weeds 2007
DESCRIPTION
As used in Otago Polytechnic's Horticulture course: http://wikieducator.org/Horticulture Original presentation by Lisa Short for Otago Polytechnic CCTRANSCRIPT
Detrimental Effect of Weeds
Look unattractive In pots in nurseries
In garden displays
In lawns
May make harvesting difficult Stinging nettles
Vine like weeds in harvesting machines
Allelopathy Toxic exudates from weeds that affect crop plants
Detrimental Effects of Weeds
Competition Weeds compete for surface nutrients Compete for bees Compete for water Compete for light
Poisonous or painful To people and animals due to chemical or physical defences
e.g. thorns
Harbour Pests and Diseases Humidity increased Over-wintering sites/alternative food source
Detrimental Effects of Weeds
Disrupt and destroy native eco-systems by competing for light, water, nutrients, physical space etc
Approximately 8 species of exotic (i.e. non-native) plants naturalise in NZ per year
Of those, approximately 10% will become invasive
Worst weeds around Dunedin?
In order of weed score rating#1 worst ecological potential= bomarea
then
old man’s beard hawthorn blackberry gorse sycamore banana passionfruit
Followed by…
buddleja ivy Darwin’s barberry broom cotoneaster convolvulus Chilean flame creeper
Benefits of Weeds
Add interest/colour to landscapes Increase diversity Edible/herbal remedies Act as subsoilers Access nutrients lower down in the soil profile Stabilise hillsides Act as indicators Act as a green manure Contain beneficial chemicals Provide food for predator adults Are a food source for a range of wildlife Provide shelter
Benefits of weeds whilst growing
Weed Examples Benefits
Knotgrass, hedge, bindweed, dandelion, poppy, teasel, thistle, chickweed, shepherds purse, plantain
• Are a food source for a range of wildlife
Birds: seed.
Field bindweed, bramble, thistle, ivy, da ndelion, campion, medick, groundsel.
Butterflies: nectar
Thistle, fat hen, medick, ivy, campion, groundsel, clover, white dead -nettle
Bees: nectar
Campion Moths: nectar
Dock, sorrel, nettle, groundsel, ragwort, burdock, charlock, bindweed.
Caterpill ars: foliage
Sun spurge, fumitory Ants: seed oils
Nettle, fat hen, medick, dandelion, nipplewort, bindweed
Predators attract ladybirds and hoverflies whose larvae eat aphids.
Creeping thistle, ground elder, nettle, shepherd’s purse, chickweed
Beetles
Benefits of weeds whilst growing
Weed Examples Benefits
Chickweed, clover, vetch • Can act as a green manure Provide ground cover. Protect soil surface from heavy rain. Encourage soil life. Dig the soil with their roots. Prevent leaching of nutrients. Inc rease fertility. Control erosion. Improve microclimate.
Corn cockle increase the yield of wheat, nettles enhance the flavour of herbs
• Contain beneficial chemicals
To enhance the growth of other plants
All weeds • Increase diversity Fewer pests. Tap the soi l for different nutrients.
Ivy • Provide shelter: Cover for birds. Hibernation for butterflies
Daisy, toadflax, red dead nettle, campion, comfrey, poppy.
• Are attractive Flowers provide colour in the garden
Dock, dandelion, comfrey • Act as subsoilers Bring up nutrients from the subsoil. Improve structure and drainage of soil
• Act as indicators Different weeds grow on different types of soils
Indicator Weeds
Weeds Indicate Comment
Field pansy, field mouse -ear, poppy, charlock
Calcareous soil Test pH. No liming required. Acid -loving plants will need to be planted in acid compost.
Corn spurrey, sorrel, plantain, parsley peirt.
Low pH (acidic) Test pH.May require liming.
Chickweed Neutral soil. Just right!
Cleavers, red dead -nettle, chickweed, borage, creeping thistle, sun spurge, fumitory, charlock, speedwell, redshank.
High in nutrients. Use organic matter to maintain fertility.
Groundsel, stinging nettle, fat hen, ground elder, dock, sowthistle, chickweed.
High nitrogen Plants may be sappy. Leafy vegetables will thrive.
Shrubs, perennials and annuals may flower less. Balance nutrients (with seaweed compost)
Indicator Weeds
Weeds Indicate Comment
Increase in weeds that flower in summer/autumn.
