Thats what caused the potato famine in 1840. It spreads, mainly by transit of infected potatoes, tomatoes etc to the next batch. It’s like any other contagion- one infected potato gets to a crop land and gets turned into the soil can spring it up in the other crops.
Really sux for the farmers there, yeah. But the farmers here are freaked out over the idea of not just killing the one season. My sister in Idaho explained this to me years ago when this happened to a few local farmers there. Government stepped in made them destroy the crops by fire, clear the burnings, grow some kind if short hay and burn that out -twice. So they had to loose entire crop, and use one full season to grow two quick crops of hay, ruined 2 full seasons in the end. But it completely stopped the issue. And now those farmers are way on top of any fungus/mold issues like the over watering or not doing sub grade drainage in naturally wet areas.
When we drive in a car or even motorcycle from Vegas to SoCal, we cross a border checkpoint where we can not take across fruit. I didn’t know this and first time I went we were going on vacation for a week camping. I bought a 5lb bag from grocery store mixed apples, oranges, etc. confiscated. Worries about fruit flies.
going into any national park here, we can not bring in any fire wood from outside that forest.