Pests and associated beneficials recorded in a Canterbury pipfruit orchard during the transition to "Bio-Gro" certification
Observations at the Winchmore Research Orchard, during 4 seasons from October 1989 to May 1993, has provided evidence of the establishment and continued survival of several key pest species, which include: leafrollers and codling moth, and of lesser importance phytophagous mites, a noctuid moth and the apple leaf curling midge. Other pest species were extremely rare, or were not recorded in the orchard during this period. Changes occurred in the numerical dominance of the major leafroller species, Epiphyas postvittana (Walker) and Planotortrix octo Dugdale. Infestations of the codling moth, Cydia pomonella (L.), remained low.
Several beneficial leafroller parasitoids, especially a braconid wasp Dolichogenidea tasmanica (Cameron) and introduced predatory mites, became established in the orchard and contributed to pest control.
In New Zealand, the majority of pipfruit orchards are conventionally managed, and rely on the intensive input of synthetic pesticides to supply high quality fruit for both the local and export markets. These intensive inputs reduce the diversity of the fauna and flora, compared to the greater diversity often associated with organic fruit production systems. Nonetheless, the apple orchard provides a complex ecological system, even in its simplest form. The Winchmore Research Orchard was established in 1985-86, as a 4 ha conventionally managed orchard with border-strip irrigation. In 1989-90, orchard management practices changed from conventional management to management consistent with full ‘Bio-Gro’ registration. This enabled studies on the influence of various understorey plant species on tree growth and pest and disease incidence, during this transition. The investigatory structure and preliminary findings of these studies were summarised in Daly and Thomas (1992).
Previous overseas research showed that soil and understorey plant management practices influence processes within the orchard ecosystem (Haynes 1980) and modify the insect interactions (Altierie and Schmidt 1985).
The presence of certain understorey flowering plants within an orchard, such as members of the Umbelliferae, can attract and enhance the survival of beneficial parasitoids, and may provide a key to sustained biological production (Crowder 1986), but Gruys (1982) concluded that floral plantings in orchards did not substantially assist in the control of leafroller populations. Other plants, such as clovers, are often planted to improve soil nutrient levels, but these may provide suitable hosts for polyphagous pests, including caterpillars and mites. At the Winchmore Research Orchard a proportion of the populations of these pests may co-exist on suitable understorey host plants and on the apple trees at the same time. Similarly, their beneficial predators and parasitoids may co-exist in these habitats, with their prey.
This paper reports the preliminary findings on the pests encountered in the orchard, the changes in the populations of leafrollers and mites on the apple trees, and the leafroller larval populations on the understorey plant complexes.
A pest survey was conducted from October 1989 to May 1990 to determine the key insect species present in the orchard. This was followed by regular, seasonal monitoring of phytophagous mites and lepidopterous insects, and casual observations of less numerous species. The leafroller larval sampling programme continued from January 1991 to April 1993.
Mites
Samples consisted of 50 randomly selected leaves of each of the apple cultivars, Red Delicious (block 1), Braeburn (block 2) and Royal Gala (block 3). The understorey of blocks 1, 2 and 3 consisted of: mixed herb ley; perennial rye grass ; and red clover respectively (refer Daly 1995, this publication). Leaf samples were collected fortnightly throughout each season from spring to autumn. Mites were brushed from leaves onto glass plates using a mite brushing machine and their life stages counted under a binocular microscope, according to the method described by Walker et al. (1990).
Lepidoptera
Monitoring of adults. A series of 4 ‘Delta’ insect traps with sticky base inserts (Suckling and Shaw 1990) replicated in each block were individually baited with species-specific synthetic pheromone for each of the three leafroller pest species: Epiphyas postvittana (Walker); Planotortrix octo Dugdale; Ctenopseustis herana (Felder and Rogenhofer); and the codling moth, Cydia pomonella (L.) (all members of the family, Tortricidae). Four International Pheromone Systems bucket traps were used for trapping each noctuid taxa of Graphania mutans (Walker) (‘North’ and ‘South’ taxa, Frérot and Foster 1991). For the leafrollers and codling moth, traps for each species were placed on trees within the orchard, while the G. mutans traps were placed on the orchard boundaries.
