Effects of Soil Silicon Amendment and Nitrogen Levels on Rice Insect Pest Complex

Abstract

Rice plants are consistently subjected to various pressures by insect pests throughout the growing season. The main insect pest complex reported in Louisiana are the rice water weevil (major early-season insect pest), fall armyworm (sporadic early-season pest), sugarcane borer and rice stalk borer (long- established but sporadic stem boring pests), Mexican rice borer (an invasive stem-boring pest), and rice stink bug (major late-season pest). Soil silicon amendment has been shown to enhance plant resistance against herbivorous pests. Rice is a typical silicon-accumulating graminaceous crop. Field and greenhouse experiments were conducted from 2015 to 2017 to investigate the effects of soil silicon amendment and nitrogen levels on the rice insect pest complex In Louisiana. In the greenhouse, we found that force required to penetrate rice stem was higher on silicon-treated rice plants compared to untreated plants. Total phenolic content on the other hand, decreased when nitrogen rate was increased. In the field experiment, the effects of soil silicon amendment on rice water weevil densities, whitehead incidences, stink bug population, and yields were found to be weaker than the effects of nitrogen fertilization. Furthermore, separate field experiments were conducted in 2016 and 2017 to investigate the effects of silicon fertilization and rice cultivars on the rice insect pests. Results showed reductions in weevil larval densities in silicon treated plots compared to untreated plots in one core sampling in 2016. Similarly, higher yields were observed in silicon treated plots compared to untreated plots in 2016. Silicon amendment did not affect whitehead incidences and rice stink bug densities in both years. The levels of infestations of rice water weevil, stem borers, and rice stink bugs were also were also found to vary among the rice cultivars evaluated in the study. Despite the weak effect of silicon on insect pests in this study, silicon could still play an important role in rice production considering the positive effects on yield and documented effects on disease suppression.