How to stop weed from eating up your maize
Friday, 07 September 2012
A weed is any plant that grows where it is not wanted. Weeds affect crops by competing with them for light, water and soil nutrients.
Maize is particularly vulnerable to weeds because it is widely spaced and its growth in the first few weeks is very slow.
It is during this period that weeds rapidly establish themselves and begin competing with the maize. Weed control during the first four to eight weeks after planting is, therefore, crucial.
Why weeding is important
Weeds compete with maize for nutrients, water, light and space. The early stage of a maize plant, especially the first three weeks, is very sensitive. If disturbed by weeds during this early stage, the maize will never recover fully, even if the troublesome weeds are later removed.
To ensure maximum maize yields therefore, weeds must be kept at a minimum level, especially during the early stage. After that the now well established and healthy growing maize is able to suppress the weeds.
Some weeds are parasitic. A parasite is a plant or animal that grows, feeds and gets shelter on another while contributing nothing to its wellbeing. One of the most notorious parasitic weeds in maize production is striga, which can cause up to 90% loss in yields.
Some weeds also provide a home to harmful pests and diseases that attack maize and interfere with its growth.
If weeds are not controlled, the maize yield will be reduced. Weeds, therefore, affect the farmer’s profits by lowering the quality, quantity and value of maize. Inefficient weed control is one of the main causes of low maize yields in Africa.
Another reason for removing weed is that they make the harvesting process slow and cumbersome. In addition, some weeds are poisonous to both human beings and animals.
When to weed maize
As mentioned earlier, the most critical period is during the first four to six weeks after planting. Although early weeding is critical to producing a good yield, late control is also important in preventing the weeds from flowering and producing seeds, which would affect the crop and increase the amount of weed in the garden in the following seasons.
Even when the maize is mature, weeds can still interfere with the harvesting process by polluting the maize grains with their seeds or offensive odour, sometimes forcing the farmer to incur extra cost to remove them.
Which weeds affect maize?
To be able to control them, a farmer needs to know the difference between the various weeds that affect maize.
Weeds can broadly be categorized into two types: annual and perennial weeds.
Annual weeds are those which live for only one season. The most common type is blackjack. Annual weeds start germinating soon after the maize is planted. Because of their fast growth rate, they interfere with the maize’s growth during the crucial first three weeks.
Perennial weeds are every year in a maize garden. They multiply through roots and stems, a common example being couch grass. Mechanical weeding only cuts off the top but the bottom continues consuming nutrients meant for the maize plants. This type of weed needs to be controlled early before the beginning of the planting season as later attempts to control it will damage the crop.
How to control weeds in maize
Weeds can be controlled through proper land preparation. This is the first step in effective weed control. It starts with bush clearing, followed by ploughing and harrowing. If done thoroughly, it will help eliminate most of the weeds.
It can also be controlled through crop rotation. Maize can be rotated with crops in the beans family, such as cow peas, groundnuts, pigeon peas, soya beans, kidney beans, labab, mucuna and bambara beans. These help enrich the soil while suppressing the weeds.
Another way to control weed is by intercropping. Maize can be intercropped with beans to help it suppress weeds.
Beans can also be grown alone as fallows (resting or recovery period) to prevent weeds from germinating. When repeatedly done, the weed seeds in the soil will be reduced. Maize is then planted in the following season after these crops are harvested.
Cover crops such as sweet potatoes are also very good at suppressing weeds. Cover crops should be fast growing, with lots of leaves to be able to cover the ground before weeds emerge.
In addition, proper spacing can help reduce weed. If planted following the recommended spacing, the maize will cover the ground quickly, reducing the need for weeding.
Crop residues can also be used to cover the spaces between the growing maize. This method, however, is not common due to a shortage of crop residues and the destruction of the mulching material by termites.
The time of planting is important too. Maize planted at the right time will grow fast and establish itself before weeds start growing. The seeds should be planted at the earliest opportunity. Soaking maize seeds in water for 24 hours before planting may help them to germinate faster and give them an advantage over the weeds.
Hoeing is the most common method used by small scale maize farmers to remove weed. This is carried out using hoes, knives or ploughs. It is usually followed by hand weeding to remove those weeds that might have come up after the hoeing. It needs two weeding sessions between week two and week seven to remove all weed.
To be effective, hoe and hand weeding should be done when the weeds are still very young. Where possible the weeding should be done when the sun is hot, so that the uprooted weeds quickly die. Hoe and hand weeding is very slow and can only be done on a small scale.
Improving soil fertility is another way of controlling weed. Applying fertilisers will enable the maize to grow fast, cover the ground and suppress the weeds at an early stage. Using quality seeds can help too. These will produce healthy plants that can fight and overcome weeds.
Some farmers use chemicals, also called herbicides, to kill weeds. The herbicides exist in the form of granules or liquids. Some of them kill the weeds before they germinate or emerge. These are called pre-emergence herbicides. They are applied on bare ground after planting, to kill weeds as they emerge. Others kill weeds when they come into contact with the chemicals. They are called contact or post-emergence herbicides.
There are both advantages and disadvantages in using herbicides. The advantages are that they save time, minimise root damage associated with hoeing, help control stubborn perennial weeds such as couch grass, and minimise soil disturbance.
The disadvantage is that herbicides are poisonous. If not handled properly, they can be dangerous to the farmer, the plants and the environment. Unfortunately, few farmers know how to handle chemicals safely. Some herbicides stay long in the soil, affecting crops grown in that garden the following season.
Conditions that favour weed growth in maize
ü Poor weeding technique
ü Weeding too late
ü Delaying to plant after preparing the land
ü Using the same land continuously to grow maize