Pest Control in Malaysia's Perennial Crops: A Half Century Perspective Tracking the Pathway to Integrated Pest Management

Abstract

Leaf eating insect outbreaks of unprecedented severity occurred on oil palms and cocoa in what became Malaysia, from the late 1950s to early 1960s. Growers faced two crucial questions, what to do about the attacks, and what caused them. The tropical climate generally continues suitable for phytophagous insects to realise their large increase capacity, a factor emphasised in the stable agroecosystem of perennial tree crops. Parasitic and predatory natural enemy insects are equally favoured and maintain control. It became increasingly evident that the prime cause of outbreak was disruption of this balance by the introduction of broad spectrum, long residual contact insecticides (bslrcs), with various contributory factors. Patchy pesticide residues would continue to eliminate inherently exploratory parasitic and predatory insects, something worsened by uneven initial application. In these conditions, there is a complete overlap of generations of both pests and enemies, with no evolution of synchronised or otherwise coordinated life cycles (‘continuous generation mode’– CGM). In outbreaks the pests tend to be at a similar lifecycle stage (‘discrete generation mode’– DGM), so that at times a high proportion of an enemy population that may be building up cannot find a suitable host stage. Simply stopping application was often enough to end the vicious circle of treatment and reoutbreak, but also, commonly, there was heavy damage in the meantime. Selective application was developed, involving inherent pesticide characteristics or method of use opposite in at least one aspect to bslrc (i.e. narrow spectrum, short residue life, or non-contact). Large areas were treated, e.g., from the air. Infestations mostly disappeared with only one or a few applications. In that era of the 1960s, chemical application compatible with biological control was known as ‘integrated control’. The bslrcs had been introduced to control other regularly occurring pests (‘key’ pests), limited localised build up of the target pests e.g., from climatic fluctuations (‘occasional’ pest), or as a ‘precaution’. Some species only appeared after disruption started (‘potential’ pest). Development of selective chemical control continued to be for key and occasional pests, aiming at effective kill once decided upon. Census monitoring ensured application only when justified economically, with timing to the most vulnerable stage in the pest lifecycle. Among non-chemical approaches, cultural methods include provision of suitable flora in the ground vegetation for food sources for adult parasitic insects. Reasonably dense ground vegetation cover is grown to suppress rhinoceros beetle damage in oil palm replantings. Other possibilities include dissemination of insect diseases, traps and attractants, and resistant plant types. This fitted ‘pest management’ which by the mid-1970s came to encompass selective chemical use, as ‘integrated pest management (IPM)’. There were similar developments in other parts of the world, and in other perennial tree crops, extended also to short term crops (e.g., rice and vegetables). IPM is not an esoteric methodology awaiting ‘complete knowledge’. It can be applied on the basis of principle and existing knowledge for the most reliable economic control, targetted to encompass any aspect, such as toxicology and environmental effects.