How to Combat the Rice Stem Borer: Protecting Rice Crops

The rice stem borer is one of the most destructive and threatening pests in rice fields. This pest damages the growth and yield of rice plants, leading to a significant reduction in final crop production. Therefore, understanding this pest and implementing effective control measures is of great importance. In this article, we will explore various strategies for managing the rice stem borer.

Introduction to the Rice Stem Borer

The rice stem borer is a major pest in rice fields and belongs to the family of moths. Its population grows rapidly, and its spread causes substantial damage.

The life cycle of this pest consists of four stages: egg, larva, pupa, and adult. The eggs are laid in clusters, usually under the leaves or near the stem of the plant. These eggs are yellowish-white in color. After hatching, the larvae move toward the rice stem and feed on its tissue. The larvae are 17-26 millimeters long and are brown or gray in color. This larval stage causes severe damage to the plant, reducing both yield and quality. Once the larvae have fed sufficiently, they transform into pupae. The pupae are typically found inside or near the stem of the plant. In the final stage, adult moths emerge from the pupae, and the life cycle begins again.

During the winter season and the period after the harvest, the rice stem borer survives as mature larvae in the weeds or leftover rice stubble in the fields. As temperatures rise, the larvae transform into pupae, and adult moths emerge from these pupae. After mating, the female moths lay their eggs on rice leaves. Once the larvae hatch from the eggs, they bore into the rice stems and feed on the inner tissues.

The rice stem borer poses a serious challenge to agriculture and rice production, with significant impacts on crop yield, quality, control costs, and the overall agricultural economy. Understanding these effects helps farmers and policymakers implement effective strategies to manage and control this pest, preventing potential losses.

Symptoms and Signs of Rice Stem Borer Infestation

Given the detrimental effects of the rice stem borer, recognizing the signs of its presence is key to successful rice field management. Early detection of infestation symptoms enables farmers to take necessary actions to control the pest.

The symptoms and signs of rice stem borer infestation include:

Damaged Stems: One of the first indicators is a change in the color of the stems to yellow or brown. This discoloration signals damage to the internal tissues of the stem. Affected stems may become soft and bend or break easily.

Small Holes in the Stems: The larvae of the rice stem borer create small holes as they feed on the stems. These holes are typically found in the lower sections of the stems.
Withered and Dry Leaves: The leaves of infested plants may become withered and dry. This symptom occurs due to reduced water and nutrient uptake caused by damage to the stems.
Visible Larvae: In some cases, the larvae of the rice stem borer can be easily seen inside the stems. These larvae are usually soft and khaki.

Presence of Pupae Inside the Stems: In advanced stages of infestation, the larvae form thin, white-colored pupae inside the stems.
Stunted Growth: Plants infested with the rice stem borer often exhibit uneven growth and may rapidly progress toward wilting.

Rice stem borers typically produce two to three generations per year, with each generation negatively impacting different stages of rice growth. In the final stage, after the panicles (grain clusters) have formed, the larvae feed on the inner part of the stem, preventing the grains from filling properly. This causes the panicles to turn white and eventually become hollow. These white panicles stand out prominently in the field and are easily noticeable. Additionally, other panicles may show damaged and undersized grains.

Prevention and Control Methods for Rice Stem Borer

Physical Control Methods

Manual Pest Collection: In the early stages of infestation and in smaller fields, manually collecting the larvae and eggs from the plants can help reduce the pest population and prevent their spread.
Use of Pheromone Traps: Pheromone traps can be an effective tool for controlling pests. These traps attract adult moths, preventing them from laying eggs. Place the traps on stands throughout the field, spaced about 10 meters apart. The traps should be positioned higher than the rice plants. They contain sex pheromones that lure adult insects for mating, trapping them in the process. This eliminates the insects and stops egg-laying. The pheromones need to be replaced monthly.
Use of Light Traps: Light traps are another method for eliminating insects. In this approach, a lantern or another light source is used to attract the insects. Once drawn to the light, the insects fall into a sticky trap or a light trap basin and are destroyed.
Clearing Plant Residue: Remove and burn weeds around the edges of the fields and any leftover plant debris in the soil, as these serve as shelters for larvae during the winter.

