Integrated management of weeds in oil palm plantations

Weeds in oil palm plantations can be divided into grasses, broad-leaf weeds (erect, creeping and woody types), ferns and brackens, sedges, epiphytes, unwanted volunteers and others. The weed floras in oil palm plantations are greatly variable from one place to another due to very diverse agro-climatic environments. Some important weeds in the cultivation of oil palm are listed according to their occurrence in nursery, immature plantings and mature plantings.Weeds can affect crop in many ways such as nutrient and water competition which resulted in yield reduction and retarding palm growth. When Asystasia intrusa (now A. gangetica) occurred in 'sheet' form, a yield loss of 13% was recorded. Ischaemum muticum is a noxious weed and as predominant interrow vegetation caused 22% reduction of FFB yield. Mikania micrantha growing in the interrow areas, reduced FFB yield by almost 20% (representing 23. 8 t FFB ha-¹) over 4.75 years of recording.Integrated management of weeds in oil palm or in short form Integrated Weed Management (IWM) involves both preventive measures and applied controls. The preventive measures are mainly planting of legume cover crops (LCC), maintenance of ground covers, EFB mulching and frond placement. The planting of legume cover crops and establishment/conservation of natural ground covers are two categories of cover crop management. In IWM, the preventive measures are complemented by applied controls which include manual weeding, mechanical slashing, organised livestock grazing, biological control measures and the spraying of herbicides. Planting at high density (160-180 palms ha-¹) in flat terrain for other benefits has suppressive effect on weed growth when compared to normal planting density (136-145 palms ha-¹), especially at the mature planting stage.Both preventive measures and one or more methods of weed control are used alone or in combination at the various stages of oil palm cultivation to achieve efficient and cost-effective integrated weed management. At this moment, biological controls are few and only effective for control of few noxious weeds. Research in biological measures to continue testing against many noxious weeds must be given more support. Meanwhile, for the control of noxious weeds and mixed weed flora, IWM uses chemical control as last resort. In the control of many weeds that are still occurring after implementation of standard preventive measures, chemical control is perhaps the only cost-effective measure available. Weed survey or weed census is not yet developed for use to gauge the need to commence chemical control. This will be one area that can yield objective data to replace the current visual inspection by planters .