Weeds control is a big problem in crop production. We all agree. From experience, weeds have caused a total loss in our maize and ginger farms. Also, they also conspired with insects and other pests to destroy our cucumber and tomato farms. we are talking about a very big threat to crop production here. Wouldn’t you want to know everything about them? I mean the weeds?
Contents
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1
What is a weed?
1.1
Why do you need to control weeds?
2
What are the Principles of weeds control and management?
3
Methods of weeds control and management
4
Integrated Weed Management (IWM)
4.1
The fundamental principles of IWM
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 “weed” is not weed if it is actually wanted. When we use the term “weeds”, we are referring to these unwanted plants growing in an area. Usually among our crops.
Why do you need to control weeds?
Weeds are very important factors in crops production. What is your experience with weeds?
- Weeds compete with your crops for light, moisture, nutrients, and space. They are very aggressive in doing so. And so, they can deprive your crops of all these resources for a good yield.
- They can reduce the yield of the crop through the release of toxic substances which inhibit crop growth. This is allelopathy. Uncontrolled weed infestation can lead to a 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.
What are the Principles of weeds control and management?
The principles of weed control are the basis for the development of the various methods of weed control and management. There are a number of ways to control weeds. They are based on these principles.
Stop weeds from contaminating an area. As much as possible, this preventive measure is the most effective means of weed control. You can achieve this by;
- Making sure you do not carry new weed in contaminated crops seeds, feed and/or machinery.
- Preventing weed from producing seeds
- Preventing the spread of perennial weeds that reproduce vegetatively.
These measures can greatly reduce weed problems.
This is the process of limiting weed infestation. And also minimizing competition with crops. When weeds are limited they have minimal effect on crop growth and yield. However, you can apply this principle when the problem of weed exists. It is not preventive.
This involves complete removal of all living weed plants including their vegetative propagules and seeds. This is a more difficult approach that preventive and control. It is justified only for the elimination of serious weeds in a limited area. Example, perennial weed in a small area of a field.
NOTE!!!
In weed control and management, is always better to prevent than to control. But, you can control if weeds arrive without notice. Also, when they are present before you can prevent them. 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. You can also manage weeds with a combination of principles.
Methods of weeds control and management
We use these methods based on the principles of weed control. You can use one or a combination of methods to either prevent, control or eradicate weeds.
Cultural weeds control uses a technique that requires that you maintain a 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.
In mechanical weeds control, we use farm equipment to control the weeds. The mechanical weed control techniques we often use are tillage (involving ploughing and harrowing), mulching, hand removal, burning and mowing.
Biological weeds control involves the use of natural enemies of weed plants. This controls 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.
This refers to any technique that involves the application of an agrochemical (herbicide) to weeds or soil to control the germination or growth of the weed species. Chemical control of weed is the commonest among 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.
Integrated Weed Management (IWM)
This is a sustainable, cost-effective, long-term weed management approach. It uses several weed management techniques such as; cultural, mechanical/physical, biological, and chemical methods.
The approach seeks to optimize crop yields and profits whiles protecting the natural resources and reducing environmental effects.
Currently, the herbicide is a powerful tool for weeds control. However, there is the issue of its sustainability. Herbicides are expensive. Weeds are building resistance and there is a growing concern about its environmental effects.
The fundamental principles of IWM
- Minimize the overall economic impact of weeds.
- Reduce herbicide use.
- Provide optimum economic returns on crop yields.
Development of IWM program is based on a few general rules that one can use on any farm.
1. Prevent weeds before they start
The best method of weed control is to keep weeds out of the field.
- Keep good 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 farm tools and 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 weeds the 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 decide spray operation
- Consider the timing of weed emergence on 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 you must control weeds to prevent yield losses.
- Look at the economic threshold. When weeds infestation gets to a certain level, there is a cost to weed control. And when you control these weeds at this level there will be an increase in yield. If the cost of controlling the weeds is equal to the value of yield increase, you may choose not to spray.
- Determine the cost of delaying weed control.
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
- The proper way 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)
