Simulated soybean pod and flower injuries and economic thresholds for Spodoptera eridania (Lepidoptera: Noctuidae) management decisions

Although defoliation economic thresholds (ETs) in soybean are well-established, there are concerns about Spodoptera spp. and Helicoverpa spp. damaging soybean pods and flowers. Moreover, S. eridania is the most common species of its genus feeding on soybean in Brazil. On this account, we quantified the feeding of S. eridania larvae on leaves, pods and flowers of BRS388RR and BRS1001IPRO cultivars in the laboratory. In the field, trials were conducted testing artificial injuries for 3 consecutive crop seasons. Results indicated that third-instar S. eridania can grow when feeding on pods (from plants at R3 stage). However, the larval stage is lengthened (27.4 days) compared with larvae feeding on leaves (19.9 days). Tests with older pods (stages R5.1 and R5.5) resulted in 100% mortality. For neonates, 100% mortality was observed for both pod and pod + flower feeding. Also, soybean tolerated all tested injuries in the field, including 25% perforated pods with 16.7% defoliation or 100% flower removal, without yield reduction. Overall, S. eridania is a leaf feeder. Older larvae (from 3rd instar) can feed on pods at an early plant reproductive stage (R3 stage). However, soybean tolerance to pod and flower injuries is high, even when occurring in combination with defoliation. Therefore, an ET of 25% of injured pods or a general defoliation ET of 15% at the reproductive stage is safe. Flower removal at R2 reproductive stage by S. eridania should not trigger management because no reduction in yield was observed even when 100% of flowers were removed. [Display omitted] •Flower loss at R2 soybean stage should not trigger pest management.•ET of 25% of injured pods is safe for S. eridania management decision.•General defoliation ET of 15% at the reproductive stage is safe for S. eridania.