Facilitating the adoption of reduced risk approaches to pest management in apples in Nova Scotia

Project Code PRR09-030

Project Lead

Dela Erith - Nova Scotia Fruit Growers' Association

Objective

To facilitate the adoption of new pest management tools (reduced risk pesticides and practices) through the verification of action thresholds for the use of organophosphate replacement chemistries

Summary of Results

Background

The apple maggot (Rhagoletis mendax) and codling moth (Cydia pomonella) are key pests of apple orchards in eastern Canada. Feeding by these pests damages the fruit, rendering them unmarketable. The apple maggot is a quarantine pest for which there is zero tolerance in many export markets. Close monitoring and continual protection of developing fruit, is required to prevent crop loss caused by these pests.

Organophosphate (OP) insecticides have been used for many years in the management of these pests. However, in light of environmental and human health concerns, a number of new insecticides have been registered in recent years. In general, the new insecticides have different modes of action, are less persistent and may be more pest specific, often targeting different life stages than the organophosphates. As a result, application timing and frequency of application may differ from that of the OP's.

The need to verify application thresholds, incorporate the new materials into orchard pest management approaches and to increase grower confidence in these materials was identified through stakeholder consultations under the Risk Reduction for Organophosphate Replacement in Pome Fruit under the AAFC Risk Reduction Program. A one year project was initiated to examine and verify thresholds for spray timing in Nova Scotia of OP replacement chemicals.

Approaches

Test blocks were established each for apple maggot and codling moth in commercial apple orchards in Nova Scotia. Local weather data (rainfall and temperature) were collected and entered into a degree day model to predict the development and proper timing of treatments for apple maggot and codling moth. Codling moth and apple maggot abundance were monitored throughout the growing season in the test blocks. Recommendations for treatments were made to grower co-operators when action thresholds were reached. Crop injury from apple maggot was assessed at the end of season and from codling moth, twice during the season. The level of risk reduction achieved through using the improved thresholds and more accurate spray timing, as opposed to the traditional use of organophosphate treatments, was calculated using the Quebec Pesticide Risk Indicator. Growers were informed of study activities and results through grower tours of field plots in conjunction with Nova Scotia Fruit Growers Association (NSFGA) summer tour, newsletter articles and through a presentation at the NSFGA Annual Convention on project.

The timing of pesticide treatments for codling moth was based on degree day modeling (Kain D. and A. Agnello. 2004. Insects, Update on Pest Management and Crop Development in: Scaffolds Fruit Journal, Sept. 7, 2004. Vol. 13 No. 35. Location of Study: New York) and the model run on Spectrum Technologies Inc. software program that used weather record data from each of the four grower farms. Organophosphates, because of their contact kill activity against moths and neonate larvae, would be timed at 250 degree days post biofix (first sustained captures of male moths). The organophosphate replacement products generally do not have activity against the adults and must be applied prior to egg deposition.  Therefore the newer timing was set at 100 degree days post-biofix.

Results

Using the new action thresholds and timing for control measures, Calypso, Assail, Delegate and Intrepid proved effective against codling moth (zero through 0.5% crop loss) while control of apple maggot (zero crop loss for all products) was adequately achieved by Calypso and Delegate. In the twelve test blocks, damage from codling moth ranged from zero through 0.5%, well within the acceptable limits. Two blocks used a second insecticide treatment. Of seventeen orchard blocks used in the assessment of apple maggot control, three received a second insecticide for subsequent pest trap captures.

September fruit injury assessment was based on examination of 100 apples on each of ten randomly selected trees in each orchard block. There were no viable apple maggot mines found in any of the orchards despite significant rainfall shortly after application of a number of sprays.

A major concern of growers is in determining the need for subsequent treatments. Unlike the organophosphates, the new insecticides do not kill adult flies, although some inhibit oviposition. Orchardists have no means of knowing whether flies caught after the 7-10 day window of pesticide activity, are old flies that have been rendered unable to lay eggs or if these are new flies that have begun oviposition. To further complicate the decision making process, new chemistry products have a shorter field life span because of weather-based degradation (i.e. UV radiation and wash off from rain fall). 

The Quebec Pesticide Risk Indicator was employed to profile new chemistry products contrasting model simulations where Guthion was the key ingredient used against codling moth and apple maggot. Both the environmental risk and the health risk components showed merit of the OP alternatives.

For both codling moth and apple maggot management, the organophosphate alternatives generally proved effective. The study helped to familiarize growers with factors to consider when incorporating new products into an IPM program. Additional year's assessment is required before major claims can be given regarding such matters as adjustments of action thresholds or timing of applications. The adoption of new chemistry alternatives is hampered by the costly nature of these new products, especially in light of the low profit margins of apple production. Actual product costs for organophosphate alternatives ranged from 1.5 to 2.5 X the cost of Guthion per hectare. There is a continued need for growers to gain more experience in new pest management programs. Precautionary, follow-up treatments will be required, particularly for apple maggot, until growers are comfortable with their use.

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