I came up with this method of protecting my young climbing beans from bean fly, whose larvae killed successive plantings of my Blue Lake and Purple King beans before I diagnosed the cause. I live in north-west Brisbane.
The plants are most vulnerable to this insidious pest in the first 4-5 weeks of life, after which bean fly larvae attack is unlikely to be fatal, though it can still reduce the harvest. Bean flies are most active in warmer months, though some gardeners report them lingering all year round. It's September as I write this and I have seen a few already. Once rain hits, I expect an explosion in numbers.
In the photo above:
Once the climbers hit the roof of the net, I wait another week or so, then remove the net and frame and put in a bigger trellis. In the months that follow I find I can safely remove - gently - most if not all of the bamboo sticks without damaging the vines.
In October I will plant snake beans in another bed and use the same method. Snake beans are actually resistant to bean fly and I have had good crops in recent years, but protecting the seedlings certainly can't hurt.
Hope you find this useful. Good information for home gardeners about bean fly is not easy to find online and this has been a frustrating journey, albeit with a happy ending. :)
Great tips. Thanks Mike.