Having problems with hair transparency using cycles. I ported over a model from daz studio (have done this a few times before with no issues). 
Using a simple mix shader, transparent top, diffuse bottom, black/white texture in the fac.
Heres the blend http://www.pasteall.org/blend/39347 with images packed.
Looks like you need to increase the maximum number of Transparent Bounces in Render settings > Light Paths:
Another workaround is to cull the bounding object to reduce bounces at the cost of increased number of vertices.
For example, There will be fewer bounces if you cull your low-poly grass into a closer shape like:
instead of using the default rectangle.
This could be used together with the LightPath - number of bounces technique above. You may find a balance point between rendering performance and image quality through trail and error.
