Cultural Tactics for Control of the Rice Water Weevil, Lissorhoptrus Oryzophilus Kuschel.

A series of field studies were conducted from 1990 to 1992, designed specifically to identify cultural tactics that may be used to control the rice water weevil, Lissorhoptrus oryzophilus Kuschel, on rice (Oryza sativa L.). The objectives of the studies were: to examine the effects of plant density on rice water weevil oviposition, to compare carbofuran and drainage as rice water weevil control tactics and to examine the impact of 1-3 days delay in reflooding after drainage on rice yields, and to assess the impact of planting date on rice water weevil larval damage. The results of the plant density study showed that there was a trend for more eggs per plant at lower densities, but a trend towards more eggs per unit area with higher plant densities. The findings of the study were that plant densities may influence rice water weevil oviposition during the first two weeks of permanent flooding. However, the conclusion was that plant spacing cannot be manipulated to control rice water weevil infestation, because recommended optimum plant densities do not differ significantly in their effect on oviposition. The results from the water management study showed that although timely draining of fields significantly that although timely draining of fields significantly reduced immature weevil populations, the tactic was unreliable. Continuous rain during the drained-period may cause leaching of soil nutrients. Also reinfestation of fields after reflooding the drained fields can nullify the benefits derived from drainage. However, the results of the study did not find any reduction in grain yields from delayed reflooding of fields. Two field experiments were conducted in 1991 and 1992 for the planting date study. The data from both years showed that yields of rice planted before mid-April were not reduced by weevil infestation. Early planted rice did not avoid damaging populations of rice water weevils, but was able to tolerate such infestations without loss of yields, unlike later planted rice. The findings from the study suggested that early rice seeding offered potential as a cultural control tactic to reduce the damaging effects of rice water weevil