Tortricid moth pest management in Canterbury apple orchards

Abstract

Orchard practices and pest abundance were monitored at five sites over three seasons. Canterbury apple orchardists could produce high quality fruit with less than 1% damage using as few as four insecticide sprays per season. To improve spray timing, key pest bionomics were studied and the pest phenology model PETE (Predictive Extension Timing Estimator) was evaluated. PETE simulates diurnal temperature variation by passing a sine wave through actual daily maxima and minima. Daily day-degrees within a pest’s developmental thresholds are calculated and compared with the pest’s thermal constants to predict pest phenology.

Meteorological stations were established inside orchards to compare temperatures with those recorded at the nearest New Zealand Meteorological Service (N.Z.M.S.) stations. Daily maximum temperatures were slightly higher inside orchards during summer, only negligible differences existed between predictions of pest phenology using either data source. In Canterbury, PETE can therefore be operated with data from N.Z.M.S. sites.

Codling moth (Cydia pomonella L.), brown headed leafroller (Ctenopseustis obliguana (Walker)), greenheaded leafroller (Planotortrix excessana (Walker)) and the light brown apple moth (Epiphyas postvittana (Walker)) have one, two, two and three generations respectively per season in this area. In laboratory studies, brownheaded (BHL) and green headed (GHL) leafroller larvae and pupae were found to develop at a linear rate between 11.5 and 22.5. Males took respectively shorter and longer periods to complete larval and pupal development than females.

At unsprayed sites, leafroller and codling moth larvae damaged up to 42.8 and 98.1% of the fruit crop respectively. Fruit damage by LBAM was significantly related only to the numbers of second generation fourth (plus fifth) instars. Similar levels of damage were done by first and second generations of BHL and GHL.

Important factors affecting codling moth and leafroller abundance were weather and parasitism. A drought in 1981-82 reduced the size of the second and third LBAM generations. The main parasites of leafroller and codling moth were Apanteles tasmanicus Cameron and Ascogaster guadridentata Ashmead which attacked up to 40.1 and 32.2% of larvae. Neither parasite prevented their hosts causing economic levels of fruit damage.

Large numbers of adult key pests migrate into Canterbury apple orchards. To determine the status of non-apple hosts commonly found within or near to orchards, oviposition and development studies were conducted. Both GHL and LBAM larvae developed faster when fed poplar (Populus nigra) than apple leaves. GHL and LBAM adults showed an equal preference for poplar and apple as oviposition sites. LBAM adults laid eggs on apple leaves rather than blackberry (Rubus strigolosus agg.) or narrow-leaved plantain (Plantago lanceolata L.).

Sampling methods for all leafroller stages were evaluated. Port wine traps indicated the relative composition of leafroller complexes, caught mainly mated females and fewer moths than pheromone traps. Sampling for pre-imaginal leafroller stages on trees revealed that a significantly greater proportion of egg batches and larvae occurred on shoots in well-kept orchards. The numbers of egg batches laid on different cluster types was significantly related to the number of leaves per cluster. Oviposition by LBAM was affected by cultivar. Significantly more batches were laid on ‘Sturmer’ trees than those of ‘Cox’s Orange', ‘Red Delicious ' or ‘Granny Smith’.

Pheromone trap catches were the only source of validation data for the PETE model for codling moth. Egg and larval numbers determined by cluster sampling were also used for LBAM. Codling moth flight could be predicted with PETE, but a single set of input parameters could not be used to predict phenology at all sites. Variation between actual and predicted LBAM phenology increased from February onwards. Widely distributed population structures had to be used for both pests to operate the model.

An envisaged supervised spray programme would require orchardists to monitor pest abundance for comparison with economic thresholds. Temperature records could be used with charts comparing percent pest development against accumulated day-degrees to enable orchardists to trace pest phenology. This alternative system could be used until an improved version of the PETE model was available. Orchardists may therefore reduce insecticide application still further depending on factors .affecting pest abundance.