Was this yellowing at the top or bottom leaves? Was the leaf completely
shrivelled and yellow when it fell? When you say the roots look
healthy, are you just talking about the surface ones? Tip out the plant
and check the entire root system. Also, hold the dropped leaf, and the
leaves on the plant to a bright light so you can see and check through
the leaf. Does everything look normal, i.e. even colour?

Cheers,
Xi

Eric wrote:
I live in SW Florida and I have a shade house. I've been watering once
a week and the roots and the rest of the plants look healthy with
larger leaves. The've been fertilized and I treat them with neem oil.
They all have spikes and are almost ready to flower. The yellowing
happend so fast and it was the entire leaf. I was wondering if the
plant was drawing energy from the leaves for the flowers because I 'm
not using enough fertilizer.