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| Figure 1. Historic coding moth catches in nine central ohio apple orchards. |
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Ted W. Gastier
Since the early 1700s, when Ohio's first apple trees were planted by French traders in the Maumee Valley, the apple industry in this state has flourished. In recent years, the Ohio apple crop has generated more than $25 million annually for Ohio farm families. However, the acreage devoted to apple production has declined since a time when almost every farm included an orchard.
To understand the reduction in apple acreage and the virtual disappearance of the apple from large areas of rural Ohio, one can look at the ravages of diseases and insects. According to Cutright (2), it is necessary to consider that "codling moth history is an integral part of the history of apple growing in the state." Among insect pests, he concluded "none have been more damaging than the codling moth. The increasing seriousness of codling moth attacks from 1870 to 1920 is shown as paralleling the decline of the farm orchard." Losses to the apple crop during this period of time were documented by annual reports of 13 horticultural societies.
Codling moth larvae are responsible for fruit injury commonly known as "wormy apple." Very little damage is tolerable, as consumers will reject apples infested with second generation larvae (worms). According to Wilson et al. (7), control of codling moth is estimated to cost from $25 to $100 per acre, based on 1977 calculations. In research work by F. R. Hall in 1974 and cited by Wilson et al., the dollar loss due to codling moth (without control measures) can be considerable. Based on 1993 dollars, a loss of $950 per acre might be expected on 'Golden Delicious,' $613 per acre on 'Jonathan,' and $350 per acre on 'Delicious,' if no control measures are attempted.
In addition to direct costs for control or potential loss without control, present-day spray schedules can exact a deadly cost on beneficial insects, including both predators and parasites of codling moth. The repeated use of insecticides to control codling moth can also lead to increased pressures from European red mite, as the spray applications can have a deleterious effect on populations of natural enemies of the mite.
Research in Ohio (2) from 1937 through 1963 indicated that "when considered either alone or in combination with the other climatic elements, temperature is the most important factor that influences codling moth behavior." Depending on temperature, Cutright showed that the emergence of the spring generation occurred during a period as short as 14 days and as long as 56 days. The summer brood emerged during a period of 32 to 75 days. A standard spray schedule based only on calendar date does not account for these wide variations in the presence of the codling moth adult.
During the 1991 through 1997 growing seasons, some 25 commercial apple blocks located in north central Ohio have been enrolled in an Integrated Pest Management (IPM) program. Supported by grower participation fees and various grant monies, the program included weekly orchard monitoring by paid scout/technicians and the trapping of codling moth (Cydia pomonella) adults. Sticky wing traps with pheromone lures (Pherocon® 1CP traps from Trece, Inc., and Scentry lures) were used to monitor adult males. Trap bottoms were replaced weekly during periods of moderate to high populations (more than three moths per trap per week) and bi-weekly during periods of light populations. Lures were replaced every four weeks.
One trap per block (approximately 10 acres) was used during the 1991 and 1992 seasons. Because of wide variations in trap catches within neighborhoods (from three to 14, for example), it was decided in 1993 to use three traps in each block, a practice that has been continued through the 1997 season. Because of the importance of keeping codling moth damage to a minimum, the determination of adult male populations has required a high degree of accuracy with the use of three traps rather than a single trap.
The pheromone traps have been used to establish moth emergence for the purpose of initiating degree-day accumulations (biofix), to confirm degree-day predictions, and to determine the adult population's relative size. This project has utilized a threshold of three adults per trap per week as the threshold to determine the need for control measures. A threshold of three is considered to be a moderate population level (5). Harvest surveys of fruit from each block have validated this threshold as adequate for protecting fruit quality. The Codling Moth Management Model (3) suggested a threshold of two to three adult males per week per trap. Further explanation of establishing the biofix for codling moth can be found in Rajotte et al. (6) and Brunner et al. (1).
Scouting reports, including records of trap catches for codling moth and other apple pests, are shared with participating growers through a weekly in-season newsletter. In addition, records are maintained and analyzed at the Ohio State University Extension office in Huron County, using Quattro Pro as a spreadsheet.
The reliability of trap catches is important in an IPM program for two reasons. A successful IPM program bases spray decisions on orchard conditions, rather than calendar schedules. Spray applications can be avoided when populations are below threshold levels; an erroneous trap catch count that missed on the low side could leave the apple fruit unprotected. The author's method of measuring reliability was to compare each of the weekly three trap counts in each production block with the average of the three. The catch count was considered to be out of tolerance if one or two values were not indicative of the relationship of the three-trap average to the threshold value of three.
Statistical analysis was done on those records considered (visually) out of tolerance during weeks when the overall average exceeded a count of three. The "Descriptive Statistics" tool within the "Analysis Tools Speedbar" of Quattro Pro v.5 was used to measure the confidence level for the values of the three trap catches. Confidence level establishes the trust that can be placed on a range of values being representative of the actual populations of adults. This is important because of potential fruit damage and loss from codling moth (as well as the environmental and economic cost of over spray).
The 1991 and 1992 growing seasons' records dealing with single trap/block records were considered only for determining a background of expected populations of codling moth (Figure 1). As was indicated earlier, the wide variation in populations within neighborhoods encouraged the use of multiple traps since 1993. Whether the decrease in weekly-average trap catches since instituting the three-trap regimen can be attributed to that change has only been suggested and not considered by this report. However, Table 1 does indicate the effects of averaging on the range of trap catches.
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| Figure 1. Historic coding moth catches in nine central ohio apple orchards. |
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Block No. 1 was considered to be out of tolerance because the value "five" is greater than the threshold of three and the average was under three (Table 2). Block No. 2 was within tolerance as all values and the average were above threshold. Block No. 3 was outside of tolerance due to the "two." Block No. 4 was also outside of tolerance because of the "eight." Block No. 5 was within tolerance, as all values were below threshold. Figure 2 indicates that, over an entire season, most or all blocks are outside of tolerance by our determination. On a weekly basis, those within tolerance in 1993 were 67%; in 1994, 62%; in 1995, 73%; in 1996, 63%; and 82% in 1997. During weeks when the average across all blocks exceeded the threshold, fewer blocks were within tolerance – in 1993, 56%; 1994, 44%; 1995, 64%; and 1996, 47%. The average across all blocks never reached the threshold values in 1997.
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| Figure 2. Blocks within and outside of tolerance observed during codling moth monitoring in north central Ohio. |
Yearly average confidence levels were calculated for those blocks out of tolerance as determined by visual inspection. Those values were 3.4148 in 1993, 3.2037 in 1994, 3.7056 for 1995, and 2.8764 for 1996. (No confidence levels were calculated for 1997 as weekly average catches never exceeded three across all 26 blocks.) As the confidence level, expressed as a positive number, increased above one, the reliability decreased.
Analysis of the trap catch numbers that were out of tolerance indicated that 41% were high readings and 59% were low readings. This can be interpreted by saying that three out of five times, when a single trap count was out of tolerance by being three or less when the average was greater than three, fruit would have been unprotected.
The additional cost of traps, lures, and scout time is estimated to be $33 per block. Based on Ohio Agricultural Statistics (4), this cost would be covered by 1% of the average per acre Ohio apple production.
The author wishes to acknowledge the cooperation and financial support of 21 farm families involved in this ongoing IPM program. The professional conduct of scout/technicians Gene Horner and Jim Mutchler also deserves public recognition for their dedication of service to the growers. A special thanks goes to Cathy Weilnau for her professional secretarial skills and to Celeste Welty for her guidance toward the constant improvement of the author's research skills.