What you see, and when
Circular patches of the crop drying and collapsing — hopperburn — usually appearing first in the middle of the field and spreading outward. By then the population is enormous.
The insects themselves are at the base of the tillers, at the water line. To find them, part the canopy and tap the base of the plants over the water and watch what falls.
Scout there from tillering onward. A canopy inspection from above finds nothing.
Why it flares up
Resurgence. Certain insecticides — some pyrethroids and organophosphates in particular — kill the spiders and mirid bugs that keep planthopper down, while the planthopper itself recovers quickly. The population then rebounds far higher than before the spray. This is a well-documented effect and it is the reason many hopperburn patches follow an earlier spray for something else.
Excess nitrogen, which makes the plant a better host.
Dense planting and continuous flooding, which give the humid, sheltered microclimate at the base that the insect prefers.
Managing it
- Resistant varieties where available for your area.
- Do not spray broad-spectrum insecticide early for minor pests. This is the single most important point.
- Alternate wetting and drying rather than continuous flooding — draining periodically disrupts the microclimate and is one of the more effective cultural controls.
- Wider spacing or alleyways every few metres, which improves air movement, spray penetration and scouting access.
- Split the nitrogen and stay within the recommendation.
- Direct the spray to the base of the plant, with enough water — 200 litres per acre or more — and a lance pushed into the canopy. A spray over the top treats nothing.
Chemistry
Use a product specific to planthopper rather than a broad-spectrum one, and rotate the IRAC group. Resistance in this pest is widespread and has developed against several groups in sequence.
The virus it carries
Brown planthopper transmits grassy stunt and ragged stunt virus. As with all vector-borne disease, control is preventive: once a plant is infected nothing reverses it.
Read the label and the leaflet on the pack before use. The approved crops, dose and waiting period printed there are what count.
