Pest outbreaks can cause serious losses in rice production and to the income of farmers. They can also threaten food security.
While insects naturally inhabit rice fields, pest outbreaks are abnormal scenarios where a sudden upsurge in the population of a destructive rice pest occurs. Pest outbreaks occur for a number of reasons, but one of the most important ones is a breakdown in the natural ecological balance often caused by misusing pesticides. Pesticide mis-use can also have other detrimental environmental impacts.
IRRI has been working hard for many years to find smarter and more effective ways to help farmers manage pests and to develop pest-resistant rice varieties to reduce the need for pesticides. We've also reduced pesticide use on our own experimental station and do other work, such as run educational campaigns and advocate to policy-makers, to help stop pesticide mis-use.
Sustainable pest management is an important part of rice production systems as pests affect the yield and quality of rice. To help farmers with pest management, IRRI develops pest- and disease-resistant varieties of rice, integrated pest management (IPM) strategies, and ecological engineering approaches.
IRRI has been instrumental in developing rice varieties with built-in resistance to common pests and diseases, including brown planthoppers, stem borers, green leafhoppers, tungro virus, blast, and bacterial blight. All IRRI-bred varieties are screened before release to ensure they have a base level of resistance to these pests and diseases. New rice varieties are also tested in pest and disease “hot-spots” to check their performance under pest and disease pressure before release so that no vulnerable varieties are distributed to farmers.
IRRI is also searching for new resistance genes to improve rice’s built-in resistance to existing and emerging pest and disease threats. Because of their built-in pest and disease resistance, IRRI pest-resistant varieties typically require less pesticide than susceptible varieties.
IRRI has had significant success in reducing pesticide use by researching and promoting integrated pest management (IPM) that, through a smarter understanding of pest dynamics, uses a variety of different strategies to minimize pest damage while eliminating or reducing pesticide use. IPM encourages farmers to manage pests through the use of pest-resistant varieties, to observe the activity of pests and natural enemies, to understand the difference between when pest levels are a problem and when they are acceptable, and to decide whether action is needed. Chemicals are used only as a last resort and their application is aimed at maximizing natural biological control.
In Vietnam, IRRI’s award-winning Ba Giam, Ba Tang (or Three Reductions, Three Gains) project used a radio drama, a television drama, a 30-second TV commercial, posters, flyers, and extension efforts to promote reductions in unnecessary and costly inputs into rice production – including pesticides. As a result, insecticide sprays declined 13–33%, seed and fertilizer rates dropped, and farmers’ beliefs about the value of high inputs changed. The reduced inputs resulted in similar or higher yields and net incomes, and the health of farmers and the environment also improved.
IRRI has also initiated a multimedia campaign in Vietnam and Thailand called No early spray. This was aimed at motivating farmers to reduce insecticide applications in the first 40 days of the crop and has reduced farmer application of insecticide sprays in Vietnam by 53% and in Thailand by 22%.
IRRI has just initiated a project to develop ecological engineering methods to restore or reinforce natural enemy biodiversity and valuable ecosystem services in intensive rice production areas to reduce vulnerability to pest invasions. Underway in China, Malaysia, Thailand, and Vietnam, this project is developing methods to increase beneficial plants, such as flowers, along bunds (the ridges between rice fields) to provide food resources for natural enemies.
On IRRI’s own research farm in the Philippines we have adopted IPM and between 1993 and 2008 we reduced insecticide use by 96%. We are now enjoying rather pest free conditions and clear restoration of natural enemy biodiversity and ecosystem services.
Planthoppers are a major insect pest of rice crops across Asia. They cause hundreds of millions of dollars of losses every year and threaten food security in the region where rice is the staple food. IRRI has developed an action plan to help nations avoid planthopper outbreaks. This plan aims to boost rice production, slash pesticide misuse,and improve ecosystem health.
Since 2004, several Asian countries have experienced severe outbreaks of planthoppers in rice.
In 2007, Vietnam suspended exports of rice because of losses caused by planthoppers, and their persistent outbreaks in Indonesia have caused severe losses over tens of thousands of hectares since 2008.
In 2009, outbreaks of planthoppers and associated virus diseases intensified in Central Thailand, the southern provinces of China, northern Vietnam, and Indonesia. Between 2009 and 2011, more than 3 million hectares in Thailand were infested, causing losses in excess of 1.1 million tons of paddy rice, with an export potential of US$275 million.
The southern rice black-streaked dwarf virus, transmitted by the whitebacked planthopper, has spread into most provinces in the Red River Delta and further south into Central Vietnam. In 2009, an estimated 300,000 hectares were heavily infested in China and Vietnam, and more than 6,500 hectares suffered complete crop failure. The virus has now also spread to Japan.
