Weeds 2007

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As used in Otago Polytechnic's Horticulture course: http://wikieducator.org/Horticulture
Original presentation by Lisa Short for Otago Polytechnic CC

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Weeds 2007

  1. 1. WEEDS
  2. 2. WHAT IS A WEED? <ul><li>Any plant growing where it is not wanted </li></ul>
  3. 3. What is a weed? <ul><li>“ A plant whose virtues have not yet been discovered.” </li></ul><ul><li>Ralph Waldo Emerson </li></ul>
  4. 4. Detrimental Effect of Weeds <ul><li>Look unattractive </li></ul><ul><li>In pots in nurseries </li></ul><ul><li>In garden displays </li></ul><ul><li>In lawns </li></ul><ul><li>May make harvesting difficult </li></ul><ul><li>Stinging nettles </li></ul><ul><li>Vine like weeds in harvesting machines </li></ul><ul><li>Allelopathy </li></ul><ul><li>Toxic exudates from weeds that affect crop plants </li></ul>
  5. 5. Detrimental Effects of Weeds <ul><li>Competition </li></ul><ul><li>Weeds compete for surface nutrients </li></ul><ul><li>Compete for bees </li></ul><ul><li>Compete for water </li></ul><ul><li>Compete for light </li></ul><ul><li>Poisonous or painful </li></ul><ul><li>To people and animals due to chemical or physical defences e.g. thorns </li></ul><ul><li>Harbour Pests and Diseases </li></ul><ul><li>Humidity increased </li></ul><ul><li>Over-wintering sites/alternative food source </li></ul>
  6. 6. Detrimental Effects of Weeds <ul><li>Disrupt and destroy native eco-systems by competing for light, water, nutrients, physical space etc </li></ul><ul><li>Approximately 8 species of exotic (i.e. non-native) plants naturalise in NZ per year </li></ul><ul><li>Of those, approximately 10% will become invasive </li></ul>
  7. 7. Worst weeds around Dunedin? <ul><li>In order of weed score rating </li></ul><ul><li>#1 worst ecological potential </li></ul><ul><li>= bomarea </li></ul><ul><li>then </li></ul><ul><li>old man’s beard </li></ul><ul><li>hawthorn </li></ul><ul><li>blackberry </li></ul><ul><li>gorse </li></ul><ul><li>sycamore </li></ul><ul><li>banana passionfruit </li></ul><ul><li>Followed by… </li></ul><ul><li>buddleja </li></ul><ul><li>ivy </li></ul><ul><li>Darwin’s barberry </li></ul><ul><li>broom </li></ul><ul><li>cotoneaster </li></ul><ul><li>convolvulus </li></ul><ul><li>Chilean flame creeper </li></ul>
  8. 8. Benefits of Weeds <ul><li>Add interest/colour to landscapes </li></ul><ul><li>Increase diversity </li></ul><ul><li>Edible/herbal remedies </li></ul><ul><li>Act as subsoilers </li></ul><ul><li>Access nutrients lower down in the soil profile </li></ul><ul><li>Stabilise hillsides </li></ul><ul><li>Act as indicators </li></ul><ul><li>Act as a green manure </li></ul><ul><li>Contain beneficial chemicals </li></ul><ul><li>Provide food for predator adults </li></ul><ul><li>Are a food source for a range of wildlife </li></ul><ul><li>Provide shelter </li></ul>
  9. 13. Characteristics of a weed <ul><li>Colonisers of disturbed habitats </li></ul><ul><li>Reproduce very quickly </li></ul><ul><li>Huge genetic diversity </li></ul><ul><li>Seed dormancy </li></ul><ul><li>Habit/Form </li></ul><ul><li>Habitat </li></ul><ul><li>Defence system </li></ul><ul><li>Resistance to herbicides </li></ul><ul><li>A wide range of dispersal mechanisms </li></ul>
  10. 14. Reproduction Methods <ul><li>Rhizome </li></ul><ul><li>Tubers </li></ul><ul><li>Root or Shoot Segments </li></ul><ul><li>Bulbs </li></ul><ul><li>Seeds </li></ul><ul><li>Stolons </li></ul>
  11. 15. Weed Lifecycles <ul><li>Annual </li></ul><ul><li>Biennial </li></ul><ul><li>Perennial </li></ul><ul><li>Ephemeral </li></ul>
  12. 16. Annuals <ul><li>A plant that completes it’s lifecycles in one calendar year or growing season. </li></ul><ul><li>Seed  Germination  Growth  Flowering/reproduction  Seed set  Death </li></ul><ul><li>Annual weeds ensure survival by seed production. </li></ul><ul><li>E.g. fathen, groundsel, cleavers </li></ul>
