A tree can't very well wash away an infection that has invaded its leaves.
The only real way is to drop its leaves.
If you've walked in the woods often enough, you'd see this.
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BMO
mmm..."infection" is quite a broader term than "fungi" - but I'll give you the benefit of the doubt that you're not moving the goalposts.
In any case, may I suggest you ask yourself "what do leaves do, and how do they do it?" Then ask yourself "what are the conditions required for fungi to propagate?"
After thinking about your answers, ask yourself why leaves would *ever* need protection from fungal infections.
(hint: fungi infect trees through the roots/bark wounds for a reason)