That is not maidencane. It looks more like cutgrass to me. Maidencane is branched like torpedograss. It should be easy to identify with the inflorscences (flower/seeds). Take a look at this: http://plants.ifas.ufl.edu/node/641
Maidencane grows more "in" the water and what you show grows more to the water's edge and "on top" of the water. You should get better results with what you're using when the plant starts to die back and pushing carbohydrates to the roots. The glyphosate will be taken there too and result in better control.