Common Nigerian Weeds: Management and Control
Plants that interfere with man’s objectives are called weeds (Unamma, 1989). Generally, weeds are unwanted plants. We can say that unacceptable plants at a given time are designated as weeds. The implication is that some plants may be considered a nuisance under some certain conditions. For examples, yam and melon may be inter-planted for obvious reasons and if any crop that is not wanted is found growing on the same plot such crop is regarded as a weed.
Generally, there are more than 1000 species of plants in Nigeria that are commonly troublesome in almost all circumstances and are commonly designated as weeds.
The role of weeds in Nigeria agriculture has received little attention from the government since the country has for years depended on small holder farmers to feed the nation and under this scale of farming operation, weed management needs focus mainly on manual approach (Udosen, Ben, Kayang, Ekpo & Etokebe,2002).
The first elements in the succession of vegetation to colonize undisturbed lands are the weeds. Weeds have the capability of surviving in any environment markedly disturbed by man. Weeds vary in their abilities to tolerate and thrive in a wide range of climatic conditions.
Observations indicate that individual species of weed tends to dominate a particular environment. In Nigeria there are variability in climatic conditions, soil types, human activities, topography and relief. These factors combine to determine the different vegetational belts found in the country. In Nigeria, rainfall decreases from the coastal regions towards the northern savanna regions, the length of dry season increases from the coastal regions to the savanna region of Nigeria. In addition, mountainous areas, hills and valleys exert micro climate and this result in different types of vegetation.
These phenomena jointly affect the types of vegetation present in different regions in the country. Consequently, some species of weed tend to be more prevalent in certain vegetational belts than the others and some weeds may not thrive in one belt but are found in another. At present, there is an increase in climate change leading to increase in the length of the growing season with attendance crop pests including weed infestation (Ayoade, 2010).
Conditions Influencing Weed Population
Changes in the population of weeds in any environment can be brought about by the following factors:
- Bush Burning: Many peasant farmers still practise bush burning. The practice enhances germination of weed seeds particularly grasses and legumes. The germination becomes possible because of the burning off of the seed-coat thereby removing the dormancy. Besides, the bush litters that cover the seeds from getting sunlight are usually destroyed by fire. Hence, exposing the weed seeds to better conditions of germination.
- Tillage: Mechanical tillage may be ineffective in the control of weeds such as spear grass, Commelina species and other weeds that can regenerate through rhizomes and underground stem. Deep tillage tends to expose more dormant weed seeds to the earth surface for better conditions of germination. Ridge and bed making usually restrict weeds infestation than flat tillage. Mulched tillage control weeds better than the conventional tillage.
Common Nigerian Weeds: Management and Control
- Deforestation: The destruction of forest species to give way for crop production on a continued basis usually results in increase weed population. For instance, in the forest belts, the woody forest species when destroyed, give way to the broad leaved weeds to invade the environment.
- However, with continuous cropping, the broadleaved weeds gradually give way to grasses such as Panicum maximum, Andropogon species or any grass species depending on the environment. Similarly, in the savanna belts, perennial grasses often succeed the broadleaved weeds which in turn are succeeded by annual grasses.
- Choice of weed control methods: The use of selective post emergence herbicides, such as 2-4-D and MCPA can cause a shift from broadleaved weeds to grass weeds which may tend to be more difficult to control. Manual control of Euphorbia heterophylla tends to increase the weed population few weeks after weeding if the weeds were allowed to seed.
- Grazing by animals: With continued grazing of an area, palatable and nutritive plants are consumed by the animals leaving behind the less palatable ones as weeds to populate the entire area of land.
- Moreover, the animals’ dungs can contain viable weed seeds which germinate to increase new weed species in the grazing area.
- Other factors: Other factors that influence weed population include crop seeds, irrigation, run-off water, and farm machinery contaminated by weed seeds.