To protect them from wind damage, birds landing, sunburn, Frost speckle, rats and Rosella's etc. A covered bunch also will ripen more quickly owing to the concentration of ethylene gas.
When to cover?
After the flower bell has descended and turned male and the female fingers have turned upwards. Remove the bell and slide the bag over the bunch. Remove any spent protectors or leaves that may cause damage to the bunch
Secure at the top by tying, taping or a rubber band. Leave bottom of the bag open!
A good tip is to mark the bag to show what month it was done as this helps determine when the Bunch is ready for harvest. Many factors such as variety and weather control this however as a guideline Ladyfinger varieties - 6 months, Cavendish varieties - 7 months.
Bagging tool available. Retail $300