Agricultural Methods for Controlling Rice Stem Borer

Crop Diversity and Rotation: Planting non-host crops during different seasons can prevent the buildup and spread of pests. This practice helps reduce the population of rice stem borers and other pests.
Cultivating Resistant Varieties: Planting pest-resistant rice varieties can lower the risk of infestation. These varieties typically possess specific genetic traits that enable them to withstand pest attacks. Varieties with higher silica content in their tissues are more resistant to stem borers. Additionally, early and mid-season rice varieties are suitable for minimizing the impact of stem borers, as they are harvested before the second generation of the pest can spread.
Weed Control: Weeds can serve as shelters and food sources for pests. Removing weeds from the field helps reduce the pest population and, consequently, minimizes damage to rice plants.
Proper Harvesting: Harvest the crop at the lowest point, close to the base of the plant. This helps reduce the number of larvae left in the field. After harvesting, spread the cut panicles in the sun to dry completely. Drying the panicles maximizes the likelihood of killing any remaining larvae. Once dried, the panicles can be threshed.
Plowing the Field: After harvesting, plow the field vertically. This helps destroy plant residues and eliminate larvae. After plowing, flood the field to ensure complete eradication of weeds.

Fertilizer Management and Control of Rice Stem Borer

Strengthening the soil and providing the necessary nutrients for the plant promotes better rice growth and enhances its resistance to pests. Like any other plant, rice requires a range of macro and micronutrients for growth. One of the most essential nutrients for rice is nitrogen. Nitrogen-based fertilizers supply the nitrogen needed for the plant. One of the best fertilizers for providing nitrogen in rice fields is ammonium sulfate. To learn more about the effects of ammonium sulfate on rice plants, refer to our dedicated article on the topic.

While nitrogen-based fertilizers are essential for rice growth, their application should be controlled in pest-infested fields. It is better to divide the nitrogen fertilizer into multiple applications throughout the growing season. Excessive use of nitrogen fertilizer at one time can lead to rapid plant growth, making it easier for stem borer larvae to penetrate and thrive in the soft plant tissues. Therefore, balanced and phased application of nitrogen fertilizers can help reduce damage caused by this pest.

Additionally, in fields affected by the pest, applying silica and potassium-based fertilizers can be beneficial. Using silica and potassium fertilizers during the growing season enhances the plant’s resistance to pest attacks. Silica strengthens the plant’s cell walls, increasing its resilience to environmental stress and pests. Potassium also plays a vital role in regulating metabolic processes and improving the overall health of the plant.

Biological Control of Rice Stem Borers

Biological control involves using natural enemies of pests to reduce their populations and prevent damage. One common method of biological control is the release of Trichogramma wasps. These wasps act as parasitoids and lay their eggs inside the eggs of the rice stem borer. The larvae of the Trichogramma wasps feed on the pest eggs after hatching, thereby preventing their progression. For greater effectiveness, these wasps are typically released twice during each generation, with approximately 120 Trichogramma cards distributed per hectare each time.

In addition to Trichogramma wasps, natural predators also help control the population of rice stem borers. Some of these predators include crickets, staphylinid beetles, frogs, dragonflies, water striders, and spiders. These creatures act as natural competitors for pests and can help reduce their populations.

The use of ducks is another effective method of biological control. As ducks move through the fields, they stir up the muddy water, preventing sunlight from reaching the soil surface. This condition reduces weed growth, allowing rice plants to thrive. Moreover, ducks act as pest predators and can assist in controlling rice stem borers.

Use of Pesticides

Chemical control of rice stem borers should be considered a last resort and only recommended when other pest management methods have not yielded satisfactory results. The best time for spraying is when the highest number of larvae have just hatched from their eggs and have not yet entered the plant stems. At this stage, the larvae are small and vulnerable, making them easier targets for pesticides. In Iran, this timing generally occurs 10 to 15 days after transplanting seedlings into the main field.

The use of granular insecticides, including diazinon, fozalon, trifluralin, and chlorpyrifos, is recommended for combating rice stem borers. Spraying should be conducted under suitable weather conditions to maximize the effectiveness of the pesticide. Selecting the appropriate concentration of the pesticide and adhering to the product label instructions is crucial. Additionally, consulting with experts and considering the plant’s growth stage and the pest’s age can improve results.