Damage patterns and growth stage-specific economic thresholds for management of sesame leaf roller (Antigastra catalaunalis) in non-shattering sesame

Sesame is a valuable oilseed crop grown for culinary uses of whole seed, paste and oil. Increasing demand, along with breeding of non-shattering (indehiscent) varieties allowing machine harvesting, has promoted interest in growing sesame in developed countries. When establishing new mechanised sesame industries, effective pest management will be essential. The most severe pest of sesame globally is Antigastra catalaunalis, however research on its management, including currently available economic thresholds, is very largely from less developed countries and traditional shattering varieties. We aimed to develop economic thresholds for non-shattering sesame infested with A. catalaunalis. We performed controlled inoculations with fixed numbers of pest larvae, using randomly assigned individual Sesamum indicum ‘S32’ plants at three age stages: juvenile, pre-reproductive and early bloom. Damage caused by larval feeding was assessed using a novel damage assessment scale ranging from 0 (no damage) to 9 (complete defoliation). Juvenile plants (8-10 leaves) often exhibited severe damage and sometimes death from just one or two larvae. Pre-reproductive plants could survive and regenerate from damage of 1-3 larvae per plant, however seed yield declined with a linear slope of 28% yield loss per larva. Growth cabinet experiments with early bloom stage plants showed a substantial drop in dry weight with increased numbers of larvae. We suggest economic injury levels of one A. catalaunalis larva per 27.9 plants for juvenile plants, one larva per 14.3 plants at pre-flowering stage and one per 8.85 plants at early bloom stage.