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Fruit Notes |
Comparison of Six Different Types of Unbaited Traps for Monitoring Plum Curculios in Orchards |
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Fruit Notes |
Ronald Prokopy, Shawn McIntire,
Jonathan Black, Max Prokopy, and Tracy Leskey |
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Fruit Notes |
We can conceive of at least four approaches to monitoring entry of plum curculio (PC) adults into orchards and orchard trees that might be useful in predicting need and time to spray for PC control. These approaches are: (1) monitoring flights of PCs exiting from overwintering sites in areas bordering orchards, (2) monitoring flights of overwintering PCs into orchard trees, (3) monitoring PCs entering orchard trees via climbing tree trunks, and (4) monitoring PCs present in orchard tree canopies. In 1998, we evaluated each of these four approaches using unbaited traps placed near or in four small blocks of apple trees. Materials & Methods Two of the four blocks of trees (one at the University of Massachusetts Horticultural Research Center and one in Deerfield, MA) received no insecticide to control PC. Each of the other two blocks one at the Horticultural Research Center and one in Conway, MA) received two sprays of Imidan: one at petal fall and the other two weeks later. All trees were on either M.7 or M.26 rootstock. To monitor exit flights of PCs from overwintering sites, we positioned unbaited Tangletrap-coated clear Plexiglas traps (2 feet by 2 feet), intended to represent empty space, 6 feet from edges of foliage of woods that bordered each block. Each of the four traps per block was fastened vertically to a wooden pole. The center of each trap was 3 feet above ground. The sticky-coated side faced the woods. To monitor flights of overwintered PCs into orchard trees, we positioned three different types of unbaited Tangletrap-coated traps 18 inches away from edges of canopies of orchard trees and facing woods. The three trap types were: a 2 foot by 2 foot square of clear Plexiglas, a 2 foot by 2 foot square of plywood painted green to mimic tree foliage, and a 1 foot by 4 foot tall rectangle of plywood painted black to mimic a tree trunk. Each trap was attached vertically to a wooden pole, with trap center 3 feet above ground. The sticky-coated side faced the woods. Each block contained four traps of each type, arranged so that traps alternated in type. To monitor PCs entering orchard trees by climbing tree trunks, we placed one unbaited black pyramid trunk-mimicking trap (described in the preceding article) next to the trunk of each of eight perimeter apple trees bordering woods in each block. To monitor PCs present in orchard tree canopies, we placed one unbaited hollow black cylinder twig-mimicking trap (described in the preceding article) in the canopy of each of the eight other perimeter apple trees (not the same trees having pyramid traps) bordering woods in each block. The black cylinder traps were maintained in vertical position by placing each one over a clipped vertical branchlet about mid-way between the edge and center of the tree canopy and at mid-height of the canopy. All traps were emplaced during the pink stage of apple bud development and were monitored twice weekly for eight weeks for captured PCs. On each monitoring day, beginning at petal fall, 12 fruit on each of 12 perimeter trees per block were examined for evidence of PC damage. Damaged fruit were allowed to remain on the tree. Results In the unsprayed blocks of apple trees, significantly more PCs (at least 10 times more) were captured by black pyramid traps next to apple tree trunks than by any other type of trap (Table 1). Sticky clear traps and sticky green traps at edges of apple tree canopies, along with black cylinder traps in apple tree canopies, captured about the same number of PCs and significantly more than the sticky clear traps at edges of the woods or sticky black traps at edges of apple tree canopies (Table 1). Despite the large number of PCs captured by the pyramid traps, captures by these traps were not useful in predicting occurrence of PC injury to fruit. Thus, increases in captures by sticky clear traps and sticky green traps at edges of apple tree canopies, but not increases in captures by any other types of traps, were positively correlated with increases in fruit damage caused by PCs during the monitoring period. In the sprayed blocks of apple trees, there were no significant differences among any of the trap types in numbers of PCs captured, although sticky clear traps at edges of woods and black pyramid traps next to apple tree trunks captured the most PCs numerically, and sticky black traps at edges of apple tree canopies and black cylinder traps in apple tree canopies captured the fewest PCs numerically (Table 1). Increases in captures by any of the trap types did not correlate significantly with increases in fruit damage caused by PCs during the monitoring period. Compared to captures of PCs by traps in unsprayed blocks, captures in sprayed blocks were (1) just as great for PCs caught by sticky clear traps at edges of woods (this is an expected finding because orchard sprays should not interfere with emigration of PCs from woods), (2) fewer by an average of about 50% for PCs caught by all three types of sticky traps (combined) at edges of apple tree canopies, (3) fewer by about 80% for PCs caught by black cylinder traps in apple tree canopies, and (4) fewer by about 95% for PCs caught by black pyramid traps at apple tree trunks. We do not know why orchard sprays apparently interfered more with captures of PCs by pyramid traps at tree trunks than captures by cylinder traps in tree canopies. Conclusions The findings from these studies in unsprayed blocks of apple trees in 1998 are similar to findings reported in Fruit Notes 63(1) on studies in an unsprayed block of apple trees in 1997. In both studies, periods of increase in captures of PCs by sticky clear traps at edges of apple tree canopies better coincided with periods of increase in fruit injury than did periods of increase in captures of PCs by black pyramid traps at tree trunks. Disappointingly, in the sprayed blocks, in no case did periods of increase in captures of PCs by any of the trap types tested in 1998 correlate positively with periods of increase in fruit injury. We believe that a more user-friendly form of a sticky trap placed at the edge of an apple tree canopy to capture PCs flying into apple trees and/or a modified form of a cylinder trap placed in an apple tree to capture PCs active within the canopy hold the most promise as effective monitoring devices. We further believe that neither of these trap types can succeed in monitoring accurately the presence of PCs in sprayed orchards unless they are baited with attractive odor. Acknowledgments This work was supported by USDA Hatch funds and the New England Tree Fruit Growers Research Committee. We thank Jim Hardigg for allowing us to use his orchard for part of this work. |
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