I think you need to have leaves to see it, so wait for spring to see and if 4% of a population has a disease it can explode so to speak, especially after stress. It affects the gold especially which is the valuable one. Look what happened in Italy as they are ahead of NZ in the disease. I think the industry is wiped out there.
I think finding PSA resistant varieties is a good idea but you would be looking at many years to get them established and have to cut out the old stuff first. Just my thoughts ... I have no special insight.