Leek moth, Acrolepiopsis assectella, a pest of Allium spp.: pest biology studies and the development of a reduced risk IPM strategy for control
Project code: MU03-ENT2
Peter Mason - Agriculture and Agri-Food Canada.
To develop an integrated control strategy involving reduced-risk insecticides for management of Leek Moth, an invasive alien pest of onions, leeks, and garlic.
Summary of Results
The leek moth, Acrolepiopsis assectella (Lepidoptera: Acrolepiidae), an invasive alien species has recently established in the Ottawa valley region. Local garlic and onion growers noted significant damage to their crops and surveys recorded up to nine mature larvae per plant in some fields. In Europe, cultivated Allium plants, particularly leek and onion, are frequently attacked by leek moth. Damage is caused when young larvae mine the green leaves and mature larvae penetrate the young leaves, the flower stalk or the inflorescence of the host plant. Larval feeding on the parenchyma causes a reduction in plant growth and if larvae are numerous, weakening or withering of the plant can occur. On old leaves, open galleries decrease the economic value of the plant. Without control, moth populations can reach such high levels that by the third generation 100% of plants are damaged.
Development of an integrated control strategy before leek moth becomes widespread in Canada will foster adoption of alternative management practices that reduce risk to the environment. Research was implemented to document the biology of leek moth in Canada, to generate data on the biologically derived insecticides Bacillus thuringiensis kurstaki (Btk) and spinosad, and to develop an integrated pest management program for growers.
Biology: Development of leek moth populations in Canada requires 453.4 day-degrees from egg to adult. In the Ottawa area, pheromone trap data indicated that there are three flight periods, a spring flight of adults that overwinter, an early summer flight of 1st generation adults and a late summer flight of the 2nd generation. Depending on ambient temperatures the life cycle can take from 3 to 6 weeks to complete in the field and three generations are possible, although not in all years or at all locations.
Insecticide trials: Dose-response studies indicated that spinosad and Btk products were effective in causing mortality of leek moth. In the field, use of spinosad-based products resulted in fewer leek moth larvae and less damage than Btk products. Minor use registration submissions for both of these products are being prepared.
Integrated management: Application of foliar reduced-risk insecticides requires precise timing because only the first instar feeds externally on plant tissues. Application windows can be determined by using pheromone trap data, ambient air temperature and the development model. Row covers provide an alternative strategy and these are used to cover crops during the adult flight periods, preventing gravid females from laying eggs. Their use significantly reduced leek moth infestation and damage to the crop, providing protection superior to that of the bio-insecticides tested. Recommendations for an integrated pest management program are being developed for dissemination to growers. Growers will be advised to use pheromone trap data and ambient temperatures records to determine appropriate times for using row covers and applying reduced risk insecticides to protect their crops. A classical biological control component will be incorporated at a later date.
Conclusions: This research project has generated essential information for developing a reduced risk IPM program for leek moth in Canada. Tools and recommendations for using them have also been developed to improve the quality of crop yields. Registrations of the spinosad and Btk products and their use with biological information for precise targeting of susceptible stages will minimize costs to producers and reduce the need for chemical insecticides.
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