Abstract:
Rice sheath mite, steneotarsonemus spinki, is an emerging problem in the rice
cultivation in Sri Lanka. This mite (0.2 mm) lives inside the leaf sheath and causes
extensive damage to panicle, affecting grain yield and quality. Its microscopic and
cryptic nature makes it difficulties to control. A series of green house and field
experiments were conducted at RRRDC Bombuwela to develop an evaluation system
for sheath mite damage and a methodology for screening varieties for resistance to the
pest. In addition, preliminary studies were conducted to identify alternate methods for
its management.
A simple and easy method was developed to artificially infest a known number of mites
to healthy plants for studies on varietal response to the pest. The lesion length on leaf-sheath found to be the best criterion to evaluate the damage caused by this mite. When
the mites were infested to rice plants at heading stage, the damage symptoms appear
faster -in 3 days- as compared to those plants infested at tillering and booting stages.
Three commercial varieties and 2 breeding lines (Bw364, Bw361, Bw272-6B, 03/2015,
04/1073) were evaluated for their resistance to mite using artificial infestation method
and found that the test varieties were equally susceptible to the pest.
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Field evaluation with neem seed kernel extract and spiromisifen revealed that the latter
when applied at booting stage could control the pest to a lesser degree. A predatory
mite, Lasoioesius spp, which occurs in large numbers, was identified as a predominant
predator of this mite.