Transcript THE WEED STORY

THE WEED
STORY
Prepared and presented by
Carla Bucknor
and
Timon Williamson
What is Good or Bad about
Weeds?
• Good
– Some indicate soil
nutrient status
– Increase plant
diversity
– Provide good wild
life habitat
• Bad
– Compete with
cultivated crops
causing yield losses
– Out compete native
plants
– Habitat for insect
pests and vectors
Principles of Weed Management
• Principles – fundamental truths
• The question is ‘What are the
fundamental truths we need to
know about weeds so that we can
effectively manage them?’
WEED MANAGEMENT
• PROACTIVE APPROACH
– Manage vs. Control
– Key aspects
• Why weeds grow
• How weeds grow
• Which weeds species are present
Principle
1 – is
What
is a weed?
What
a Weed
?
•A plant growing out of place?
•An undesirable plant?
•Plant with a negative value?
•A pest?
•A plant that competes with other plants and
man for soil?
Life span of weeds
• Annuals
• Produce a seed crop in one year;
• Competitive - succeed in highly unstable
and unpredictable environments (frequent
tillage, drought etc.) as they must make a
seed crop before the next disturbance;
• Seed dormancy
• Long lived seed
• Yield more seed than perennials
Life span of weeds contd.
•
Perennials
• Produce seed crop in excess of one year;
focus is to preserve the parent plant and
produce seed for future generations
• Competitive - more stable environs
• Perennating parts – stolons, bulbs, tubers,
rhizomes
• Storage parts – Perennating parts serve as
stored food reserves for rapid re growth
Morphology of weeds
• Grasses
– Family Gramineae
• Sedges
– Family Cyperaceae; thin triangular stem,
absence of a ligule
• Broadleaves
– Other families of Monocotyledonae and
Dicotyledonae; fully expanded broad leaves
Grass and Grass-like Weed ID
• Key features to look for on
grasses
– ligule
– auricles
– blade/sheath hairs
• Not all features will be present
• Most ID keys begin with the
type of ligule
Ligule
Hair-like
ligule
No ligule
present
Collar region
Membranous ligule Auricles and ligule
Broadleaf Weed ID
Key features to look
for:
• Leaf arrangement on
stem
– alternate
– opposite
• Leaf and/or cotyledon
shape
• Other features to
consider:
– leaf margin traits
– leaf texture/hairs
– odor
• Most seedling keys
begin by asking for leaf
arrangement, then leaf
shape
Broadleaf Weed ID contd.
• Leaf arrangement
on stem
– alternate
– opposite
Alternate – leaves emerge at different
points or times on the stem; older
ones are larger.
Leaf arrangement
Opposite – leaves emerge at the
same point and time and are the
same size.
Broadleaf Weed ID contd.
•Leaf and/or cotyledon
shape
First true leaves
Cotyledons
•Cotyledons or “seed
leaves” emerge first and
are always opposite. Do not
confuse them with the first
true leaves, which are used
to determine leaf shape on
most ID keys.
Broadleaf Weed ID contd.
Various
leaf
margins
and
shapes
Note toothed
leaf margin
Johnson grass
Perennial
(Sorghum halepense)
• Key features
–
–
–
–
Membranous ligule
Prominent midrib
Reddish-brown seed
Rhizomes
• Lifecycle
– Perennial
Rhizome with new
shoot
Nutsedge (Cyperus)
Perennial
• Key features
–
–
–
–
No ligule
Triangular stem
Shiny blades
Nutlets
• Lifecycle
– Perennial
Jimsonweed
(Datura stramonium)
• Key features
Annual
– Long lanceolate
cotyledons with
prominent midrib
– Smooth, lanceolate
/elliptic true leaves
– Purple stems
– Odor when crushed
– Large white/purple
trumpet-shaped flowers
– Egg-shaped seed pod
with spines
• Lifecycle
– Summer annual
Why and where weeds grow?
• ‘Nature’s means of restoring stability by
protecting bare soils and increasing
biodiversity’
• Succession –‘The cycle of a natural
progression of different plant and animal
species over time’.
Why and Where? contd.
• Year 1 – Annual weeds
• Year 2 – Briars and bush
• Years 3 to 4 – Perennial vegetation
• Year 5 – Young trees and/or Perennial
grasses
How and when weeds grow?
• How do they survive ?
• Why are they so prolific?
WEED SEED BANK CONCEPT
Diagrammatic Model of Plant Population Behavior
Harper, J.L. 1977. Population
Biology of Plants. Academic
Press, London
WEED SEED BANK CONCEPT
Diagrammatic Model of Plant Population Behavior
• I Weed seed
bank
• II Environmental
sieve
• III Seedlings,
reproductive
adults
• IV Seed
production
Weed Seed Bank Concept
I Weed seed bank
II Environmental sieve:
Weed managers and nature manipulate the
number of sieves and the ‘leakiness’ of the
sieve. For example: dormancy, the influence
of the previous year’s weed control
Weed Seed Bank Concept contd.
III Seedlings and reproductive adults:
These have survived II and have germinated.
They also have en effect on I due to spectral
quality because they can now act as a cover
crop and so smother or prevent the
germination of other weed seeds in I.
IV Seed production:
The adults from III have now produced seed
which go back into the seed bank.
Timeline for a typical weed infestation
Infestation develops over a period
of several years
Activation – several days to
50-80 years
120 days
This shows that weed management
CANNOT be done in ONE YEAR
SUMMARY
WHAT?
WHERE and WHY?
HOW?
Answers to the above questions will help us to
know more about the weeds we need to
manage.
With this information a suitable weed
management plan can be created.
The End