An apple tree, once infected, can colonize junipers and cedars as far as 6 miles away(!). Yes, a highly infectious and amazing organism.

https://portal.ct.gov/CAES/Fact-Sheets/Plant-Pathology/Cedar... "As many as 7.5 million spores may be produced in a single gall and these spores have been known to be carried as far as 6 miles."