Monitoring of leafroller eggs and larval stages. Since immature leafrollers can exist either on suitable understorey host plants or on the apple trees within the orchard, a sampling method incorporating timed (ten minute) visual searches with destructive sampling was used for both the trees and groundcover. Leafroller larval stages and their associated parasitoids were sampled fortnightly, thus providing alternate 28-day samples from the trees and understorey vegetation, respectively. Individual blocks were arbitrarily divided into three separate sections, and each section randomly sampled on each sample date. Collected larvae were reared to maturity on artificial diet in the laboratory and the species recorded.
Mites
Twospotted spider mite (TSM), Tetranychus urticae Koch (Tetranychidae), populations increased following cessation of pesticide applications in 1988-89, and resulted in tree foliage damage during 1990-91 and 1991-92 (Figure 1). Infestations of TSM also developed on the groundcover plants during this period, the clovers especially supporting high populations. At the end of the first summer season (1989-90), 5% of the harvested Royal Gala fruit had over-wintering adults of TSM present, but none were found on fruit during the following three seasons. Generally, it can be stated that TSM had reduced in importance on trees in the orchard by the end of the third season of ‘transitional organic’ fruit production management. TSM populations appeared to have reached a state of equilibrium, due mainly to predation by Stethorus bifidus Kapur (Coccinellidae) and Phytoseiulus persimilis Athias-Henriot (Phytoseiidae) (Burnip and Thomas 1993). P. persimilis was especially prevalent on ground cover plants following its release in December, 1990, but another phytoseiid identified as Amblyseius cucumeris (Oudemans) (Phytoseiidae) was also occasionally recorded on the apple leaves from Block 1.
Figure 1: The numbers of phytophagous mites and their predators, recorded fortnightly from apple leaf samples (n=50) collected each growing season, between November 1990 to April 1993, in Block 1 at Winchmore Research Orchard
European red mite (ERM), Panonychus ulmi (Koch) (Tetranychidae), was recorded rarely during 1989-90, but became prevalent in the second season in two of the blocks (1 and 2), following their accidental introduction via ERM-infested grafting bud-wood. Despite the application of a fatty-acid (soft soap) pesticide to these blocks, populations were not adequately reduced.
During 1990-91 and 1991-92 the ERM predatory mite, Typhlodromus pyri Scheuten (Phytoseiidae) was released. Although initial levels of establishment were high, T. pyri persisted from one season to the next only at low levels. It is possible that these predators suffered mortality from the sulphur applied for disease control. ERM infestations increased steadily during the period of study, resulting in localised areas of leaf bronzing and premature leaf fall. The endemic coccinellid, S. bifidus, was recorded at low levels among the ERM infestations, although this predator is known to be an effective control agent of phytophagous mites.
The predatory bug, Sejanus albisignata (Knight) (Miridae) was present during October, 1990 to April, 1993. Observations were that this predator was very common on occasions. In particular, high numbers of S. albisignata were observed during December of 1992-93, in association with high ERM populations. An observed subsequent decline in this ERM population, and the apparent absence of other predacious insects or mites, suggested S. albisignata acted as a predator of ERM at Winchmore Research Orchard (Burnip and Thomas 1993).
A third phytophagous mite, the brown mite, Bryobia rubrioculus (Scheuten) (Tetranychidae), became established on both the understorey plants and the apple trees, during the period of study. Little direct foliar damage could be attributed to this mite, but continued monitoring is required.
While it appeared that predators had an important controlling influence on the populations of TSM towards the end of the three year transition period for the orchard, ERM infestations were not being controlled adequately.
Lepidoptera
Monitoring of adults. During the period of study, more moths of all species were caught in the last two growing seasons than during 1989-90 and 1990-91 (Figure 2). Numbers of P. octo caught increased at a greater rate than E. postvittana and by 1993 P. octo was the most common male leafroller moth. C. herana was caught in fewer numbers than either E. postvittana or P. octo during the four years. Codling moth was caught in low numbers at Winchmore during 1989 to 1993, reflecting a low population. Further interpretation of codling moth pheromone trap catches is not possible due to pheromone mating disruption trials carried out at the Winchmore Research Orchard during this period.
The mean trap catches of ‘North’ and ‘South’ taxa of the noctuid, G. mutans, during 1990 to 1993, were summarised in Burnip and Thomas (1993) and are not reproduced here. No major differences in either adult phenology or abundance, were evident between the two pheromone separable taxa of G. mutans. Peak flights of males occurred in the spring and again in mid- to late summer of each season. Additional information is provided in Burnip et al. (1995).
