What you are noticing is Asian Cycad Scale insect, an introduced insect that has killed many sagos throughout Florida. For the homeowner, horticultural oil sprays presently appear to give the best control. Apply the spray weekly to affected plants, treating the upper and lower surfaces of leaves, the central dome, and also the trunk. After the third week use a strong stream of water along with brushing the fronds to wash the insect residue from the plants. If the infestation continues, repeat oil applications as needed following label instructions. 

Additional Resource
http://edis.ifas.ufl.edu/IN253