P. syringae / phytophthora in H.C's.

[APC]

As mentioned in another thread, we possibly have the aforementioned infections on one of our H. chestnuts and also on one of our limes. I have been asked to investigate nearby rhododendron for signs of the infection. If this is healthy, it will rule out those infections. But, what sort of distance should I be investigating? Bare in mind the trees stand in a parkland setting where there are clumps of rhodie dotted around the place from within 10 metres. Do I check just the immediate area? Do I widen search for 50, 100, 250 metres?

Any help would be much appreciated.

Ta!