Determination of potential interaction between nitrogen fertility and insecticide seed treatments for control of the rice water weevil (Lissorhoptrus oryzophilus)

The benefits associated with insecticide seed treatments (IST) are well documented, but there have been instances where rice water weevil (RWW) damage has occurred despite the treatment. Rice plants are dependent on the uptake of nitrogen (N) for vigorous growth and high yields. For this reason, N might contribute to the variability in IST performance. Trials were conducted to examine plant growth and insect responses to different ISTs and N rate combinations. ISTs included clothianidin (NipsIt INSIDE 5FS), thiamethoxam (CruiserMaxx Rice 5FS), and a non-treated (fungicide only) control. Nitrogen was applied at 0, 45, 90, 135, and 180 lbs urea-N/a. NipsIt INSIDE and CruiserMaxx resulted in significantly greater stand density than the no insecticide control. RWW larval populations were greatest in rice with no insecticide seed treatment. N uptake was not affected by insecticide seed treatments. Grain yield increased as N rate increased. Grain yield from rice plants with no insecticide was equal to or lower than that of rice having either insecticide seed treatment, which were always similar. Preliminary results indicate that N has no effect on the efficacy of rice ISTs, and ISTs do not affect the uptake of N.