Agriculture contributes significantly to Nigeria's GDP, but weeds pose a major threat to crop production. Dr Okon G. Okon, Plant Stress Physiologist at Akwa Ibom State University, notes that Nigeria's varied ecological zones produce different common weeds, from drought-resistant types in the north to broadleaf species in the rainforest. This guide covers common weeds, their scientific names, regional prevalence, and control methods.
Common Weeds and Their Scientific Names
Siam weed, or Chromolaena odorata, can grow up to three metres tall in open fields. It thrives in tropical and subtropical regions, invading riparian zones, forest margins, bushland, waste sites, roadsides, disturbed sites, neglected pastures, crops, and plantations.
Spear grass, or Imperata cylindrica, is a perennial grass that grows up to one metre tall. It has an extensive system of rhizomes, leaves in tufts, and dense, white, fluffy, cylindrical, spike-like heads. It is persistent in upland crops like maize, cassava, rice, and sorghum.
Dayflower, or Commelina benghalensis, is a perennial creeping herb with lily-like leaves and reddish hairs towards the tip. It invades moist soil areas like grasslands, roadsides, and disturbed areas, forming dense stands that can smother food plants.
Jimson weed, or burundanga, also known as Datura stramonium, can reach 5 feet in height. It bears white or purple flowers and has prickly seed pods. This plant is poisonous but has medicinal uses, and it is an aggressive invasive plant in temperate climates worldwide.
Nutgrass, or Cyperus rotundus, is a colony-forming perennial that adversely impacts agriculture. It affects plantation crops in tropical and warm temperate climates and is challenging to manage with organic or conventional weed control strategies.
Milkweed, or Euphorbia heterophylla, thrives in orchards, cop plantations, roadsides, gardens, and waste areas. It is short-lived with an upright, branched main stem, usually growing 20-80 cm tall but can reach up to two metres.
Bahama grass, or Cynodon dactylon, is found in all tropical and subtropical areas. It is dominant in uncultivated areas like sea-coast sandy dunes, roadsides, and along rivers. It is tolerant to drought and heavy grazing, making it valuable for pasture and hay, but it is a menace in plant farming.
Elephant grass, or Pennisetum purpureum, is among the highest-yielding tropical grasses and can grow in dry or wet conditions. It forms dense, thick clumps up to one metre across, with finely-toothed leaf margins and a prominent midrib.
Carpet grass, or Axonopus compressus, is common on roadsides, gardens, waste areas, and plantations. It thrives in moist, warm environments with full sunlight and can withstand trampling, but not long periods of waterlogged conditions.
African Club Moss, or Selaginella kraussiana, is native to Africa. It is low-growing and mat-forming, thriving in rich, moist to wet soils. Trimming does not control its rapid spread because retained cuttings root and sprout quickly.
Buffalo grass, or Stenotaphrum secundatum, invades roadsides, gardens, river banks, swamps, coastal areas, and other disturbed sites. It is considered an environmental weed, and while it can be used for lawns, it competes for nutrients and space with food crops.
Creeping foxglove, or Asystasia gangetica, is a fast-growing, spreading, herbaceous groundcover that attracts butterflies. It produces white flowers and is regarded as an environmental weed.
Falsethistle, or Acanthus montanus, is native to tropical Western Africa. It is a thinly branched perennial with basal clusters of oblong, dark green leaves with silver marks and wavy margins. The leaves are thorny, and while it has medicinal value in some communities, it is a nuisance to food crop farmers.
Nuke-Noh, or Tridax procumbens, is a flowering plant in the daisy family. It has great drought resistance and tends to outlive all grasses and most broad-leaved plants. In Nigeria, this plant is fed to poultry, and some communities use it for medicinal purposes.
Regional Prevalence of Weeds
Dr Okon explains that specific weeds thrive in different regions due to variations in climate, soil type, cropping systems, and land use practices. In the Sudan and Sahel Savanna (Northern Nigeria), low rainfall and semi-arid conditions favour drought-resistant weeds such as Striga hermonthica (Witchweed), Cenchrus biflorus (African foxtail), Echinochloa colona (Jungle rice), Tribulus terrestris (Puncture vine), and Sida acuta (Wireweed).
In the Guinea Savanna (Central Nigeria – Middle Belt), moderate rainfall and mixed farming systems lead to weeds like Imperata cylindrica (Speargrass), Chromolaena odorata (Siam weed), Aspilia africana (Wild sunflower), Ageratum conyzoides (Goat weed), and Digitaria horizontalis (Smooth crabgrass).
In the Rainforest (Southern Nigeria, including Akwa Ibom State), high rainfall and dense vegetation support fast-growing broadleaf weeds and climbers like Aspilia africana, Pueraria phaseoloides (Tropical kudzu), Panicum maximum (Guinea grass), Centrosema pubescens (Butterfly pea), and Mimosa pudica (Sensitive plant).
