Tropical climates with ample sunshine, heat and moisture mean that weeds thrive and may compete with crops for space, water and nutrients, and shade the crop plants, especially when they are young. A large number of annual and perennial weeds infest oil palm plantations. However, if effectively managed, with ‘noxious’ species being removed, many weeds have longer term benefits.A number of insects are potentially damaging to oil palm in various parts of the world including: palm weevils (Rhynchophorus spp.), rhinoceros beetles (Oryctes spp.), weevils (Strategus aloeus, Temnoschoita quadripustulata), leaf-miners (Coelaenomenodera elaeidis, Hispolepis elaeidis, Alurunus humeralis), slug caterpillar (Parasa viridissima), nettle caterpillar (Setora nitens) and bagworms (Cremastophysche pendula, Mahasena corbetti, Metisa plana).Oil palm diseases include: blasts (Pythium splendens, Rhizoctonia lamellifera), freckle (Cercospora elaeidis), anthracnose (Botryodiplodia palmarum, Melanconium elaeidis, Glomerella cingulata), seedling blight (Curvularia eragrostidis), yellow patch and vascular wilt (Fusarium oxysporum), basal trunk rot (Ceratocystis paradoxa, Ganoderma spp., Armillaria mellea); crown disease and fruit rot (Marasmius palmivorus). Spear (bud) rot is caused by the bacterium Erwinia spp., which has been devastating in Central Africa.Other pests include soil nematodes (e.g. Aphelenchus avenae, Helicotylenchus spp., Meloidogyne spp.) which damage roots; and rodents which can eat seedlings and fruit.Integrated pest managementA sustainable approach to crop production relies on protecting the crop by an integrated system of pest management (IPM). There are many examples of how managing species other than the crop, rather than attempting to eliminate them, has benefits in oil palm. For example:Elaeidobius kamerunicus, a weevil introduced into South East Asia in the 1970’s eliminated the need for costly and inefficient hand pollinating, resulting in a sharp increase in oil yieldsOwls are encouraged for rodent controlLeaving less competitive species of weeds provides a habitat for predators of insect pests and helps to prevent soil erosion.Weed management“Paraquat has always given good value, with fast and effective weed control, especially of difficult weeds like ferns, woody shrubs and volunteer oil palm seedlings, even in the rainy season. These days, it is important to use paraquat in Conservation Agriculture to prevent weed succession problems caused by glyphosate.”Professor Gembira Sinuraya, a weed scientist at North Sumatra University who also owns and manages an oil palm and rubber plantation and is involved with the Indonesian Weed Science Society.Paraquat effectively controls volunteer oil palmseedlings which grow as weeds from seeds in fallen fruit.Weed management plays a central role in IPM. Initially, plantation floors are cleared of vegetation, but are usually sown with legume cover crops. Circles around newly planted oil palms are kept weed-free to ensure the successful establishment of the crop. Paths are sprayed-out for access and as the oil palm canopy develops, the cover crop becomes shaded out. This allows a wide range of weed species to invade and broad spectrum non-selective herbicides are used to control these.Intensive use of one particular type of non-selective herbicide, notably glyphosate, has led to changes in plantation weed flora (‘weed succession’) as species more tolerant to that mode of action become more dominant. ‘Soft’ weeds which are easily controlled, and can have some benefits such as helping to minimise soil erosion, are replaced by re-invasion of cleared land by more aggressive ‘noxious’ weeds which reduce crop yields. Apart from having a virtually unique mode of action (shared only by its sister, the desiccant diquat), paraquat only removes the top growth of well established weeds, allowing them to re-grow after 1-2 months. In this way, soft weeds can be controlled but not eliminated.Examples of soft weeds are the prostrate grasses Axonopus spp., Digitaria spp., Ottochloa spp. and Paspalum spp. A controlled presence of soft weeds maintains the balance of the weed flora and prevents weed succession by noxious species simply because bare ground for them to colonise is less available.Noxious weeds include the perennial grass Imperata cylindrica, and the creeping broad-leaved weed Mikania micrantha which aggressively compete with the crop for nutrients and moisture. Other noxious weeds affect spray operations, fertilizer application and harvesting because of the presence of thorns (Mimosa spp.) or dense coverage (Asystasia spp., Ischaemum spp., Pennisetum spp. and Stenochlaena spp.). The ferns Dicranopteris linearis, Lygodium flexuosum and Stenochloena palastris are found in mature shaded areas obstructing harvest. Paraquat is specifically recommended for managing ferns.Extensive field trials and practical experience have shown the advantages of using an integrated approach to weed management by, for example, using two spray rounds of paraquat products followed by one of glyphosate (Lam et al, 1993, Lim et al, 1996, Quah et al, 1997). This program keeps a controlled presence of soft weeds and removes noxious weeds.