Rhs year 2 week 18 presentation
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  • 1. RHS Level 2 Certificate Year 2 Week 18 – Weeds, identification and control.
  • 2. Learning Objectives
    • 2. Understand the problems posed by weeds in horticulture and how these problems can be minimised.
    • 2.1 Describe what is meant by a weed.
    • 2.2 Describe how weeds reduce crop productivity and reduce the visual appeal of plantings for display.
    • 2.3 Describe the role of weeds as alternative hosts for plant pathogens.
    • 2.4 Describe the biology of ephemeral, annual and perennial weeds.
    • 2.5 State the botanical names of TWO examples of EACH of the types described in 2.4.
    • 2.8 State what is meant by contact, residual, translocated and selective herbicides, and describe ONE situation where EACH type would be used appropriately.
    • 2.9 State the active ingredient of ONE example of EACH type of herbicide described in 2.6.
  • 3. What is a weed?
    • Any plant in the ‘wrong’ place.
    • However some plants are generally undesirable in cultivated ground
    • Some weeds are serious invasive threats to the environment e.g. Fallopia japonica but most simply compete with cultivated plants for water, nutrients and light.
  • 4. Weeds as hosts for pests and diseases
    • Weeds can provide pests such as aphid with a place to overwinter – leading to rapid infestation of cultivated plants in spring.
    • Weeds can also host viruses and fungal plant diseases that can then be transmitted to cultivated plants.
    • Removing weeds can break the life cycle of the pest or remove the source of disease and therefore reduce the chances of plant problems arising
  • 5. Types of weed
    • Ephemeral – a number of generations produced from seed to seed each year.
    • Annual – germinates, grows, flowers, sets seed and dies in one year.
    • Perennial – live for a number of years, growing and flowering and setting seed each year.
  • 6. Ephemeral weeds
    • Cardamine hirsuta – Hairy Bitter Cress; Senecio vulgaris – Groundsel.
    • Produce vast amounts of seed that remains viable in the ground for a number of years.
    • Shallow rooted and very quick growing.
  • 7. Annual weeds
    • Chenopodium album (Fat Hen); Gallium aparine (Cleavers, Goosegrass)
    • Shallow rooted and quick growing
    • Reproduce by seed and die after setting seed.
  • 8. Perennial weeds
    • Aegeopodium podagraria (Ground Elder); Taraxacum officinale (dandelion) and Plantago major (Greater Plantain)
    • Reproduce by seed, but also vegetatively, which makes them hard to eradicate.
    • Live and grow for many years.
    • Typically deep or extensive root systems, tap roots etc.
  • 9. Means of control
    • Physical – hand weeding, hoeing, digging.
    • Chemical – herbicides
    • Cultural – mulching, weed fabric, ground cover plants.
  • 10. Herbicides
    • Contact – kill what they touch e.g. diquat
    • Systemic or translocated – taken up by the plant, so they will kill all parts if enough is absorbed, e.g. glyphosate
    • Residual – usually combined with a contact herbicide, these kill emerging seedlings, e.g, metosulam.
    • ‘ hormone’ or selective – kill broadleaved weeds (dicotyledons) only, e.g dicamba.
  • 11. Worksheet answers
    • Hand weeding or hoeing – trying not to turn the soil over or damage the rows of cabbages.
    • Hand weeding – chemical control would be difficult as the hedge would also be damaged.
    • Digging or careful spot treatment with glyphosate whilst the perennials are still dormant.
    • Dicamba – selective for broadleaved weeds or a daisy grubber to dig up.
    • Very little (apart from growing a GM grass with resistance to glyphosate).
  • 12. Learning Outcomes
    • 2. Understand the problems posed by weeds in horticulture and how these problems can be minimised.
    • 2.1 Describe what is meant by a weed.
    • 2.2 Describe how weeds reduce crop productivity and reduce the visual appeal of plantings for display.
    • 2.3 Describe the role of weeds as alternative hosts for plant pathogens.
    • 2.4 Describe the biology of ephemeral, annual and perennial weeds.
    • 2.5 State the botanical names of TWO examples of EACH of the types described in 2.4.
    • 2.8 State what is meant by contact, residual, translocated and selective herbicides, and describe ONE situation where EACH type would be used appropriately.
    • 2.9 State the active ingredient of ONE example of EACH type of herbicide described in 2.6.