Historically speaking the nectar flow in our area begins tapering down in the second half of July. Most nectar bearing plants reduce flowering after the summer solstice (June 20th). Combined with the typical reduction in rainfall in late July and August the nectar simply dries up. Contrary to this, every year is a little different and early July rainfall can extend the flow. A good beekeeper always wants to leave room (ie an extra super) on the top of the hive for any extra flow. Empty storage space encourages the bees to work harder and longer trying to fill this space. This is especially true for stronger hives.
Late August and early September can produce a smaller flow from goldenrod and purple loosestrife ( an invasive species). The goldenrod flow is very problematic. Some beekeepers remove their honey supers prior to this flow so that the bees will be forced to store this nectar, if it occurs, in the brood boxes in preparation for winter.
Late July and early August is also the time to treat for varroa mites. Only formic acid treatments (Formic Pro or MAQS) are approved for use while the honey supers are in place. This requires removing the hopefully heavy honey supers, inserting the treatment, and then replacing the honey supers. An alternate approach is to simply remove the supers and extract them if the honey is capped. The approach you take is up to you as an individual beekeeper.
We can discuss both approaches at the next ECWBA meeting, which will be on July 18th at the Rushford Meadery outside of Omro. Start time is 9:30AM, but early arrival is encouraged for additional information exchange. See you there.