Managing Food crop pests without compromising yield and environment

By DR. Chandrasiri Kudagamage

Insect pests cause substantial damage to our food crops. Insecticides are normally applied to combat them. However, dependency solely on insecticide for pest management has resulted in various undesirable environmental and human health problems. Human health is affected by the consumption of food with insecticidal residues. Also, the destruction of friendly insects such as pollinators, predators and parasites, is among some of environmental effects of indiscriminate use of insecticides. Long-term persistence of some chemicals in the environment and frequent exposure to these chemicals may also result in different forms of cancers. Sri Lanka ranks very high as regards pesticide-related health hazards and around 20,000 poisoning cases are reported per year and of them 1,600 are fatal. Seventy percent of them were related to suicide. (Registrar of Pesticide)

With the development of herbicide resistant crops like soya bean, corn and wheat the use of total weed killer glyphosate has increased and become most widely used herbicides in history. Farmers, in 2014, sprayed enough of the chemical to cover every acre of cropland in the entire world with nearly a half- pound of the herbicide, according to a 2016 study published in Environmental Sciences Europe. With this intensity of use glyphosate is likely to cause problems and as a result, this herbicide is being increasingly scrutinised for human health impacts. Scientists say it also could be altering the wildlife and organisms at the base of the food chain.

DDT was a widely used insecticide during post world war times. The popularity of this insecticide was due to it less acute toxicity. However, it was subsequently known that this insecticide accumulated in the fat layer of fish and mammals. It was banned in 1970s in our country. However, the use of insecticides continued and many farmers believed chemicals are important input for reducing yield losses.

Undesirable effects of chemicals came to be realised worldwide shortly after the wide use of agro-chemicals in post-world war times. Famous environmentalist and a marine biologist by profession, Rachel Carson in her book, ‘Silent Spring 1962’ highlighted the bad effects of indiscriminate use of chemicals. This inspired grass root environmental movements and others to highlight these effects in various forums. Carson did not anticipate a total ban on pesticide. However, she predicted consequences of over use of chemicals on biodiversity and target pests developing pesticide resistance etc. This led to establishment of environmental protection agency(1970) by an executive order from US President Richard Nixon. The purpose of this agency was to protect human health and environment. Similar legislature also being adopted in our country. The pesticide law 33 of 1980 was enacted to regulate import, manufacture, distribution and use of agro-chemicals in Sri Lanka.

Alternative Approach

To address the above issues new concept of pest management popularly known as Integrated Pest Management or IPM was launched and it evolved into an Eco-friendly and economical pest management tool. This approach has been recognised as a policy for the management of pests by successive governments. However, enough funding in the form of manpower, funding for conducting research, laboratory and analytical facilities has been limiting. This has slowed the progress of IPM in pest management in several crops.

The primary objective of IPM is to develop an economical eco-friendly pest management package where pesticides are used as the last resort when other control measures fail and the pest population exceed a certain threshold called the economic threshold. IPM integrate well with other available control methods and can be applied to any ecosystem such as crop based, home garden, greenhouses and domestic pest control.

Following globalisation and transboundary movements of food and with the increase of demand for diverse food, there has been a concern for contamination of food with various pathogens and chemical residues. Hence agriculture practices need to be introduced to minimise these effects. Recently-introduced Good Agriculture Practices (GAP) fulfil this requirement and goes beyond the scope of IPM.

IPM has various components such as mechanical control (use of bags for fruit fly control), use of resistant varieties, biocontrol (use of predators, parasites and microorganism) and legislative and quarantine (banning of imports from infested country).

