White speckles are apparent on the upper surface which eventually turn yellow or brown as they dry up. This is called leaf stippling. Under severe conditions, the whole leaf turns grayish-white and dries up. The mite also spins a very delicate web on the lower surface of the leaf blade, that appears as a powdery substance. Infected plants appear light yellow or pale from a distance due to chlorophyll loss, as the mite pierces the leaf tissue and sucks the exuding sap.
The symptoms are caused by the leaf sap sucking of the rice leaf mite, Oligonychus oryzae. The mite is minute but it colonizes the underside of leaves in large numbers. The mites' entire life cycle can take 8-18 days, depending on the environmental conditions. Adults are sexually mature when they emerge and mate as soon as possible. Eggs are laid individually on the lower side of the leaves, in rows along the leaf midribs and veins. The damage is most serious during periods of high temperature (25°C and above) and high relative humidity. Severe attacks also take place on the wetland weed (Echinochloa colona) commonly found with rice, which may be an alternate host. Usually their infestation will reoccur in the succeeding year in a rice field, where the incidence was noticed during the previous year.
Biological alternatives include the treatment of seeds with bacteria of the Pseudomonas type at 10 g/kg of seeds. Application of urea mixed with neem cake to the rice plants also provide good results. Spray wettable sulfur (3 g) after detection of symptoms.
Always consider an integrated approach of preventive measures together with biological treatments if available. Mitcides containing spiromesifen are highly effective against O. oryzea. However, the treatment should be considered in regard to the level of infestation, the cost and the potential effect on the population density of the mites. Timely application is essential.