to the surface
seed production
Seed production
  • A big lambsquarters can produce 100,000 seeds / yr
  • A big redroot pigweed can produce 250,000 seeds / yr
most agricultural weeds depend on humans for dispersal
Most agricultural weeds depend on humans for dispersal
  • In feed grain -- velvetleaf
  • In manure
  • On tractor tires and tillage machinery
  • On combines
some key points
Some key points
  • Breaking up perennials promotes sprouting
  • Tillage, surface conditions, and absence of plants stimulates germination
  • Species have characteristic seasons
  • Seeds often persist in the soil for many years; they die at a constant rate
  • Produce many small seeds
  • Seed size controls depth of emergence, ability to emerge through mulch, and growth rate
  • It is easy to bring in “new” weed species
opportunities for control
Opportunities for control
  • Breaking up perennials increases sprouts but each sprout is weaker
  • Can use cultivation to flush weeds out of the soil
  • If seeds miss their annual opportunity, many may die before next year; more die with tillage
  • The difference in seed size between crops and weeds provides opportunities for control
  • Avoid seed production
  • Guard against invasion of “new” weeds