Herbicide Application Timing of Scirpus juncoides var. ohwianus for Control of Sorghum Plant Bug, Stenotus rubrovittatus (Hemiptera: Miridae).

Abstract

Scirpus juncoides is a noxious weed species in rice fields that intensifies damage to rice grains caused by the sorghum plant bug Stenotus rubrovittatus, by serving as the oviposition site. In this study, we examined whether herbicide application for the elimination of S. juncoides has a controlling effect on the bug. In the non-bentazon-applied fields, the bug s invasion into the rice fields prior to the heading period of rice and the nymphal emergence were observed. When bentazon was applied 41 days or 62 days after transplanting in S. juncoides-infested rice fields, the bug s invasion into the fields occurred only after the heading period of rice, and the nymphal emergence of the bugs was not observed. When bentazon was applied 77 days after transplanting, the bug s occurrence resembled that in the non-bentazon-applied fields. These results indicated that the bug s propagation could not be avoided, when the herbicide application timing is later than the occurrence of the first-generation adults. The effects of the timing on damage to rice grains were unclear. Therefore, judging from differences in the bug s occurrence between the rice fields studied, it seems reasonable to conclude that the elimination of S. juncoides with herbicides before the occurrence of the first-generation adults is effective for the control of the bug.