1. In the previous section, we examined the changes that occurred in two subsistence systems (rice and maize-cowpea intercropping) and one commercial cropping system (sugar beet). Two technological developments made an important contribution to these changes: the use of mechanisation to reduce labour intensive practices and the development and availability of chemical pesticides.

  2. We also noted that these case studies illustrated that pest problems and how they are dealt with involve interactions between “Natural systems” and “Human use systems”. An important role that the use of pesticides can often play is to uncouple decisions made about crop production practices from those concerning plant protection. 

  3. We examine these more complex plant protection systems in Part 2. They involve dynamic interactions between pest populations, beneficial organisms, technological developments, and decisions made by farmers, chemical manufacturers, pesticide distributors, food retailers, consumers, and policy and regulatory authorities.

  4. Although pesticides can play an important role in plant protection, they can also cause negative impacts. We consider how Integrated Pest Management (IPM) strategies, alternative control methods, government regulation, training, and quarantine measures can reduce these undesirable outcomes. 

  5. Finally, we discuss how the role of stakeholder workshops can facilitate a better understanding of the relevant components of “natural-human use” systems that need to be considered when designing smarter and more collaborative and resilient approaches to plant protection in the future.

The increasing use of pesticides worldwide

  • The development pathways we observed for rice, maize/cowpea intercropping, and sugar beet, demonstrated that a number of factors caused the type of plant protection measures adopted by farmers.
  • The replacement of farm labour by machinery, the development of new crop varieties, and the increasing use of chemical fertilisers, were often aimed at increasing crop yields and revenue.

  • This development often resulted in an increase in the use of pesticides to “protect” the higher value investment.

  • This general, worldwide trend is well illustrated by data for China, shown in the diagram.

The influence of the market on plant protection

  • Apart from farm-related factors, the market and the behaviour of consumers can influence the level of pesticide use. With increased affluence and an increasing percentage of the population purchasing their food from various types of market, the appearance of fruit and vegetables has become an important factor affecting a consumer’s decision to purchase these products.
  • Apart from farm-related factors, the market and the behaviour of consumers can influence the level of pesticide use. With increased affluence and an increasing percentage of the population purchasing their food from various types of market, the appearance of fruit and vegetables has become an important factor affecting a consumer’s decision to purchase these products.

  • On the other hand, many customers have become more concerned about pesticide residue in their food and will accept some pest damage for pesticide-free, “organic” produce.

Problems with Pesticides
While pesticides can play an important role in plant protection, there can be three downsides to their use:

  • Pesticide resistance can result from the overuse of pesticides, which imposes strong selection pressure on a pest population, resulting in an increasing percentage of individuals becoming resistant and making the pesticide ineffective. Colorado beetle (a pest of potatoes) and Diamondback moth (affecting cabbage and other brassica crops) are two important pests that have developed resistance to many pesticides.
  • Pest resurgence occurs where pesticide use against a target insect pest causes the resurgence of another pest. For example, rice farmers sometimes spray against leaf feeding insects early in the crop, although the defoliation they cause often has little or no impact on crop yield. However, pesticide use early in the crop can kill parasites and predators of planthoppers, inadvertently causing damaging planthopper outbreaks later in the crop (see photograph and view a short video).


  • Health and other problems associated with pesticide use can be experienced by spray operators, cause pesticide residue in food and water, and can cause damage to wildlife and vegetation, and contaminate adjacent crops.

Developing ways of reducing pesticide use

  • For many decades, public and private Research & Development has focused on finding ways to reduce the problems associated with chemical pesticide use through three main activities:
  • Reducing the amount of pesticide use by improving application techniques, better targeting and timing of pesticide application, and only using pesticides when needed.


  • Developing alternatives to chemical pesticides, such as breeding crop varieties resistant to pests, including the use of genetic modification (GM) techniques, rearing and introducing parasites and predators, developing biopesticides and traps, using genetic modification and pheromones to disrupt pest population development, etc.
  • Re-adjusting and developing new crop production practices, such as trap crops to attract pests that are then sprayed, timing of irrigation practices, developing insect and fungal spore traps and other monitoring techniques to determine whether and when to take action, increasing crop resilience through new cropping practices, and better integration of alternative pest control methods.

Integrated Pest Management (IPM) 

  • The original concept of IPM developed from the concern that farmers spray their crops routinely rather than first observing the level of pest attack and then deciding whether it is worth spraying.
  • Since the application of pesticides costs money, the original idea of IPM was to determine a threshold of pest attack at which the benefit of spraying (by reducing crop loss) is likely to exceed the cost of spraying. Many research projects have aimed at determining this “action threshold” for many crops/pests.


  • The example considered here concerns an apple IPM project. The aim was to replace the existing strategy (routine spraying of insecticide) by developing an IPM strategy, involving pest monitoring and only spraying when an “action threshold” is reached.

Notes for the diagram above:

One study, carried out a number of years ago, found there were 4 major on-farm and off-farm reasons why growers were unlikely to implement the IPM strategy.

