Integrated pest management in apple orchards in the Netherlands : a solution for selective control of tortricids

Field trials to compose a coherent system of Integrated Pest Management (IPM) for apple orchards in the Netherlands were started in 1967, when the 12 ha apple orchard "De Schuilenburg" at Kesteren became available for experiments on IPM. Natural control of one of the most severe pests under conventional control, the fruit tree red spider mite <em>Panonychus ulmi</em> , is a central part in IPM. Many broad-spectrum pesticides exterminate the predacious mite <em>Typhlodromus pyri</em> , which is responsible for the natural control in IPM in the Netherlands. Only selective agents are applied, therefore, against pests which are not, or only partially, naturally controlled, preserving <em>T. pyri</em> and other useful arthropods.The aim of the present study was to investigate the feasibility of the following selective compounds for leafroller control in IPM in apple orchards: (a) a bacterial agent, <em>Bacillus thuringiensis</em> (Dipel), (b) a chitine synthesis inhibitor, diflubenzuron (Dimilin) and (c) insect growth regulators (IGR) with juvenile-hormone activity, epofenonane and fenoxycarb.Initial studies were carried out at the experimental orchard "De Schuilenburg", in 0.5-1.0 ha plots, for five consecutive years. The degree of leafroller fruit damage in untreated plots ranged from 5 to 13%; this damage was caused by a complex of leafroller species. <em>Adoxophyes orana</em> was most abundant in the summer, whereas <em>Spilonota ocellana</em> , <em>Pandemis heparana</em> and <em>Hedya nubiferana were</em> dominant in the spring. Under Dipel regimes, both the total leafroller population and the leafroller fruit injury were halved. Dipel was relatively ineffective against <em>P.</em><em>heparana, H. nubiferana</em> and, in particular, <em>S. ocellana</em> . Dimilin also halved leafroller fruit injury. This compound was very effective against S. <em>ocellana</em> , <em>H. nubiferana</em> and <em>Archips podana</em> . Dimilin, however, did not affect <em>A. orana</em> and the population of <em>P. heparana</em> was only reduced to about one-third of the blanco value. Leafroller control with epofenonane, which was applied twice in the spring, was not succesful. This may be due to reinfestation from the untreated plots, which lay adjacent to the treated plots in our experimental set- up. Dipel, Dimilin and epofenonane did not appear to affect the level of parasitism of <em>A. orana</em> by <em>Colpoclypeus florus</em> . However, in this respect the standard plots, treated with broad-spectrum insecticides, gave similar results, so no firm conclusion can be drawn.A second series of experiments concerned the effect of fenoxycarb and epofenonane. Apple trees were either artificially infested with A. orana and P. heparana or harboured several naturally occurring leafroller species. The caterpillars were restricted in gauze-bags on leaf-clusters after the apple trees had been sprayed once or twice, and the morphogenetic effect was observed. Fenoxycarb was effective at a concentration about 10 times lower than that of epofenonane. The foliar residue of fenoxycarb remained active for at least 4 weeks. Laboratory experiments indicated that although the foliar residue of epofenonane caused severe morphogenetic effects on the host <em>A. orana,</em> the ectoparasite <em>Colpoclypeus florus</em> completed its development on the host. When the host and parasite were exposed to fenoxycarb, however, the parasite often died at the pupal stage. Similar experiments with the endoparasite <em>Apanteles ater</em> in the host <em>Archips rosana</em> did not reveal higher mortality of the parasite than in the control.In a following study, large-scale application of fenoxycarb and epofenonane in various IPM apple orchards were tested for several consecutive years. The IPM orchards were carefully selected to include IPM orchards adjacent to conventionally sprayed orchards, and IPM orchards well isolated from other orchards. The population of the leafroller species as well as the leafroller fruit injury level could be kept low by spraying twice in spring, irrespective of the location of the orchard. Reinfestation from adjacent orchards, if it occurred at all, played only a minor role in the final effect.The determination of the timing of epofenonane and fenoxycarb required sampling of larvae and periodical observations on the larval stage. In order to facilitate the timing simulation models were developed to predict the emergence of the last instar of <em>P.</em><em>heparana</em> and <em>A. orana</em> in the field. These models were based on laboratory experiments and on data from the literature and included only the temperature as a driving variable. The simulated curves of emergence of last-instar larvae, pupae and adults corresponded well with the field observations. To investigate whether the time of IGR application could be related to a temperature sum, the relation between emergence curves of last-instar larvae and temperature sum was studied for several years. For this purpose simulated curves were used, because field-observations on emergence of last-instar larvae covered only two years. Using the established relation between temperature sum and developmental stage of the leafroller population, only temperature sums need to be calculated for the timing of applications of IGR's.