Developing a growing degree day model to guide integrated pest management of Eucosma giganteana, a pest of a novel perennial oilseed crop.

Eucosma giganteana (Riley) (Lepidoptera: Tortricidae) is a specialist pest on Silphium spp. including Silphium integrifolium. This pest is currently one of the major limiting factors to the development and commercialization of S. integrifolium in Kansas as a more sustainable oilseed alternative within its native range. One of the factors making E. giganteana difficult to manage is the lack of knowledge about when pest management tactics should be applied for maximum effect. To aid with proper timing, our objectives were to determine a lower activity threshold, then use it to develop a growing degree day model to estimate important phenological events in the life history of adult E. giganteana in the field. In addition, we found a good fit between the actual phenological events for E. giganteana from 2020, 2023, and 2024 and the predicted phenological events from trapping data collected in 2019 in Salina, Kansas. The lower activity threshold was determined to be 17 °C using a series of environmental chamber experiments with overwintering E. giganteana larvae. Furthermore, we found a significant correlation between predicted growing degree days for phenological events in 2019 and the actual degree day measurements for those events in subsequent years. Finally, the model was able to accurately predict adult E. giganteana emergence in the field during 2024. We anticipate the model will continue to provide accurate predictions for the coming years, which would allow for improved timing of pest management practices for E. giganteana to be implemented.