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Fruit Notes |
Evaluation of Unbaited Pyramid Traps
for Monitoring Plum Curculio in Commercial Apple
Orchards |
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Fruit Notes |
Ronald Prokopy, Michael Marsello, Tracy Leskey, and
Starker Wright |
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Fruit Notes |
In the 1997 Winter issue of Fruit Notes, we reported on a 1996 study evaluating unbaited black pyramid traps as devices for capturing plum curculio adults and predicting need and timing of insecticide sprays against plum curculio based on trap captures. That study, conducted in a small commercial apple orchard in Conway, showed that even though black pyramid traps in optimum positions (next to apple tree trunks) captured reasonable numbers of plum curculios, there was no correlation between periods of substantial capture and periods of substantial damage by curculios to fruit. In other words, trap captures were poor predictors of when insecticides should be applied against curculio in that orchard in 1996. Black pyramid traps, intended to mimic tree trunks, are currently receiving much attention as potential monitoring devices for plum curculio in peach orchards in the South. Here, we report on a study in which black pyramid traps were evaluated at three positions in eight large commercial orchards in Massachusetts in 1997. Materials and Methods Pyramid traps were the same as used in 1996 and were a modification of traps designed for monitoring pecan weevils in the South. Three traps were placed in each of six blocks of apple trees in each of eight commercial orchards. All blocks contained 49 trees (seven rows of seven trees each) of mixed cultivars of fruit-bearing age. Of the six blocks per orchard, there were two blocks each of trees on M.9, M.26, and M.7 rootstock, giving rise to what we term here as small, medium, and large trees, respectively. For each block, one trap was placed within 30 cm of the tree trunk (termed trunk trap) of a perimeter tree, one mid-way between the canopy of a perimeter tree and the first interior tree (termed inter-tree trap), and one at the margin of the nearest woods (termed border trap). The ground beneath and between orchard trees was either free of vegetation or vegetation was mowed to prevent obscuring of traps. Traps were deployed during bloom and were examined for captured plum curculio adults every 3-4 days thereafter for 4-5 weeks. At each trap examination, beginning at petal fall, 15 fruit per tree of each of the seven perimeter trees were examined for presence of plum curculio oviposition scars (total of 105 fruit per block per sampling date). Scarred fruit were allowed to remain on the tree. All blocks received either two or three grower-applied sprays of Guthion or Imidan, beginning at petal fall and 8-11 days later(second spray), as well as 16-20 days (third spray) thereafter. Growers applied sprays according to their own estimation of need, without access to our data for making application decisions. To protect against insecticide, a plastic bag was used to envelope each trap completely just before spraying and was removed immediately thereafter. This was done because in a preliminary test, only about 40% as many curculios (0.8 vs. 1.9 per trap, a significant difference) were captured by traps sprayed with Imidan as by unsprayed traps. Results We combined data for the two blocks of similar tree size per orchard and segregated data according to sampling dates before, between, and after insecticide applications. The data (Table 1) show that no fruit injury was detected prior to the first insecticide application even though some curculio captures by traps in each position had occurred. For none of the trap positions in any block type (i.e. tree-size type) was there a significant positive relationship between mean number of captured adults per block and mean number of sampled fruit injured per block. This was true for sampling data between the first and second insecticide application, between the second and third insecticide application, and following the last insecticide application. In every block type, mean fruit injury increased between the first and second, between the second and third, and after the third insecticide application. Conversely, in most cases, mean trap captures either successively decreased from levels that were reached prior to any insecticide treatment or were nil throughout. The greatest fruit injury in any of the 48 blocks was in a block of large trees in Orchard D (a mean of 2.5% fruit injured). Not a single plum curculio was captured by any trap in this block. Conversely, in the two blocks receiving the greatest trap captures (small trees in Orchard D and large trees in Orchard F), there were means of only 0.24 and 0.19% injured fruit, respectively. Most blocks received injury greater than this. Conclusions Data from this study in eight large commercial apple orchards in 1997 are in agreement with data from our 1996 study in a single small orchard and do not support the use of captures of plum curculio adults by unbaited black pyramid traps as accurate predictors of the need to apply insecticide against curculio. This conclusion holds irrespective of the position at which unbaited pyramid traps were placed in an orchard. For the future, we need either a different type of trap or a powerful attractive odor to enhance the value of black pyramid traps. In succeeding articles in this issue, we describe progress toward developing alternative types of traps and attractive odors to incorporate into traps. Acknowledgments This work was supported by grants from the USDA Northeast Regional IPM Competitive Grants Program, State / Federal IPM funds, and the New England Tree Fruit Growers Research Committee. 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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