Brown planthopper

What you are looking at

A circular or irregular patch of rice that collapses and dries to a scorched brown within a matter of days, a pattern growers across Asia call hopperburn. Part the canopy at the base of the stems in or near an affected patch and the cause is usually obvious: dense clusters of small, brown to grey-brown, wedge-shaped insects packed close to the waterline rather than on the upper leaves, where damage from most other rice pests shows up instead.

A population includes both short-winged adults, which stay and breed within a field, and long-winged adults, which appear once crowding or declining plant quality builds and disperse to colonise new fields, which is part of why an outbreak can spread so quickly across a growing area. Before a patch collapses outright, affected plants often show yellowing and stunting, and sticky honeydew with sooty mould frequently coats the lower stems and leaves of a heavily infested area.

Asia’s most destructive rice insect, spread on seasonal winds

Established across South and Southeast Asia, East Asia and parts of Oceania wherever rice is grown intensively, this planthopper is considered the single most destructive insect pest the crop faces across that range. In the coldest parts of its range, including areas of China, Japan and Korea, it does not survive the winter at all; instead, each growing season is recolonised afresh by adults carried in on seasonal winds from overwintering populations further south, a long-tracked migration pattern that means a local outbreak can begin from insects that travelled hundreds of kilometres to get there.

Historically, this pest has flared into some of its worst outbreaks after periods of heavy insecticide use against other rice pests, because broad-spectrum products remove the spiders and mirid bugs that would otherwise keep it in check while doing comparatively little to the hopper itself. It has not established outside Asia and the Pacific, and New Zealand treats a suspected find as reportable given its freedom from the pest to date.

Feeding damage is not the whole story either. This insect also transmits rice ragged stunt virus and rice grassy stunt virus, both of which stunt and distort the plant separately from hopperburn, so a crop showing stunting or virus-like symptoms alongside a hopper population should be assessed for both rather than assumed to have only the one problem.

What to do about it

Grow a variety with resistance suited to the local hopper biotype, following current regional guidance rather than an older recommendation, since new biotypes able to overcome specific resistance genes have repeatedly emerged.

Avoid excess nitrogen and overly dense planting, both of which favour the warm, humid microclimate low in the canopy that this insect needs.

Avoid routine, broad-spectrum insecticide use and protect the spiders and mirid bugs that provide the most effective natural control available, since outbreaks have repeatedly followed periods of heavy spraying against other pests.

Check for a building population by tapping plants over a white tray and counting what falls, and drain the field briefly if hopperburn appears, to disrupt the conditions the insect needs.

Treat this insect with an insecticide only as a last resort, once cultural measures and conserved natural enemies have failed to hold a genuine outbreak back; a selective product applied low on the plant, checking current local guidance first given how widespread resistance to older insecticide classes already is, does less damage to the predators an area depends on long-term than a broad-spectrum spray.

What it gets mistaken for

Physiological leaf scorch develops gradually across a field from an environmental cause and has no insects clustered at the base of the stems. Hopperburn expands rapidly from a discrete patch and shows dense clusters of small brown hoppers low on the plant the moment the canopy is parted, which a straightforward scorch never does.