Efficacy of Cydia Pomonella granulosis virus (cpgv) in controlling codling moth in the Emilia-Romagna region
Vergnani, S.1,Caruso, S2, Boselli, M.3, Pasqualini, E.4,
Key words: Apple orchard, Pear orchard, Cydia pomonella, Granulosis virus, Efficacy
During the period 1999 to 2007, numerous field trials were carried out in the Emilia Romagna region in order to test the efficacy of Cydia pomonella Granulosis Virus-based (CpGV) products in controlling codling moth, Cydia pomonella (L.). The trial results demonstrate that CpGV-based products can be considered among the best larvicides currently available on the market. Good results were achieved against I generation larvae, while applications against successive generations did not always provide satisfactory control.
The introduction of Cydia pomonella Granulosis Virus-based (CpGV) products in the Emilia Romagna region, often complemented by the method of mating disruption, has favoured the development of organic apple (Malus communis) and pear (Pyrus communis) orchards, even in areas with high codling moth, Cydia pomonella L. (henceforth CM), pressure, and has suppressed CM damage to fruit. CM control is becoming increasingly challenging not only in organic farming, but also in integrated and conventional production due to ecotoxicological, residue, and resistance issues (Riedl and Zelger, 1994; Sauphanor et al., 1998; Ioriatti et al., 2000). CpGV-based products could be valuable tools to be included in resistance management strategies, could help to avoid the presence of undesired residues in the final production, and to meet the requirements of the most stringent production regulations.
Materials and methods
During the study period (1999-2007), the efficacy of different CpGV-based products in comparison to chemical reference insecticides and an untreated control was tested in a total of 14 trials conducted in both organic and integrated pear orchards. Ten trials (henceforth Trial Group 1) aimed at evaluating the efficacy of a CpGV-based product (formulated product: Carpovirusine; applied rate: 100 ml/100 l; no. applications: 3 at 7-10-day time intervals) in comparison to that of chemical insecticides and an untreated control. Out of these 10 trials, 7 were targeted against I generation CM larvae, while other 3 trials were directed against II generation CM larvae. Four additional trials (henceforth Trial Group 2), instead, aimed at comparing the efficacy of different CpGV-based products (tested products: Madex, Virgo/Carpostop, Carpovirusine), and an untreated control against I generation CM larvae.
In each trial, a randomised block design with four replicates per treatment, and with a mean number of 5 trees per plot was used. Since we decided to assess fruit damage on 100 fruits per plot (see below), the number of trees per plot differed among trials according to the number of fruitlets present on the trees. In all trials, treatments were applied according to label instructions with a motorised barrow sprayer (spray volume: 1200-1500 l/ha, depending on vegetative growth and tree height). Indications provided by climate/insect development models (MRV- codling moth) of the Emilia-Romagna region and by CM monitoring traps (threshold: 2 adults per trap per week) were used to choose the correct timing of the applications. In each trial, fruit damage was assessed by counting the number of fruits damaged by CM larvae (fruits with deep entries) on 100 randomly selected fruits per plot at the end of the CM target generation, and percent fruit damage was calculated.
In several trials of Trial Group 1, the CpGV-based product was compared to more than one chemical reference insecticide. In order to provide a clear and concise description of the results concerning CpGV efficacy, for each trial, we decided to report observed percent fruit damage values only for the CpGV-based treatment, the chemical reference treatment that showed highest efficacy (see Table 1 for details), and the untreated control, and to omit the results obtained with the other chemical treatments tested within the same trial that showed intermediate efficacy.
In the 7 trials of Trial Group 1 carried out against I generation CM larvae, percent CM fruit damage in the CpGV-based treatment was always comparable to or lower than that recorded for the chemical reference treatment, and considerably lower than in the untreated control (Figure 1). In the 3 trials of Trial Group 1, conducted against II generation CM larvae, percent CM fruit damage recorded for the CpGV-based treatment was again always lower than in the untreated control, but comparable to that registered for the chemical reference treatment in one trial, and higher in the other two trials (Figure 2). No significant differences among the different CpGV-based products emerged in the trials of Trial Group 2: all products considerably reduced percent fruit damage compared to the untreated control, with efficacy values being comparable among products (Figure 3).
Table 1 – Active substance, applied rate and number of applications of the chemical reference insecticides in the different trials of Trial Group 1.
Figure 1: percentage of fruits damaged by I generation CM larvae in the different treatments and trials.
Figure 2: percentage of fruits damaged by II generation CM larvae in the different treatments and trials.
Figure 3: Percentage of fruits damaged by CM larvae in the different CpGV-based treatments and in the untreated control in four trials.
The results of our trials are evidence of the excellent larvicidal activity of CpGV-based products: irrespective of the formulation tested, CpGV-based products were able to considerably reduce percent CM fruit damage, with efficacy values being comparable to those of the chemical reference insecticides, especially when the treatments were applied against I generation larvae (Boselli et. al., 2001). CpGV-based products can therefore be considered valuable tools for the control of C. pomonella not only in organic farming but also in any other plant protection strategy.
However, there are also some negative aspects related to CpGV-based products: they may show reduced efficacy against II and III generation CM larvae; they have short shelf life at room temperature (CpGV-based products should be stored in the refrigerator or in the freezer; because of the mode of action of CpGV, superficial damage, depreciating the commercial value of fruit especially on apple, is more likely to occur in CpGV-treated orchards than in orchards treated with chemical insecticides. In organic farming, where CM populations are repeatedly exposed to CpGV treatments over years, because at the moment CpGV is the only efficient active substance available for the control of CM, resistance to the microbial control agent may develop. In fact, cases of CM populations resistant to the Mexican isolate, the active ingredient of the CpGV-products currently available on the market, have already been reported in several European countries (Fritsch et. al., 2004). Different new CpGV isolates are now being studied to overcome resistance (Jehle, 2008). In our opinion, the inclusion of additional natural plant protection substances, such as Ryania and Spinosad into Annex II B of Reg. EEC 2092/91, could be useful for the development of efficient resistance management programs also in organic farming.
These studies are part of an experimental programme of the Emilia-Romagna region that involved numerous organisations: the University of Bologna, the Phytosanitary Service of Emilia-Romagna, the Consorzio Fitosanitario of Modena, and CRPV (Crop Production Research Centre). Activity carried out within the project co-ordinated by CRPV (Vegetal Production Research Center) in collaboration with ProBER (Organic Producers of E.R.), and funded by the Emilia-Romagna Region (L.R. 28/98).
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