The fine fescues don't need as much nitrogen as tall fescues or KBG, especially in a shady area. I'm afraid I don't know what summer lawn food is. If it is an organic grain like soybean meal then anytime is ok. If it is fertilizer, I'm with bpgreen. Assuming you used fertilizer at planting then water and mulch mowing should be sufficient through the summer.

Dave wrote, in part: "I have ground dog food into powder. In retrospect, it was a waste of time. Just scatter the chunks out, water it briefly, and you'll be surprised how soft they become. Soft and mushy means the birds and squirrels can't carry it away. Another thing I don't worry about is salt content of pet food. Once a month is plenty." +1

I would not expect Preen to have any effect at all on grass. It might kill all your shrubs and the tree, but it should not harm grass. Is it an optical illusion or is the grassy area (to the left of the plants to the left of the AC units) higher than the ground where the plants and AC units are? If so you have much worse problems than you realize.

The topic is Japanese maple trees, not tender non-woody annual or perennial plants like tomatoes or sunflowers!! The reaction to herbicide drift will be very different between the two types of plants. One will react to the herbicide virtually overnight with browning, drying and death. The other will not die unless it is directly sprayed with herbicide and even something like gylphosate or concentrated brush killer will take multiple applications to kill an established woody plant like a tree. This is not supposition but fact......documented by literature and confirmed by several decades as a professional horticulturist!