Sago Palms are a type of living Fossil. There are actually a couple of types, when speaking of Sago Palms most people are talking about Cycadophyta. These palms are mostly problem-free plants. Yellowing is a natural reaction to nutrients conserving nutrients: however, there are certain precautions and measures to take when caring for your Sago Palm.
Caring for Your Sago Palm
As these plants grow upward, the bottom layers become yellow and should be removed; however, if the tops are yellow, it could indicate a few different things that require action to maintain the health of the plant. There are a couple of possible issues that cause the tops of these plants to turn yellow.
Florida has very porous ground, a mixture often of soil and at least some sand to higher ratios of sand to soil. This causes nutrients to wash past the roots of many plants. You can read more about this problem, diagnosis, and solutions at ufl.edu
Cycad Aulacaspis Scale
Cycad Aulacaspis Scale, or Aulacaspis Yasumatsui, is a scale insect that feeds on your Sago Palm, and some other poor unsuspecting plants of the same family. For further reading, take a look at this PDF by ufl.edu.
Yellowing of your Sago Palm can be simply a result of too much water in the soil. This can lead to root and other issues. Better timing of your irrigation system could fix this problem.