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

Abstract

Timing insecticide applications with insect emergence is critical for the management of cranberry pests like Sparganothis fruitworm (Sparganothis sulfureana, Lepidoptera: Tortricidae). The annual peak flight of S. sulfureana 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 S. sulfureana development. In this study, we present two new degree-day models for predicting S. sulfureana 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 S. sulfureana 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 S. sulfureana 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 S. sulfureana, allowing for improved timing of management strategies against this pest.