Weed Suppression Results: How Cover Crops Cut Herbicide Costs on Tropical Plantations

The Weed Problem on Tropical Plantations

Weed management is a major recurring expense for plantation operations in the Philippines and across Southeast Asia. Tropical conditions (high rainfall, warm temperatures, and long growing seasons) create ideal conditions for aggressive weed species that compete with tree crops for nutrients, water, and light.

Conventional weed control relies heavily on repeated herbicide applications through the year, depending on weed pressure. Manual weeding is even more labor-intensive and costly.

These costs are not one-time expenses; they recur every year for the life of the plantation. Over the life of an oil palm or coconut planting, weed management represents a substantial cumulative expenditure per hectare. Any reduction in this cost flows directly to the bottom line.

How Cover Crops Suppress Weeds

Cover crops suppress weeds through three primary mechanisms. Physical shading is the most important. A dense cover crop canopy blocks sunlight from reaching the soil surface, preventing weed seed germination and inhibiting the growth of established weed seedlings. Cover crops that produce thick, overlapping leaf cover are the most effective at light exclusion.

Root competition is the second mechanism. Cover crop root systems occupy the upper soil layers where weed roots also develop, competing for water and nutrients. Vigorous cover crop species with extensive root networks leave fewer resources available for weed growth.

Allelopathy may play a part in some species: certain cover crops release compounds through their roots or decomposing leaf litter that can inhibit weed seed germination or growth. How much this adds in the field is uncertain, so treat shading and competition as the main mechanisms, including for Mucuna bracteata.

Weed Suppression Timeline by Species

Calopogonium mucunoides (CM)

CM provides early weed suppression. It grows rapidly and covers the soil 3 to 6 months after sowing (sooner on newly cleared, fertile land), forming a dense sward at 4 to 5 months; in mixtures it is the first to establish and also the first to be shaded out (PROSEA 11).

Pueraria javanica (PJ)

PJ establishes more slowly: in Malaysia it reached 60 to 70 percent ground cover after about 4 months and 90 to 100 percent after 8 months, and once established it is very vigorous: its climbing, twining stems overgrow and smother weeds (PROSEA 11).

Mucuna bracteata (MB)

MB delivers long-lasting weed suppression once established. Recommended seeding rate (our recommendation): 1 kg/ha sown alone, drilled or planted in holes. MB can also be raised in a nursery and transplanted, as in the two trials below. How fast it covers depends on the site: on mineral soil, 680 seedlings/ha reached about 100 percent ground cover at 6 months (Samedani et al., 2015), while on deep peat 320 seedlings/ha gave 31 percent cover at 6 months and 75 percent at 18 months (MPOB TT No. 501). In the Samedani trial under oil palm, the cover crop treatments together had 97.3 to 99.9 percent lower weed dry weight and 94.77 to 99.73 percent lower weed density than unweeded plots, 9 to 24 months after planting. MB's thick leaf litter layer also helps keep weed seed from germinating.

Centrosema pubescens (CP)

CP provides moderate weed suppression. Its primary advantage is maintaining weed control under shade conditions where other species decline. In mature plantations with significant canopy cover, CP can still sustain meaningful weed suppression.

Economic Impact: Herbicide Cost Reduction

Plantations with well-established cover crops report fewer herbicide rounds, with spot treatment targeting only areas where the cover is thin or damaged. How large the saving is depends on how many rounds the cover replaces on your blocks.

On a per-hectare basis, converting from chemical-only weed control to a cover crop system with supplemental spot treatment typically reduces annual weed-control costs, after accounting for the one-time cover crop establishment cost.

How quickly the establishment cost pays back depends on your block, your labor and input costs, and how many spray and weeding rounds the cover actually replaces, so work it out from your own estate records.

Lessons from Field Implementation

Several practical lessons emerge consistently from plantation cover crop programs. The establishment period is critical: weed control during the months before the cover canopy closes is essential. A combination of pre-planting herbicide application and cover crop seeding helps the cover establish. Some managers apply a single round of herbicide before planting, then allow the cover crop to take over weed suppression as it establishes.

Mixed-species plantings provide faster, more reliable coverage. Combining a fast-establishing species like CM with a long-term performer like MB creates a two-phase weed suppression system: CM covers the ground early while MB builds up to provide longer-term suppression. For a mixture, the quantity of each species is set on the quotation for your site.

Some growers apply SoilBoost EA alongside the cover crop as part of a broader soil program, where it may support soil structure and root-zone conditions; it does not replace weed control during establishment.

Monitoring and spot treatment of gaps or thin areas maintains overall weed suppression effectiveness. A cover crop stand is not maintenance-free, but the management required is a fraction of what conventional weed control demands.

Take the First Step

If weed control is a significant recurring expense on your plantation, a cover crop program is worth testing on one block and measuring against your own records. Contact Kudzu Seeds Trading via WhatsApp or request a quote to discuss which species best fit your weed pressure profile and plantation conditions.

Browse our cover crop seed catalog and SoilBoost EA products, or read more on our FAQ page.

Related Resources

• 5-Species Cover Crop Comparison
• Cogon Grass Control with Cover Crops
• Best Cover Crop for Oil Palm
• PJ vs MB Comparison

Sources

• Halim, R.A. (1997). Pueraria phaseoloides (Roxb.) Benth. In: Faridah Hanum, I. & van der Maesen, L.J.G. (eds), Plant Resources of South-East Asia No. 11: Auxiliary plants. Backhuys Publishers, Leiden. Reproduced on Pl@ntUse: Pueraria phaseoloides (PROSEA)
• Chen Chin Peng & Aminah, A. (1997). Calopogonium mucunoides Desv. In: Faridah Hanum, I. & van der Maesen, L.J.G. (eds), Plant Resources of South-East Asia No. 11: Auxiliary plants. Backhuys Publishers, Leiden. Reproduced on Pl@ntUse: Calopogonium mucunoides (PROSEA)
• Samedani, B., Juraimi, A.S., Rafii, M.Y., Sheikh Awadz, S., Anwar, M., & Anuar, A.R. (2015). Effect of cover crops on weed suppression in oil palm plantation. International Journal of Agriculture and Biology, 17(2), 251-260. CABI PDF
• Hasnol Othman, Farawahida Mohamad Darus & Zulkifli Hashim (2012). Best management practices for oil palm cultivation on peat: Mucuna bracteata as ground cover crop. MPOB Information Series 588 / MPOB TT No. 501. Malaysian Palm Oil Board. MPOB PDF