Weeds Flashcards
Why are weeds a problem?
- Competition for light, water and nutrients. Reduces crop/plant productivity and growth.
- Weeds are alternate hosts for pests and diseases that can also infect cultivated plants. eg Capsella bursa-pastoris can harbour White Blister Rust and Club Root.
- Weeds reduce the visual appeal of a carefully planned garden.
What is a weed?
A plant growing out of place
Describe the characteristics of Ephemeral weeds, using two examples.
State two non chemical control methods.
Life cycle completes in a few weeks or months/Several life cycles in one growing season or year.
Have shallow roots, concentrating their energy on quickly maturing (usually self-fertile) and producing copious amounts of seed.
Usually grow in recently disturbed ground, in cracks etc. Can be introduced by poor quality compost/manure.
Examples:
Cardamine Hirsuta (Hairy Bittercress)
Capsella bursa-pastoris (Shepherds Purse)
Cultural controls:
Regular weeding, avoiding soil disturbance in spring/summer and exposing seeds to light thus encouraging germination. Instead, apply a mulch of organic matter to a depth of 15cm to suppress weeds.
Physical controls:
Hand pull, fork or hoe (during dry weather) weeds prior to flowering and/or setting seed in order to prevent spread.
Describe the characteristics of Annual weeds, using two examples.
State two non chemical control methods.
Annuals complete their life cycle in one growing season/year.
Have shallow roots, concentrating their energy on maturing, flowering once (usually self-fertile) and setting seed quickly (usually copiously).
Seed remains viable for a long period.
Usually grow in recently disturbed ground, in cracks etc. Can be introduced by poor quality compost/manure.
Examples:
Poa annua (Annual meadowgrass)
Veronica persica (Speedwell)
Cultural controls:
Regular weeding of beds and lawn, and raking/scarifying and mowing of lawn. Avoid soil disturbance in spring/summer and exposing seeds to light thus encouraging germination. Instead, apply a mulch of organic matter to a depth of 15cm to suppress weeds.
Physical controls:
Hand pull, fork or hoe (during dry weather) weeds prior to flowering and/or setting seed in order to prevent spread.
If in lawn (eg Poa annua), scarify/rake regularly, ensure seed heads are lifted above lawn level when mowing.
Describe the characteristics of Perennial weeds, using two examples.
State two non chemical control methods.
Perennial weeds persist over many years. They have perennating organs such as large tap roots or woody above ground structures.
Whilst perennial weeds do flower and set seed, they often spread mainly via vegetative reproduction, eg through rhizomes (Aegopodium podagravia) or runners (Ranunculus repens). Many have very deep or wide ranging roots that are hard to extract in one piece, and in a driveway or perennial border, will be almost impossible to remove completely.
Aegopodium podogravia will regenerate from a tiny fragment of rhizome left in place, often hiding in the root system of surrounding perennials.
Ranunculus repens will spread via runners, and can quickly colonise large areas if left unchecked.
Cultural controls:
Ensuring good drainage in lawns by spiking regularly (Creeping buttercup thrives in poorly drained conditions). Regular weeding of beds and borders will keep on top of newly occurring and re-sprouting perennial weeds such as Ground Elder.
State the meaning of a Contact herbicide, with two examples including the active ingredient.
Kill on contact with the part of the plant they touch, so mainly used for ephemerals and annuals, which will not regenerate from roots, like perennials. Applied to leaves via spray, gel etc. Non selective (kill all plants), so care must be taken when applying to keep to a specific area, protecting other areas of planting with (for ex) polythene sheeting or cardboard as necessary. Non residual (doesn't remain in soil) Examples: Pelargonic acid Fatty acid Acetic acid
State the meaning of a Translocated herbicide, with two examples including the active ingredient.
Herbicide is transported via the vascular system through the plant.
Usually non-selective and so care must be taken when using near cultivated perennials.
Non residual (doesn’t remain in soil)
Example is Glyphosate
- High toxic to marine environments and animals
- Usually used on hard to extract perennials such as ground elder.
- Easiest to use on paths or uncultivated ground
- Can be used around woody plantings as long as non- suckering.
State the meaning of a Selective herbicide, with two examples including the active ingredient.
Selective weed killers kill some plants, but not others, eg only dicots.
Usually non-resisdual
Examples
2,4-D
Describe what type of weeds might be found in Recently Cultivated Soil, and what type of herbicide might be used to control them.
Ephemeral and annual weeds are commonly found in recently cultivated soil, as their seeds may have been exposed to the light as a result of cultivation, and therefore encouraged to germinate. Examples include Cardamine hirsuta, Capsella bursa-pastoris, Poa annua and Veronica persica.
A contact herbicide with an active ingredient such as pelargonic acid should be used, taken precautions against overspray if in cultivated area.
Describe what type of weeds might be found in Herbaceous Perennial Borders, and what type of herbicide might be used to control them.
Ephemeral, annual and perennial weeds may be found in Herbaceous perennial borders, although less likely to have been cultivated recently (if established), weeds can and will still take advantage of any bare patches. Can be spread through poor quality compost/manure used as mulch, for example. Examples include Cardamine hirsuta, Capsella bursa-pastoris, Poa annua and Veronica persica.
Whilst regular weeding and mulching will take care of ephemeral and annual weeds, perennial weeds are likely to be more of a problem in planted areas, as their root systems will blend with the cultivated plants and be harder to successfully extract without damaging surrounding plantings. Eg Aegopodium podogravia (ground elder), which will regenerate from the smallest part of rhizome.
A translocated weedkiller with an active ingredient such as glyphosate is likely to be the best choice on difficult to extract perennials, applied carefully as a foliar treatment so as not to damage surrounding plants roots (as a gel, for example) to all visible parts and then reapplied on all re-sprouting, following manufacturers instructions on timing and conditions.
Describe what type of weeds might be found in Woody Perennial Plantings, and what type of herbicide might be used to control them.
Ephemeral, annual and perennial weeds may be found in Woody Perennial Plantings, although less likely to have been cultivated recently (if established), weeds can and will still take advantage of any bare patches. Can be spread through poor quality compost/manure used as mulch, for example. Examples include Cardamine hirsuta, Capsella bursa-pastoris, Poa annua and Veronica persica.
Whilst regular weeding and mulching will take care of ephemeral and annual weeds, perennial weeds are likely to be more of a problem in planted areas, as their root systems will blend with the cultivated plants and be harder to successfully extract without damaging surrounding plantings. Eg Aegopodium podogravia (ground elder), which will regenerate from the smallest part of rhizome.
A translocated weedkiller with an active ingredient such as glyphosate is likely to be the best choice on difficult to extract perennials, applied carefully as a foliar treatment so as not to damage surrounding plants roots (as a gel, for example) to all visible parts and then reapplied on all re-sprouting, following manufacturers instructions on timing and conditions.
Another choice is a soil based residual herbicide, which can be applied to the soil around woody plantings, as long as the plants are non-suckering, which will remain active for a few months.
Describe what type of weeds might be found in Lawns, and what type of herbicide might be used to control them.
Lawns can contain dicot perennial weeds such as Ranunculus repens, which will respond to the use of selective weedkillers such as 2,4-D, which target dicots only, and do not impact monocot plants (ie grass in this case).
