Chapters 6.9
6.9 - Removing Weeds Before They Produce Flowers
Brooke Murdoch,University of Guelph, Canada
Suggested citation for this chapter.
Murdoch,B. (2025) Removing Weeds Before They Produce Flowers. In Farmpedia, The Encyclopedia for Small Scale Farmers. Editor, M.N. Raizada, University of Guelph,Canada. http://www.farmpedia.org
Introduction
Weeds are one of the biggest constraints on agricultural productivity for smallholder farmers in regions such as sub-Saharan Africa and South Asia, where limited access to herbicides and mechanical equipment can make weed management an ongoing struggle. Weeds reduce crop yields by competing with crops for nutrients, water, and sunlight, especially during the critical growth stages (Knezevic et al., 2002). Where resources are scarce, ineffective weed control can lead to rapid buildup of a “weed seedbank” – a hidden reservoir of viable weeds in the soil that can last many years – forcing farmers into a continuous cycle of weeding and reinfestation season after season (Norsworthy et al., 2012). In some cases, even a single flowering weed plant can contribute a significant number of seeds that jeopardize future crop performance. In one study, a single common lambsquarters weed plant per 0.9 m row of soybean reduced soybean yields by 30% (Curran et al., 2018). A common lambsquarters plant can produce more than 70,000 seeds (Curran et al., 2018).
A practical solution to break this cycle is the removal of weeds early in the crop season. Specifically, farmers can remove weeds with manual or mechanical methods before they flower and produce seeds By intervening during a weed’s early life cycle, farmers can effectively prevent seed return to the soil, curtailing the weed seedbank buildup and reducing future weed infestations. Four commonly used methods (see Figure 1) include:
Figure 1. A simple overview of four techniques—hand-pulling, hoeing, shallow cultivation, and flaming—that can help smallholder farmers remove weeds before they can flower and set seed (Created with BioRender.com).
• Hand-Pulling:
This technique involves grasping weeds near the base and pulling out the entire plant (including roots) by hand. It is recommended to pull weeds with physical protection, such as gloves, to prevent injury. Hand-pulling is easy and straightforward, but labor-intensive. It is highly selective, making it the best for carefully removing weeds that have already begun to produce seeds (Carlberg, 2014.• Hoeing:
This technique involves using a hoe to slice or uproot weeds at or just below the soil surface. This method works best on very small scales to remove young weed seedlings (Carlberg, 2014) .• Shallow Cultivation:
This technique involves lightly disturbing the top layer of soil with a cultivator or similar tool to dislodge young weeds without excessively harming crop roots.• Flaming:
Flaming involves applying controlled heat from a handheld propane-fueled device to wilt or kill small weeds before they set seed. Flaming can be applied pre-planting (as part of the stale seedbed technique), pre-emergent, or even post-emergent in certain crops. For example, in corn, early flaming is most effective when the plants are 3 to 5 centimeters tall, while application should be avoided when corn is around 10 centimeters tall, as it is most vulnerable at that stage (Carlberg, 2014) Flaming is often used as a band treatment along crop rows, typically combined with inter-row cultivation (Carlberg, 2014). Although flaming is an effective method of pre-flowering weed removal, it requires precise control to avoid crop damage and is best performed under hot, dry conditions. The method also involves safety considerations related to fuel handling and higher equipment costs (US$400–3,000), making it less accessible to small-scale farmers without proper investment (Carlberg, 2014; Curran et al., 2018).
Figure 2. A tractor-mounted flame weeder in operation at Holcomb Farm in Connecticut. Smaller-scale flame weeders are also available, ranging from hand-pushed models that span bed widths to backpack-mounted units (Calberg, 2014).
Figure 3. A farmer demonstrates a hand-pushed flame weeder for pre-emergent weed control in a cornfield (FlameWeeders.com, n.d.).
Figure 4. Hoeing works best on very small scales to remove young weed seedlings. Shown here are several types of hand-held hoes, from left to right: a collinear hoe, a swan neck hoe, a stirrup hoe, a “regular” hoe, and an eye-hoe units (Calberg, 2014).
Figure 5. An S-tine cultivator with sweeps and a wheel that acts as a harrow on the back. This setup lightly disturbs the soil to dislodge weeds while minimizing damage to crop roots units (Calberg, 2014).