Declining fertility/neglect. Add organic matter. Sow green manures. Recycle nutrients. Maintain ground cover.
Clover, medick, vetch. Low nitrogen. Grow nitrogen -fixing green manures (tares, clover)
Silverweed, greater plantain, pineapple mayweed.
Compact soil. Sow green manures. Make deep beds. Cover soil. Add organic matter. Double dig..
Creeping buttercup, horsetail, silverweed, coltsfoot.
Poor drainage. Aerate soi l. Make deep beds. Sow green manures. Add organic matter. Double dig.
Speedwell, fumitory, chickweed.
Well-aerated, moist soils. Just right!
Spurges, chickweed, groundsel, fat hen, dandelion.
High in humus. Just right!
Characteristics of a weed
Colonisers of disturbed habitats Reproduce very quickly Huge genetic diversity Seed dormancy Habit/Form Habitat Defence system Resistance to herbicides A wide range of dispersal mechanisms
Annuals
A plant that completes it’s lifecycles in one calendar year or growing season.
Seed Germination Growth Flowering/reproduction Seed set Death
Annual weeds ensure survival by seed production.
E.g. fathen, groundsel, cleavers
Biennials
Year 1 Grow from seed and develop strong root systems and cluster of leaves
Year 2 Mature, produce seeds and die
Biennial weeds ensure survival by seed production
E.g. brassicas, shepherd’s purse
Perennial
A plant that persists and produces reproductive structures year after year.
Reproduces by Seed and Vegetatively.
taproots
rhizomes
creeping stems
bulbs/corms
E.g. dock, creeping buttercup, couch, oxalis
Ephemeral
A plant that completes many lifecycles within one calendar year or growing season. Ephemeral weeds are very short lived.
Seed Germination Growth Flowering/reproduction Seed set Death
Within weeks
Ephemeral weeds ensure survival by seed production.
Implication for weed control
Suitable control measures Lifecycle stage
Annual/ Mowing, cultivation or contact herbicide.
Ephemeral Before flowering.
Biennial Cultivation or contact herbicide.
Preferably in the first year of growth or in the second year before flowering.
Perennial Individuals removed, systemic herbicides.
Preferably before maturity – in any year before flowering.
Remember the saying:
“One year’s seeding
means seven year’s weeding!”[1873 Harland & Wilkinson Lancashire Legends 190]
Weeds – adaptations and survival
Plant type (life cycle) Plant vigour/Growth rate Weed habit Seed production Seed dispersal Seeding height Physical and chemical defences Root and specialised underground storage systems Herbicide resistance
Weeds – distribution and growth
Different environmental conditions favour different patterns of weed distribution and growth.
Coastal areas Amenity turf Bush/woodland areas Wetlands Wasteland Garden bed/borders
Categorising Weeds
Dicotyledons
- Plants which produce two seed leaves. Includes broad leaved weeds
Monocotyledons
- Plants which produce a single seedling leaf and includes grasses and cereals
Many herbicides are selective in their mode of action. I.e. they only kill a certain type of plant
Monocotyledon versus Dicotyledon
Broad leaves Net-like pattern of
veins in leaf Flower parts in
multiples of 3 One cotyledon
Long, narrow leaves Parallel pattern of
veins in leaf Flower parts in
multiples of 2, 4 or 5 Two cotyledons
Weed Management
Cultural control Biological control Chemical control
Legal methods to enforce the 3 methods above
Combined together =
Integrated weed management
Cultural Weed Control
Prevention
Keep surrounding areas weed free Mow before flowering General hygiene - machinery, tools, mulches Don’t buy in with mulch, compost or plants
CultivationHand weeding, hoeing, cultivation.Cheap, time consuming.annual/perennial seedlings
Heat treatmentwater or heat/fireannual/perennial seedlings
Mulches (organic and inorganic)Suppresses weed growth by eliminating lightNo light = No weed
Physical control of weeds
Stale Bed Technique
Preparing the bed in advance so that the weeds germinate and can be removed before you sow your crop
Digging
Turn the soil over and bury the weeds upside down - Instant Gratification
- Digging when the soil is wet may destroy the soil structure and cause compaction
- Some weeds may be slow to decompose and go slimy - don’t replant too soon
- Digging will bring weed seeds to the surface- Try digging in the dark!