1. Difficulty of designing Action thresholds for a range of insect pests.
2. Trained labor for sampling and identifying insect pests expensive or unavailable.
3. Apples are a high value crop when sold to supermarkets. There appeared to be an unacceptable risk of lower quality fruit and therefore a lower price with the IPM strategy.

4. A disease (“mildew”) was the main “pest” of apples, controlled by routine spraying of fungicide. If insecticide is added to control insects, when routine spraying fungicide, the only additional cost was for insecticide (since labour and machinery costs were already paid for).

Examples of successful IPM

The previous example of apple IPM illustrates the importance of designing a strategy that suits the particular objectives and constraints faced by growers.

  • The role of independent crop consultants and field scouts, employed by large scale farms and plantations, has been to advise on the design and implementation of IPM strategies. This has resulted in the development of much broader concepts of IPM, involving monitoring and release of biocontrol agents.

  • In the closed environment of glasshouses, insect pests are often managed by monitoring the pest and strategically introducing appropriate parasites and predators. This strategy often has to be modified to maintain the overall greenhouse IPM strategy. For instance, if a new insect pest gains access to the glasshouse crop, the control strategy for that pest has to be very carefully designed and managed to avoid any disruption of the control strategies used for the existing pests.
  • Another example of research and development leading to successful IPM strategies concerns the management of certain fungal diseases. In this case, meteorological monitoring of temperature and humidity records enabled disease infection periods to be forecast, allowing appropriate and timely control measures to be deployed.

Off-farm and On-farm influences on production ecosystems

  • The previous examples illustrate that plant protection strategies adopted by farmers are determined by:
  • On-farm opportunities and constraints, associated with farmers’ objectives (subsistence, income, risk), their resources (land, labour, capital), and the advice and information they receive.

  • Off-farm opportunities and constraints that affect farmers’ access to important options, such as new varieties, machinery, markets, and plant protection options. It also includes government intervention considered later.

Note: A common trend worldwide is the decline in government advisory services, providing one-on-one advice to farmers on plant protection issues. While this service is provided by independent advisors in some countries, in many developing countries this role is now performed by pesticide companies and distributors, with the possibility that financial incentives to increase sales results in poor advice and inappropriate and excessive use of pesticide.

Government role in developing and implementing plant protection practices:

  • National governments can directly
    intervene to prevent the introduction
    or spread of invasive species by
    implementing quarantine and other
    measures [See invasion curve
  • More generally, government policies and regulations regarding pesticide training and safety and other plant protection activities can have an important influence on both on-farm and off-farm decision makers.
  • Other government activities to improve plant protection practices include providing funds to public agencies and NGOs to engage in research, development and training activities.
  • This includes research into factors affecting pest population dynamics, the development of pest
    identification and diagnostics, and pest forecasting systems.

  • Government investment in online, smartphone and published information, training and communication services can improve how practical plant protection decisions are made.

How stakeholder decisions can impact plant protection, food production, and ecosystem services

  • The stakeholders shown in this diagram make decisions on the basis of how different options available to them are likely to meet their specific


  • The objectives of profit, risk minimisation, sustainable production, maintaining ecosystem services, and other goals of stakeholders often conflict with the goals of others.
  • To achieve an overall “better off” outcome by minimising conflicts is unlikely to be easy but in the long term would probably be well worth the effort.

The role of stakeholder workshops

  • As we have seen, given the complexity associated with the range of decision makers involved and their different objectives, trying to improve overall plant protection strategies can be challenging. One approach is to bring the key stakeholders together at a facilitated workshop. 
  • The diagram outlines the types of stakeholders involved and the process used for a number of workshops in Australia, focused on how to improve the overall strategy for dealing with specific pest problems. This included Parthenium, an invasive weed, regional insect pest management strategies for cotton, brassica & tomato pests, and biocontrol development and implementation.

  • The initial “problem specification” process usually involves an historical review. Participants chart changes in prices, weather, new technology, pest status, pesticide use, etc., and collectively explore the major factors involved in the current scenario. This process helps achieve an exchange of ideas about the major driving variables, providing a common basis for the next phase.

Identifying opportunities and constraints for improving crop protection.

  • This second phase of the workshop aims to collectively identify the key “opportunities and constraints” for improving the overall situation. Using a pin-boarding technique [see photograph], participants write their ideas on cards, pin them to a board, and use this as a forum to discuss and condense their collective ideas regarding the main issues.
  • The third stage – “needs analysis and action plans” focuses on three major issues:
  • Identifying which of the identified issues should be
  • What components need to be analysed and addressed, and
  • Developing a list of action plans, including which
    participants will take a lead; determining a feasible
    timetable; and the process to be developed for keeping participants informed of progress.

    • Action plans usually fall under four main topics: policy issues, training needs, R&D priorities, and designing and implementing on-farm trials. 


  • The Action-Research cycle has been used in some cases, resulting in a series of annual workshops to reflect and plan for subsequent action.

Finally, since the science and practice of plant protection operates within a global context, the issues to be addressed to achieve good plant protection outcomes increasingly need to be made within the broader context outlined below.