Three years of large-scale control of codling moth by mating disruption in the South Tyrol, Italy

Walther Waldner

• Introduction
• Mating disruption is now used on a quarter of the South Tyrolean orchard area
• Planning a mating disruption project is like fitting together a jigsaw puzzle
• Barriers
• Number of dispensers per ha and their placement
• Monitoring tools, orchard checks and action thresholds
• Results 1988-1996
• Is mating disruption feasible in small orchards?
• Mating disruption on slopes
• Taller trees - more damage
• Effectiveness of the various dispenser types for codling moth
• Final considerations

Abstract - In 1990 it became apparent that populations of codling moth, Cydia pomonella, were increasing in orchards treated with diflubenzuron. In 1992 it was shown that some codling moth strains had developed a strong resistance to chitin synthesis inhibitors (CSI); the resistance appeared after about 25 CSI applications. After having thus lost an important component of our pesticide list, there was the danger that we would not be able to maintain an integrated pest management programme that would come up to international standards. Therefore we introduced the mating disruption method on a large scale. In 1991 we started with RAK 3+4 dispensers on 110 ha. As in 1992 RAK 3+4 were not available, we made a new start with Isomate-C dispensers on 232 ha in 1993. In the following year, the area under mating disruption expanded to 2 500 ha and reached 4 500 ha in 1995, in 1996 the treated area is 3 500 ha. The paper contains the results obtained with different dispenser types (Isomate-C, Isomate-C-Plus, Isomate-C-Special, RAK 3+4, Ecopom Combi) against codling moth and leafrollers. Mating disruption was successful even in hillside orchards and smaller plots. Finally, organizational problems connected with the planning of mating disruption projects are discussed.

Key words - sex pheromone, mating disruption, monitoring, insecticide resistance, integrated pest management, pome fruit orchard, codling moth, Cydia pomonella

Introduction
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In 1977 the chitin synthesis inhibitor (CSI), Dimilin, was registered in Italy. Until about 1982 this pesticide had been used exclusively for leaf miners in the South Tyrolean apple growing area. Since 1983 my organization increasingly recommended it for codling moth, Cydia pomonella L. At the end of the 1980s some further chitin synthesis inhibitors (teflubenzuron, triflumuron, hexaflumuron) were registered in Italy.

Up to 1990, one treatment with 75 to 100 g active ingredient/ha against each codling moth generation was sufficient. In 1990 for the first time, more treatments or higher doses were no longer efficacious in a few locations. In 1991, 10 to 40% fruit injury at harvest in spite of 3 to 5 sprays with CSIs was not unusual in these areas.

In 1992 H. Riedl (Oregon) and R. Zelger (Laimburg) proved that some codling moth strains had developed a strong resistance to diflubenzuron. Further tests by R. Zelger showed that those strains were also resistant to all other CSIs. The resistance appeared after approx. 25 CSI applications and seems to be very stable. The descendants of resistant codling moths could not be controlled by CSIs, either.

At the end of 1992 we estimated that this phenomenon appeared on 1 200 ha of our 18 000-ha apple growing area. According to our observations, these "red zones" with CSI-resistant codling moth populations have increased to 15 000 ha in the meantime.

From 1993 onwards we were forced to warn against the use of CSIs on larger and larger areas. In the so-called "red zones" the growers would have been forced to use again only organophosphates, mainly Azinphos. Their undesirable side-effects on beneficials (e.g. typhs, stethorus, lacewings, parasitic wasps) are already well-known. After we had stopped recommending this pesticide and others which are very noxious to typhs in 1983, we could do without acaricides in approx. 70% of the South Tyrolean orchards. Phosalone (Zolone), which worked quite well against codling moth north of the Alps, failed under our conditions. Fenitrothion (Fenitrocap) and quinalphos (Ekalux), which are about as effective as azinphos (Gusathion) but less acutely toxic, are throwbacks in comparison with CSIs. Therefore the Advisory Service tried to introduce mating disruption on a large scale in the South Tyrol.

Mating disruption is now used on a quarter of the South Tyrolean orchard area
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Since preliminary trials with the dual dispenser RAK 3+4 since 1988 showed promising results, we continued to test this product in 29 orchards on a total area of about 100 ha in 1991. Unfortunately, we could not carry on in 1992, because BASF decided to change the contents of the dispensers significantly.

