Basic Principles of Weeds Control and Management

What is a weed?

A weed is a plant considered undesirable in a particular situation, “a plant in the wrong place”. Examples commonly are plants unwanted in human-controlled settings, such as farm fields, gardens, lawns, and parks. (Wikipedia)

By definition weeds in one context may not be a weed when it is actually wanted. When we use the term “weeds”, then we are referring to these undesirable plants growing in an unwanted area, usually amongst our crops. Then, weeds control and management come to mind.

Why do you need to control weeds?

Weeds are very important factors in crops production, you really need to pay particular attention to them considering these reasons.

• Weeds compete with your crops for light, moisture, nutrients, and space. They are very aggressive in doing so and so may deprive your crops of all these resources for optimum yield.
• They can reduce the yield of the crop through the release of toxic substances or exudates which inhibit crop growth. This is called allelopathy. Uncontrolled weed infestation can lead to 95% yield loss in cassava, 40% in maize and 53% in cowpea, soybean and pigeon pea. (agrihunt.com)
• Weeds serve as hosts for diseases and insects.
• They increase production and processing costs.
• Severe weed infestation can reduce the quality and value of the produce.

Read also: Detailed steps on how to Start a Farm

Principles of weeds control and management

These principles are the foundation or basis for the development of the various methods of weed control and management. A number of methods are developed to control weeds based on these principles.

• Prevention

Stop weeds from contaminating an area. As much as possible, this preventive measure is most effective means of weed control. You can accomplish this by;

1. Making sure new weed seeds are not carried in contaminated crops seeds, feed and/or machinery.
2. Preventing weed from producing seeds
3. Preventing the spread of perennial weeds that reproduce vegetatively.

These measures can greatly reduce weed problems.

• Control

This is the process of limiting weed infestation and minimizing competition with crops. When weeds are limited they have minimal effect on crop growth and yield. However, this principle is applied when the problem of weed exists. It is not preventive.

• Eradication

This involves complete elimination of all living weed plants including their vegetative propagules and seeds. This is a more difficult approach that the preventive and control. It is justified only for the elimination of serious weeds in a limited area eg. perennial weed in a small area of a field.

NOTE!!!

In weed control and management, is always better to prevent than to control. However, control is required because weeds arrive without notice and are present before they could be prevented. Prevention and eradication require long-term thinking and planning.

So, every single method or combinations of methods of weed management will seek to either prevent, control or eradicate. A combination of principles may also be achieved.

Methods of weeds control and management

These methods are applied based on the principles of weed control. You may adopt one or a combination of methods to either prevent, control or eradicate weeds.

• Cultural

Cultural weeds control uses a technique that involves the maintenance of good field condition so that weeds do not establish or increase in number. Examples are the adoption of crop rotation, mulching, cover cropping, avoiding overgrazing and maintaining good soil fertility.

Read also: 10 Benefits of Cover Crops

• Mechanical/Physical

In mechanical weeds control, we use farm equipment to control the weeds. The mechanical weed control techniques often used are tillage (involving ploughing and harrowing), mulching, hand removal, burning and mowing.

• Biological

Biological weeds control involves the use of natural enemies of weed plants to control the germination of weed seeds or the spread of established plants. This is fast becoming a popular method. Examples include sheep to control tansy ragwort or leafy spurge, cinnabar moth and the tansy flea beetle to control tansy ragwort. Further, the chrysolina beetle is used to control St. John’s Wort, and the use of goats to control weeds on rangeland.

• Chemical

This refers to any technique that involves the application of a chemical (herbicide) to weeds or soil to control the germination or growth of the weed species. Chemical control of weed is the commonest amongst farmers in this region. Common examples of chemicals used to control weeds in forages are 2,4-DB; (Dichlorophenoxyacetic acid), EPTC (selective herbicide), bromoxynil, paraquat (gramoxone) and glyphosate.

Join the discussion on : Chemicals : Is it the best way to deal with Weeds,Insects, Diseases?

Integrated Weed Management (IWM)

This is a sustainable, cost-effective, long-term weed management approach, using several weed management techniques such as; cultural, mechanical/physical, biological, and chemical methods.

So, summarizing all of the above, we can say we use either or a combination of cultural, mechanical, biological and/or chemicals means to prevent, control and/or eradicate weeds.

The fundamental principles of IWM are;

• Minimize overall economic impact of weeds
• Reduce herbicide use
• Provide optimum economic returns on crop yields

The approach seeks to optimize crop yields and profits whiles protecting the natural resources and reducing environmental effects.

Development of IWM program is based on a few general rules that can be used on any farm.

1. Prevent weeds before they start

Best method of weed control is to keep weeds out of the field

• Field sanitation
• practices that prevent weeds from entering or spreading across your field
• Planting certified seed is a good starting point to reduce weeds
• Control of volunteer weeds along field edges and ditches
• Cleaning equipment before moving from field to field

2. Help the crop compete against weeds

There are several things you can do to give the crop an advantage over weeds.

• Fertilizer placement. Place the fertilizer where the crop, but not weeds, have access. This allows the crop to be more competitive.
• Banded spraying reduces competitiveness and the population density of weeds.
• Choose competitive crop varieties. Taller varieties close the canopy more completely than shorter types, which helps shade weeds.

3. Keep weeds off balance

• Don’t give them a chance to adopt. Practise crop rotation. Rotating crops with different life cycles will help prevent weeds from adapting. Besides, rotating crops allows rotating herbicide practices.

4. Making a spray decision

• Scout your field to assess the type and number of weeds to help determine spray operation
• Consider the timing of weed emergence relative to the crop growth stage. Use the concepts of CPWC and economic thresholds
• Consider the Critical Period for Weed Control (CPWC) - the period in the crop growth cycle when weeds must be controlled to prevent yield losses.
• Look the economic threshold, where the level of weed infestation at which the cost of weed control equals the increased return on the crop yield
• Determine the cost of delaying weed control.

Read also: Safety Precautions in Agrochemicals handling and usage.

In summary

Effective weed control requires that you;

• Identify the problem
• Select the right control measure(s)
• Implement the program

When it comes to chemical weed control, do the right things.

• Use prescribed herbicide(s)
• Apply the correct herbicide rate
• Proper placement of material
• Apply at the right time
• Proper manner of application

References

Basic principles of weed management (C. Odero et al, 2011)

Describe the five general categories of weed control methods (forages.oregonstate.edu)

Economic Importance of Weeds by Asad Riaz (CABB, University of Agriculture, Faisalabad)

Integrated weed management (environment.gov.au)