What are the leaf shader settings like? I've tooled around with piping the texture through a mult/div and into the translucency, got pretty good results.
It's easy to use the mult/div for making translusency. First of all make a mia_material_x. Under it's attributes make it "thin walled" and uncheck "skip reflections on inside". Under refraction you need to set a transparency value or it won't work. To make it easy say you put it to 0.25. Then go under the translusency tab of the mia material x and check "use translusency" and put the weight to 1. I'm assuming that your using physical sky. So now create a gamma correct node and make the gamma .454 .454 .454. Then under the value checker box choose your file. Now create a mult/divide node and plug your gamma correct into input 1. Now click on input 2 of the mult/div and type in 4 4 4. The reason for that is cause our refraction transparency is 0.25, and to make it work the number we put in the mult/div node has to equal 1. Now just middle mouse drag the mult/div node to translusency color on the mia material x
And now you have translusency