Some trace metals can be toxic, I have seen deficiencies, color changes in the leaves usually yellow or lighter shades of green become apparent in different patterns, depending on the elemental deficiency. Leaf necrosis occurs usually with too much of a trace metal, especially when waste sludges are used, or near a septic tank.
Magnesium might be the problem. There can be too much of a good thing.
Soil and tissue samples could confirm.
This is just a possibility, a WAG (
) more than a hypothesis.
