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Rice leaffolder (Cnaphalocrocis medinalis) larvae fold or roll leaves lengthwise and scrape the green tissue inside, leaving pale white longitudinal streaks. It is a nearly universal rice pest but rarely justifies insecticide use - the plant compensates for moderate damage and natural enemies keep populations in check when spraying is avoided.

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When rice is most vulnerable

Maximum damage matters most at booting to heading, when the flag leaf is the main photosynthetic source. Early damage is usually compensated by later growth.

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How leaffolder shows in satellite data

  • NDVI reduction across the whole affected field in severe outbreaks - the pale scraped leaves lower the field’s average greenness.
  • Pattern is uniform across the affected area rather than patchy - unlike hopperburn or disease patches.
  • Mild to moderate infestations do not cross the satellite detection threshold; scouting is more reliable.
Leaffolder is chronically over-sprayed because folded leaves look dramatic on the ground. Do not spray until scouting confirms the economic threshold, and do not spray at booting or later where you risk killing pollinators and beneficials.

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Field symptoms

  • Leaves folded lengthwise, tied with silk, containing a green larva inside
  • Longitudinal white to pale-green streaks on unfolded leaves
  • Skeletonized leaf blades in severe cases
  • Reduced grain filling if the flag leaf is heavily damaged during heading

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Reduce the damage by

  • Preserve natural enemies - egg parasitoids (Trichogramma) and larval parasitoids (Cotesia) provide most of the control. Avoid broad-spectrum insecticides.
  • Grow moderately resistant varieties where available.
  • Avoid excessive N and dense planting.
  • Selective insecticide (chlorantraniliprole or emamectin benzoate) only if scouting shows the economic threshold is crossed during booting. Never spray prophylactically.
  • Do not spray on visible damage alone - by the time damage is visible, the larva has often already pupated.

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Set an alert for early warning

Turn the diagnosis into a trigger. Focus alerts on the booting-to-heading window, when leaffolder damage actually affects yield.
Recommended settings for leaffolder on rice:
  • NDVI drop alert at booting - trigger on a drop of 0.08 or more.
  • New Imagery alert during the flag-leaf period on fields with a history of leaffolder outbreaks.