1. Weed Control methods Level 2 – Plant Health Problems

2. Weed prevention  You can prevent weeds by inhibiting their growth and development, there are two main methods of weed prevention: mulching and ground cover planting. In both cases the intention is to prevent weeds growing by limiting their space and light.  Mulching: Mulching is the covering of the surface of cultivated soil in order to inhibit weed growth. Materials used for mulching belong to two groups: organic mulch and inorganic mulch.

3. Organic mulch material  Materials such as chipped or shredded bark, cocoa shells, composted waste or leaf mould are spread on the ground between plants.  For effective weed prevention, the covering should be about 50mm deep.  Annual weeds will not germinate but strong perennial weeds will grow through.  Benefits of organic mulch are that in addition to effective weed prevention, it provides other benefits such as:  conserving soil moisture,  enriching the organic content of the soil,  protecting the soil surface structure,  insulating the soil from extreme temperatures  and it looks good.

4. Inorganic mulch materials  Aggregate mulch: Materials such as pea shingle, limestone, chippings, slate and other aggregates can be used to mulch around plants and form an attractive and effective barrier to weed growth.  Porous membranes: Porous membranes, which suppress weed growth but allow water and air exchange, can be used with plants planted through holes made through the membrane. A decorative mulch can be used over it, if necessary.  Total cover: Black polythene, or even old carpet, can be used as a total cover on the ground, which can be left for a growing season. This total cover will eliminate all weeds which grow. They will expire due to lack of light.

5. Mechanical control  Weeds can be physically removed or damaged to prevent their subsequent growth or infestation.  Operators should be trained in the use of certain equipment and must wear protective clothing.  These methods involve: cultivations, surface burning and steam.

6. Cultivations  Cultivating the soil will help remove weeds. You can do this by:  hoeing,  hand weeding  and rotary cultivations.  The method chosen will depend on the site and whether the ground is being prepared for development.

7. Surface burning  This is known as thermal weed control and uses burners to scorch weeds and kill them by rupturing their cells.  This method is ideal for dealing with weeds growing on pavements, or for clearing areas for planting.

8. Hot water and steam  This method will cook and kill the weeds and any weed seeds on the surface. Pavement weeds can be controlled in this way.  Note: The equipment is bulky and may require traffic control in public areas.

9. Chemicals  Application  It is important to time applications of weedkillers (Herbicides) correctly.  The best time is at the seedling stage for all types of weeds.  Biennial weeds are more easily killed in their first season.  For perennials an application of a systemic weedkiller in the autumn when they are passing sugars to the underground parts for winter storage can be very effective.  Normally apply weedkillers when the weeds are in active growth.

10. Contact Weedkiller types  These give a rapid knock-down of all top growth and are ideal for clearing ground prior to sowing or planting. They do not kill the root system or stems of perennial plants, but repeated applications may exhaust their reserves  Paraquat – (withdrawn 2005) was one of the most widely used herbicides to control broad-leaved weeds. Ingestion of the active ingredient is fatal, even in small quantities and for this reason it is banned in many European countries (including the UK since 2005)  Gluphosinate ammonium (Glufosinate) – is a broad spectrum contact herbicide and is a natural compound from two fungi. This causes photosynthesis to stop and the plant dies within a few days.  Sodium Chlorate – a non-selective contact herbicide, killing all green plant parts and has a soil-sterilant effect. It may persist in soils for 6 months to 5 years

11. Systemic (translocated) Weedkiller types  The active ingredient is taken up by the foliage and transported down to the rest of the plant including the perenniating stems and roots. They take about 10 – 14 days to work so may not prevent weeds producing seed before they die.  Glyphosate – Acts on enzymes in the plant which produce amino acid, so reducing the production of protein in the plant. It is not usually absorbed from the soil so it can be used to clear ground for planting. This makes it less useful by itself on paths and gravel.

12. Residual Weedkiller Types  Are non-selective and remain in the soil, killing emerging seeds and perennial roots.  Some can be used with care around established shrubs and trees, but not where bulbs are planted.  Usually they are used in combination with other weedkillers on paths and gravel and should keep them relatively weed-free for the whole of the growing season.  Diuron – used to control a wide variety of annual and perennial broadleaf and grassy weeds. It can remain in the soil for up to a year.  Simazine – (withdraw in 2004 in UK) Plants take up simazine mainly through the roots. It remains active in the soil for between 2 – 7 months.

13. Selective Weedkiller Types  Usually applied to lawns, their action is usually hormonal effecting growth rates. Monocotyledonous and Dicotyledonous plants are affected differently. This works due to the different growth habits of each group of plants  2,4-D – (withdraw 2003) A plant growth regulator, it is taken up by leaves, stems and roots and moves through the plant.  Dichlorophen – kills moss and is quick acting  Mecoprop –P (MCPP) – absorbed by the leaves and translocated to the roots. Good against small creeping weeds like Yarrow.

14. Safety and Health  Whenever a herbicide is used care must be taken. Some can be absorbed through the skin and contact can lead to rashes,  Always follow manufacturer’s instructions carefully.  Wear rubber or vinyl gloves  Keep a separate watering can for herbicides  Only make up enough to do the job in hand.  NEVER store herbicides in “pop” bottles etc.  Store containers away from children and pets  Wash hands after handling chemicals.