Coastal and Mangrove Swamps (South-South Nigeria – Niger Delta region) are waterlogged and saline, supporting aquatic and salt-tolerant weeds like Eichhornia crassipes (Water hyacinth), Nymphaea lotus (White water lily), Paspalum vaginatum (Saltgrass), Ipomoea aquatica (Water spinach), and Typha domingensis (Southern cattail).
The Derived Savanna (a transition zone between Rainforest and Guinea Savanna) supports a mix of woody plants and herbaceous weeds, including Andropogon gayanus (Gamba grass), Commelina benghalensis (Benghal dayflower), Panicum repens (Torpedo grass), Rottboellia cochinchinensis (Itch grass), and Tridax procumbens (Tridax daisy).
Harmful vs Useful Weeds
Dr Okon emphasises that distinguishing between harmful and useful weeds requires looking at several key factors, including morphological characteristics, ecological impact, and economic and medicinal value.
Harmful weeds are often fast-growing, invasive, and spread rapidly (e.g., Chromolaena odorata), while useful plants are typically cultivated and well-managed (e.g., Telfairia occidentalis - Fluted pumpkin). Harmful weeds may have thorns, spines, or irritating hairs (e.g., Mimosa pudica), whereas useful plants generally have softer or edible leaves (e.g., Vernonia amygdalina - Bitter leaf). Harmful weeds often have deep, aggressive root systems (e.g., Imperata cylindrica), while useful plants might be tuberous or shallow (e.g., Dioscorea spp. - Yam). Harmful weeds produce many seeds with dispersal adaptations (e.g., Tridax procumbens), compared to useful plants that have fewer, larger, or cultivated seeds (e.g., Zea mays - Maize).
Ecologically, harmful weeds compete aggressively for nutrients, water, and sunlight, reducing crop yields (e.g., Striga hermonthica - Witchweed), while useful plants often complement crops by improving soil fertility or repelling pests (e.g., Tephrosia vogelii - Fish poison plant). Harmful weeds deplete soil nutrients, increase erosion, or release toxic chemicals (allelopathy) (e.g., Rottboellia cochinchinensis - Itch grass), whereas useful plants may fix nitrogen, improve soil structure, or act as cover crops (e.g., Mucuna pruriens - Velvet bean).
Economically, harmful weeds are mostly non-edible, poisonous, or cause crop damage (e.g., Datura stramonium - Jimsonweed, toxic to humans and animals), while useful plants have economic importance as food, medicine, fodder, fiber, or fuel (e.g., Colocasia esculenta - Cocoyam, Elaeis guineensis - Oil palm).
Weed Control Methods in Nigeria
Effective weed management is critical, and Dr Okon details several methods used by Nigerian farmers. Traditional methods include hand weeding and slash-and-burn (bush burning), common among subsistence farmers. Although hand weeding is cheap and environmentally friendly, it is labour-intensive. Mechanical methods like hoeing, tilling, and mowing help physically remove weeds but can damage soil structure or be ineffective against deep-rooted species.
Cultural methods such as crop rotation, cover cropping, proper plant spacing, and dense planting reduce weed growth by suppressing light and nutrients available to weeds. Chemical methods using selective, non-selective, pre-emergence, and post-emergence herbicides offer rapid control but must be managed carefully to avoid herbicide resistance. Biological methods use natural enemies such as specific insects or grazing animals, a sustainable approach with minimal chemical impact. Integrated Weed Management (IWM) combines multiple methods and is often the most effective and environmentally friendly approach because it reduces herbicide resistance, minimises labour costs, and protects the environment.
Dr Okon also notes challenges in weed control in Nigeria, including the high cost of herbicides and farm machinery, lack of awareness of sustainable methods, climate change affecting weed patterns, and resistance of some weeds to herbicides.
Common weeds are plants that grow where they are not wanted, competing with cultivated crops, lawns, or landscaping for light, water, nutrients, and space. There is no single scientific name for weeds, as "weed" is a descriptive term for any undesirable plant; each species has its own unique botanical name. The botanical name of Bahama grass is Cynodon dactylon, and the botanical name of Carpet grass is Axonopus compressus. Ten common Nigerian weeds and their botanical names include Siam weed (Chromolaena odorata), spear grass (Imperata cylindrica), dayflower (Commelina benghalensis), Jimson weed (Datura stramonium), nutgrass (Cyperus rotundus), milkweed (Euphorbia heterophylla), Bahama grass (Cynodon dactylon), elephant grass (Pennisetum purpureum), carpet grass (Axonopus compressus), and African club moss (Selaginella kraussiana).
All farmers must learn about common weeds and their scientific names with pictures in Nigeria. This information is useful for identifying problem species early and choosing the right traditional, mechanical, cultural, chemical, or biological control method, whether managing a small farm or a large agribusiness operation. Legit.ng recently published a list of the best career opportunities in agriculture in Nigeria, including agribusiness management, agricultural engineering, food science, and agronomy, with high-demand roles like farm managers, agricultural consultants, and veterinary doctors. The key courses to select for these paths include B.Sc. in Agriculture, Agricultural Economics, Horticulture, or Animal Science, and specialised fields like soil science, fisheries, and animal science help improve productivity and sustainable farming practices.