Benefits of Pre-Flowering Weed Removal
The primary benefit of pre-flowering weed removal is improved crop productivity due to fewer weeds causing irrevocable yield reduction (Knezevic et al., 2002). Crops can have a critical period for weed control (CPWC), when even brief periods of crop competition from weeds can lead to permanent losses in yield that cannot be fully recovered later in the season (Knezevic et al., 2002). There are also many secondary benefits to pre-flowering weed removal, such as lowering overall production expenses and limiting the spread of herbicide-resistant weed varieties (Knezevic et al., 2002; Norsworthy et al., 2012). By removing weeds before they flower, weed infestations can be reduced in subsequent seasons, and the need for more expensive, targeted approaches like herbicide use is diminished, thereby improving net returns for farmers (Norsworthy et al., 2012). For instance, improved weed control in sub-Saharan Africa has been associated with reductions in herbicide expenses of up to 25-40% (Mrema et al., 2019). Additionally, if herbicide-resistant varieties appear, culling them before they can seed is absolutely necessary to prevent the further propagation of resistance genes and the establishment of a persistent, problematic seedbank (Heap, 2014).
Pre‐flowering weed removal also provides many secondary benefits that are often overlooked, particularly for women farmers in developing countries, who not only carry the bulk of manual weeding but also face a wider “gender gap” in agriculture that limits their access to land, inputs, and credit (FAO, 2011). Globally, women make up about 43% of the agricultural labor force in developing countries yet tend to have fewer resources than men, which reduces their productivity and overall earning potential (FAO, 2011). Because women are often responsible for both farm work and household tasks, including childcare, they and their daughters can have fewer opportunities to pursue education or training, further perpetuating this gender gap. By eliminating weeds before they flower, the overall labor burden is lowered, allowing women to allocate more time to other critical farm or family responsibilities, as well as to pursue higher levels of education (FAO, 2011).
Critical Analysis
While the benefits of pre-flowering weed removal are significant, several challenges and limitations must be considered. First, there is often a short-term increase in labour costs. Manual methods, such as hand-pulling, hoeing, or shallow cultivation can increase labour demands by 15-35% during peak weeding periods (Curran et al., 2018). For resource-limited smallholder farmers, this additional work can be especially burdensome during busy planting and harvesting seasons, with women and children disproportionately undertaking these weeding tasks. Nonetheless, the upfront labour tends to be offset by reduced expenses for herbicides by preventing problematic seedbanks and the spread of herbicide-resistant weed varieties.
Another consideration is the potential for unintended consequences, such as soil disturbance. Frequent shallow cultivation may degrade soil structure or contribute to erosion, especially on sloped or fragile soils (FAO, 2003). To prevent soil disturbance, it is important to follow an integrated approach that considers crop rotation, cover cropping, and reduced tillage practices to maintain soil health (FAO, 2003).
Lastly, but most importantly, precise weeding strategies are crop-specific. Hand-weeding might be effective for some crops, while tillage or flaming may work better for others (Curran et al., 2018). This variability underscores the need for more advanced education and support, ensuring that smallholder farmers can identify the best combination of methods for their local weed species and cropping systems. A single method may also lead to weed shifts or only partial control over time, making an integrated weed management plan essential (Norsworthy et al., 2012). A good resource, specifically for African farmers, is to utilize the African Plant Database, which provides taxonomic details and distribution data on numerous plant species found across the continent (African Plant Database, n.d.). By identifying the specific weed species in their fields, farmers can tailor the pre-flowering removal tactics previously discussed to target each weed’s vulnerabilities, thereby improving long-term control and minimizing the risk of re-infestation. The African Plant Database is listed in the “Further Reading” section as a key reference for regional weed identification and management.
Application to Small-Scale Farmers
Pre-flowering weed removal is particularly advantageous for smallholder farmers due to its reliance on simple, low-cost tools and techniques. Basic hand tools such as hoes, rake-harrows, and manual cultivators are typically affordable, costing between US$20 and US$200 (Curran et al., 2018). The simplicity and affordability of these tools allow farmers to effectively manage weed populations without requiring large capital investments. There are also many international and national organizations that aim to support small-scale farmers through educational resources, guidance, and, in some cases, subsidized equipment. One example is the Kenya Agricultural and Livestock Research Organization (KALRO). Additionally, local extension services may provide training through pictorial guides and demonstration videos that are tailored to local weed species and cropping systems, making these methods accessible even to farmers with limited literacy.
