- Fruits: grapes
- Pest Management: integrated pest management
Japanese beetle (JB) (Coleoptera: Scarabaeidae) is an invasive generalist insect, feeding on over 300 plant species. JB are pests in a variety of field and fruit crops including corn, soybean, and grapes. Grape is a highly suitable host for adult JB, and turfgrass, a highly suitable oviposition site for JB, is commonly used in vineyards as groundcover between grape rows. JB adults found in a vineyard may have overwintered there as larvae or may have moved in from surrounding landscapes. In this project, we studied how the composition of surrounding landscapes affects JB movement into and abundance within vineyards over time. We assessed landscape composition of the surrounding landscapes of Wisconsin vineyards using classifications derived from the NASS USDA 2016 Cropland Data Layer, and selected 20 vineyards that fell on a gradient from high to low cropland in the surrounding area. We collected weekly samples of adult JB, and performed a weekly assessment of leaf damage at these vineyards from mid-June to early September. The longitude of the vineyards explained most of the variation in JB abundance with vineyards located further east typically having higher populations of JB possibly a result of large scale landscape differences across the state, however we observed no significant relationship between the amount of cropland in the surrounding landscape and the abundance of JB. We additionally observed a significantly greater abundance of JB and associated leaf damage toward the edges compared to further inside the vineyards, which suggests management strategies could focused towards field edges. Adult and larvae of JB were subsampled, from 4 vineyards where an N15 enriched fertilizer was applied in order to use nitrogen isotopic analysis to determine whether JB collected feeding on vines as adults overwintered in the respective vineyards where they were collected. At three of the four vineyards where we applied an N15 enriched fertilizer, the enrichment was not clearly detected which prevented us from using the N15 signatures of the beetles to determine their origins. The intended outcomes of this project were for growers to have a better understanding of how surrounding landscape impacts phenology, abundance, and movement of JB within vineyards, as knowledge of JB population dynamics and landscape risk assessments are essential in developing effective management plans. The results of our research have been shared with grape growers through the Wisconsin Fresh Fruit and Vegetable Conference and through the Wisconsin Fruit News Newsletter.
The learning outcomes of this project are as followed: (1) Growers will have increased knowledge on how surrounding landscape influences JB movement into vineyards, (2) Growers will have increased knowledge on the phenology of JB and their spatial distribution within vineyards, and how these are affected by surrounding landscape (3) Growers will have increased knowledge concerning JB larvae overwintering in vineyards.
The action outcome of this project is as followed: Growers will make decisions on ground cover used between rows of grape plants, informed by our research on JB population dynamics.