Refining Degree-Day Models for Sparganothis Fruitworm in Cranberry by Biofix and Variety

Timing insecticide applications with insect emergence is critical for the management of cranberry pests like Sparganothis fruitworm (<i>Sparganothis sulfureana</i>, Lepidoptera: Tortricidae). The annual peak flight of <i>S. sulfureana</i> has previously been predicted using a degree-day model with a biofix date of 1 March; however, this biofix is not suitable for regions where winter and spring temperatures are warmer and flooding of cranberry beds is relied upon, which inhibits <i>S. sulfureana</i> development. In this study, we present two new degree-day models for predicting <i>S. sulfureana</i> peak flight based on six years of trapping data from New Jersey (USA): one with a biofix of 15 April, a date when drainage of cranberry beds occurs on average, and another using individual bed drainage dates. These models project peak flights at 525.5 and 521.0 degree-days using 15 April and water draw date as biofixes, respectively. These models can be used interchangeably, with both biofixes being suitable for regional grower guidance. Furthermore, differences in <i>S. sulfureana</i> peak flight were observed across four cranberry varieties; however, the effect of variety was influenced by year (significant variety-by-year interaction). This year-to-year variation in peak flight was strongly associated with spring (April–May) temperatures. Using these models, we project that with climate change, the peak flight of <i>S. sulfureana</i> in New Jersey cranberry beds may occur up to a week earlier by 2050. The use of a region-specific biofix and variety-specific models will help to better refine degree-day models for <i>S. sulfureana</i>, allowing for improved timing of management strategies against this pest.