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Fruit Notes |
Preliminary Study of IPM Options for
Peaches: Major Fruit-damaging Insects |
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Fruit Notes |
Karen I. Hauschild Arthur Tuttle and Daniel R. Cooley Ronald J. Prokopy
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Fruit Notes |
At harvest, the most severe damage on peach fruit is caused by true bugs (primarily insects in the group Pentatomidae, stink bugs) and Japanese beetles. Fruit may show scarring or fresh feeding wounds accompanied by a gummy ooze. Often this injury is severe enough that damaged fruit must be culled or, at the very least, downgraded to processing quality. With the greatest profitability gained from fresh-quality peaches, growers need and want to keep insect-damaged fruit at the lowest level that is economically and environmentally feasible. There are three species of stink bugs that are known to attack peaches and cause cat-facing injury: the brown stink bug (Euschistus servus), the dusky stink bug (E. tristigmus), and the green stink bug (Acrosternum hilare). These insects are all highly mobile, and usually remain in the orchard for only a short period of time. Stink bugs reproduce on the trees, laying eggs on the lower surface of peach leaves. These eggs are easily identified; they are barrel-shaped, shiny, and appear in clusters of about seven eggs each. After the eggs hatch, the young nymphs move into the orchard groundcover. Nymphs do little feeding on peaches. Primary damage is the result of adult feeding. Numbers of brown and dusky stinkbugs are greatest within a month of shuck fall. Green stink bug numbers tend to increase throughout the growing season. The most severe damage to peach fruit occurs between petal fall and the time when fruits are 0.5-0.75 inch in diameter. If fruit that is damaged during this time period fails to abscise, at maturity, it is heavily scarred or malformed (injury commonly referred to as "catfacing"). As the fruits enlarge, damage by stinkbugs is less dramatic. Injury results in holes with gummy exudate or dry, corky areas just below the fruit surface. The Japanese beetle (Popillia japonica) is a serious pest of ornamentals, grapes, and plants in the family Roseaceae. Adult beetles chew on leaves and fruit. Leaf damage ranges from minor tissue loss to complete skeletonization. Fruit damage is restricted to the fruit surface (surface damage), but can be extensive and contaminated with beetle frass. Damage caused by Japanese beetles often attracts other insects or disease organisms. Because Japanese beetles tend to congregate, damage can occur very quickly and become quite severe in a short period of time. The objective of this study was to determine the incidence of damaged caused by these pests under reduced-pesticide regimes. Brown rot incidence from the same study was reported [Fruit Notes 62(4)]. Materials & Methods Until pit hardening in early June, all treatment plots received standard calendar-based pesticide applications every 7 to 10 days. After pit hardening occurred, four different treatment protocols were employed. These treatments are outlined in Table 1. Refer to Fruit Notes 62(4) for additional information on experimental design. Results & Discussion For Redhaven peaches (Table 2), the incidence of stink bug damage was twice that of Glohaven (Table 3), while the incidence of Japanese beetle damage was substantially less than that on Glohaven. These differences most likely reflect the timing of activity of each of these two insect pests relative to the timing of fruit development of the two cultivars and the last insecticide spray. The four treatment regimes resulted in similar levels of stink bug damage on Redhaven and Glohaven fruit(Tables 2 and 3). Because these were 3-tree plots, with different treatments applied to adjacent trees, it is possible that spray drift could account for at least some of the lack of effect. Timing of insecticide applications could have affected results as well. Redhaven fruit under the reduced-spray regime had the greatest amount of Japanese beetle feeding, and those under the other treatments were similar (Table 2). Likewise, Glohaven fruit under the reduced-spray treatment had the most damage, but for Glohaven, the no-spray treatment had significantly less damage (Table 3). It is unclear why these results occurred. It is likely, however, that real differences did not occur in this experiment. High mean values were likely the result of very localized infestations of Japanese beetles. Clearly this experiment should be repeated, perhaps with closer attention paid to timing of insecticides. Weekly scouting of plots would help to determine more accurately when each insect pest is present, and whether timing of insecticide applications coincides with the timing required for fungicide applications. Closer attention to pest status would also help to explain how these pests enter and move within the orchard. It is obvious from this data, however, that both stink bugs and Japanese beetles can have a substantial effect on fruit quality at harvest. Better timing of insecticide treatments and alternative pesticides or methods of control could impact results in another year. |
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