What would most likely happen to the grass if most of the fungi and bacteria die?

Grass will not grow

Explanation:

Fungus, is a disease that results from improper mowing, droughts, humidity etc. There are irregular brown patches that result from the growth of fungus and if the disease gets severe it gets really difficult to treat

Bacteria grows on the roots of the grass, and when that bacteria and fungus die it leaves the grass unproductive and as a result the areas that are affected by dead fungi and bacteria, does not grow further

sorry, but you do not have posted the diagram.