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

2. 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

3. 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?’

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

5. 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?

6. 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

7. 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

8. 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

9. 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 ligule Membranous ligule Hair-like ligule Collar region Ligule

10. 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

11. 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.

12. 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

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

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

15. Perennial Nutsedge (Cyperus) Key features –No ligule –Triangular stem –Shiny blades –Nutlets Lifecycle –Perennial

16. Annual Jimsonweed (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

17. 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’.

18. 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

19. How and when weeds grow? How do they survive ? Why are they so prolific?

20. Harper, J.L. 1977. Population Biology of Plants. Academic Press, London WEED SEED BANK CONCEPT Diagrammatic Model of Plant Population Behavior

21. WEED SEED BANK CONCEPT Diagrammatic Model of Plant Population Behavior I Weed seed bank II Environmental sieve III Seedlings, reproductive adults IV Seed production

22. 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

23. 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.

24. Deposition Germination Activation – several days to 50-80 years Established seedling 5-10 days Infestation Infestation develops over a period of several years Seed Production Dispersal 120 days 30-60 days Timeline for a typical weed infestation This shows that weed management CANNOT be done in ONE YEAR

26. 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.

27. The End