You will not see rice stem borer destroy your crop all at once. That is what makes it so dangerous.

While fall armyworm announces itself with visible feeding damage across entire fields within days, rice stem borer works quietly from inside the stem. By the time the damage becomes obvious from a distance, the larva has already severed the growing point of the plant or destroyed the developing grain inside the panicle. The yield loss has already happened. What you are looking at is the result of weeks of invisible feeding that you missed because you were not looking for it.

Rice stem borer is responsible for yield losses of between 20 and 30 percent in Nigerian rice farms during normal seasons, and up to 80 percent in severe infestation years. It is most destructive in the major rice-growing states of Kebbi, Niger, Ebonyi, Benue, Anambra, and Ekiti, but no rice-producing state in Nigeria is free from its pressure.

This article will show you how to find it before it causes serious damage, how to control it using both chemical and organic methods, and how to prevent it from becoming a recurring problem on your farm.

Two Types of Damage You Need to Recognise

Rice stem borer causes two distinct types of damage depending on what growth stage the plant is at when the larva bores into the stem. Understanding both helps you identify the pest at any point in the season.

Dead Heart

Dead heart occurs when stem borer attacks rice during the vegetative stage, from transplanting up to the point just before panicle emergence. The larva bores into the base of the tiller and severs the growing point from inside. The central shoot of the affected tiller turns yellow and then brown while the outer leaves remain green. When you pull the dead central shoot it comes out easily with no resistance and sometimes with a faint rotting smell at the base.

Dead heart is the easier of the two damage types to catch early because the colour contrast between the dead central shoot and the surrounding healthy green tillers is visible during field scouting.

White Ear

White ear occurs when stem borer attacks rice during the reproductive stage after panicle emergence. The larva bores into the stem below the panicle and severs the flow of water and nutrients to the developing grain. The entire panicle turns white and the grain inside is either empty or absent. The white panicle remains upright, which distinguishes it from panicles that turn white due to disease, which tend to collapse or lodge.

White ear damage is the more economically devastating of the two because it occurs at the stage when grain filling should be happening. Every white ear panicle is a total yield loss from that tiller.

Which Stem Borers Attack Nigerian Rice

Several stem borer species attack rice in Nigeria but the two most economically significant are the yellow stem borer, Scirpophaga incertulas, and the striped stem borer, Chilo suppressalis. Both species have similar life cycles and cause the same types of damage, though the yellow stem borer is more prevalent in flooded lowland rice systems in Kebbi and Niger states while the striped stem borer is more common in upland and rain-fed rice systems in Ebonyi and Benue.

Adult moths lay egg masses on rice leaves, typically on the upper surface of the leaf blade. The egg mass is covered with brown hairs from the female moth’s abdomen, giving it a woolly appearance. Eggs hatch within five to seven days and the young larvae immediately bore into the nearest stem. Each larva passes through five to six growth stages inside the stem before pupating, either inside the stem or in the soil at the base of the plant.

How to Scout for Rice Stem Borer Correctly

Start scouting from two weeks after transplanting or from the three-leaf stage in direct-seeded rice. Walk through the field in a W-pattern covering the full area. Check twenty hills in at least five different locations across the field.

At each hill examine every tiller for dead heart symptoms by looking for the central yellow or brown shoot among otherwise green tillers. During the reproductive stage check every panicle in your sample for white ear. Count the number of affected tillers or panicles out of your total sample.

The economic threshold for chemical treatment is five percent dead heart during the vegetative stage and two percent white ear during the reproductive stage. Below those thresholds the natural enemy population and the crop’s own compensatory tillering will manage the infestation without the need for insecticide application.

Step-by-Step Control Methods

Chemical Control

Cartap hydrochloride is the most effective and widely used insecticide for rice stem borer control in Nigeria. It is sold under brand names including Padan and Caldan and is available at major agro-chemical markets in Kebbi, Abuja, and Onitsha. Mix 20 grams of cartap hydrochloride 50 percent wettable powder per 15 litres of water. Apply by directing the spray to the base of the rice plants and along the lower stems where young larvae are entering. Apply in the early morning between 6am and 9am. Repeat every 14 days during an active infestation for a maximum of three applications per season.

Chlorpyrifos granules are particularly effective for lowland flooded rice systems where applying liquid spray is difficult. Broadcast chlorpyrifos 10 percent granules at 10 to 15 kilograms per hectare directly onto the flooded field. The granules dissolve slowly in the water and the active ingredient is absorbed by the rice roots and distributed throughout the plant. Apply at transplanting and again at the beginning of panicle initiation for season-long protection.

