Brown plant hoppers
Two species of planthopper infest rice. These are the brown planthopper
(BPH), Nilaparvata lugens ; and the whitebacked planthopper
(WBPH), Sogatella furcifera .
What it does
High population of planthoppers cause leaves to initially turn orange-yellow
before becoming brown and drying. This condition, called hopperburn, kills the
plant.
BPH can also transmit
Rice Ragged Stunt and
Rice Grassy Stunt
diseases. Neither disease can be cured.
Why and where it occurs
Planthoppers can be a problem in rainfed and in irrigated wetland
environments. It also occurs in areas with continuous submerged conditions
in the field, high shade, and humidity.
Closed canopy of the rice plants, densely seeded crops, excessive use of
nitrogen, and early season insecticide spraying also favors insect
development.
How
to identify
Check for the presence of insect:
- crescent-shaped
white eggs inserted into the midrib or leaf sheath
- white to
brown nymphs
- brown or
white adults feeding near the base of tillers
Check the field for:
- hopperburn
or yellowing, browning and drying of plant
- ovipositional
marks exposing the plant to fungal and bacterial infections
- presence
of honeydew and sooty molds in the bases of areas infected
- plants
with ragged stunt or grassy stunt virus disease
Hopperburn is similar to the feeding damage or "bugburn" caused by
the rice black bug. To confirm hopperburn caused by planthoppers, check for the
presence of sooty molds at the base of the plant.
How to manage
Outbreaks result when pesticides destroy natural enemies (BPH eggs hatch
unchecked, and surviving BPH quickly build-up populations to damaging levels),
or when longwinged planthoppers are carried in by the wind.
To prevent outbreaks:
- Remove
weeds from the field and surrounding areas.
- Avoid
indiscriminate insecticide use, which destroys natural enemies.
- Use a
resistant variety.
- Critical
numbers: At a density of 1 less there is still time to act in
case the numbers increase.
- Look for
BPH daily in the seedbed, or weekly in the field, on stems and the water
surface. Check each side of the seed bed (or direct-seeded fields). For
older rice plants, grasp the plant, bend it over slightly, and gently tap
it near the base to see if planthoppers fall onto the water surface. For
transplanted rice look at bases of 10 to 20 hills as you cross the field
diagonally. There is no need to scout for BPH beyond the milk
stage.
- Use light
traps (e.g., an electric bulb or kerosene lamp near a light colored wall
or over a pan of water) at night when rice is prone to planthopper attack.
Do not place lights near seedbeds or fields. If the light trap is inundated
with hundreds of BPH, it's a signal to check your seedbed or field
immediately; then scout every day for the next few weeks.
Mechanical & physical measures
- Flood the
seedbed, for a day, so that only the tips of seedlings are exposed will
control BPH.
- Sweep
small seedbeds with a net to remove some BPH (but not eggs), particularly
from dry seed beds. At high BPH densities, sweeping will not remove
sufficient numbers of BPH from the base of the plant.
Biological control
- If natural
enemies out-number BPH the risk of hopperburn is low. Even rice already
damaged by hopperburn should not be treated with insecticides if natural
enemies out-number BPH. Natural enemies of BPH include water striders,
mirid bugs, spiders, and various egg parasitoids.
Chemical control
Only apply an insecticide to the seedbed for BPH or WBPH if all of these
conditions are met:
- an average
of more than one planthopper per stem,
- on
average, more planthoppers than natural enemies,
- flooding
the seedbed is not an option.
