Question
HELLO - I HAVE 4 SAGO PALM TREES - 2 ARE IN PART SHADE AND 2 ARE IN FULL SUN - THE ONES THAT ARE IN PART SHADE ARE LOOKING AND DOING GREAT - THE ONES IN FULL SUN HAVE YELLOW/BROWN PRONGS TO ABOUT HALF WAY DOWN THE TREE - THE BOTTOM PRONGS ARE GREEN AND LOOK GOOD - I DON'T SEE ANY MILDEW OR SCALES BUT THE TREES ARE DYING AND I DON'T KNOW WHAT TO DO - THEY DO GET ENOUGH WATER - PLEASE HELP!

Answer
Sharon you may just need a good shot of fertilizer as trees in the sun tend to use more fertilizer than those that arent.  There are many nutritional elements that change as a result of more of less light.
You may also need a plant enima as your problems could be systemic.  Bacteria or fungus may be blocking the flow of nutrients for proper growth and greenup.  

I have been using a product on Sagos for about 8 years now called Atomic Grow.  Its a foliar spray and will make Sago Palms look amazing.  It will remove scale too.

atomicgrow.com
atomicgrow.net

James