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 would reduce vine loss and production costs, providing a quality crop with reduced chemical inputs. This project will quantify the costs of JB defoliation to growth, winter cold-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, will also be evaluated as a strategy to reduce need for cover sprays close to harvest. 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.
Materials and Methods
Objective 1: A research vineyard was established in May 2006 at the UK Horticulture Research Farm in Lexington, KY. The vineyard is planted in a 6 × 3 factorial design with two American (‘Concord’ and ‘Norton’), two European vinifera (‘Cabernet Franc’ and ‘Cabernet Sauvignon’), and two French-American hybrids (‘Chambourcin’ and ‘Frontenac’) maintained under three intensities of insect management. There are eight replications in a randomized complete block design with two vines per experimental unit. Vines are trained to a single high-wire bilateral cordon system and managed according to University of Kentucky recommendations. Three insecticide treatments, carbaryl (label rate) applied every 7 or 14 d during the JB flight period, or no insecticide treatment, have been used for 2 years to provide varying levels of protection from JB defoliation. Standard JB traps and lures (Trécé, Adair, OK) placed in two locations near vineyards and orchards at the UK farm are used to monitor JB flight.
Response variables evaluated in the first 2 years included percent defoliation (rated by two independent observers every 2 wks), cordon development, and LT50 (lethal temperature to kill 50% of the primary bud) (Hammons et al. 2006, 2007). Those evaluations will continue in 2008 and 2009, along with the first evaluations of dormant pruning weight, and fruit yield and quality as the vines reach crop-bearing age. Concentration of total soluble solids (% TSS), which are mostly sugars (Potter and Hotchkiss 1995), in their juice, will be measured with a PAL-1 Digital Refractometer (ATAGO, Bellevue, WA), in addition to juice pH and titratable acidity to monitor berry development. Harvestable yield data will be recorded when the preferred %TSS is reached for each treatment/cultivar combination. Dormant pruning weights will be recorded in mid-February to evaluate the previous season’s vine size.
The LT50 of ‘Norton’, ‘Chambourcin’, and ‘Cabernet Sauvignon’ will be evaluated using bud freeze analysis in mid-Feb. 2008 and 2009. Dormant canes of selected cultivars for each spray treatment/cultivar combination will be sampled. Canes will be pruned to three buds and bundled in groups of four cuttings for four replications and nine temperature blocks for each spray regime (16 cuttings (48 buds)/spray treatment/temperature). LT50 temperature treatments will begin at 0oC and end at -40oC. Temperatures in the chamber will be lowered -5oC progressively for 2 h “ramp time” and then held constant at that temperature for 1 h “soak time”. Samples for each temperature block will be removed from the freeze chamber every 3 h and thawed at room temperature for 48 h before evaluation of oxidative browning. Buds will be dissected by making lateral cross-section cuts across the dormant bud with a razor blade, exposing the primary bud. Numbers of live/dead primary buds will be recorded. Data will be subjected to ANOVA for main treatment effects and interactions, with transformations if needed to stabilize error variances, and by regression against defoliation level (Snedecor and Cochran, 1980).
Objective 2: A second experimental vineyard consisting of six early-, mid-, and late-maturing cultivars planted in a randomized complete block was established at the UK Research Farm in 2006 for use in evaluating the phenological resistance hypothesis. There are eight replications with duplicate vines planted per experimental unit [EU] (error df = 35, total df = 47 for n = 48 EU). Cultivars and their respective days to harvest are, Early-ripening: ‘Foch’ (90 d) & Jupiter (85 d); Mid-ripening: ‘Chancellor’ (100 d) & ‘St. Croix’ (99 d), Late-ripening: ‘Norton’ (125 d) & ‘Chambourcin’ (115 d). All have blue/black fruits to eliminate confounding effects of fruit color. The vines were not cropped during the 2006-07 growing seasons, and are being maintained according to Univ. of Kentucky recommendations. They were protected from JB defoliation with carbaryl during the first two growing seasons.
For the 2008 and 2009 growing seasons, number of clusters per vine will be standardized . Weekly during GJB flight, vines will be inspected in early afternoon and number of fruit clusters with JB and GJB feeding aggregations will be recorded. Seasonal flight of GJB overlaps with JB flight (Hammons et al. 2008) and will be monitored concurrently using similar traps with a larger funnel opening (JB Xpando trap) and a TRE-8643 experimental food-type lure (Trécé, Adair, OK). Twenty representative berries will be sampled from each EU (50 per vine) and analyzed for toughness (g), % TSS, juice pH, and titratable acidity on the days that cluster damage is evaluated. Relative toughness of intact berries will be measured using a digital force gauge with a pointed punch (MARK-10 Model EG-2; Hicksville, NY). Beetle counts on fruit and in traps will be evaluated in relation to toughness and TSS.
To supplement on-vine beetle counts, representative grape clusters of each cultivar will be harvested weekly for 3 weeks during peak beetle flight. The clusters, varying in ripeness, will be confined with beetle cohorts (20 JB & 6 GJB) in the screened bait wells of large vane traps to test attractiveness of feeding-induced volatiles to additional beetles. The trap design, consisting of corrugated plastic vanes over a steel tractor funnel, was tested in 2007 and found to be highly effective for capturing GJB attracted to yeast-treated or beetle-damaged grapes (Hammons, unpublished data). We hypothesize that clusters from early-ripening cultivars will incur more feeding, inducing volatiles that attract many additional beetles, whereas midseason and late-ripening cultivars will be fed upon sparingly or not at all, depending on degree of ripeness, and attract few or no beetles. Trap captures will be related to berry ripeness of the different cultivars as described above. Data will be compared among early-, mid-, and late-season ripening cultivars by one-way ANOVA and planned single degree of freedom orthogonal contrasts. We hypothesize that late-ripening varieties, in particular, and possibly mid-season cultivars, will be relatively resistant to beetle attack.
University of Kentucky
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Lexington, KY 40546
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