IOBC wprs Bulletin Vol 22(9), 1999
Control of Cydia pomonella in walnuts by mating disruption
Gino Angeli, Franco Rama,1 Diego Forti, Laura Dalla Montà,2 Simone Bellinazzo2
Istituto Agrario San Michele all'Adige, San Michele, ItalyAbstract: Experimental trials have been carried out over two years to evaluate the efficacy of the mating disruption technique for control of Cydia pomonella L. in walnut orchards, in the Rovigo district (North-East of Italy). Codling moth male populations were monitored within two blocks nearby; traps were hung at two different heights in the tree canopy. A 4.1 ha block was treated with 400 dispensers/ha, using Isagro's dispensers Ecopom® in 1996 and Ecopom Combi® in 1997, while the second block was split into two plots, insecticide-treated and untreated. Catches of male moths were reduced over 85% in the pheromone-treated block each year. Pheromone treatment was also very effective in reducing injury (77.7% in 1996, 88.2% in 1997). Damage was higher in the pheromone-treated block in the first year (4.5%) if compared with the insecticide plot, but in the second year, the best results (2.7%) were obtained with the mating disruption technique. Overwintering populations increased across all blocks from 1996 to 1997.
Key words: sex pheromone, mating disruption, Cydia pomonella, walnut, Euzophera bigella
Introduction
The walnut infestation by codling moth (Cydia pomonella L.) is well known in the whole of Europe, Asia, and the United States (Balachowsky 1966). The economic importance of damages ascribed to this pest depends on several factors, among which the area of production, the walnut cultivar and the climatic conditions appear to be the most important ones.
In North-East of Italy the first generation of codling moth involves the early drop of the fruit, while the second and the possible third generations cause the harvest of damaged fruits and sometimes the presence of the larvae into the nuts. With soft nutshell cultivars or with those provided with a large hole for the stalk, mature codling moth larvae of second and third generation could prepare the exit hole before pupating. In many walnut growing areas of Italy the damage by codling moth is known to reach even 40-60% of the whole production.
Mating disruption gave excellent results on apple for the control of codling moth and it is widely adopted in Northern Italy, mainly in Trentino and South Tyrol (Waldner 1997). The present paper describes and discusses the first application of mating disruption on walnut orchards carried out in Italy, during 1996 and 1997.
Material and methods
Pheromone dispensers for mating disruption
Dispensers distributed by Isagro under the trade name Ecopom®, are made of biodegradable, resin-treated filter paper and their shape makes it possible to easily hang them on the branches, thus avoiding the use of plastic or metal wires. For the mating disruption against C. pomonella, dispensers contain 250 ± 25 mg codlemone, (E,E)-8,10-dodecadien-1-ol (E8,E10-12:OH) (Navarro et al. 1995; Angeli et al. 1997; Rama 1997). Ecopom® Combi dispensers contain in addition 200 ± 20 mg (Z)-11-tetradecenyl acetate (Z11-14Ac), a pheromone component of a number of leafroller moths (Rama et al. 1997; Ioriatti et al. 1997; van Deventer et al. 1997). The amount of pheromone released during the season by the dispensers has been evaluated by gas-chromatographic analysis.
Monitoring traps
Carpotrap traps (Isagro) baited either with 1 mg or 10 mg of E8,E10-12OH were deployed at 4.5 m and at 1.8 m above ground inside the pheromone treated plot and in an adjacent, chemically treated walnut orchard. Trap catches were recorded twice a week from the last ten days of April to the end of September.
Field trials
A walnut orchard of 4.1 ha was treated for two years running with mating disruption dispensers. Ecopom® was used in 1996 while Ecopom Combi® was used in 1997. The only cultivar was Lara and the planting density was 408 plants/ha (6.5x3.5 m). Trees canopies were 5.5 m high and they formed, from June onwards, a single vegetational block. The orchard was well isolated, with a second walnut orchard 200 m east and an apple orchard 400 m south.
Dispensers deployment occurred on May 10 and July 17 in 1996, while in 1997 the first application was done on May 2nd, preceded by a chemical treatment (diflubenzuron) to decrease the pest population; the second application was performed on July 8. The dispensers were applied 4.5-5 m high, with a density of 408 per ha, i.e. 1 disp/tree.
From the beginning of June of each year fruits were visually inspected every week for codling moth damage. 500 fruits were randomly inspected on each side of pheromone-treated, untreated and chemically treated plots and a further 1000 fruits inside each plot. At harvest, 4000 fruits per plot were sampled in order to evaluate the final damage.