Planthoppers migrate and can be displaced by wind over long distances to invade new rice fields. In a healthy rice landscape, the number of invading planthoppers is controlled by natural enemies, such as spiders, aquatic bugs, predatory bugs, and parasitoid wasps. When such predators and parasitoids are absent, invading pest populations have unconstrained exponential growth, which results in outbreaks.
Insecticide misuse: The principal cause of predator and parasitoid decline is the overuse and misuse of insecticides. Farmers who routinely spray insecticides in the early crop growth period to control leaf feeders such as leaffolder, for example, use chemicals that are highly toxic to parasitoids and spiders. Planthopper outbreaks are ten times more likely to occur in such sprayed fields.
Preventive sprays, especially with broad-spectrum insecticides that are toxic to parasitoids, render rice ecosystems extremely vulnerable to planthopper outbreaks. Also, insecticide applications do not kill planthopper eggs that later hatch into an enemy-free environment.
Excessive fertilizer use: High use of nitrogen fertilizer leads to a crop that is high in protein, which forms a nutritious food for planthoppers and accelerates population growth.
High cropping intensity: Increases in rice cropping intensity from single to double and triple cropping promote the buildup of planthopper populations and eventual outbreaks if they are accompanied by short fallow periods in between the crops and by asynchronous planting. The absence of sufficiently long fallow periods (or of a nonrice crop) and asynchronous planting mean that migrating planthoppers have a high chance of finding a rice crop in a suitable growth stage that will allow them to feed and multiply.
Capacity to adapt: Finally, planthoppers can rapidly overcome resistant rice varieties, especially where planthopper densities are high and when a small number of varieties are widely planted. In addition, planthoppers rapidly develop resistance to insecticides; in some parts of China, this resistance can reach 200-fold.
IRRI calls on all stakeholders to join forces to implement this action plan. We encourage:
Governments to review, adapt, and enforce pesticide regulations and policies to prevent overuse and misuse in rice production.
The private sector to collaborate on market regulations to prevent the use of insecticides that may promote planthopper outbreaks when used in rice.
Nongovernment organizations and civil society to help disseminate information about proper insecticide use and how to restore ecological resilience in rice landscapes.
IRRI will develop and disseminate tools that enhance ecosystem resilience and facilitate dialogue among stakeholders to implement the action plan.
Enhance biodiversity and ecosystem resilience
- Introduce landscape elements such as flowers to promote the buildup and sustenance of a healthy population of parasitoids and predators of planthoppers.
- Promote synchronized planting and fallow periods of one month in between successive crops of rice.
- Implement crop diversification schemes across time and space. As far as possible, avoid insecticide spraying in the early crop stages (the first 40 days after sowing) to enhance the buildup of biodiversity, ecosystem services, and resilience.
- Deploy resistant and/or tolerant varieties judiciously by using a combination of varieties that differ in their resistance or tolerance mechanisms, and avoid using the same varieties for more than two years as this promotes the development of resistance in planthoppers.
Regulate the marketing and use of insecticides
- Regulate insecticides: Support national and local governments in market regulation of insecticides that shift their classification from consumer goods to regulated materials.
- Stop certain insecticides: Support governments in exploring options to stop the use of broadspectrum insecticides that induce the resurgence of planthoppers, especially those containing the active ingredients cypermethrin, deltamethrin, abamectin, or chlorpyrifos.
- Certify pesticide retailers: Urge governments to certify pesticide retailers to prevent sales of fake, banned, or unapproved products, and to foster the promotion of integrated pest management and proper pesticide use.
- Train pesticide retailers and extension agents on the correct use of insecticides: This is in conditions under which they should be avoided, the correct chemicals to use in case of application, alternating between chemicals with different modes of action to prevent pest resistance, the proper use of spray equipment, and the discouragement of broad-spectrum insecticides and preventive spray schedules.
Tips on smart insecticide use
Invasions of brown planthopper (BPH) are usually not uniformly distributed. If a particular spot in a field has received a large number of “immigrant” BPH, the following control measures are recommended:
- Do NOT spray the immigrants. Wait 10 to 15 days after the immigration has occurred and check fields for nymphs.
- If there is a large presence of nymphs, such as more than a hundred in a hill, then use insecticides that specifically control nymphs such as growth regulators containing the active ingredient buprofezin. In spraying the nymphs, it is vitally important that sprays be directed at the base of the crop, not on the top. Spot-spray: spray only those parts of the field where the nymphs are located.
- Do NOT use broad-spectrum insecticides such as pyrethroids or organophosphates as they are highly toxic to bees, parasitoids, and egg predators.