Infrastructure means the basic structure of an organization or system. A company's infrastructure would include all the fixed assets, i.e., the building, equipment, machinery and tools required to manufacture their product. Although people are not fixed assets they would be included in the company's infrastructure too.
Rarely a serious problem. Look-alikes: Jumping oak gall, tubakia leaf spot, oak leaf blister, other fungal leaf spots. Jumping oak gall Brown leaves appear on trees in the white oak group in late spring. Severe infections may cause the leaves to turn black, curl up and fall. On the underside are brown galls with the larva of a small wasp inside.
There'll be outlier trees-- I've seen sick trees drop their leaves in August, and leafed deciduous trees in January as far north as Manhattan-- but there's a clear peak. In tropical climates, there's more variation in when the trees drop their leaves: it has to do with wet and dry seasons, soil quality, wind and elevation. To get a view that looks like autumn in Mexico, for example, you have to go into the mountains.