There are plenty of opportunity for pathogens to spread when you divide and process irises for shipping.
Failure to sanitize tools between cuts, could spread pathogens easily.
Washing or soaking rhizomes together in a tank of some sort seems potentially dangerous too.
If pathogens are present they would probably develop much more easily if planted during a wet and rainy period. A vendor growing in an arid area might never have problems themselves and may not even be aware that there is a problem, but in a different climate it could be a different story.
Iris4U's greenhouse branch in Europe started putting their irises in a greenhouse because they had problems acclimatizing their Colorado grown irises into the excessively moist German climate. Read what they say themselves here:
https://www.iris4u.de/en/about...
They still import the rhizomes they sell by mail order from Colorado and personally I have had much more success with their irises once I realized I needed to keep their irises fairly dry the first year.
