Overview
- What pests affect rice crops?
- Yellow stem borer
- Brown planthopper
- Rice water weevil
- Rice stem borer
- Rice leaf folder
- How do I manage rice pests?
- Summary
Rice is one of the most important crops in the world, especially in India. The country produces 120 million tonnes of rice each year, making it the second-largest producer globally. However, rice crops in India and other countries face serious threats from pests, including various insects. These pests can destroy an estimated 10-30% of the annual rice yield. Protecting crops from these threats is crucial for the global rice market and the Indian economy. This article will highlight the major pests affecting rice in India and worldwide and explore rice pest management solutions, using integrated pest management strategies like biological control.
What pests affect rice crops?
Rice crops are vulnerable to many pests that attack different parts of the plant at various growth stages. Insects like stem borers and planthoppers harm stems and leaves, leading to leaf loss (defoliation) and lower yields. Other pests, such as the rice water weevil and rice leaf folder, also cause major damage. They feed on roots, stems, and leaves, resulting in stunted growth, dead central shoots (deadhearts), and leaf discolouration. In severe cases, entire crops can fail. Pests not only reduce grain yield and quality but also raise production costs due to pest control efforts. Depending on the type of pest and when it attacks, infestations can reduce yields by 20% to 100%.
Yellow stem borer (Scirpophaga incertulas)
Yellow stem borer (also known as rice yellow stem borer) is a type of stem borer that attacks rice, with this species causing some of the worst damage to crops. It is a moth species from the Crambidae family. The adults are usually brown, yellow, or straw-coloured, with a small black dot on each forewing. Males have a wingspan of around 22 mm, while females are larger, reaching up to 34 mm. This pest does the most harm during its larval stage, especially in deepwater rice farming. The larvae feed on young rice shoots (tillers), bore into the stem, and cause deadhearts, where the central shoot dries out and dies. Signs of damaged plants include faecal matter inside the stems, deadhearts, and dead tillers that can be pulled out easily. In minor cases, damage appears as tiny holes in tillers and stems. Depending on the time the damage occurs in the growing season, this pest can cause crop losses ranging from 20% to 80%. These are striking figures that highlight the importance of managing pest populations before they become severe.
Brown planthopper (Nilaparvata lugens)
Adult brown planthoppers are yellow-brown and grow up to 5 mm long. Their nymphs (developmental stage) start out white when they hatch and turn brownish-purple in their final phase, reaching about 3 mm in length. Their crescent-shaped eggs are laid directly on rice plants. Unlike some other pests, both adult and nymph brown planthoppers cause damage, especially in humid environments. They feed at the base of rice tillers, weakening the plant. Early signs of damage include small yellow patches that later turn brown. Severe infestations dry out the plant, giving it a scorched look called “hopper burn.” This pest also produces honeydew, which attracts sooty mould near the plant base. In addition to direct damage, it spreads diseases like wilted stunt disease. In extreme cases, brown planthopper populations can wipe out entire crops, causing 100% yield loss.
Rice water weevil (Lissorhoptrus oryzophilus)
This tiny insect is a type of beetle that damages rice crops. Adult rice water weevils are about 3.5 to 4 mm long, with a large beak (or snout), and are usually grey with black markings on their backs. Their larvae are fully aquatic and live in the soil around the roots (rhizosphere) of host plants. The larvae are white and pass through four growth stages (instars), which take about a month to complete, growing up to 1 cm in length. Most of the damage is caused by larvae feeding on the root systems of rice plants, but adult weevils also feed on leaves. Larval root damage weakens the plants, leading to stunted growth and lower yields. Signs of adult weevil feeding appear as long, thin cuts through the leaves. This damage is more harmful to young seedlings than to fully developed plants. Additionally, weevil infestations promote weed growth, which competes with rice plants for vital nutrients, further affecting rice production.
Rice stem borer (Chilo suppressalis)
This moth species, also called the Asiatic rice borer or striped rice stem borer, is a major pest of rice crops across Asia, including India. Males have brown and white colouring with an 18 mm wingspan, while females are more orange and can have a wingspan of up to 20 mm. The larvae start off white or grey but turn yellow as they mature. This pest forms cocoons (pupae) inside the plant stem. The larvae damage crops by boring into the stem, while adult moths suck sap from leaves. The larvae mainly live inside the stem, feeding from within, while the adults weaken plants by draining their sap. Signs of infestation include deadhearts, stunted growth, and rotting. If an infestation is severe, this pest can completely destroy a rice crop, leading to a 100% loss in yield, making it a serious threat to rice production.