We asked Pacific Biocontrol to supply Isomate-C dispensers for a new series of tests. Based on the reports by G.J.R. Judd and M.G.T. Gardiner (Canada), as well as A. Knight (USA), we started a pilot project with 85 fruit growers in six different locations in 1993. The total area consisted of 232 ha. Per ha we recommended 1 000 dispensers at 112 mg (E,E)-8,10-dodecadienol (codlemone) each.

In 1994 our growers used Isomate-C-dispensers on 2 250 ha. Shin-Etsu delivered two dispenser types: Isomate-C (white) which were formulated with 112 mg codlemone and Isomate-C (brown) which contained 126 mg codlemone. RAK 3+4, which contained approximately 165 mg codlemone and 270 mg leafroller pheromone blend, were used on 200 ha. There were also two projects with other dual dispenser types: Isomate-C Special on 15 ha and Ecopom Combi on 9 ha.

In 1994 mating disruption was used in 1 600 South Tyrolean orchards on 2 500 ha altogether. We counted 131 projects. The smallest area covered by mating disruption was 0.4 ha, the largest 135 ha.

In 1995 the total area with mating disruption expanded to 4 500 ha. This corresponds to a quarter of the whole South Tyrolean apple growing area. No other fruit growing area in the world had such a high share of mating disruption orchards. 3 500 ha were furnished with Isomate-C types, 1 000 ha with RAK 3+4 and 20 ha with Ecopom Combi. Dual dispensers were used on 2 500 ha out of the total area of 4 500 ha.

In 1996 the area with mating disruption has decreased to 3 500 ha. There are two reasons: On the one hand we tried to get the growers to organize the projects themselves, on the other hand the growers ordered fewer dual dispensers. This year the South Tyrolean orchardists are using Isomate-C-Plus on 2 700 ha, RAK 3 on 400 ha, RAK 3+4 on 200 ha, Isomate-C-Special on 165 ha and Ecopom Combi on 10 ha (Figure 1). In absolute numbers, only the USA used mating disruption on a larger orchard surface in 1996.

Planning a mating disruption project is like fitting together a jigsaw puzzle
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A typical South Tyrolean fruit farm is about 4 ha in size. The single orchards, however, are situated at different sites. It is already common knowledge that mating disruption works better in larger applications. We advise our members to assemble projects of at least 10 ha. This requires the team-work of 10 to 20 growers. As a rule, one or a couple of growers consent to ask the owners of the neighbouring orchards if they are willing to participate in a mating disruption project. We have calculated that it takes about an hour of organizational work (map drawing and completing the order forms) per ha of mating disruption.

In some districts the packing houses have charged one of their employees with the assemblage of suitably large areas for mating disruption.

Barriers
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Until 1994 we recommended so-called "exterior" barriers. Dispensers were applied as far as 20 m deep in the orchards adjoining a project. Although this was very useful we had to stop doing it for two reasons: we required about 25% more dispensers on an average, which increased the costs; some "clever" growers, whose orchards were sometimes not wider than 20 m, did not participate in a project because they profited from it all the same.

Since 1995 we have been working with "interior" barriers only. If tree height exceeds 4 m, twice as much dispensers are placed on the perimeter trees than inside the orchard. If the trees have a small canopy we double the number of dispensers in the two border rows.

This constitutes an additional expenditure for dispensers and other costs of about 10% for projects over 10 ha, and of up to 30% for smaller projects. For new plantings situated within a project we recommend applying half the usual number of dispensers/ha or interior barriers.

Number of dispensers per ha and their placement
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With Shin-Etsu ropes we recommend in the first couple of years 1 000 dispenser/ha, without regard to tree height, size of the project and exposition. For projects over 10 ha in lower locations where mating disruption was applied in the two previous years and where the damage at harvest was below 1% without supplemental treatments we recommend in the third year only 800 dispensers/ha if tree height is below 4 m.

With RAK we recommend 750 pieces/ha for trees with big canopies, and 500/ha for trees with small canopies. Ecopom and Checkmate-CM have to be applied twice during the vegetative period. Both types are used here only on an experimental basis. No grower in our area would use a dispenser which requires two applications a season as long as there is an alternative. With large trees the application takes up to 15 hr/ha, on ground level we calculate about 4 hr/ha for smaller trees.

Where should the dispensers be placed? We recommend attaching the dispensers 0.5 to 1 m below the tree trop. This seems very important to us because we have had several cases where mating disruption failed because the dispensers were positioned too low.

