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Horticulture 1000
HT1102 - Plant management 2 - Weed control
Weeds Cultivation
3

Weed control

There are many methods used to control and reduce weed numbers. Integrated control involves using a combination of any of three methods of control (chemical, cultural, biological). This can be effective and cheaper than using one method alone.

Integrated weed control

Chemical weed control

Herbicides are chemical sprays used to control weeds.

The advantages of herbicides are that they:

However, herbicides have some disadvantages:

Undesirable effects of herbicides

Types of herbicides

Specific herbicides are used to control different types of weeds.

A knapsack can be used to apply herbicide to weedsA knapsack can be used to apply herbicide to weeds.
It is important to use protective clothing when using chemicalsIt is important to use protective clothing, gloves, gumboots and face mask when using chemicals.
 

Cultural control

There are many methods of cultural control. It is important to try to avoid introducing weeds in the first place. Don’t buy or transplant plants that are weed infested. These plants should be destroyed. Couch and oxalis are weeds that spread easily.

Weeding

Digging out the whole plant is a useful method of control of weedsDigging out the whole plant is a useful method of control of weeds.

Digging or hoeing out the whole plant is a useful method of control of annual and perennial weeds.

This stops the plant spreading and producing seeds.

Cultivation buries the weed and seeds, which prevents them from germinating or brings them to the surface where they dry.

 
Rotary hoe bladesRotary hoe blades.

On large areas the soil may be ploughed or rotary-hoed to chop up and bury the weeds.

 

Mulching

Bark has been put around these plants to make the garden low maintenanceBark has been put around these plants to make the garden low maintenance.

Mulch is a layer of material on top of the soil that reduces water loss and    prevents light from entering.

It is used to stop annual weed seeds germinating. Untreated sawdust, hay, bark chips, straw, grass clippings and black polythene are all materials that can be used. Mulch is not so effective to control perennial weeds because they still can push through as they grow vigorously and have large food reserves.

 
Bark has been put around these plants to make the garden low maintenance.

Weed mat is sometimes used with mulch. The matting is put down first and then mulch. This looks more attractive.

 
Weed mat must allow water through to the soilWeed mat must allow water through to the soil.

Weed mat which is either made of woven or non-woven material. Because the matting in this photo is woven it means that water can still get through to the soil and provide the plants with water.

You can see weed mat in this photo, which shows there is not enough mulch covering it.

 

Biological control of weeds

Gorse mites attacking gorseGorse mites attacking gorse.

Biological weed control involves using insects and diseases. In New Zealand an example of biological weed control is the use of a mite to control the spread of gorse.

Continued research is being carried out to find out further biological control methods.

 

Complete Activity 3A in your workbook

Key points   Key points

  • Weeds can be controlled by chemical (herbicides), biological (use of insects for example, gorse spider mite) or cultural methods such as cultivation, mulching and hoeing.
  • Weeds are now controlled more commonly using integrated control, which is a combination of chemical, biological and cultural methods.
  • Weeds have characteristics that let them grow successfully in harsh conditions.
 

What's next?

Go to: 4 Cultivation.

Weeds Cultivation