Photo credit: Tracey Baute
Mexican Bean Beetle (Epilachna varivestis)
Mexican bean beetle infestations are rare in Ontario. Mexican bean beetle is the only member of the lady beetle family in Ontario that feeds on plants. All the other lady beetles are beneficial predacious insects. The adult beetles are oval in shape, approximately 6 mm (0.25 in.) in length with 16 small black spots on their coppery-red backs, resembling a lady beetle. The heads of the Mexican bean beetle, however, are the same coppery-red colour as their backs.
Damage and Scouting
The decision to spray is dependant on the level of defoliation and is not based on the number of insects per plant, though the insect still needs to be present and actively feeding for the application to be cost effective.
In 10 areas of the field, pick trifoliate leaves that are fully expanded in the middle of the plant canopy from five plants. Discard the least- and most-damaged 350 Agronomy Guide for Field Crops leaflets from each trifoliate collected, leaving only one leaflet per trifoliate to evaluate average percent defoliation.
|Bean Growth Stage||Defoliation Threshold|
|Prior to bloom (vegetative stages)||35%|
|After bloom up to pod-fill||15%|