Based on what I've read here, mulching in the winter in an invitation to rot. This link has information. There were a few more hits when I searched this forum for "mulch'.

This information on borers came from another post.
Life History
Adults (moths) emerge in September and October from the soil, mate, and deposit eggs on the dead leaves, particularly those that are dried and crinkled. Eggs usually are laid in crevices or rolled areas of the leaves, in groups of three to five or more. A single female moth is capable of depositing up to 1,000 eggs in her lifetime.

The egg overwinters and begins to develop in early spring. Eggs hatch during April and May and the young larvae begin to feed on young, rapidly growing iris leaves.

After feeding on leaf surfaces, causing scars from which sap runs down the leaf, the larvae assume a boring habit, entering the leaves and gradually mining downward. Leaf mining injury is characterized by dark, water-soaked areas or slits in the leaves. Some chewing also occurs on leaf margins.

When about half-grown (one-half to three-fourths inch long), iris borers reach the rhizomes, where they feed until late July or early August. As the borers feed, bacteria infect the rhizome, initiating the soft rot.

When fully grown, iris borer larvae are about 2 inches long, cylindrical, smooth, and plump with whitish to pinkish bodies and dark brown heads. Shortly after this stage is reached the larva leaves the iris rhizome and constructs a "cell" in the soil where the pupa stage is passed.

The pupa is a non-feeding transition stage between the larva (or worm) and the adult moth. Pupae are dark brown to black and are usually found in the top 2 inches of soil. After two to three weeks in the pupa stage, the iris borer moth emerges and the cycle is completed when the eggs are deposited. Moths are typical millers--dark grey to brown, with a wingspan of about 2 inches. There is only one generation per year.

Prevention
One key to iris borer prevention is removal and destruction of the previous year's dead foliage before April 1. This sanitation practice will reduce the problem by destroying overwintering eggs in the residues.

Also on prevention....................
You can significantly reduce the likelihood of a large borer infestation by keeping all dead and diseased iris leaves and other vegetative matter cleaned out of your iris beds, esp in late summer/early fall when borer moths are looking for such materials on which to lay their eggs. Another thorough garden clean-up in early spring with help to further reduce the number of surviving borer eggs before they can hatch. Burn or discard all garden cleanings; DO NOT COMPOST!

Here is a link that might be useful: mulch

This is a great summary, thx.

When I re-planted the rhizomes, I bleach washed them. The new beds are newly dug. All this should help.

If the rhizomes can over-winter without any problem, then I do not have to mulch the beds. I just need to weed the beds more often next season.

New Jersey has the most ardent gardeners :-)

I have clay soil... I absolutely do not mulch bearded iris ever. Never ever. Was that worded strongly enough LOL?

I have clay soil too. I couldn't get iris to grow in it until I started placing the rhizomes on top of the soil with just the roots buried and large gravel to hold them in place. Otherwise the rhizomes would rot.