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Use of Bt Bait Solutions and Beauveria for Control of Adult Onion Maggot 1998

Project Leader: Jan van der Heide

Objectives:

1. Investigate the possibility of using bait solutions containing Bt for the control of adult onion maggot flies under limited field conditions, at doses lower than those used in 1997.

2. Investigate the effectiveness of Beauveria bassiana for the control of adult onion maggots under limited field conditions. (This material is commercially available as Mycotrol ES.)

Results:

Field cage experiments with Bt bait solutions indicate that control of onion maggot flies is most effective when flies emerge in a relatively short period, concentrating fly numbers immediately prior to application of the bait solutions. Dry weather after application of the bait solutions ensures persistence of the bait in the field and enhances control. An extended wet weather period in 1998 probably washed bait solutions off onion plants, resulting in no significant reduction of onion maggot damage. Treated and untreated cages suffered 4-12 % damage on average.

Similar field cage experiments with Beauveria in 1998 resulted in a significant reduction of onion maggot damage levels from 30% in check plots to 8% in treated cages. Spores of the fungus Beauveria need high humidity to germinate and penetrate the insects’ cuticle. Wet weather could still result in poor control by washing spores off plants and consequently reduced exposure of the flies to the spores. The use of Beauveria in combination with a cereal nurse crop may enhance effectiveness of Beauveria by providing the spores with protection from desiccation and damage from UV light.

It appears that Bt bait solutions could provide an additional means of control of onion maggot to NYS onion growers, but only under certain conditions. Results from experiments with Beauveria are encouraging, but further testing in commercial production fields is necessary.