The white Camellias or of clear color, they are affected by the strong Sun. Also for the intense cold. The petals suffer and become brown.
In the Camellias with strong pink colors or red fort, they do not appreciate so much the effects of the Sun and of the cold.

But there are diseases of the Camellia that are difficult to see. And that turn of brown color the petals.

And also there are plagues. " Cosetacus camelliae " is very common.
It is possible to estimate his presence in the floral cocoons.
" Ciborinia camelliae ", is another very bad disease for the flowers and for Camellia's plants.

Regards.

COSETACUS CAMELLIAE
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Here is a link that might be useful: Ciborinia camelliae

It looks like the problem in the #2 picture, but that site was in Spanish? Anymore advice?

Pardon. The Link, which I put in the previous commentary, was to see the photographies of the effects of " Ciborinia camelliae " in the petals of the flowers.

Now I put a Link, written in English, on the prevention and control of " Ciborinia camelliae ".

Regards.

Here is a link that might be useful: Ciborinia camelliae Control