Few questions: is it in the ground or in a pot? When was the sequestrene applied precisely, both times? Is the Camellia in full sun?

Thanks for the reply. It's in the ground. As for the feed as precisely as my friend was able. It is in full sun. Hope you find an answer. Thanks for your trouble.

I'm sorry, I must not have phrased my queries well. I'm asking when the sequestrene was applied - you say its had two lots, were they both done this year, and if so, when?

Probably my mistake. It was fed first a month ago and then two weeks after that. Thanks for your hard work and good luck finding an answer.

Okay. Sequestrene should only be applied about once every six months, from what I recall, first of all. Second, it's not a feed, its simply an iron tonic. I suggest that your friend either goes out and buys a specialist feed for acid loving plants (Miracle gro makes one called Rhododendron and Azalea/Camellia feed), OR applies a few handfuls of fish, blood and bone, OR Vitax Q4 around the base of the plant, lightly forked or raked in, and then give the plant a thorough soaking with the hose, either by leaving it trickling and moving it occasionally for a few hours, or buy sprinkler. The yellowing of the leaves could have been corrected by the sequestrene, if we'd had enough rain to wash it down to the roots, but it might be a magnesium shortage - using the specialist acid feed I mention will put that right.
All this assumes that your friend has inspected the leaves, stems and branches thoroughly for signs of infestation, particularly by scale insect, or disease/damage.

Thank you very much and my friend is very grateful.

As bamboo has said it is usualy caused by an iron deficiency or lack of magnesium.

Thanks.