Rice leaf folder (Cnaphalocrocis medinalis)
This moth species, also called the rice leaf roller, is a serious pest of rice plants. Both male and female adults have a bright yellow colour with wavy black markings. They have a wingspan of around 16 mm and grow to about 8 mm in length. The larvae go through 5-6 instar stages, reaching up to 16 mm in length before fully maturing. This pest is named after the way its larvae feed. They roll or fold rice leaves, using silky threads to tie the edges together. This forms a shelter where they hide while eating the green parts of the leaves. This feeding weakens the plant, reducing its ability to grow. Folded leaves are a key sign of infestation, and in some cases, the leaf tip bends back toward the stem. Damage also appears as long white streaks on the leaves. These pests can cause significant harm to rice crops, leading to major yield losses and negatively impacting overall rice production.
How do I manage rice pests?
Rice insect pests cause major damage to crops and reduce yields. Luckily, there are many ways to manage these pests. While some pests need specific control methods, there are common strategies that help simplify pest management. These strategies can be grouped into four key areas:
Monitoring
Monitoring strategies are essential for detecting pests and assessing infestation levels. Some damage, especially in deepwater rice fields, is harder to see, particularly below the water’s surface. However, signs like leaf damage and deadhearts, as described earlier, can indicate pest activity. Specific symptoms, such as leaf rolling, can help identify the exact pest causing the problem. In some cases, pests can be spotted feeding on plants, like the brown planthopper, which is often found at the base of rice plants. Regular monitoring is key to early detection and effective pest control.
Cultural control
Cultural control strategies are broadly effective against many rice pests, though specific methods depend on the pest type. One common approach is planting trap crops, which attract pests away from rice fields. For example, Napier grass is an effective trap crop for rice stem borers. Deep ploughing during summer helps expose larvae to sunlight and predator birds, reducing their numbers. Removing and destroying deadhearts and infested shoots can also eliminate pests that are actively feeding. In some cases, pheromone traps are useful and are considered a type of mechanical pest control.
Growing pest-resistant rice varieties is another way to protect yields. Additionally, adopting rice production systems like System Rice Intensification (SRI) can enhance plant health and resilience, reducing vulnerability to pest infestations by improving root strength, soil conditions, and water management. Growing early maturing and high-yielding rice varieties may boost productivity and reduce pest risks by limiting crop exposure. Many natural enemies feed on rice pests, and farmers can encourage their presence by planting vegetation that supports their growth and reproduction. Alternate wetting and drying can help reduce pest populations by limiting the breeding conditions for water-dependent insects
Biological control
Biological control methods use agents derived from nature to combat pests in a more environmentally friendly manner. There are four major categories of biological control methods:
- Natural substances: These are typically derived from plants and can be used in sprays to repel or kill pests. For example, azadirachtin is an extract from the fruit of neem trees and can protect crops by disrupting pest development and by being toxic to some species.
- Semiochemicals: These are messaging compounds that can be used to disrupt pest behaviour. They are often used to attract pests to traps.
- Microbials: These are microorganisms like bacteria, fungi, and viruses that harm pests but not crops. Bacterial species like Bacillus thuringiensis can help to tackle rice pests like yellow stem borers, brown planthoppers, and rice leaf folders in their larval stage.
- Macrobials: These are larger animals, like certain insects, that feed on or parasitise pests. For example, rice leaf miners can be controlled by parasitic wasps.
Chemical pesticides
As a world leader in nature-based pest management knowledge implementation, CABI encourages Integrated Pest Management (IPM) as the preferred, ecologically-based approach to producing healthy crops, which allows for chemical pesticide use only as needed, and when adhering to measures that limit the exposure of people and the environment to them (see FAO, International Code of Conduct on Pesticide Management).
Before considering the use of chemical pesticides, farmers should explore all available non-chemical control solutions highlighted above and consult the CABI BioProtection Portal for identifying and applying suitable biological control products.
In case chemical pesticides are considered for use, farmers should look to select lower-risk chemical pesticides which, when used as part of an IPM strategy, help manage pest problems while minimizing harmful effects on human health and the environment. Agricultural advisory service providers can provide information on lower-risk chemical pesticides that are locally available and are compatible within an IPM strategy. These experts can also advise on the required personal protective equipment.
Summary
Rice pests pose a significant threat to global food security and the livelihoods of farmers, especially in India. With infestations capable of reducing yields by up to 100%, effective pest management is crucial. By integrating monitoring, cultural, biological, and chemical control methods, farmers can mitigate damage and protect their crops sustainably. Implementing these strategies, including planting insect resistant varieties, not only helps maintain production levels but also reduces economic losses. The International Rice Institute plays a crucial role in researching and developing sustainable pest management strategies to protect rice crops and improve global food security. A proactive approach to pest control is essential for securing the future of rice cultivation.
Consider visiting the CABI BioProtection Portal to discover solutions to specific pest problems. Our guide to tackling coffee crop pests offers broader information on pest management strategies.
