Hi, 

Unfortunately there isn't an herbicide that you could spray to kill the grass as it is now. It is actually dead right now so any spray would be ineffective. With the irises and rose being present in the bed anything you spray in close proximity with most likely damage and kill the irises or roses as well. The best solution if you can't physically pull the grass to remove the roots, would be to remove the dead growth that is there now and wait for any new growth to come up this season and try to target spray the new green growth that comes up. You can use a piece of cardboard or gathered newspaper to help shield the irises and roses, or put some of the herbicide in a plastic disposable cup and paint on any new foliage that emerges so that any spray wouldn't drift onto the wanted plants. 

If you aren't capable of removing the dead grass, maybe there is a neighborhood child that could assist for a small allowance? Or cookies? - just a thought. Maybe it would be a great teaching experience an you could pass on the gift of gardening. 

 You could also try to remove with an 'extension grabber tool ' like ones that are similar for trash pick up. Or try to use a small wire toothed rake to gently rake out the dead grass. Some damage might occur to the iris from raking but they would be able to recover. 

If you do that and see the new growth come up, and want to send another photo of that, we may be able to identify what the weed or grass is to have a better idea on how to treat or control it. As it is in this state, it is difficult to know for sure what is taking over the garden area.

Emily