IPM experience with major food crops

There are about five or six major insect pests in our staple crop rice. These pests infest different stages of the crop. Among the pests, rice brown planthopper (BPH) and rice gall-midge play an important role causing low to high of damage depending on the prevailing climate. Due to the cultivation of resistant varieties the incidence of rice gall-midge was very low compared to the times when susceptible varieties were cultivated. With respect to rice brown planhopper , the first resistant variety was introduced to farmers in 1980s. Although resistant varieties are ideal as an insect management method, evolution of new strains that can attack these resistant varieties remain a problem. This has happened with respect to gall-midge resistance where resistance broke down in rice varieties cultivated in the 1980s. However, rice breeders and entomologists were able to introduce a new resistant variety by 1984. There are reports of breaking down of this resistance in the recent times. This indicates importance of constant attention in monitoring resistance, management of resistance and finding new sources of resistance. The availability of molecular genetic tools make it easy for the incorporation novel forms of resistance, which is more stable.

The pests that attack at the seedling stages such as thrips are best approached by following correct planting time as heavy infestation is observed in late planted crop. With respect to rice bug which infest crop after flowering, use similar planting time in a Yaya, weeding around the bunds before weeds flower are important non-chemical methods

Although IPM in rice is fairly successful, it is not widely applied in vegetables and other crops. A study conducted by the Department of Agriculture (DOA) in four major vegetable growing Districts in Sri Lanka showed that 85% of farmers in the Badulla District applied pesticides to their crops before the appearance of any pests or symptoms. In the Nuwara-Eliya District this was recorded at 66%. This shows that chemical controls are used even before pest damage has exceeded economic threshold levels and the use of pesticides as a precautionary measure has become common.

Cucurbit fruitfly and melon fly infestation is the most common limiting factor in the cultivation of cucurbit crops for local consumption and export. The melon fly lays eggs deep inside the fruit. The emerging larvae feed inside the soft tissue. This results in fruit dropping and decay. The larvae pupate in soil. Insecticide control is difficult since larvae feed inside the fruit and avoid direct contact with insecticide. In the export consignment, if a single larva is present the whole consignment can get rejected. Therefore, alternative control strategy based on IPM concepts are required. There are several strategies such as bagging of fruits, collection of crop residues and decaying and fallen fruits into a black polythene bag which help to destroy the larvae due to heat developed inside the bag. Together with these cultural methods, application of protein bait is an innovative approach to control this pest. The female flies are attracted to protein substance and consumption of protein help to mature their eggs. Proteinous material prepared from locally available substances are mixed with soft insecticide and applied to leaves instead of fruits. To reduce the amount of insecticide used application to few spots of the crop is sufficient to reduce the female melon fly population. For more effective results these IPM methods need to be applied on wide area basis such as Yaya or cropping area.

Mealy bug was reported to infest papaya fruits in different parts of the country in the late 1980s. This insect is a invasive pest rapidly infesting many species crops. However, main host is papaya. Due to its rapid multiplication rate and wide host range insecticide control is not successful. In other countries where this insect was found, the population of mealy bug is kept at lower level because of the action of the predators and parasite. DOA has already released a effective parasite obtained from United State Department of Agriculture’s Animal and Plant Health Inspection Service parasite rearing facility, in areas where this pest was found.

In Dec. 2018, another pest Fall Army Worm was observed infesting maize in all major maize growing areas. It was also found to infest sugar cane. This pest is native to America. Outside its native habitat it was first found in Central and Western Africa in 2016, and then quickly spread to sub Saharan Africa and in 2018 it was reported from many Indian states. It is a good example of trans boundary movement as the adult moth is capable of flying hundred of kilometres per night. Also, in the absence of native parasites and predators, other control methods based on IPM concepts need to be developed. Initially, experience of small farmers of South America, where the pest is endemic will be valuable tool for the development of control methods. However, research and farmer awareness programme is of paramount importance to develop more realistic management programme for this new pest.

Taking IPM into farmers’ fields

Many believe the concepts developed in IPM is too complex for the average farmer to understand because it involves counting, record keeping and various calculation for economic threshold determination. Hence, farmers need to be introduced to simpler approach to study the crop growth, pest infestation and natural enemy abundance. This is achieved by a group-based learning process. This is known as the Farmers’ Field School. According to this method around 20- 25 rice farmer groups collectively, study the progress of their crop from establishment to harvesting. For this farmers meet together once a week and observe their fields and share their experience with respect to growth of the crops and those factors that limit the growth including the action of pests, and abundance of natural enemies, etc. Depending on the outcome of the observation of their fields, decision will be taken to take action if the pest population grows up. This is a learner centred process where the agriculture instructor is only a facilitator. The impact of this programme was felt by the increases in yield, reduced insecticide use and favourable bio-diversity factors like abundance of predators and parasites.

