Natural incidence of stem borer damage in US rice varieties

Lepidopteran stem borers (Crambidae) are economically important pests of rice in Louisiana and Texas, and diversified management tactics are needed. Rice varieties differ in susceptibility to stem borers, but resistance has not been studied in modern varieties. Analysis of stem borer injury levels (densities of unfilled panicles or "whiteheads") was conducted on data from 37 separate field experiments in Acadia and Calcasieu Parishes, LA from 2016 to 2021. In all years, stem borer infestations were predominantly comprised of the Mexican rice borer, Eoreuma loftini (Dyar). Whitehead density was least in 2016 (0.1 whiteheads m-2) and greatest in 2019 (4.0). Across all years, whitehead density was strongly affected by rice genotype. Whitehead densities for 16 common commercial varieties are reported herein. Stem borer infestations were greatest in PVL01 having approximately 7-fold greater whitehead density than the least infested varieties, CL152, Jefferson, and Jazzman. Mean whitehead densities were approximately two-fold higher in inbred varieties than in hybrid varieties. In addition, medium grain varieties showed higher whitehead densities than long grain varieties. Whitehead densities did not differ between imidazolinone-resistant "Clearfield" varieties and conventional varieties. Results suggest varietal resistance can be incorporated into integrated management programs of rice stem borers to reduce reliance on chemical controls.