Monitoring leafroller life-history stages.The results of the 10 minute searches and destructive sampling programme are summarised for the years 1990-91, 1991-92, and 1992-93, in Figure 3. A total of 3,938 leafroller larvae were collected and successfully reared to maturity during the three seasons of study. Of these 75% were found on the apple foliage, and 25% on the understorey. There was a strong trend for the species composition of the leafroller larvae collected during this period from both apple foliage and ground cover plants, to change from a dominance of E. postvittana to P. octo. Of the total leafroller larval stages collected during the three seasons of sampling, January 1991 to May 1993, the lowest numbers (14%) were collected during the first season, the highest during the second season (53%), and an intermediate number during the third season (33%). It is possible that the high numbers found during 1991-92 can be explained by the absence of sheep grazing of the understorey, during the previous winter. This management technique was employed in the winters prior to the 1990-91 and 1992-93 seasons, and was successful in removing leafroller larvae and over-wintering hosts in the understorey. The leafroller Merophyas leucaniana (Walker) was found only on clovers in the groundcover.
Figure 2: Seasonal trap catch (Nov. 1 - Mar. 31), of three species of male leafroller and codling moths, from four years pheromone trapping, at Winchmore Research Orchard
The highest percentage of leafroller larval parasitism was recorded for the braconid parasitoid, D. tasmanica (Hymenoptera: Braconidae). This species appears to have preferred E. postvittana as a host (Thomas and Burnip unpublished data), and could have been partly responsible for the decline in dominance of this host species, during the study. In general, the levels of parasitism of the eggs (not encountered) and larval stages by other parasitoids was very low. The incidence of the larval parasitoids, Glyptapanteles demeter (Wilkinson) (Hymenoptera: Braconidae), Diadegma sp. (Hymenoptera: Ichneumonidae), Goniozus sp. (Hymenoptera: Bethylidae), and Pales funesta Hutton (Diptera: Tachinidae) varied on hosts between seasons and between apple and groundcover foliage.
The percentage of leafroller larval parasitism resulting from all parasitoids was highest during the 1991-92 season (43.5%), when the leafroller larval incidence was also recorded at its highest level, which suggests a density dependent relationship. Greater numbers of Goniozus sp. were associated with larval M. leucaniana on clovers, than with other leafrollers on groundcover plants.
Within the three understorey types, consisting of mixed herb ley, rye grass, and red clover, the compliment of plant species changed over time, in that adventive species (‘weeds’) replaced a proportion of the initial sward components. These changes are likely to have affected the number and species composition of leafroller larvae in the three blocks. In block 2 in particular, the rye grass sward was partially replaced by white clover (Trifolium repens L.) by year 3. This allowed for a much higher incidence of leafroller larvae in this understorey treatment, than during the previous two seasons. In general, clovers in the orchard provided the major ground cover hosts of leafrollers.
Figure 3: Species composition of the key leafrollers and associated parasitoids, on apple and groundcover foliage, at Winchmore Research Orchard, during 1990-91 to 1992-93
A number of other apple tree pests present in New Zealand were absent from the Winchmore Research Orchard. These included woolly apple aphid (Eriosoma lanigerum (Hausmann) (Homoptera: Pemphigidae)), mealybugs and armoured scale insects. Apple leafcurling midge (Dasineura mali Keiff.) (Diptera: Cecidomyidae) and Froggatt’s apple leafhopper (FAL) (Edwardsiana (=Typhlocyba) froggatti Baker) (Hemiptera: Jassidae), although present were not troublesome. It was initially suggested that the relative absence of FAL may have been linked to the use of sulphur sprays for disease control. However, control of FAL has not been achieved on the "organic" apple plantings at Clyde Research Orchard (C.H. Wearing pers. comm.) where similar trials include the use of sulphur sprays.
It is believed that the isolated nature and young age of the orchard had an impact on the absence, or reduced incidence of pests that were recorded during the study. There were potential cost benefits in the management of the Winchmore Research Orchard, because of its isolation, since there were no requirements for controlling pests not present, such as woolly apple aphid and mealy bugs. The composition of the understorey plant complex was also important, since leafrollers which accidentally fell to the ground were not able to survive on such hosts as ryegrass, but were able to feed and survive on many others, including those which were purposefully planted (e.g. red clover) and those that became introduced adventitiously (e.g. white clover). Careful management of the groundcover was found to be important for both disease and pest control, with both mowing and grazing influencing leafroller larval survival on understorey plants (Thomas and Burnip 1993).
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