Fipronil granules at five kilograms per hectare broadcast into flooded fields at transplanting provide excellent early-season protection against newly hatching larvae before they bore into the stem. Fipronil is more expensive than chlorpyrifos granules but provides longer residual protection in flooded conditions.

For all chemical applications wear rubber gloves, a nose mask, and a long-sleeved shirt. Avoid entering treated flooded fields for 48 hours after granule application. Do not apply near fish ponds or water sources used for drinking. Observe the pre-harvest interval stated on the product label, typically 14 to 21 days for cartap and chlorpyrifos products.

Organic and Low-Cost Methods

Neem seed kernel extract is the most accessible organic option for Nigerian rice farmers working on tight budgets. Crush 500 grams of dried neem seeds into a fine powder. Soak the powder in five litres of water overnight. Strain through a cloth and add the extract to 15 litres of total spray volume. Apply to the base of rice plants every seven days from transplanting through the vegetative stage. Neem extract disrupts larval development and acts as a repellent against egg-laying moths.

You can also read: Neem oil pest control for African farmers

Light traps hung over the rice field at night attract and kill adult stem borer moths before they lay eggs. A simple light trap can be made from a kerosene lantern or a bulb powered by a small solar panel suspended 50 centimetres above the rice canopy over a basin of water with a thin layer of kerosene on the surface. Moths attracted to the light land on the water surface and are trapped by the kerosene film. Set up light traps from the beginning of the season and empty them every two to three days.

Egg mass removal by hand is practical for small plots of less than half a hectare. Walk through the field every three days from transplanting and remove the woolly brown egg masses from leaf surfaces by hand. Drop them into a bucket of soapy water. This method alone will not control a heavy infestation but reduces the population significantly when combined with other methods.

Timing Your Treatment for Maximum Effectiveness

The two most critical treatment windows for rice stem borer in Nigeria are the early vegetative stage between two and four weeks after transplanting, and the panicle initiation stage approximately 60 to 70 days after transplanting depending on the variety.

The early vegetative window targets the first generation of larvae before dead heart damage becomes significant. The panicle initiation window protects the developing panicle from the second generation larvae that cause white ear.

Missing either window, particularly the panicle initiation timing, is the most common reason Nigerian rice farmers experience severe white ear damage despite having applied insecticide earlier in the season. Set a calendar reminder for both treatment windows at the beginning of each planting season.

Apply all liquid insecticides in the early morning between 6am and 9am when dew on the leaves helps the spray adhere to plant surfaces and before the heat of the day degrades the active ingredient.

Prevention Strategies That Reduce Stem Borer Pressure

Synchronised planting within a farming community is the single most effective cultural practice for reducing rice stem borer pressure. When all farmers in an area plant within the same two-week window, the moths emerging from one generation find no young susceptible rice nearby to lay eggs on between generations. This breaks the population buildup that leads to severe infestation. Communities in Kebbi State that practise synchronised planting consistently record lower stem borer damage than areas where planting is staggered across weeks or months.

Flood management in lowland rice systems reduces stem borer survival significantly. Maintaining a consistent flood depth of five to ten centimetres drowns pupae in the soil at the base of plants and prevents adult emergence. Allow the field to dry out only when necessary for crop management, not as a routine practice during the growing season.

Remove and destroy rice stubble immediately after harvest. Stem borer pupae overwinter in rice stubble left in the field and emerge as moths to infest the next crop. Burning or ploughing under stubble within two weeks of harvest breaks the cycle between seasons.

Use improved rice varieties with better stem borer tolerance where available through NAFDAC-approved seed sources. FARO 44, FARO 52, and several NERICA varieties show better field tolerance to stem borer damage than older local varieties commonly grown in Nigeria.

You can also read: How to prevent weevils in stored maize

Common Mistakes Nigerian Rice Farmers Make With Stem Borer

Spraying over the top of the rice canopy instead of targeting the base of the plant. Stem borer larvae enter the stem at the base. A spray that covers the upper canopy and leaves does not reach the entry point where it matters. Direct your nozzle to the lower stem and base of each hill.

Applying insecticide only after white ear is visible across the field. White ear is the end result of damage that happened three to four weeks earlier when the larva first entered the stem. By the time you see white ear the larva has already finished its damage and is either pupating or has moved to the next plant. Preventive and early treatment at the correct growth stage windows is the only approach that protects yield.

Using the same insecticide every season without rotation. Rotating between cartap hydrochloride, chlorpyrifos, and fipronil across seasons reduces the risk of resistance developing in local stem borer populations and keeps each product effective longer.

Ignoring egg masses during early scouting. An egg mass contains between 50 and 150 eggs. Removing ten egg masses during a scouting walk eliminates up to 1,500 potential larvae without spending a single naira on insecticide.