  13. 17. Biennials <ul><li>Year 1 Grow from seed and develop strong root systems and cluster of leaves </li></ul><ul><li>Year 2 Mature, produce seeds and die </li></ul><ul><li>Biennial weeds ensure survival by seed production </li></ul><ul><li>E.g. brassicas, shepherd’s purse </li></ul>
  14. 18. Perennial <ul><li>A plant that persists and produces reproductive structures year after year. </li></ul><ul><li>Reproduces by Seed and Vegetatively. </li></ul><ul><ul><ul><li>taproots </li></ul></ul></ul><ul><ul><ul><li>rhizomes </li></ul></ul></ul><ul><ul><ul><li>creeping stems </li></ul></ul></ul><ul><ul><ul><li>bulbs/corms </li></ul></ul></ul><ul><li>E.g. dock, creeping buttercup, couch, oxalis </li></ul>
  15. 19. Ephemeral <ul><li>A plant that completes many lifecycles within one calendar year or growing season. Ephemeral weeds are very short lived. </li></ul><ul><li>Seed  Germination  Growth  Flowering/reproduction  Seed set  Death </li></ul><ul><li>Within weeks </li></ul><ul><li>Ephemeral weeds ensure survival by seed production. </li></ul>
  16. 20. Implication for weed control <ul><ul><li>Suitable control measures </li></ul></ul><ul><ul><li>Lifecycle stage </li></ul></ul><ul><li>Annual/ Mowing, cultivation or contact herbicide. </li></ul><ul><li>Ephemeral Before flowering. </li></ul><ul><li>Biennial Cultivation or contact herbicide. </li></ul><ul><li>Preferably in the first year of growth or in the second year before flowering. </li></ul><ul><li>Perennial Individuals removed, systemic herbicides. </li></ul><ul><li>Preferably before maturity – in any year before flowering. </li></ul>
  17. 21. <ul><li>Remember the saying: </li></ul><ul><li>“ One year’s seeding </li></ul><ul><li>means seven year’s weeding!” </li></ul><ul><li>[1873 Harland & Wilkinson Lancashire Legends 190] </li></ul>
  18. 22. Weeds – adaptations and survival <ul><ul><li>Plant type (life cycle) </li></ul></ul><ul><ul><li>Plant vigour/Growth rate </li></ul></ul><ul><ul><li>Weed habit </li></ul></ul><ul><ul><li>Seed production </li></ul></ul><ul><ul><li>Seed dispersal </li></ul></ul><ul><ul><li>Seeding height </li></ul></ul><ul><ul><li>Physical and chemical defences </li></ul></ul><ul><ul><li>Root and specialised underground storage systems </li></ul></ul><ul><ul><li>Herbicide resistance </li></ul></ul>
  19. 23. Weeds – distribution and growth <ul><li>Different environmental conditions favour different patterns of weed distribution and growth. </li></ul><ul><ul><li>Coastal areas </li></ul></ul><ul><ul><li>Amenity turf </li></ul></ul><ul><ul><li>Bush/woodland areas </li></ul></ul><ul><ul><li>Wetlands </li></ul></ul><ul><ul><li>Wasteland </li></ul></ul><ul><ul><li>Garden bed/borders </li></ul></ul>
  20. 24. Categorising Weeds <ul><li>Dicotyledons </li></ul><ul><li>- Plants which produce two seed leaves. Includes broad leaved weeds </li></ul><ul><li>Monocotyledons </li></ul><ul><li>- Plants which produce a single seedling leaf and includes grasses and cereals </li></ul><ul><li>Many herbicides are selective in their mode of action. I.e. they only kill a certain type of plant </li></ul>
  21. 25. Dicotyledon Source: University of California www.ipm.ucdavis.edu
  22. 26. Monocotyledon
  23. 27. Monocotyledon versus Dicotyledon <ul><li>Broad leaves </li></ul><ul><li>Net-like pattern of veins in leaf </li></ul><ul><li>Flower parts in multiples of 3 </li></ul><ul><li>One cotyledon </li></ul><ul><li>Long, narrow leaves </li></ul><ul><li>Parallel pattern of veins in leaf </li></ul><ul><li>Flower parts in multiples of 2, 4 or 5 </li></ul><ul><li>Two cotyledons </li></ul>
  24. 28. Weed Management <ul><ul><li>Cultural control </li></ul></ul><ul><ul><li>Biological control </li></ul></ul><ul><ul><li>Chemical control </li></ul></ul><ul><ul><li>Legal methods to enforce the 3 methods above </li></ul></ul><ul><ul><li>Combined together = </li></ul></ul><ul><ul><li>Integrated weed management </li></ul></ul>
  25. 29. Cultural Weed Control <ul><li>Prevention </li></ul><ul><li>Keep surrounding areas weed free </li></ul><ul><li>Mow before flowering </li></ul><ul><li>General hygiene - machinery, tools, mulches </li></ul><ul><li>Don’t buy in with mulch, compost or plants </li></ul>