Apart from government extension, NGOs such as Sarvodaya, CARE and Sri Lanka Red Cross have provided their support on IPM by conducting training programmes on IPM, but, focusing mainly on paddy.

Pesticide Management

A comprehensive pesticide control procedure in the form of pesticide law 33 of 1981 is in existence in the country, but enforcement is low due to several reasons. Often advice regarding pesticide selection was given by the pesticide seller in the village. As a result farmers may select the wrong pesticide, Over use of pesticide is common. They do not use correct dose and dilution. Often they apply pesticide even before appearance of the pest. Also, they do not follow correct post harvest interval. Although, provisions are available to mitigate these shortcomings via the pesticide law, the best way to tackle is through farmer training based on a good extension program.

Under the pesticide law, every product imported to the country has to be registered. Further field monitoring and enforcement of correct use, laboratory testing for quality and residues, imports regulations in the form of banning and restricting the pesticide are carried out. Over the years, the use of WHO Class1 pesticides has been prohibited and these products banned.

Instead of conventional pesticide, there are several specific pesticide registered in the country having low toxicity to humans. Some of these products affect insect hormone system and hence specific to them. Also, available in the market are several neem based botanical pesticide which are effective particularly on caterpillar pests. Additionally, there are bacterial insecticides which result in gastric problems in insects. Insect become sick and die when they consume leaves treated with these insecticide. These insecticides act on few species of insects and easily break down when exposed to light and other environmental factors. Hence, these products are not very popular with farmers although they are safe and environmentally friendly. For these specific pesticides, there are opportunities for use in home gardens and in greenhouses

Future development and promotion of IPM

There are several shortcomings in the development and implementation of IPM. There is a dearth of trained extension workers to deal with large number of farmers involved in crop production. To address this issue, leader farmers can be trained in IPM methods and they can be used to train other farmers in a Yaya or in a village. The government extension workers can be facilitators in this training programme as explained above with respect to Farmers’ Field School method of training. However, more intensive training programme for extension workers covering many aspects of IPM and successful experience of IPM particularly from rice IPM programme needs to be integrated into their training curriculum. Farmer field school programme has been adopted in many countries the world over and the knowledge is shared in the form of reports, videos, manuals, field guides and podcasts. Hence there is lot of avenues to incorporate relevant information in the training curriculum of the extension workers in our country.

Consumer awareness of environmental and health hazards of pesticides and particularly of the persistence in the environment needs to be created to reject food contaminated with pesticides. For this facilities for pesticide residue analysis needs to be improved.

Field demonstration of IPM methods with the involvement of researchers, extension workers and farmers needs to be established. By following IPM methods used in these demonstration, farmers can pick up the most appropriate IPM methods to test in their fields. More investment is needed to promote innovative research such as melon fly control as explained above. Participatory IPM trials and development of simplified IPM packages for major pests and diseases are also necessary for popularising IPM among farmers.

Globalisation of trade and travel, and introduction of improved planting materials can cause accidental introduction of pests. Papaya mealy bug and fall army worm are recent examples of such pest introduction. Facilities available at the plant quarantine station need to be improved for identification of pests of quarantine significance.

There is also an increasing interest in utilising information technology in agriculture to help extension advisers and other intermediaries in delivering up to date information to farmers to manage their crops. Development Mobile Apps that work offline for early warning and surveillance of pests helps farmers make quick decisions for the management of pests.

Author is Former Entomologist, FAO Rice IPM project’s Research coordinator, Director Horticulture Research and Development Institute and Director General Department of Agriculture