Forgot to mention this bed is about 200 ft from the other two

The fungi that cause Rhubarb Crown Rot thrive in heave, wet soils so what is the soil there like?
How much organic matter is in the soil?
How well does the soil drain?

The first two beds were well draining soil with much organic matter added every year added when the plants were dormant the last was bit heavier but still drained pretty well , Do think a fungicide might help ?

Not after rot begins.

You might try digging up a plant or two and putting them in large pots (10-15 gallons), and keeping them on the dry side. I found that too much organic matter (composted cow manure in my case) caused some rot in the rhubarb, but that making things drier seemed to cure the problem. Rhubarb is pretty hardy.
Renais