  26. 30. <ul><li>Cultivation </li></ul><ul><li>Hand weeding, hoeing, cultivation. </li></ul><ul><li>Cheap, time consuming. </li></ul><ul><li>annual/perennial seedlings </li></ul><ul><li>Heat treatment </li></ul><ul><li>water or heat/fire </li></ul><ul><li>annual/perennial seedlings </li></ul><ul><li>Mulches (organic and inorganic) </li></ul><ul><li>Suppresses weed growth by eliminating light </li></ul><ul><li>No light = No weed </li></ul>Physical control of weeds
  27. 31. <ul><li>Stale Bed Technique </li></ul><ul><li>Preparing the bed in advance so that the weeds germinate and can be removed before you sow your crop </li></ul><ul><li>Digging </li></ul><ul><li>Turn the soil over and bury the weeds upside down - Instant Gratification </li></ul><ul><ul><li>- Digging when the soil is wet may destroy the soil structure and cause compaction </li></ul></ul><ul><ul><li>- Some weeds may be slow to decompose and go slimy - don’t replant too soon </li></ul></ul><ul><ul><li>- Digging will bring weed seeds to the surface </li></ul></ul><ul><ul><li>- Try digging in the dark! </li></ul></ul>
  28. 32. Mulching <ul><li>Mulches </li></ul><ul><li>Prevent weeds germinating - excludes light/unsuitable surface </li></ul><ul><li>Conserve soil moisture - reduces evaporation </li></ul><ul><li>Prevents rapid fluctuations in soil temperature </li></ul><ul><li>Reduces winter heat loss from soil (can prevent them from warming thus increasing frost damage) </li></ul><ul><li>Prevents soils splashes - reduces soil borne fungal diseases </li></ul><ul><li>Reduces erosion caused by rain run-off (can prevent water getting into the soil) </li></ul>
  29. 33. Organic Mulches <ul><li>Sawdust </li></ul><ul><li>Bark chips </li></ul><ul><li>Peat </li></ul><ul><li>Hay </li></ul><ul><li>Straw </li></ul><ul><li>Leaf mould </li></ul><ul><li>Spent mushroom compost </li></ul><ul><li>Fowl manure </li></ul><ul><li>Stable manure </li></ul><ul><li>Grass clippings </li></ul><ul><li>Wood shavings </li></ul><ul><li>Newspaper </li></ul>
  30. 34. Inorganic Mulches <ul><li>Black polythene </li></ul><ul><li>Woven plastic fabrics/’Weedmat’ </li></ul><ul><li>Gravel </li></ul><ul><li>Scoria </li></ul><ul><li>Pebbles </li></ul><ul><li>Rocks </li></ul>
  31. 35. Biological Control of Weeds <ul><li>The use of insects or diseases to control weeds </li></ul><ul><li>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 </li></ul>
  32. 36. Biological Control of Weeds <ul><li>Weeds </li></ul><ul><li>Weeds are mostly introduced (accidentally or deliberately) </li></ul><ul><li>They often flourish in NZ because: </li></ul><ul><li>- of the more favourable climate </li></ul><ul><li>- insects and disease which naturally control them are not here </li></ul><ul><li>Biological control </li></ul><ul><li>Biological control can be initially slow to show any results. However once it is established it costs nothing. </li></ul><ul><li>The insect damages the host plant only, therefore there are minimal environmental side effects. </li></ul>
  33. 37. <ul><li>To control gorse: gorse weevil ( Apion ulicis ) and gorse spider mite ( Tetranychus lintearius ) </li></ul><ul><li>To control Californian thistle : leaf beetle ( Lema cyanella ) </li></ul><ul><li>To control old man’s beard : old man’s beard leaf miner ( Phytomyza vitalbae ) </li></ul>Examples of Biological Agents
  34. 38. Selection of Biological Agents <ul><li>Scientific testing </li></ul><ul><li>Host specific </li></ul><ul><li>MAF permission </li></ul><ul><li>Quarantine </li></ul><ul><li>Breeding up </li></ul><ul><li>Release </li></ul><ul><li>Assessment </li></ul>
  35. 39. Chemical control of weeds <ul><li>How Herbicides Work </li></ul><ul><li>Block a Fundamental Growth Process </li></ul><ul><li>- destroy chlorophyll </li></ul><ul><li>- stop cell division </li></ul><ul><li>- stop respiration </li></ul><ul><li>Cause stunting, unnatural growth, and dry out the plant (desiccant) </li></ul>
