How to control cogon grass (Imperata cylindrica) with cover crops

How to control cogon grass (Imperata cylindrica) with cover crops

Short answer: Mucuna bracteata is generally the strongest cover crop for suppressing cogon grass (Imperata cylindrica) in tropical plantations. Once it is well established, its vigorous growth and dense canopy shade out cogon, and growers commonly see a marked reduction in cogon over roughly 6 to 12 months. Cover crops suppress cogon by competition and shading rather than killing its rhizomes, so they are a long-term management tool rather than a replacement for herbicide or a means of eradication. On heavy infestations an initial spot-treatment is usually still needed to let the cover crop establish. Results vary with soil, rainfall, shade and cogon density.

Why cogon grass is a serious problem

Imperata cylindrica, known locally as cogon in the Philippines, is widely listed among the world's worst weeds. It spreads aggressively through rhizomes and wind-dispersed seed and colonises disturbed plantation soils quickly. Left unmanaged, cogon competes strongly with young palms and tree crops for water, light and nutrients, creates a fire hazard in the dry season, and adds significant recurring labour and herbicide cost for plantation managers.

Conventional management relies on repeated herbicide applications and manual slashing. Both are costly and labour-intensive, and both address the standing foliage rather than the rhizome bank, so the relief is temporary. Cover crops add a biological, longer-term layer of suppression by occupying the ground and cutting off the light cogon needs, and they are best used alongside rather than instead of conventional control.

Please read: cover crops suppress cogon through competition and shading. They do not kill cogon rhizomes and should not be treated as a herbicide substitute or as a means of eradication. Nothing on this page is a guarantee of a particular level of control. Where a herbicide is used, follow the product label and the pesticide regulations that apply in your country.

Cover crop effectiveness against cogon

Cover crop Relative suppression (field experience) Establishment method and rate Typical time to closed cover How it suppresses cogon
Mucuna bracteata (MB) Strongest of the four Transplanted only, from nursery-raised seedlings: about 320 seedlings per hectare, equal to roughly 85 to 100 g of seed per hectare About 6 to 12 months Dense smothering canopy, strong light exclusion
Pueraria javanica (PJ) Good Broadcast, 4 to 6 kg/ha About 12 to 18 months Dense ground cover, light exclusion
Calopogonium mucunoides (CM) Moderate Broadcast, 4 to 6 kg/ha About 12 to 18 months Fast initial cover, less persistent over time
Calopogonium caeruleum (CC) Good Broadcast, 3 to 4.5 kg/ha About 12 to 18 months Stoloniferous spreading, better shade tolerance

Ratings are a qualitative summary of plantation field experience, not measured trial results. Timings are indicative and site-dependent.

Recommended approach: MB plus PJ combination

For heavy cogon infestations, a two-phase approach is usually the most practical.

Phase 1 (months 0 to 3): spot-treat active cogon patches, following the herbicide label and local regulations, and allow 2 to 3 weeks for die-back. Then transplant nursery-raised Mucuna bracteata seedlings from polybags into the treated areas. This gives MB a head start before cogon regrows.

MB is transplanted, never broadcast. Mucuna bracteata is raised in a nursery and planted out at roughly 320 seedlings per hectare, which works out to about 85 to 100 g of seed per hectare. Rates quoted in kilograms per hectare, such as 2 to 4 kg/ha, are the pattern for broadcast covers like PJ and are roughly forty times too much seed for MB. Following them wastes expensive seed and will not improve establishment.

Phase 2 (months 3 to 6): once MB is established and actively running, broadcast Pueraria javanica seed at 4 to 6 kg/ha in the inter-rows and in areas MB has not yet reached. PJ fills the gaps and carries longer-term cover as the crop canopy closes and MB naturally thins.

Where establishment goes well, growers commonly see the combined MB and PJ cover reduce cogon to a minor component of the ground flora within about a year. The cover then helps limit re-establishment from rhizome fragments and windblown seed, but it does not remove the rhizome bank, so keep monitoring gaps and disturbed ground and expect to spot-treat occasional regrowth. Outcomes differ between sites, and you should verify the approach against your own field conditions before scaling it up.

Frequently asked questions

How long does it take for cover crops to suppress cogon?
With Mucuna bracteata, growers commonly report a marked reduction in cogon within about 6 to 12 months of good establishment. Pueraria javanica generally takes longer, in the order of 12 to 18 months. These are typical field ranges, not guarantees: the pace depends on cogon density, rainfall, soil fertility and how much light reaches the ground. Cogon rhizomes can persist in the soil under a closed cover for several seasons, so plan for ongoing suppression rather than a one-off clearance.
Can cover crops alone control cogon without herbicide?
Cover crops alone can suppress cogon, but establishment is slower and less reliable without an initial knockdown. On light infestations, planting Mucuna bracteata directly can work. On heavy infestations (roughly over half ground cover) an initial herbicide spot-treatment generally gives the cover crop a much better chance of closing over before cogon regrows. Cover crops are not equivalent to a herbicide programme and should be planned as part of an integrated weed management approach.
Will cogon come back after cover crops are established?
Cogon can return. A dense, healthy cover crop stand blocks much of the light that cogon needs to regenerate from rhizome buds, which keeps it in check, but the rhizomes are not killed. If the stand is thinned or damaged by fire, heavy pruning, grazing or drought, cogon commonly re-establishes in the gaps. Maintaining cover crop health and closing gaps promptly is the main defence.
What about using cover crops with coconut trees?
Cover crops work well under coconut. The wider spacing of coconut plantings (commonly 8 to 9 m triangular) leaves more inter-row space and light for a cover crop. Pueraria javanica is often a good fit under coconut because of its moderate shade tolerance.

Tell us your block size, crop and cogon pressure and we will recommend a seed mix and quantity.

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Recommended seed: Mucuna bracteata (MB) and Pueraria javanica (PJ).