Monitoring tools, orchard checks and action thresholds
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L. Gut and J. Brunner (Washington) found a relation between trap catches in high-load lures and harvest damage in mating disruption orchards in their region. Under the climatic conditions in Washington each moth caught after an initial period of two weeks corresponds to an average harvest damage of 0.1%. Based on these findings we recommend at least one pheromone trap with a 10-mg lure per ha orchard area. The trap should be hung in the upper third of the canopy and the lure should be changed every 40 days. The traps are to be checked once a week.

According to our experiences a cumulative trap catch of more than eight moths is a signal that special attention is required. In this case, fruit checks are necessary after 10 to 14 days. Certainly, this monitoring method is not absolutely reliable but it helps to reduce the number of fruit checks or to determine the most convenient dates for fruit sampling.

In the preceding years we invited the growers to at least four fruit checks together with our consultants. During those checks at least 1 000 fruits/orchard were controlled for fresh entry holes. We recommend the following action thresholds in mating disruption orchards: 0.3% fruits with fresh entry holes (June); 0.5% fresh entry holes (July to mid-August); 0.8% fresh entries (from mid-August on); 1.0% wormy fruits (at harvest).

If harvest damage exceeded 1% in the previous year or is unknown as well as in small projects we recommend a supplemental treatment in any case, as soon as according to the degree day model 30% of the larvae of the first generation have emerged or when the first entry holes are detected.

Results 1988-1996
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The positive experiences with mating disruption in two orchards in the South Tyrol from 1988-1990 aroused the interest of the South Tyrolean orchardists in this method. In 1991, 40 fruitgrowers participated in 29 different projects with a total area of about 100 ha. On 93 ha there was less than 2% fruit injury at harvest without an additional pesticide application against codling moth. On 7 ha, that is about 7%, the fruit growers had decided to use an insecticide. On 5 ha there was a surprisingly high damage at harvest. We used 500 to 800 RAK 3+4 dispensers/ha loaded with at least 420 mg codlemone and 420 mg leafroller pheromone blend. From the beginning of May to the end of October about 100 g/ha of both pheromones evaporated. More than half remained in the dispensers.

BASF did not sell this dispenser any more in 1992. In 1993 we made a new start with Isomate-C dispensers. Table 1 gives an overview of the results obtained up to now.

In 1994 the data collected in 913 disrupted orchards at harvest showed an average codling moth damage of 0.4%. In comparison with conventional orchards, the number of insecticide sprays decreased by two thirds, the average number of additional treatments was 1.4. In 1995 the average number of supplemental treatments could be reduced to 0.6. The average percentage of codling moth damage was slightly higher in 1995 with all types of dispensers. In my opinion this was mainly due to the following two reasons: In 1995 we did not recommend exterior barriers; the share of orchards with not so favourable conditions for mating disruption was higher than in 1994.

Naturally, we have not yet obtained all the data about harvest damage in 1996. However, the first data we have collected so far indicate that harvest damage will be lower than in 1995 (Figure 2). In the Leifers area we have recorded codling moth damage in 20 mating disruption orchards over the period from 1992-1996. The results show that there is considerably less fruit injury after four years of mating disruption (Table 1).

Is mating disruption feasible in small orchards?
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I would like to adduce as an example a small 0.5-ha orchard with partly 4 to 5 m high trees in the centre of Lana, where there are very favourable conditions for codling moth. The orchard is bordered by a barn, two houses, a street, a tall nut tree and another orchard.

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Damage at harvest during four years is shown in Figure 3. In 1993, four treatments with phosalone (Zolone) and one with Azinphos resulted in a harvest damage of 25 to 30%. Mating disruption was employed for the first time in 1994; 1 000 Isomate-C dispensers on 0.5 ha were supplemented with two applications of Azinphos, damage at harvest was 5%. In 1995, Isomate-C Plus were used; a consultant of the Advisory Service checked the orchards weekly for fresh entry holes. The first ones were found on July 7th, and a week later 0.5% of the fruits were already damaged. On July 17th Fenitrocap at 250 ml/hl was applied. The damage at harvest was 1%. In 1996, the orchard, which was again furnished with Isomate-C dispensers, was checked once a week. After the first stings had been detected at the end of July, Fenitrocap was applied. The damage at harvest is 0.1% this year (Figure 3).

The example shows that it is very well possible to use mating disruption on small plots. It is not only of ecological importance, but it can also be economical. In this case, three organophosphate sprays were saved in 1993, and in the last couple of years even four such treatments. Nevertheless, with small plots, the grower has to be prepared to check the fruits regularly at short intervals and to allow for one or two supplemental treatments.

