just guesses:
spray it out your attic window?
maybe run aircraft cable to the top of the tree and with your dispenser
head attached to a pulley riding on the cable, guide dispenser head
into place and send it properly diluted liquid?
explore electric [or propane?] operated foggers?

JimL wrote:
Any ideas on a 'cheap' way to spray fungicide/insecticide on my 50
foot tall pecan tree.

I really don't understand why a pressure washer couldn't be used, but
evidently they don't work as a long distance sprayer.