Conclusion
Removing weeds before they produce flowers is a simple yet highly effective way to break the cycle of weed proliferation in smallholder farming systems. By preventing weed seeds from entering the soil, farmers can steadily reduce the weed seedbank, minimize the risk of herbicide-resistant plant varieties, and improve crop yield over time. Although there are short-term trade-offs, particularly with respect to additional labor or basic equipment costs, the long-term benefits for both productivity and sustainability are substantial. It is important to utilize an integrated weed management strategy in order to maximize the effectiveness of weed management, prevent weed shifts, and avoid soil disturbance. Overall, pre-flowering weed removal can significantly enhance food security, profitability, and ecological balance for resource-limited farmers in Africa and other regions.
Further Reading
https://www.kalro.org Link to Kenya Agricultural and Livestock Research Organization (KALRO), contains educational resources and guidance for smallholder farmers within Kenya
https://www.fao.org/4/y5031e/y5031e00.htm Link to a useful resource for more information on weed management in developing countries
https://africanplantdatabase.ch Link to the African Plant Database, useful for plant identification and information
https://www.youtube.com/watch?v=6UOHhyyRQ_4 Demonstration of different weeding techniques in Kenya, including hoeing and hand-pulling.
https://oneacrefund.org Organization that works directly with smallholder farmers in Sub-Saharan Africa, providing them with financing, high-quality inputs, and training to increase yields and incomes.
Picture lessons for farmers in SAKBooks.com
South Asian Version – Chapter 7.7 - https://sakbooks.com/south-asia-english-version-all-chapters/
East/Southeast Asia version – Chapter 7.7 - https://sakbooks.com/east-south-east-asia/
Sub-Saharan Africa/Caribbean version – Chapter 7.7 - https://sakbooks.com/sub-saharan-africa-caribbean/
Latin American version – Chapter 7.7 - https://sakbooks.com/latin-america/
Middle East/North Africa version – Chapter 6.7 - https://sakbooks.com/north-africa-middle-east-english-version/
References
1. African Plant Database (n.d.) Conservatoire et Jardin botaniques de la Ville de Genève & South African National Biodiversity Institute. http://africanplantdatabase.ch/
2.Carlberg, Z. (2014). Sustainable Weed Management for Small and Medium-Scale Farms (ATTRA Publication #IP490). Butte, MT: National Center for Appropriate Technology. https://attra.ncat.org/product/sustainable-weed-management-for-small-and-medium-scale-farms/
3. Curran, W. S., Lingenfelter, D. D., & Hartwig, N. L. (2018, revised). Integrated Weed Management: Fine Tuning the System. Penn State Extension (The Pennsylvania State University). https://extension.psu.edu/integrated-weed-management-fine-tuning-the-system
4. Food and Agriculture Organization of the United Nations. (2003). Weed Management for Developing Countries: Addendum 1 (R. Labrada, Ed.) (FAO Plant Production and Protection Paper 120 Add.1). Rome, Italy: Food and Agriculture Organization of the United Nations.
5. Food and Agriculture Organization of the United Nations. (2011). The State of Food and Agriculture 2010–2011: Women in Agriculture: Closing the Gender Gap for Development. Rome, Italy: Food and Agriculture Organization of the United Nations.
6. Flameweeders.com. (n.d.). Flameweeding 1-2-3: How to Use a Flame Weeder for Pre-Emergence Weed Control. https://flameweeders.com/flameweeding123.html
7. Heap, I. (2014). Global Perspective of Herbicide-Resistant Weeds. Pest Management Science, 70(9), 1306–1315. https://doi.org/10.1002/ps.3696
8. Kenya Agricultural and Livestock Research Organization (KALRO). (n.d.). Crops. https://www.kalro.org/divisions/crops/
9. Knezevic, S. Z., Evans, S. P., Blankenship, E. E., Van Acker, R. C., & Lindquist, J. L. (2002). Critical Period for Weed Control: The Concept and Data Analysis. Weed Science, 50(6), 773–786. https://doi.org/10.1614/0043-1745(2002)050
10. Mrema, G., et al. (2019). Comparative Effects of Weed-Management Strategies on Smallholder Maize Production in West Africa. Journal of Crop Improvement, 33(4), 512–525.
11. Norsworthy, J. K., Ward, S. M., Shaw, D. R., Llewellyn, R. S., Nichols, R. L., Webster, T. M., Bradley, K. W., Frisvold, G., Powles, S. B., Burgos, N. R., Witt, W. W., & Barrett, M. (2012). Reducing the Risks of Herbicide Resistance: Best Management Practices and Recommendations. Weed Science, 60(sp1), 31–62. https://doi.org/10.1614/WS-D-11-00155.1