Soil application of silicon reduces yellow stem borer, Scirpophaga incertulas (Walker) damage in rice

The effect of soil application of rice husk ash (RHA), a cheap renewable source of silicon, and imidazole (a silicon solubilizer and carrier) on yellow stem borer (YSB), Scirpophaga incertulas (Walker), and its damage to rice plants were investigated. Treatments included soil application of RHA (T1), imidazole (T2), RHA+imidazole (applied once at vegetative stage, T3) and RHA+imidazole (applied twice at both vegetative and booting stages of crop growth, T4) with an untreated control (T5). The effect was tested in five varieties, viz., BPT 5204, KRH2, Pusa Basmati 1, MTU1010 and Vandana. All the soil treatments reduced damage by YSB at vegetative and reproductive phases across five varieties as compared to untreated control. Scanning electron micrograph and electron-dispersive X-ray spectrum analysis of stem tissue of rice variety BPT 5204 treated with silicon revealed the enhanced deposition of silicon in cell walls and 2.1- to 5.3-fold increase in silicon content across treatments. Larvae collected from the silicon-treated plants had worn mandibles, and the histological studies showed rupture of the peritrophic membrane, increased vacuolation, disintegration of columnar cells and discharge of cellular contents into the gut lumen due to abrasion of midgut epithelium, as compared to untreated control where the columnar cells and midgut lining were intact. Although all the treatments were effective, T4-imidazole applied twice along with RHA was more effective in reducing YSB damage followed by T3-imidazole applied once with RHA at tillering stage, T2-imidazole alone and T1-RHA in the descending order of efficacy.