Personally, I don't take chances. I use a product called Physan 20. It's an environmentally friendlier version of Consan Triple 20 or Triple Action 20. The manufacturer claimed to me (via telephone) that it could be used to control pathogens in the soil as well(the product begins to dissipate after coming into contact with the pathogens. Usually gone in 8 hours). No data available as to what extent that it could do this, but I live in an area where I've got way too many pathogens and diseases not to try it. I grow heirlooms that catch everything and I did disinfect my cages with Physan. So far so good. Hope this helps.

If you had foliage diseases the previous year then yes, some spores and bacteria could have overwintered on the supports.

But, they would also have been shed to the ground and so can cause splashback reinfection the next year. Mulching helps.

Also, since all NEW foliage infections are airborne, disinfecting cages or PVC or whatever cannot help prevent that at all. Only rigorous spraying can help prevent the fungal foliage diseases which are the worst, compared to the bacterial ones.

Carolyn