The year that I started my raspberries, I mulched and water a lot as well. Like you, I had a couple crowns that got root rot. Maybe 2 out of 25. The following years, I only watered for about a 2 week period when the berries are swelling. I do still mulch in the fall. Not knowing your zone, it hard to say what would help. Add your zone in the spot following your user name if you want to get accurate advice.

Zones are helpful for advice, in this instance annual rainfall pattern is more important.

In general, if watering by hand with a hose and sprayer attachment, when water starts puddling near or around the plant, stop watering. If the puddle immediately disappears, water until a puddle takes tens of seconds to disappear.

Don't water again for a week unless it is blazing hot and dry.

If you are simply placing an open hose by the plant and letting the water run, it would not take many minutes to get 5 or 10 gallons of water on the plant, way more than enough.

Keep a bit of open ground near your raspberries and water it too. Then probe it to see how dry the ground is getting before watering again.

My new plan for watering all of my plants that are planted in the ground is this: When it has hasn't rained for quite a while I should get around to watering them. This includes my 4yo raspberry bush that had some canes 6' high (as tall as me) before fruit started bending them over. They are berrying like crazy now and watered haphazardly about 5 times this year in zone 5 near Omaha NE.

Drainage is the key!

If the soil remains soggy, root rot wins.

Other the other hand, it can rain, rain, rain as long as the drainage is good.

Around here with our clay-based soils, we always suggest raised beds. Beds without rigid sides (stone or wood, etc) are best.

This might be useful
http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/18936/ec1306.pdf

Here is a link that might be useful: growing raspberries

Thanx 4 all the replies, i'm using a garden hose and usually spray each bush 4 about 5 seconds each, couple times a week and more if it's searing hot...i'm still confused about how much and how often, i understand the standing water theory but i have these bushes on raised mounds , maybe 1 good soaking a week as opposed to couple times a week.......maybe i'll buy a soil moisture tester to be sure, less mulch which i use for weeds

"maybe 1 good soaking a week as opposed to couple times a week"

Yes, all the experts say infrequent long soakings is best.
It may be something like nematodes in the roots. rare, and unusual, but it could be that. As your watering seems fairly normal.
Usually every spring compost should be added around the top. Mix 1/2 compost with 1/2 peat(which is really a compost too!) to loosen soil and improve drainage, and feed the plants! I also use a mulch, I can get all the pine needles I want so I use them. They are also great for potted plants. My in-laws live in upper Michigan and have hundreds of pine trees on their property. When visiting I also bring a bunch of yard waste bags to stock up.
What I don't like about mulch is you can't see the soil, you have to feel. I don't use it around my potted cacti, I need to see the soil.