Pest population and parasitoids
The overwintering population of codling moth was assessed by means of 80 cardboard traps per plot. These were applied in August and removed and checked in November. From August onwards, the development of newly hatched larvae was observed in order to evaluate till when they are able to penetrate not only the husk but also the nutshell, and consequently damage the kernel.
To assess the extent of parasitism of overwintering larvae in the pheromone-treated block, at the end of the second year of testing, 1265 codling moth larvae were collected by cardboards, kept in rearing and checked in the following spring.
Results
Pheromone traps
Pheromone trap catches in the untreated walnut orchard and in the mating disruption block were recorded from end of April to beginning October (Fig. 1). During this long period of flight, three generations of codling moth emerged, even if the second and especially the third one did so only partially.
Figure 1. Codling moth curve of flight 1996-97.
Trap catches in treated- and untreated-orchard were highest for 1-mg-baited traps placed on tree tops, while the fewest catches were recorded for 10-mg-baited traps placed in the lower part of the tree (see Table 1).
In the mating disruption block, inhibition of 1-mg-baited traps was almost complete in both years; at the beginning of July a slight increase in trap catches indicated the exhaustion of dispensers, but once they were replaced, catches went sharply down. The greatest number of individuals was recorded for the 10-mg-baited traps placed high in the trees, where the threshold value of 7-9 cumulated catches had already been exceeded by the end of June.
Table 1. Pheromone traps mean catches. Influence of trap height and pheromone bait on codling moth captures.
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| Higher (4.5 m) |
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| Middle (1.8 m) |
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Dispenser release
Ecopom® dispensers were periodically collected in the field and analyzed by solvent extraction and gas chromatography (column SPB-5, 10 mt, 0.53 mm i.d., oven program 100° to 280° @ 15°/min, internal standard n-C16:OH), to assess the residual pheromone content. Results indicate a good linearity of pheromone release and a field persistence of about 80 days for both applications (Fig. 2).
Codling moth attack on fruit
In 1996, at the end of June, when the threshold value was reached by the 10-mg-baited traps, the visual control on fruits indicated a damage of 1.4% inside the block and of 2.9% on its borders. This required a chemical treatment, first with dimethoate and then with diflubenzuron, limited to the two outer rows. During the August controls, unexpected penetrations by Euzophera bigella Zeller (Lepidoptera, Pyralidae) were observed besides those of codling moth and the attack increased up to the harvest.
The codling moth damage recorded at harvest in the pheromone treated block was 4.5% in addition to the 1.2% of depreciation due to the browning of the nutshell. In the untreated orchard the final damage was 29%, with 5.1% of depreciation (see Table 2).
Figure 2. Codlemone release in walnut orchard - Rovigo 1996.
In 1997, at the end of June, again when the threshold value was reached by the 10-mg-baited traps, the visual control on fruits indicated a damage of 0.5%, increased to 1% just before the second application of dispensers. Then the attack was held within 1.1-1.8% with the exception of two borders where a chemical treatment on the outer last row was required.
At harvest the final damage by codling moth registered in the mating disruption plot was 2.7%, in addition to the 1.2% depreciation, while in the untreated orchard the damage was 22.9%, with 4.2% depreciation and in a conventionally treated block of 4 ha, which received 5 organophosphates sprays, the damage was 4.6%, with 0.8% depreciation.
Table 2. Codling moth attack on fruit and overwintering population.
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| mating disruption 1996 |
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| control 1996 |
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| mating disruption 1997 |
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| control 1997 |
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| chemical control 1997 |
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| (*) only depreciation of nutshell | ||
Active penetrations in the kernel
The incidence of damage caused by larvae hatched during the second half of the summer decreased with time. On average, 68% of codling moth larvae hatched in the first half of August reached the kernel, but only 46% of those hatched during the second half of month managed to do so.
The kernel was damaged by 40% of larvae hatched between end August and the first days of September, while none of the larvae that hatched later reached the kernel, but only perforated the husk (100%) and many reached the outer nutshell (60%).
Overwintering population
In 1996, the cardboads traps placed in the mating disruption block contained an average of 6.2 larvae/cardboard, while in the untreated orchard there were 12.7 larvae/cardboard (see Table 2). In 1997, 9.5 larvae/cardboard were found in the mating disruption block at the end of the second year, while in the untreated and the chemically treated plots 16.7 and 11.1 larvae/cardboard, respectively, were recorded.
Parasitism level
On the overwintering population the parasitism level was 5.7%, of which 96% was due to terebrant hymenopterans mainly Ascogaster quadridentata Wesm., Trichomma enecator Rossi and Pristomerus vulnerator Pranz.
