Question
I have two (2)date palm trees and both have a thick white web type substance that is spreading on the trunks, the male has more on him than the female. The web is very close to the trunk and looks like it is a thick mass. Can you tell me what it is.

Answer
Sounds like powdery mildew.  It could become a serious problem if it manifests in the heart.

You need to rebalance your trees nutrient flow and nutrition.  

I would use Atomic Grow from CrowleysNursery.net.  It is systemic so you will need to spray it in on th fronds and down into the heart.

James