Integrated control of citrus pests in China and Southeast Asia

• Guangdong Entomological Institute, China
• Department of Agriculture, Thailand
• Department of Agriculture, Thailand
• National Institute of Plant Protection, Vietnam
• Department of Agriculture, Malaysia

China is one of the richest centres of citrus variety in the world and has become increasingly important in global production. More than one million hectares of citrus are planted, making citrus the country's second largest fruit crop planting. Despite this, local demand still outstrips supply.

Citrus is also an important fruit crop in Thailand, where heavy use of chemical insecticides was practised. In Malaysia the expansion of citrus plantations had been curtailed by fungal and viral diseases and the industry had collapsed in Sarawak. In Vietnam the government had announced its desire to diversify the agricultural base of the country to include fruit crops as well as the traditional staples such as rice.

Citrus trees suffer from a wide range of insect and mite pests. These can cause serious reductions in yields or simply ruin fruit. The use of broad-spectrum insecticides in Asia and Australia has had mixed effects. Long-term worries of insecticide use include reductions in the population of beneficial insects, which are predatory on the pest species, as well as the development of resistance and the existence of residues.

Integrated pest management (IPM) is a broad approach to pest control that does not rest solely on chemical insecticides. It aims to be practical, effective, economic and protective of public health and the environment. It can make use of biological control as well as substances that are inimical to the pests without being toxic.

In citrus pest management, PSOs have emerged as a significant new factor in IPM programs. They do not pose a threat to the environment at the doses used, and target insects cannot develop resistance. Operators need only minimal protection when using them. Previous ACIAR research had shown that these oils can provide a level of control of all the main leaf and fruit pests of citrus equivalent to conventional insecticides.

This project aimed to develop sustainable ways of controlling insect pests on citrus trees in Southeast Asia. The project used the techniques of integrated pest management (IPM) and concentrated on China, Malaysia, Thailand and Vietnam. The work also sought to refine existing IPM programs for citrus that are currently used in Australia. The main technology studied was the application of petroleum spray oils (PSOs).

The major experiment conducted as part of this project evaluated the cost and control efficacy of PSO-based IPM programs in 12 locations throughout China and Southeast Asia over 3 years. Experimental locations were also used to monitor natural enemy populations and commence extension of the results. Another large experiment conducted in four locations was designed to determine the upper seasonal limit of oil, which can be applied without causing either acute or chronic phytotoxicity. Other studies allowed further information on specific pests or natural enemies to be obtained, to further refine the IPM programs developed.

This project clearly demonstrated that petroleum spray oil is an effective selective pesticide across all 12 experimental locations in China and Southeast Asia. This supported previous research findings that incorporation of PSOs into citrus IPM programs provides as effective or better control of most major citrus pests than control programs based on broad-spectrum synthetic pesticides. Populations of natural enemies are also better conserved in plots using oil-based IPM than other spray programs. Studies conducted for 2 years at four locations demonstrated that up to 10 applications of 0.5% narrow range, phyto-protected oil sprays per season did not cause visible phytotoxicity or have any effect on yield. It also produced more attractive looking fruit in three of the four locations.

Cost comparisons of IPM programs based on petroleum spray oil and spray programs based on broad-spectrum synthetic pesticides in nine locations provided mixed results. In Guangdong Province China the cost of the oil-based program was consistently less than the broad-spectrum pesticide program, but in the Mekong Delta in Vietnam the cost of the oil-based program was much higher than that of conventional practices. However, the trend was evident that as oil is used for a longer period of time in a particular location, the more likely it is that the cost of oil-based IPM will be less than other pest control programs. This may be because the badly degraded natural enemy populations need a period of a number of seasons to recover to a level where they can effectively contribute to pest control.

The comprehensive results of this project obtained from locations throughout China and Southeast Asia provided important basic information about how to incorporate petroleum oil sprays into citrus IPM. The data were particularly pertinent because one of the major problems currently encountered in citrus IPM in the region is the diminishing number of effective selective chemicals as a result of the development of pest resistance. The project thus made a valuable contribution to the pool of information for development, refinement and extension of citrus IPM programs in China and Southeast Asia.

The project results if effectively extended would bring significant benefits to the environment, the health of farmers and workers who apply agricultural chemicals, and the health of consumers who eat the products. This is because PSOs allow the use of broad-spectrum pesticides to be minimised, they do not pose a threat to the environment at rates used to control horticultural pests, they are safe for use with minimum protective clothing and they allow conservation of natural enemy populations.

The major challenge ahead for citrus IPM in China and Southeast Asia is the extension of research results to the end-users. This is an enormous task because most citrus farming in the region is conducted on a very small scale by farming families. In China the average farm size is less than 0.5 ha and more than 3 million farmers are involved in the industry. Ideally extension could be achieved by a combination of the commercial companies who supply oil to the farmers, government extension agencies and non-government organisations.