Mm, iron chlorosis doesn't really look like a completely white leaf, as I recall. More of a yellow leaf with green veins. This looks more like maybe a soil pH problem to me.
I'd do a soil test around those plants, asap. You can get a pretty good soil test kit for about $10 at any garden center.
Is the fence made of concrete or stucco, by any chance? Or has it been power-washed or otherwise treated with anything recently? It could be leaching something into the soil that is causing this.
