Effect of artificially-generated wind on removing guttation and dew droplets from rice leaf surface for controlling rice blast disease

The incidence and severity of leaf and panicle blasts were efficiently reduced in the wind-treated fields. Artificially-generated wind was performed on rice paddy field in order to measure the changes in temperature and humidity during and after the blowing process and to investigate the effects of sending wind on the formation and removal of guttation and dew droplets on rice leaves. A large electric fan was used to send wind with a depression angle of 30° at 4:00 am for 30-40 min. During the blowing process, the humidity percentage was 100% in both treated and control paddy fields, the temperature was 0.8°C higher in the treated than the control field and the dew weight was rapidly decreased from 21 to 8 g in 20 min in the treated field. After the blowing process, the temperature started to rise at 6:28 am (10 min earlier than the control block). It reached 29°C at 6:48 am (30 min earlier than the control block) and remained higher than the control block till 7:20 am (1-7°C higher). The humidity decreased to 95% at 6:30 am (20 min earlier than the control block) and remained 95% till 6:42 am, then rapidly decreased to reach 68% at 6:46 am, and finally reached 60% at 7:20 am. The humidity was 5-30% lower than that in the control block. Moreover, the dew weight increased to the initial level within 10 min and then decreased rapidly in both blocks starting from 6:20 am. Using wind speed of 4.3 m/s or 3.2 m/s for 60 s per rotation at 4:00 am, almost all the guttation droplets except those of less than 0.5 mm were removed from the surfaces of the 1st and 2nd uppermost leaves after two rotations (at velocity 4.3 m/s) or three rotations (at velocity 3.2 m/s) and the dew droplets were mostly removed after five rotations (at velocity 4.3 m/s) or nine rotations (at velocity 3.2 m/s). Sending wind at a speed of 3.2 m/s or faster removed guttation and dew droplets and suppressed the subsequent dew formation. Our data indicates that the removal of dew droplets on rice hills resulted in reduction of the disease development of Pyricularia oryzea.    Key words: Generated–wind, rice blast, microclimate, guttation, dew droplets.