Mulching
Mulches
Prevent weeds germinating - excludes light/unsuitable surface
Conserve soil moisture - reduces evaporation Prevents rapid fluctuations in soil temperature Reduces winter heat loss from soil (can prevent them
from warming thus increasing frost damage) Prevents soils splashes - reduces soil borne fungal
diseases Reduces erosion caused by rain run-off (can prevent
water getting into the soil)
Organic Mulches
Sawdust Bark chips Peat Hay Straw Leaf mould Spent mushroom compost Fowl manure Stable manure Grass clippings Wood shavings Newspaper
Biological Control of Weeds
The use of insects or diseases to control weeds
Biological control does not aim to eliminate the weed but to reduce it to a level where it can be effectively controlled by other methods
Biological Control of Weeds
Weeds Weeds are mostly introduced (accidentally or deliberately) They often flourish in NZ because:
- of the more favourable climate
- insects and disease which naturally control them are not here
Biological control Biological control can be initially slow to show any results.
However once it is established it costs nothing. The insect damages the host plant only, therefore there are
minimal environmental side effects.
To control gorse: gorse weevil (Apion ulicis) and gorse spider mite (Tetranychus lintearius)
To control Californian thistle: leaf beetle (Lema cyanella)
To control old man’s beard: old man’s beard leaf miner (Phytomyza vitalbae)
Examples of Biological Agents
Selection of Biological Agents
Scientific testing Host specific MAF permission Quarantine Breeding up Release Assessment
Chemical control of weeds
How Herbicides Work
Block a Fundamental Growth Process
- destroy chlorophyll
- stop cell division
- stop respiration
Cause stunting, unnatural growth, and dry out the plant (desiccant)
Modes of action
Contact Herbicides
- foliar applied sprays
- enter leaves by diffusion entering the xylem
- kills the plant at point of spray contact
- use on annuals and young perennials
e.g. Universal Weed Killer, Preeglone
Systemic or Translocated Herbicides
- absorbed either through the roots or leaves
- the chemical is then translocated or moved about within the plant as it grows
e.g. Roundup
Herbicide Selectivity
Selective Herbicide
- Kills the weeds without harming the desired plants
e.g. Lawn weedkillers
kill broadleaves and leave grasses
e.g. Grasskiller
Non-selective herbicides(broad spectrum)
- Kills all vegetation for total control
- Do not use on lawns
e.g. Amitrole, Round-up
What makes a herbicide selective?
Herbicide selectivity:
Can be a feature of the herbicide
- how it is made, active ingredients, different chemical reaction to different types of plants
The way we apply it i.e. Timing
Timing of herbicide use
Pre-planting
- Spray before planting or sowing.
- Target is germinating and existing weeds e.g. Round-up
Pre-emergence
- Spray to control weeds before weeds/crop emerges
- Weed free seed bed and reduced competition
e.g. Foresite
Post-emergence
- Spray herbicide after weed/crop emerges
- True selective e.g. Yates Grasskiller
Soil acting herbicides
Soil acting herbicides are absorbed by weed shoots as they emerge through the soil resulting in weed death
Soil acting herbicides that stay in the soil and continue to control weeds for a extended period of time are called ‘Residual Herbicides’
Prefix D 12 months
Foresite 3 months +
DAS 12 months
Integrated Weed Management
Using a combination of control methods to get the best results
- Cultural
- Biological
- Chemical
Using minimal amount of herbicides Using herbicides safely Promoting plant health Understanding weed lifecycles to enable effective control
Weed management - Example
Poor lawn management gives weeds a competitive advantage.
Encourage a healthy lawn- regular mowing (little & often)- regular fertilising- Water in dry conditions- Scarifying- Pest & disease control
Discourage weeds- choose good quality lawn seed- control weeds in surrounding areas- don’t let weeds flower- don’t buy weeds in
Control existing weeds using a combined approach
Weed Books
Weed books on close reserve at the Bill Robertson Library
Taylor, R. L. (1981). Weeds of roadsides and waste ground in New Zealand. Nelson: Taylor
Uprichard, E. A. (1985). A guide to the identification of NZ common weeds in colour. Palmerston North: NZ Weed and Pest Control Society.
Taylor, R. L. (1983). Weeds of crops and gardens in New Zealand. Nelson: Taylor
Parham, B. E. V; Healy, A. J. (1976). Common weeds in New Zealand. Wellington: D.S.I.R.