The growing problem of stem borer in rice-growing areas: causes and preventive measures

(Ch Bahadur Ali Akbar, M.Sc. Agronomy, Depalpur Campus, University of Agriculture Faisalabad Punjab Pakistan)

Rice is one of Pakistan’s major food and cash crops and the livelihoods of millions of farmers are associated with its cultivation. However, in recent years, pest attacks have become a serious problem in rice-growing areas. Among these pests the stem borer, a caterpillar that bores into the plant stem is particularly important. The pest enters the stem of the rice plant and feeds on the internal tissues, adversely affecting plant growth and potentially causing significant yield losses.Stem borer infestations are also affecting hybrid rice crops in rice-growing areas, resulting in reductions in average yield. The cultivation of two rice crops in succession can provide the stem borer with a longer period and more favorable conditions to reproduce and complete its life cycle. As a result, its population may increase and the risk of crop damage may become greater. Particularly in hybrid rice, timely monitoring and effective preventive measures are essential to avoid significant yield losses.Identification of Stem Borer
Stem borer larvae enter the stems of rice plants and feed internally. During the early stages of infestation, mild symptoms may appear on the leaves, while later the central portion of the plant begins to dry. When infestation occurs during the early vegetative stage, a symptom known as Dead Heart may appear. At the panicle stage, infestation can cause affected panicles to turn white and dry, a symptom commonly known as White Head. Under severe infestation, both the number and weight of grains may be reduced. One of the major difficulties in managing stem borer is that its presence is not easily detected during the early stages of infestation. Therefore, farmers need to inspect the crop carefully and regularly.Causes of the Increasing Stem Borer Infestation
The female moth of the stem borer generally lays eggs on the leaves. After hatching, the larvae may initially remain on the upper portions of the leaves before eventually entering the plant stem. Once a larva enters the stem, it becomes difficult to detect the infestation from outside, while damage to the internal tissues of the plant begins. Therefore, farmers should conduct regular and close monitoring of their crops. There may be several reasons for the increasing stem borer problem.1. One of the most important reasons is the continuous cultivation of rice. When rice is grown year after year in the same area, a continuous host crop remains available to the pest, increasing the chances of its population building up.2- Another important factor is the presence of crop residues and infested stems in the field. Different stages of the pest may survive in these residues and subsequently infest the next crop.3-The excessive use of fertilizers, particularly nitrogen, may also contribute to the problem. Excessive nitrogen can make plants more lush and succulent, which under certain conditions may create a favorable environment for stem-boring insects. Therefore, fertilizers should be applied according to soil-test results and crop requirements with an emphasis on balanced nutrient management. 4-Climate change is also playing an important role in the spread of agricultural pests. Rising temperatures, changes in seasonal patterns and relatively favorable humidity conditions may enhance pest reproduction and increase the number of generations completed during a growing season.5-In addition, inappropriate sowing or transplanting times, continuous presence of weeds, infested nursery seedlings and inadequate field monitoring may contribute to the spread and buildup of stem borer populations.
Preventive and Control Measures: 1- For effective management of stem borer, farmers should not rely solely on pesticides. Instead, Integrated Pest Management (IPM) should be adopted as a more effective and environmentally friendly approach. 2-Healthy and quality seed and nursery plants should be used, and the transplantation of infested seedlings into the field should be avoided.
3- Rice should be cultivated or transplanted at the recommended time so that early crop growth does not coincide with conditions that are highly favorable for pest development.
4- After harvesting, infested stems and crop residues remaining in the field should be properly managed or destroyed. Weeds should also be controlled because some weeds can provide alternative hosts and shelter for insect pests. 5- Fertilizers should be applied according to soil-test results and crop requirements. Unnecessary or excessive nitrogen application should particularly be avoided. Balanced NPK fertilization can improve plant health and may increase the crop’s ability to withstand pest pressure.6- Farmers should regularly inspect their crops and consult agricultural experts or the Department of Agriculture as soon as early symptoms appear. Pheromone traps and light traps can be used to monitor the presence and activity of adult moths.
The conservation of natural enemies, particularly parasitoid wasps and other beneficial insects, is also important because these organisms can help naturally suppress pest populations.
7-If the pest population reaches the economic threshold level, an appropriate insecticide should be used according to the recommendations of the Department of Agriculture and the label instructions of locally registered agricultural pesticides. The selection of the insecticide, its application rate, and timing are extremely important. Unnecessary and repeated spraying not only increases production costs but can also contribute to insecticide resistance and harm beneficial insects.8-
For the timely detection of stem borer infestation, crop inspection should be carried out carefully, particularly during the evening. Early symptoms on leaves and plants should be examined closely, and suspicious plants should be inspected thoroughly so that infestation can be detected at an early stage. Early detection makes control measures considerably more effective.
9- The selection of an appropriate insecticide should be based on the severity of infestation and local agricultural recommendations. Under such circumstances, an insecticide with systemic action may be used according to the recommendations of agricultural experts. However, the selection, dosage, and method of application should always comply with the approved recommendations of the relevant Department of Agriculture and the registered product label.
10- It is important to understand that the stem borer problem cannot be permanently solved through pesticide spraying alone. Timely monitoring, balanced fertilization, healthy nursery plants, proper management of crop residues, appropriate agronomic practices, and Integrated Pest Management are essential for protecting rice crops from stem borer damage and achieving better yields.
One important factor contributing to the problem is the cultivation of two rice crops in succession. Growing two rice crops in the same area during a year provides the stem borer with a continuous host crop, increasing the chances of its reproduction and population persistence. Consequently, pest pressure in the following crop may become higher, increasing the risk of yield losses.
11- In view of this situation, the government should pay attention to appropriate crop zoning and regional agricultural planning for rice cultivation. Rice production in specific areas should be managed according to agricultural conditions, environmental considerations, and the availability of water resources. Where feasible, policies should encourage greater diversification of cropping systems rather than continuous rice cultivation. This can help reduce pest pressure while also limiting unnecessary use of water resources.
Rice is a relatively water-intensive crop. Therefore, cultivating two rice crops consecutively in areas with limited water resources places additional pressure on already scarce water supplies.
Through crop zoning, areas suitable for rice cultivation can be identified based on environmental and water-resource conditions. In other areas, crops that require less water can be promoted.
Conclusion
There is a need for farmers to move away from a reactive approach in which action is taken only after severe pest infestation has occurred. Instead, regular crop monitoring, early detection, and Integrated Pest Management should be adopted from the early stages of crop development. At the same time, the government should develop a long-term strategy for sustainable rice production through appropriate crop zoning, efficient water use and suitable cropping systems. A coordinated approach involving farmers, agricultural experts, research institutions and government agencies can help to reduce stem borer pressure, conserve water resources, improve rice productivity, and promote a more sustainable rice production system in Pakistan.