The plant known by various names such as Black jack, Spanish needle, hairy beggar ticks, chepkotiwe (in Kalenjin), and maceege (in Kikuyu) has its origins in tropical America.
This plant is a tall, upright annual herb ranging from 20 to 150cm in height. It primarily reproduces through seeds. Its stem is green and square-shaped with brown stripes. One distinctive feature is its elongated fruits, which are adorned with hooked bristles that easily cling to clothing and animal fur.
This resilient weed possesses the ability to invade a wide array of habitats, including infertile soil, moist soil, sandy lime rock, and dry soils. It demonstrates adaptability in altitudes ranging from low to high, reaching up to 3600m above sea level. Furthermore, it exhibits the capacity to survive in regions with varying rainfall patterns, enduring severe droughts with precipitation levels ranging from 500mm to 3500mm per annum. With regards to temperature, it thrives within a broad range of 15-45 degrees Celsius, and it can even tolerate frost. While it is not fire-tolerant, it has the propensity to quickly invade areas that have recently experienced a fire.
Reproduction and Dispersal:
Bidens pilosa typically behaves as an annual weed, although the variety Bidens pilosa var radiata exhibits perennial characteristics.
The plant produces complete flowers, allowing for both cross-pollination and self-pollination to occur.
A single plant has the potential to generate up to 3000 highly fertile seeds, which can remain viable for a period of 5-6 years. The seeds are capable of germinating in shallow soils, specifically at depths of approximately 1cm. However, seeds that are buried deeper in the soil will not germinate, yet they retain their fertility over an extended period of time.
Seed dispersal takes place through the attachment of fruits to the clothing and fur of animals. Additionally, the seeds can be dispersed by wind, water, and soil.
Competitive Ability of Bidens pilosa
Bidens pilosa exhibits a high level of competitiveness compared to the actual crop.
It demonstrates rapid growth, often surpassing the growth rate of the desired crop.
The plant produces a large quantity of seeds, which remain viable for an extended period of up to 5 years.
Bidens pilosa possesses allelopathic properties, which hinder the nutrient and water uptake of the main crop, placing it at a disadvantage.
Furthermore, the plant has a substantial root biomass, enabling it to outcompete the main crop in terms of nutrient and water absorption.
The longevity of the seeds also contributes to the plant’s competitive advantage, as they can persist in the environment for a significant duration.
Environmental and Economic Impact
Bidens pilosa has significant environmental and economic implications.
In agricultural systems, it poses a serious threat as a weed, causing reduced crop yields due to its rapid growth and strong competitive abilities.
Additionally, it serves as a host and vector for various harmful parasites, including root knot nematodes and the tomato spotted wilt virus.
In open areas, dense stands of Bidens pilosa can impede access to roads, trails, and recreational areas. It can also cause damage to pavements and walls, leading to maintenance costs.
The fruit of Bidens pilosa is equipped with burs that easily stick to people, birds, and animals, causing inconvenience and annoyance.
Furthermore, the presence of this weed increases the cost of production, as frequent weeding becomes necessary to control its growth and prevent yield losses in crops.
The approach to managing this weed is contingent upon factors such as the severity of infestation, terrain, cost considerations, and the availability of labor.
Effective control measures are most successful when implemented early, targeting the weed while it is still in its small and vulnerable stage. This prevents its establishment and further spread.
To prevent the future generation of the weed, it is crucial to control it before it reaches the stage of seed production. This hinders the dispersal and germination of its seeds.
There are two primary methods for managing this weed: physical methods and the use of chemicals. Physical methods involve manual removal, such as hand-pulling or cutting the weed. Chemical methods, on the other hand, involve the use of appropriate herbicides to effectively control its growth and spread. The choice of method depends on various factors and should be implemented with caution and adherence to safety guidelines.
Physical methods can be employed to manage the growth and spread of this weed. Here are some effective approaches:
- Persistent mowing: Regularly mowing the area where the weed is present helps to control its growth. By consistently cutting back the weed, it weakens its ability to establish and reproduce.
- Hand pulling: Physically removing the weed by hand is a labor-intensive but effective method. Care should be taken to ensure the complete removal of the root system to prevent regrowth.
- Mulching: Implementing mulching techniques, such as using either plastic mulch or organic mulch, can effectively smother the growth of the weed. This creates a barrier that inhibits its access to sunlight and restricts its growth.
- Hoeing: Utilizing a hoe to disturb the soil around the weed can prevent its infestation. By disrupting the root system and exposing it to the elements, the weed’s growth and spread can be impeded.
These physical methods offer environmentally friendly alternatives for managing the weed without relying on chemical interventions. It is important to apply these methods consistently and as appropriate, considering the specific conditions and severity of the weed infestation.
Chemical methods involving the use of herbicides can be employed to manage the growth and spread of this weed. The choice of herbicide depends on the selectivity required for the specific situation, whether the land is cropped or fallow.
- Selective Herbicides:
- AGROMINE 480SL: This herbicide is suitable when the weed has invaded crops such as maize, rice, wheat, and barley. It selectively targets the weed while minimizing damage to the crop.
- COMMANDER 240EC: If the weed has invaded an onion farm, this herbicide is recommended. It effectively targets the weed while safeguarding the onion plants.
- HOTLINE 450 SC: When the weed is established in a carrot and coriander farm, this herbicide is an appropriate choice. It specifically targets the weed while minimizing harm to the desired crops.
- Non-Selective Herbicide:
- CLAMPDOWN 480SL: This herbicide is specifically designed for use in fallow lands where the weed has established itself. It is commonly used during land preparation to control the weed effectively.
When utilizing chemical methods, it is essential to follow the instructions and guidelines provided by the herbicide manufacturer. Proper safety precautions should be taken, including wearing protective clothing and considering any potential environmental impacts. Additionally, it is important to be mindful of any legal regulations or restrictions regarding the use of herbicides in your specific region.