Remember the classic vascular test used in grade school with food colour and a stalk of celery?
We used phosphorescent blue dye and saturated a drip-zone on a 75-yr old live oak, began detection up 25ft in the canopy in 24hrs on .25" twig samples. It can travel fast or it can creep-up in weeks.
Many factors undermine the science in this. Relative humidity, seasonal norms, extended drought, saturation precipitation, transporation rates and sunlight intensity, time of day (stomata opening), etc.
Some motts of live oak, which generally vegetatively reproduce instead of acorn survival, are genetic clones..a single specie with many stems..so are predispositioned to infection but single-stand trees are more resistant to engrafting being a mode of inoculum.
I've witnessed negative isolation tests for fagacearum only to watch an oak die from wilt in 48 hours. It happens, there are no "norms" as location, stand, altitude, weather all play a role as do more virulent strains of the disease.
Transportation rates of treatment injections also vary, most failing to translocate effectively in the tree or if so, fatally damage xylem and other vascular activity..if they do. The reason I sought alternatives to useless injection. A chemical "girdling" of the tree at the root collar, more often a mortal blow than a therapeutic.
Trenching to distant root grafts had failed 100% in my research..but that was Texas/Oklahoma/Arkansas work..on Quercus fusiformis-virginianna and post oaks/black jacks. Backfilling dripline trenching just invited a mass of new root shooting, regrafting in as short as 2 months. So we NEVER advocated the tool chest the State promoted.