Weeds & Weed Control PDF Print E-mail

DEFINITION:

A weed is any plant growing in the wrong place.

A weed is any unwanted plant.

WHY CONTROL WEEDS?

1.  To improve the appearance of an ornamental area.

2.  To prevent competition for water and nutrients.

3.  To avoid the build up of pests and diseases.

4.  To prevent problems with harvesting e.g. of vegetables.

METHODS OF CONTROLLING WEEDS:

1.  CULTURAL METHODS:

a.  Physical hand pulling.

b.  Hoeing.

c.  Duck shovelling – skimming the surface with a spade.

d.  Mulching:

A mulch is a layer of material which is laid on the surface of the soil.

Uses of mulches:

1.  To reduce evaporation.

2.  To alter soil temperature.

3.  To reduce the number of weeds.

Materials used for mulching:

1.  Organic materials that decompose readily e.g. straw, hay, composted leaves, animal manure and seaweed.

2.  Organic materials that decompose more slowly e.g. pine bark chippings, wood chippings and spent mushroom compost.

3.  Mineral materials e.g. pebbles, gravel and sand.

Essential points to remember to ensure success when mulching:

a.  Mulch should be aesthetically pleasing.

b.  Mulch should be free from weeds and seeds.

c.  Mulch should be laid at a depth of 50mm.

d.  Mulch should be applied to level soil.

2.  CHEMICAL METHODS OF CONTROL (HERBICIDES):

a.  Contact herbicide:

A contact herbicide kills green tissues by contact with them.  It should only be used on annual weeds as perennial weeds will regrow because  it does not kill the roots.  Uses:  Control of annual weeds on paths. Control of annual weeds amongst shrubs.  Control of grass around tree trunks.

b.  Translocated herbicide:

A translocated herbicide is absorbed by the foliage of the weeds.  It is transported (translocated) to the roots.  It is used to kill perennial weeds.  There needs to be an adequate amount of leaf growth for them to work.

There are two types of translocated herbicide:

Selective:  This has a selective action, e.g. it kills broad leaved weeds and not grass.  This type of herbicide is slow acting and causes distortionin the plants before they die.

Non selective:  This kills all perennial weeds including grass.  It is suitable for clearing  ground for planting.  After application no planting should take place for at least six weeks.

c.  Residual herbicide:

A residual herbicide does not kill the existing weeds or plants when applied to moist, weed free soil.  The chemical forms a residue in the surface of the soil which kills any germinating weed seedlings for up to six months.  This herbicide is normally used to keep beds clear of weeds.  N.B.  The beds need to be weed free first and not disturbed afterwards.

d.  Total herbicide:

A non-selective, translocated and residual herbicide.  This is slow acting and takes about two weeks for any signs of death and about four weeks for total control.