It's deadly:

http://www.mindfully.org/Pesticide/chiquita/chiquita07.htm

But don't worry. Thiabendazole is also used to control ear infections in cats and dogs, so just feed your bananas to your pets if they get an ear infection :o)

It seems the organic growers have a method (although it's not a sure method):

Black Sigatoka fungus disease, Mycosphaerella fijiensis, and the toppling nematode, Radopholus similis, are the biggest organic banana production problems. Often organic bananas are grown in areas that have not had bananas before, in order to evade Black Sigatoka and the toppling nematode. Standard sanitary practices can be used against Black Sigatoka - cutting away dying leaves, keeping the topsoil clean, removing the flowers from the bunches at the right time, and covering the racemes with bags to encourage growth and prevent damage from birds and surrounding leaves.

From:
http://www.newfarm.org/international/features/0603/cost_rica/index.shtml

I visited coffee and banana plantations in Costa Rica years and years ago but I must confess, I never saw anyone applying any chemicals but I'm sure they did!



>Have a Chiquita Banana. While looking at a box of Chiquita Bananas I was pleased that the following chemicals had been “applied to maintain freshness”:
>
>Thiabendazole or Imazalil or Azoystrobin. Gee that sounds so nice. Those words just roll off of the tongue.
>
>I have noticed that most bananas including Chiquita will have a green outside and be soft like mush, indicating that it is too ripe.
>
>Black Sigatoka is a leaf spot disease that attacks banana plants and can cut a tree's fruit production in half. 15 to 20% of the cost of a banana is for the control of Black Sigatoka. Never fear – the growers apply fungicides to kill the fungal disease. However, Black Sigatoka is becoming immune to fungicides. New more powerful fungicides must be developed to resolve this problem.
>
>How do Organic Bananas feel about all this?
>
>Remember do not eat, breath or drink anything. It might contain harmful chemicals. The truth is that we have little knowledge as to what chemicals we come in contact with in our daily lives. Then there is food from China! :)