Mating disruption on slopes
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The harvest damage in orchards situated on hillsides and in plains was 0.7% and 0.4%, respectively, in 1994; and 1.0% and 0.6% in 1995. The number of additional insecticide sprays in orchards situated on slopes and in plains was 1.5 and 1.4, respectively, in 1994.

In hilly country it is more difficult to compose larger areas with homogeneous and favourable conditions for mating disruption projects. Therefore we suppose that the slightly higher injury level on slopes is mainly due to the small size of the plots.

Taller trees - more damage
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The average percentage of fruit injury was considerably higher on trees taller than 4 m (0.8%) than on smaller trees (0.5%), as we found out through checks in 411 orchards on seedling and 429 orchards on dwarfing rootstocks in 1995.

Effectiveness of the various dispenser types for codling moth
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In Table 2 the results obtained with Isomate-C-Plus and Isomate-C-Special as well as RAK 3+4 dispensers in 1995 are summarized.

Economic aspects
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In Table 3, I have listed the costs of the various types of dispensers per ha. At present Isomate-C-Plus has the best cost/effectiveness ratio. One application of 800 dispensers/ha has the same price as three treatments with Fenitrocap (a micro-encapsulated fenitrothion). Organophosphates are noxious to typhs, among others. If mating disruption helps to do without acaricides the dispensers have already paid their way, because one acaricide application costs more than half of the dispensers/ha.

Final considerations
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By now we have gathered enough facts to be able to assess the possibilities and limits of mating disruption sufficiently so as to recommend it under certain conditions as a standard measure in the future.

(1) Mating disruption will be recommended for orchards where otherwise three or more organophosphate sprays against codling moth would be needed; (2) the mating disruption area should not be smaller than 10 ha, if possible; (3) with a view to cost reduction we will continue to recommend only interior borders, that means that the number of dispensers should be doubled in perimeter tree rows; (4) mating disruption orchards have to be furnished with monitoring traps baited with 10 mg codlemone; (5) the growers will be asked to check their orchards as soon as fresh entries are found in special orchards which will be monitored by us; (6) if there are some catches in the 10-mg traps, we will recommend fruit checks after 8-10 days; (7) in orchards with a harvest damage of more than 1% in the previous year: we recommend an additional treatment in border rows, transitionary areas from small to high trees, as well as near stacks of wood, nut trees and buildings; (8) in areas with less than 1% fruit damage at harvest, after using mating disruption for two years, we will suggest 800 Shin-Etsu ropes instead of 1 000/ha.

By now the majority of the South Tyrolean fruit growing experts and fruit growers is convinced of the ecological advantages of the mating disruption technique for codling moth.

Whether the mating disruption area will further expand in the following years will largely depend also on the costs of the dispensers. The growers will base their decisions mainly on the comparison of the costs of the dispensers per ha including one eventual supplemental treatment with the expenses for three to five organophosphate sprays.

Acknowledgements
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We are indebted to many researchers who helped us to avoid mistakes when introducing this new technique. The research work by Pierre Charmillot and Heinrich Arn, Switzerland, Albert Minks, Netherlands, Gary Judd, Canada, as well as Jay Brunner, Larry Gut and Alan Knight from the USA and many others have laid the foundations for a good start. Finally I am sincerely grateful to all my collaborators who contributed by supplying data.

References

Gut LJ, Brunner JF (1996) Implementing codling moth mating disruption in Washington pome fruit orchards. Tree fruit research and extension center Information Series 1

Judd GJR, Gardiner MGT (1991) Large scale commercial trials of pheromone-mediated mating disruption for control of codling moth in British Columbia apple and pear orchards. Research Station Summerland, B.C., VOH 12O

Knight AL (1992) Mating disruption of codling moth and leafrollers, pp. 98-100 in Arn H, Ioriatti C (eds.) Use of pheromones and other semiochemicals in integrated control. IOBC/WPRS Bulletin 15(5)

Österreicher J (1996) Flugüberwachung des Apfelwicklers in Anlagen mit Verwirrung. Obstbau Weinbau 33, 104

Riedl H, Zelger R (1994) Erste Ergebnisse der Untersuchungen zur Resistenz des Apfelwicklers gegenüber Diflubenzuron. Obstbau Weinbau 31, 107-109

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