Discussion
The pheromone dispenser used in the two years of mating disruption trials brought about a significant reduction of damage by codling moth, which was comparable to that of five insecticide sprays.
The walnut orchards where mating disruption was applied, in spite of being located in a territory where they had not been planted before, were severely attacked by the codling moth. Although it was undoubtely necessary to resort to measures of damage reduction, the choice of the defense stategy was also the key to manage other minor pests. Observations over several years had shown that the repeated treatment with organophospates like dimethoate and fenitrothion, till now the only codling moth pesticides allowed on walnut in Italy, led to further chemical sprays mainly against aphids (Callaphis juglandis Goeze, Chromaphis juglandicola Kalt) and mites (Panonychus ulmi Koch), which are usually controlled by natural enemies. During the two years of application of mating disruption no specific chemical treatment was necessary against these pests.
It is important to notice also the control operated by mating disruption on the population of Euzophera bigella, which sometimes is more dangerous of codling moth itself. During the first season of trials, an unexpected attack by this pyralid, at the beginning of August with symptoms very similar to those of the codling moth, made it very difficult to clearly evaluate the damage attributable to each species. In the following season, close inpections of fruits with fresh penetrations confirmed the difficulty to identify in the field the pest responsible for the damage. Anyway, the use of Ecopom Combi® dispensers containing also Z11-14:Ac to control leafrollers, reduced the level of attack by E. bigella by more than 90%. Further studies are required to establish if this achievement is really due to Z11-14:Ac or if it is a secondary effect of the pheromone cloud present in the orchard.
In both years of mating disruption trials, pheromone traps either baited with 1 mg and especially those baited with 10 mg of codlemone were not completely inhibited. Catches occurred mainly when the critical level of damage, observed by visual controls, has been reached. The curative chemical treatments, however, were necessary only on the outer two rows during both seasons.
The damage recorded in the mating disruption plot was slightly higher than in blocks treated 4-5 times with pesticides, while during the second year the best results were obtained in the pheromone- -treated orchard. Mating disruption on high trees like walnuts seems to be more effective than chemical control, especially in the upper part of the tree, already beginning from the second year of application, as already observed on apple orchards (Ioriatti et al. 1997).
The reduction of overwintering larvae with respect to both the chemically treated and the untreated control plot, confirms the efficacy of mating disruption on codling moth population density; the high number of larvae caught by cardboards is to be ascribed to the smooth bark of walnut trees and consequently to the poor availability of natural shelters. The increase of the overwintering population observed in all plots in 1997 is likely to be associated with the general increase of codling moth population in the whole area.
References
Angeli, G., Antonaroli, R., Nanni, C. & Rama F. 1997: Prime esperienze di contenimento delle due tortrici del castagno C. fagiglandana e C. Splendana con la tecnica della confusione sessuale. Informatore fitopatologico 1: 65-70.
Balachowsky, A.S. 1966: Entomologie appliquèe a l'agriculture, Tome II Lepidoptères: 697-704.
Ioriatti, C., Forti, D., Rizzi, C., Pontalti, M. & Dallago, G. 1997: La confusione sessuale su melo per il controllo di carpocapsa e ricamatori. L'Informatore Agrario 30: 69-74.
Navarro, E., Aymard, J. & Navarro, A. 1995: La confusion sexuelle. Expèrimentation d'une nouvelle technique de lutte contre le Carpocapse des pommes et des poires. Phytoma 478: 60-63.
Rama, F. 1997: Ecopom dispensers for mating disruption in apple orchards. In: Technology Transfer in Mating Disruption, IOBC/WPRS Bulletin Vol. 20(1): 65-72.
Rama, F., Ioriatti, C. & Rizzi, C. 1997: Sette anni di esperienze con la confusione sessuale nel contenimento di carpocapsa e ricamatori del melo. Informatore fitopatologico 4: 36-41.
van Deventer, P., Minks, A.K. & Rama, F. 1997: Experiments of simultaneous control of codling moth and apple leafrollers by mating disruption. Proc. Meeting "Mating Disruption of Leafrollers in Fruit Orchards", S. Michele a/Adige (Italy), 3-4 Sept. 1996. In: La difesa delle Piante, Vol. 20(1-2): 63-67.
Waldner, W. 1997: Three years of large-scale control of codling moth by mating disruption in the South Tyrol, Italy. In: Technology Transfer in Mating Disruption, IOBC/WPRS Bulletin Vol. 20(1): 35-44.