  36. 40. Modes of action <ul><li>Contact Herbicides </li></ul><ul><li>- foliar applied sprays </li></ul><ul><li>- enter leaves by diffusion entering the xylem </li></ul><ul><li>- kills the plant at point of spray contact </li></ul><ul><li>- use on annuals and young perennials </li></ul><ul><li>e.g. Universal Weed Killer, Preeglone </li></ul><ul><li>Systemic or Translocated Herbicides </li></ul><ul><li>- absorbed either through the roots or leaves </li></ul><ul><li>- the chemical is then translocated or moved about within the plant as it grows </li></ul><ul><li>e.g. Roundup </li></ul>
  37. 41. Herbicide Selectivity <ul><li>Selective Herbicide </li></ul><ul><li>- Kills the weeds without harming the desired plants </li></ul><ul><li>e.g. Lawn weedkillers </li></ul><ul><li>kill broadleaves and leave grasses </li></ul><ul><li>e.g. Grasskiller </li></ul><ul><li>Non-selective herbicides(broad spectrum) </li></ul><ul><li>- Kills all vegetation for total control </li></ul><ul><li>- Do not use on lawns </li></ul><ul><li>e.g. Amitrole, Round-up </li></ul>
  38. 42. What makes a herbicide selective? <ul><li>Herbicide selectivity: </li></ul><ul><li>Can be a feature of the herbicide </li></ul><ul><li>- how it is made, active ingredients, different chemical reaction to different types of plants </li></ul><ul><li>The way we apply it i.e. Timing </li></ul>
  39. 43. Timing of herbicide use <ul><li>Pre-planting </li></ul><ul><li>- Spray before planting or sowing. </li></ul><ul><li>- Target is germinating and existing weeds e.g. Round-up </li></ul><ul><li>Pre-emergence </li></ul><ul><li>- Spray to control weeds before weeds/crop emerges </li></ul><ul><li>- Weed free seed bed and reduced competition </li></ul><ul><li> e.g. Foresite </li></ul><ul><li>Post-emergence </li></ul><ul><li>- Spray herbicide after weed/crop emerges </li></ul><ul><li>- True selective e.g. Yates Grasskiller </li></ul>
  40. 44. Soil acting herbicides <ul><li>Soil acting herbicides are absorbed by weed shoots as they emerge through the soil resulting in weed death </li></ul><ul><li>Soil acting herbicides that stay in the soil and continue to control weeds for a extended period of time are called ‘Residual Herbicides’ </li></ul><ul><li>Prefix D 12 months </li></ul><ul><li>Foresite 3 months + </li></ul><ul><li>DAS 12 months </li></ul>
  41. 45. Integrated Weed Management <ul><li>Using a combination of control methods to get the best results </li></ul><ul><li>- Cultural </li></ul><ul><li>- Biological </li></ul><ul><li>- Chemical </li></ul><ul><li>Using minimal amount of herbicides </li></ul><ul><li>Using herbicides safely </li></ul><ul><li>Promoting plant health </li></ul><ul><li>Understanding weed lifecycles to enable effective control </li></ul>
  42. 46. Weed management - Example <ul><li>Poor lawn management gives weeds a competitive advantage. </li></ul><ul><li>Encourage a healthy lawn </li></ul><ul><li>- regular mowing (little & often) </li></ul><ul><li>- regular fertilising </li></ul><ul><li>- Water in dry conditions </li></ul><ul><li>- Scarifying </li></ul><ul><li>- Pest & disease control </li></ul><ul><li>Discourage weeds </li></ul><ul><li>- choose good quality lawn seed </li></ul><ul><li>- control weeds in surrounding areas </li></ul><ul><li>- don’t let weeds flower </li></ul><ul><li>- don’t buy weeds in </li></ul><ul><li>Control existing weeds using a combined approach </li></ul>
  43. 47. Weed Books <ul><li>Weed books on close reserve at the Bill Robertson Library </li></ul><ul><li>Taylor, R. L. (1981). Weeds of roadsides and waste ground in New Zealand . Nelson: Taylor </li></ul><ul><li>Uprichard, E. A. (1985). A guide to the identification of NZ common weeds in colour . Palmerston North: NZ Weed and Pest Control Society. </li></ul><ul><li>Taylor, R. L. (1983). Weeds of crops and gardens in New Zealand . Nelson: Taylor </li></ul><ul><li>Parham, B. E. V; Healy, A. J. (1976). Common weeds in New Zealand . Wellington: D.S.I.R. </li></ul>
  44. 48. References <ul><li>University of California www.ipm.ucdavis.edu </li></ul>

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