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Fruit Notes |
Commercial-orchard Trial of Unbaited Traps for Monitoring Plum Curculio: 1998 Results |
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Fruit Notes |
Starker Wright, Stephen Lavallee, and
Ronald Prokopy |
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Fruit Notes |
For the past 3 years, we have performed field and laboratory studies aimed at developing an effective trap for monitoring plum curculio (PC) in commercial orchards. Our goal in trap development is to establish a system whereby growers can predict the need for and timing of sprays. In 1996, we evaluated unbaited black pyramid traps in small orchard blocks in Belchertown, MA, Conway, MA, and South Deerfield, MA. Our principal finding in this study was that unbaited pyramid traps are ineffective in warm weather. When the temperature rises above 20oC (when most PC injury occurs), PCs enter trees largely by flying directly into the tree canopy, bypassing the tree trunks and trunk-associated pyramid traps. In 1997, black pyramid traps were evaluated at three positions in 48 blocks of trees in commercial orchards. In each block, one trap was placed immediately adjacent to the trunk of a perimeter tree, one trap was placed at the midway point between the perimeter tree and the first interior tree, and one trap was placed at the margin of the nearest woods. Data from this study extended our 1996 findings. Irrespective of trap position, captures of PC in unbaited pyramid traps did not reflect accurately the need for or proper timing of insecticide spray. A second (preliminary) study was conducted in 1997 intended to develop a trap to monitor PC abundance and activity within tree canopies. From this work, we developed a twig-mimicking black cylinder trap as an alternative to trunk-mimicking black pyramid traps. In 1998, we repeated and expanded our trial of trap types in the same 48 commercial orchard blocks used in 1997. We compared the performance of black pyramid trunk traps with black cylinder canopy traps as indicators of the potential for PC injury. Materials & Methods As in 1997, traps were placed in six blocks of trees in each of eight commercial orchards. All blocks contained 49 trees (seven rows of seven trees each) of mixed cultivars. Of the six blocks in each orchard, two were considered high tree density (M.9 rootstock), two medium tree density (M.26 rootstock), and two low tree density (M.7 rootstock). Prior to bloom, we placed two unbaited black pyramid traps in each of the 48 blocks, each trap adjacent to the trunk of a perimeter tree (the most effective postion for traps of this type). We also placed two unbaited black hollow cylindrical (3 inches diameter x 12 inches height) twig-mimic traps in perimeter trees of each block, kept in a vertical position within the canopy by a clipped twig (Figure 1). In early May 1998, when all traps were placed, we knew of no attractive odor which could be used in conjunction with these traps (see study of odors attractive to PC, this issue). Every 3-4 days from petal fall until five weeks afterward (the period of fruit susceptibility to PC injury), we examined 15 fruit on each of the seven perimeter trees of each block. The number of PC egglaying scars was recorded, and scarred fruit were allowed to remain on the tree. At each sample date, captures of PC were recorded for each trap, and all captured PCs were removed from traps and returned to the laboratory. All blocks were treated according to the growers' standard orchard management practices, receiving two to three applications of Guthion or Imidan at 9- to14-day intervals beginning at petal fall. Results We combined data for the two blocks of each planting density for each orchard and categorized fruit injury and trap capture data according to spray interval. The data (Table 1, Figure 2) show that PC egglaying injury was very light in all blocks prior to the first insecticide application. Injury to fruit increased sharply between the first and second spray, and increased further between the second and third spray. Interestingly, PC damage to fruit subsided in most blocks after the third spray, but in a few blocks of high density trees, there was a flurry of PC egglaying activity in mid-June, after the final spray. Captures of PCs by unbaited black pyramid traps were greatest prior to the first insecticide application, decreased moderately between the first and second spray, and decreased substantially after the second spray (Table 1, Figure 2). In fact, in several blocks which continued to accumulate substantial PC damage after the second insecticide application, not a single PC was captured during this interval by unbaited pyramid traps. A similar trend occurred for captures within the tree canopies by unbaited black cylinder traps (Table 1, Figure 2). Conclusions Results of the 1998 field trial of unbaited PC traps confirm our findings of 1996 and 1997. For commercial use, captures of PC in unbaited trunk-mimic or twig-mimic traps are not accurate indicators of the need for or timing of insecticide applications. If development of traps for other species related to PC (such as cotton boll weevil and sugar cane weevil) can be used as a guide, then the most effective trap for PCs should be baited with a combination of attractive pheromone and host odor (neither of which was available at the start of the 1998 season). For 1999, we intend to maximize the visual attractiveness of traps, and incorporate use of attractive odor lures. Acknowledgments This work was supported by State/Federal IPM Funds, the New England Tree Fruit Growers Research Committtee and SARE Grant #97 LNE 97-90 (USDA 96-COOP-1-2700). We are grateful to the eight growers that participated in this study: Bill Broderick, Dana Clark, Dave Chandler, Dave Cheney, Dave Shearer, Joe Sincuk, Tim Smith and Mo Tougas. |
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