Weeds are great threats to successful crop production. Weeds are deleterious and the harms they cause are enormous; starting from their unruly competition for nutrient, space, water, and air with the sown crops, they also harbor pests which in turn cause devastating crop diseases, thus, reducing the quality and quantity of the sown crop. But do you know you can use insects to control weeds? Have you heard of mycoherbicides? If no, relax and get liberated as you read through this article.
Weeds, directly or indirectly, increase the cost of production of most farmers; such that, at the end of each production, farmers are left with little or no profit. The issue of weeds is a very important issue in crop production.
Farmers have been trying their best to ensure the eradication of weeds from their farm but most times, the hardy and aggressive nature of weeds render their efforts futile. A good farmer needs to understand and define weeds.
So what are weeds?
Weeds are crops growing out of place; weeds are unwanted crops. After successful land preparation and planting, weeds emerge. You may wonder why weeds are so “stubborn and oppressive”; this is because weeds are persistent and difficult to eradicate.
A good example is the Cyperus spp. Some weeds produce a large number of seeds, like Amaranthus spinosus, their seeds are very tiny and can survive for a very long period of time under the soil.
Some weeds have reproductive parts like Cynodon spp and Napier or elephant grass; the stolon is a reproductive part that enables the weed to multiply rapidly. Most times, if the weeds are slashed, it is the leaves that are ripped off; the stolon is still under the ground. This stolon produces new shoots that are more vigorous and persistent.
A farmer may plant maize and sees Talinum triangulae (waterleaf) on the farm; he feels the waterleaf is an edible vegetable and decides to spare it. This practice is detrimental to the maize plant because the waterleaf, in this case, is a weed and should be eradicated.
If any crop grows spontaneously in the midst of your sown crop, such crop is a weed and should be eradicated; even if it is edible, it should not be spared. Competition with the sown crop is still manageable but its ability to habour pest makes it unwanted and makes its eradication imperative.
Types of weeds
There are different types of weeds that can be found on the farm; they are categorized into 3 forms based on the shape of their leaves, namely:
- Grasses: These types of weeds have the length of their leaf blade widely larger than the breadth. Examples are Imperata cylindrica (spear grass), Panicum maximum (Guinea grass) Andropogon gayanus (Nothern gamba), Napier grass.
- Broadleaves: These types of weeds have the size of their breadth is closely the same as that of their leaf blade. Examples are: Talinum triangulare (water leaf), Sida acuta, Tridax procumbens etc.
- Sedges: In this type of weed, all the leaves of the weeds tend to arise from the same point. Examples are Mariscus alternifolius, Cyperus rotundus, Cyperus esculentus etc.
The object of classification here is their appearance; I feel this is most important to farmers. There are other forms of classification; weeds can be classified based on their lifecycle, growth habit and habitat. The most important classification is the shape of the leaves because it can be used to control weeds.
Effective Methods of Weed Control
Effective weed control is fundamental and starts from the land preparation. There are several ways of controlling weeds. They are:
- Cultural weed control method.
- Biological weed control method.
- Integrated weed control method.
- Chemical weed control method.
Cultural weeds control methods
Cultural method of weed control is an indigenous approach to reduce the presence of weeds on a farm. It is also an option for organic farming as it does not involve the use of chemicals. It is basically a preventive measure of weed control. It is also very effective when done as required. It involves:
- Proper tillage practice: I am talking about the conventional tillage practice here; where the land is ploughed twice and harrowed before planting.
- Flooding: Flooding is one of the cultural ways of controlling weeds. It is most effective in a rice farm. Rice is tolerant to flood but weeds within the rice farm are not tolerant to flood or waterlogged areas. Flooding is more effective in rice cultivation.
- Mulching: Mulching is another traditional way of controlling weeds; the use of dry grasses or synthetic material like polyethylene sheet or plastic to cover the soil helps to control weed and also conserve soil moisture. The weeds are denied access to sunlight which aids their growth.
- Manual and mechanical weeding: These two are the most effective ways of weed control. They are environmental compliance but quite expensive, especially the manual weeding.
Biological weed control methods
Biological weed control is the use of other organisms to suppress weeds. It is another option for organic farming. Biological control of weeds involves the use of the following:
Cover crops are crops that are used to control weed due to the flamboyance of their leaves. Cover crops are crops that have their leaves in form of shade; they are mostly creepy in nature. Examples of cover crops are sweet potatoes, Ugu vegetable (fluted pumpkin), etc.; they can be or planted as companion crops to control weeds for the main crops. They are mostly intercropped with crops like maize.
Use of invertebrate animals like insects to control weeds:
In some parts of the world today, insects are being used to control weeds. In India, cactoblastis moth was used to control weeds in prickly pear farm; also, in some parts of Africa, some insects are also used to control weeds. As seen in Zambia where Paulina acuminata (grasshopper) was used to control Salvinia molesta. These are new developments.
Use of microbes to control weed:
This is another new development in the agricultural sector. The use of microorganisms to control weeds is another easy way to control weeds in your farm; viruses, fungi, nematodes and bacteria can be modified to control weeds. They are collectively called mycoherbicides; that is, the use of plant pathogens to control weed. Examples of microbial weed control include the use of soil borne fungi, Phytophthora palmivora, sold as mycoherbicides-sevine, to control strangler vine, Morrenia odorata; also fungus Collectotrichum gloeosporoides called mycoherbicides-collego to control northern joint vetch in paddy rice farm. More research works are on-going regarding this method of weed control. Read this Bioherbicide Book for better understanding of mycoherbicides.
Chemical or inorganic Weed control
This is the widely used method of controlling weeds. It is quite controversial as its detrimental effects are becoming more pronounced. Chemical compounds used in controlling weeds are called herbicides.
The use of herbicides on crops is becoming wary; there is a global campaign against its use as it is not environmental compliance. Excessive use of herbicides has caused underground water pollution and contamination. However, herbicides have been seen to be very effective in weed control.
Integrated weed control
Integrated weed control is another way of controlling weed; it is the combination of two or more weed control methods to achieve effective action. It is the combination of two or more of the above methods of weed control to achieve effective weed control.
Weeds are pests to crop production; it is imperative a profit-oriented farm proffer an effective way to manage weed control to attain optimum yield and reasonable profit. Remember to share this as wide as possible for others to benefit from it just as how you have benefitted.
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