the weed story prepared and presented by carla bucknor and timon williamson
TRANSCRIPT
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?’
• PROACTIVE APPROACH– Manage vs. Control– Key aspects
• Why weeds grow• How weeds grow• Which weeds species are present
WEED MANAGEMENT
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?
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
No ligule present
Auricles and liguleAuricles and ligule
Membranous liguleMembranous ligule
Hair-like ligule
Collar region
Ligule
Broadleaf Weed IDKey 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
– oppositeLeaf arrangementLeaf arrangement
Alternate – leaves emerge at different points or times on the stem; older ones are larger.
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.
Opposite – leaves emerge at the same point and time and are the same size.
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.CotyledonsCotyledons
First true leavesFirst true leaves
Pere
nnia
lJohnson grass(Sorghum halepense)
• Key features– Membranous ligule– Prominent midrib– Reddish-brown seed– Rhizomes
• Lifecycle– Perennial
Rhizome with new shootRhizome with new shoot
Pere
nnia
lNutsedge (Cyperus)
• Key features– No ligule– Triangular stem– Shiny blades– Nutlets
• Lifecycle– Perennial
Annu
alJimsonweed
(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
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
Harper, J.L. 1977. PopulationBiology of Plants. AcademicPress, London
WEED SEED BANK CONCEPTDiagrammatic Model of Plant Population
Behavior
WEED SEED BANK CONCEPTDiagrammatic Model of Plant Population
Behavior• I Weed seed
bank
• II Environmental sieve
• III Seedlings, reproductive adults
• IV Seed production
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
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.
Weed Seed Bank Concept contd.
Deposition
Germinatio
n
Activation – several days to 50-80 years
Established seedlin
g
5-10 days
Infestation
Infestation develops over a period of several years
Seed Pro
duction
Dispersal
120 days 30-60 days
Timeline for a typical weed infestation
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.