This document provides information about weeds, including their definitions, life cycles, and identification. It discusses that a weed is an undesirable plant that competes with crops for resources. Weeds can be annuals that complete their life cycle in one year, or perennials that live for multiple years. The document describes key morphological features used to identify common weed types, such as their leaves, stems, seeds, and underground structures. It explains that weeds grow for reasons such as restoring bare soil and increasing biodiversity. Effective weed management requires understanding their life cycles and why they grow, rather than simply trying to control them annually.

1. THE WEED
STORY
Prepared and presented by
Carla Bucknor
and
Timon Williamson

2. Principle 1 – What is a weed?What is 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?

3. 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

4. • PROACTIVE APPROACH
– Manage vs. Control
– Key aspects
• Why weeds grow
• How weeds grow
• Which weeds species are present
WEED MANAGEMENT

5. 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

6. 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

7. 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

8. 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
No ligule
present
Auricles and liguleMembranous ligule
Hair-like
ligule
Collar region
Ligule

9. 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

10. Broadleaf Weed ID contd.
• Leaf arrangement
on stem
–alternate
–opposite
Leaf arrangement
Alternate – leaves emerge at different
points or times on the stem; older
ones are larger.
Opposite – leaves emerge at the
same point and time and are the
same size.

11. Broadleaf Weed ID contd.
•Leaf and/or cotyledon
shape
•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.Cotyledons
First true leaves

12. Broadleaf Weed ID contd.
Various
leaf
margins
and
shapes
Note toothed
leaf margin

13. PerennialJohnson grass
(Sorghum halepense)
• Key features
– Membranous ligule
– Prominent midrib
– Reddish-brown seed
– Rhizomes
• Lifecycle
– Perennial
Rhizome with new
shoot

14. PerennialNutsedge (Cyperus)
• Key features
– No ligule
– Triangular stem
– Shiny blades
– Nutlets
• Lifecycle
– Perennial

15. AnnualJimsonweed
(Datura stramonium)
• Key features
– 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

16. 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’.

17. Activation – several days to
50-80 years
Infestation develops over a period
of several years
120 days
Timeline for a typical weed infestation
This shows that weed management
CANNOT be done in ONE YEAR

18. The End