Prodiamine for Crabgrass

I am in Massachusetts.

I know Prodiamine is touted for Crabgrass due to long lasting pre-emergent effects. Does the chemical also impact post emergent Plants, like some other pre-emergents do? I want a product that DOESNT impact post-emergence at all, just pre emergence.

I understand Prodiamine can last 120 days. If I apply in April, that takes me through July. Do I need to apply again? Can Crabgrass still germinate in Summer?

Thanks!