Sustainable Management for Scarab Pests Impacting Grape Production in the Southern Region

Grape growers in the southeastern United States contend with two major pests, Japanese beetle (JB), Popillia japonica Newman, and green June beetle (GJB), Cotinis nitida L., that are absent or less troublesome in other grape-growing regions. JB severely defoliates vines, whereas both beetles feed upon and contaminate ripe fruits and are key pests close to harvest when spray restrictions limit management options. Grape cultivars adapted to the southern region vary in foliar characteristics and phenology of ripening in ways that likely affect resistance to both scarabs. Establishing vineyards with resistant cultivars should reduce vine loss and production costs, providing a quality crop with reduced chemical inputs. This project quantified costs of JB defoliation to growth, winter hardiness, berry development, and yield of vines of representative American, European, and hybrid cultivars maintained under conventional and reduced insecticidal regimes. In addition, phenological resistance, the use of cultivars that ripen before or after peak beetle flight, was shown to reduce or eliminate the need for fruit cover sprays close to harvest. Information gained from this project will help guide growers who favor organic or sustainable growing practices to cultivars that produce quality crops with minimal loss from the aforementioned scarab pests.

Introduction

This project had two goals: to support field-based economic thresholds for JB defoliation of young grapevines, and to evaluate use of phenological resistance, i.e., planting of cultivars that ripen outside of peak periods of beetle activity, for alleviating Japanese beetle and green June beetle damage to ripe grapes close to harvest. Varietal resistance and the impact of JB defoliation on vine growth, fruit yield and quality has not previously been reported for planted vines, or for anything close to the severity of damage that occurs in KY.
The South has a long history of involvement with viticulture and enology. The Kentucky Vineyard Society, formed in 1789, was the first organization of its kind in the USA. By the mid 1800s North Carolina had become the largest, and Kentucky was the third-largest wine-producing state in the nation. Grape acreage in Tennessee in the late 1800s was 5–6 times greater than it is today. Although Prohibition resulted in the sharp decline of wineries, there is an ongoing resurgence in viticulture throughout the South. In Kentucky, where viticulture, especially a tourist-based winery-direct distribution model, is a promising agricultural alternative, most growers are new to the industry and either currently grow or until recently grew tobacco.
Cultivar choice and pest control are crucial to new growers due to the high cost of vineyard establishment and the fact that economic return may not occur for 3–4 years. The cost of re-establishing a failed planting could be devastating for small family owned farms. Most growers currently manage JB and GJB by weekly cover sprays. Registration of carbaryl, the most commonly used insecticide, is likely to be withdrawn. Label restrictions prohibit spraying most insecticides close to harvest which for many early and mid-season table and wine grape cultivars coincides with peak JB and GJB activity. Current recommendations (e.g., Midwest Grape Growers Guide 2008) provide relatively little information on sustainable or organic control options for JB and GJB.
This project contributed data to support economic thresholds for Japanese beetle which relatively recently has become a major grape pest in the Southeast. Such data have not been reported anywhere for planted vines. Our project quantified impact of JB defoliation on growth and winter hardiness of young vines, as well as tolerance differences among cultivar. It demonstrated that planting phenologically-resistant cultivars can reduce or eliminate need for cover sprays during veraison. This work supports best management practices for two key pests impacting the resurgent viticulture industry in the southeastern USA.