In article ,
(Twobtold) wrote:

Seeking opinions on what to do, if anything, about brown spots
and discoloration on Rhododendron leaves. I found info about brown
spots with white in the middle but there is no white spots on these
leaves. Well-establishes plants in Zone 6, NJ

1) Wind and cold damage is indicated when the edges of the leaves become
distorted and turn brown. This occurs frequently in plants that may be
in a colder climate than recommended or in a location with severe
exposure. Note, boron poisoning will create the same symptoms.

2) Large leaved rhododendron are susceptible to sunscald if the plants
do not receive enough moisture before the soil freezes. The leaves curl
in cold winter weather, exposing the central part of the leaf but not
the edges, resulting in the area near the main vein becomes desiccated
and turns brown. To prevent this, water plants thoroughly before the
first hard frost, protect from drying winds, apply mulch, and locate in
partial shade.

3) If a leaf has brown areas with white spots, it probably has a local
fungal infection of Pestalotia leaf spot. This is seldom controlled with
fungicides and is best mitigated by good sanitation and avoiding
excessive moisture.

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