Rice Brown Planthopper: Hopperburn, Why Outbreaks Happen, and How to Control It

Brown planthopper is one of the most destructive insects of rice in Asia, and it also occurs across the Pacific and in Australia.

It is only a few millimetres long, it hides at the base of the plant, and most farmers do not notice it until patches of their crop turn brown and collapse.

That damage has a name: hopperburn.

There is a twist in this story.

Brown planthopper outbreaks are very often caused by the very insecticides sprayed to prevent them. In this video: how to recognise the insect and its damage, why outbreaks happen, how to scout, the natural enemies that keep it in check, how to manage the crop to prevent outbreaks, and, if you must spray, how to choose an insecticide by its IRAC group. The advice is general.

Your local extension service and product labels always come first.

The brown planthopper, Nilaparvata lugens, is a small, brown, sap-sucking bug, about three to four millimetres long.

Adults come in two forms.

Long-winged adults fly, and are carried hundreds of kilometres on monsoon winds, from one rice region to the next.

Short-winged adults cannot fly far; they stay in the field and breed, and when you see many short-winged females, a population is building up.

The nymphs are smaller, wingless and white to brown.

All stages live at the base of the rice plant, just above the water, where the stems are thick and the air is humid. That is why they are so easy to miss.

Look at the leaves and you see nothing.

Part the plants and look at the base, and you may find hundreds.

Planthoppers suck sap from the phloem at the base of the stem. A few do little harm. When numbers explode, the plants yellow, then turn brown and dry out, starting in round patches that spread outward as the insects move. That is hopperburn.

Hopperburned plants often lodge, and a field can be lost within days at the grain-filling stage.

The brown planthopper also transmits two virus diseases in Asia, grassy stunt and ragged stunt, which stunt the plants and reduce the number of grains. And the honeydew it excretes can be colonised by sooty mould at the base of the plant.

In a healthy rice field, brown planthoppers are usually kept at low numbers by a community of predators and parasites.

Outbreaks happen when that balance is broken.

The main cause, documented again and again since the nineteen seventies, is insecticide misuse.

Broad-spectrum sprays applied early in the season,

often against leaf-feeding insects that cause little real yield loss, kill spiders, predatory bugs and parasitic wasps. The planthoppers, which breed faster, recover first.

Some insecticides even increase their reproduction.

The result is called resurgence: more planthoppers after spraying than before.

Other factors push in the same direction.

Too much nitrogen makes the plants lush and the hoppers more fertile.

Dense planting keeps the base of the plants humid.

Continuous, staggered rice cropping gives them food all year round. And repeated use of the same insecticide has made many populations resistant.

Scout every week, and more often from the late tillering stage onwards,

and after any reports of planthopper flights in your area. Walk diagonally across the field, and check the base of the plants in at least twenty hills.

Gently bend the plants and tap the base over the water or a tray, and count the hoppers that drop. Note whether they are long-winged or short-winged, and count the spiders and other predators you see at the same time.

Light traps at night show when long-winged adults arrive, and many countries run regional warning networks based on them.

Compare your counts with your local action threshold.

Thresholds are often a set number of hoppers per hill, adjusted for the number of predators present. Many spiders and predatory bugs mean the field can tolerate more hoppers.

The brown planthopper has a long list of natural enemies.

Wolf spiders hunt the hoppers at the base of the plants, and a single spider can eat several a day. A small green mirid bug sucks out their eggs.

Water striders and other bugs on the water surface catch the nymphs that fall.

Tiny wasps parasitise the eggs, and fungal diseases kill hoppers in humid weather.

Protecting these allies is the heart of planthopper management.

In practice, that means avoiding insecticide sprays during the first forty days or so after transplanting, unless a serious pest is present. In several Asian countries, campaigns that taught farmers to skip these early sprays reduced insecticide use sharply, with no loss of yield.

Some farmers also grow flowering plants such as sesame on the bunds, which feed parasitic wasps and other beneficial insects.

The crop itself can be made less inviting.

Plant resistant varieties where they are available.

Many modern varieties carry resistance genes, although planthopper populations adapt over time, so follow your local list of currently effective varieties.

Split the nitrogen into several doses rather than one heavy dose, and use the amount the soil test and crop need, not more. Avoid very dense planting.

In some regions farmers leave narrow alleys, about thirty centimetres wide, every two to three metres, to let light and air reach the base of the plants and to make scouting and spraying easier.

Where the water can be controlled, alternate wetting and drying, or draining the field for a few days when hopper numbers rise, makes the base of the plants less favourable. And where possible, plant at the same time as your neighbours, so that the hoppers do not have a continuous supply of young rice.

Spray only when your counts pass the threshold,

and natural enemies are clearly not keeping up. Aim the spray at the base of the plants, where the hoppers are, not at the leaves.

Choose an insecticide by its IRAC group.

Groups used against planthoppers include the insect growth regulator buprofezin in group sixteen, which acts on the nymphs; group nine, which stops feeding; group twenty-nine, another feeding blocker; and several chemistries in group four, which act on the nicotinic receptor, including the neonicotinoids in four A, the sulfoximines in four C, and a newer mesoionic group, four E. Brown planthopper populations in many parts of Asia are highly resistant to some neonicotinoids, especially imidacloprid, so check local advice before relying on any product in group four.

Avoid pyrethroids, group three A, and broad-spectrum organophosphates against planthoppers, because they are well known to cause resurgence.

Rotate groups between sprays and seasons, never exceed the label number of applications, and respect the pre-harvest interval.

Registrations differ from country to country.

To recap.

Brown planthoppers live at the base of the plant, so part the plants and look there.

Round brown patches that spread are hopperburn. Most outbreaks follow insecticide misuse, too much nitrogen and dense planting.

Scout weekly, count hoppers and spiders, and use your local threshold.

Skip early-season sprays and protect the natural enemies.

Use resistant varieties, split nitrogen, alleys, water management and synchronous planting.

And if you must spray, aim at the base, choose by IRAC group, avoid pyrethroids, and rotate.

For more on rice pests, and on every other crop pest, visit laisha.ai. Thank you for watching.