Hello, I have 5 of the same palm trees. I think they are Queen Palm, but am not really sure.

The three in the front yard look amazing!

Two, in the back yard, are not nearly as healthy, so I gave them some "Southern AG, Palm Nutritional Spray. I actually put it in the soil since it was an option. The directions say 2-4 oz for a medium sized tree, so I was using 3oz mixed with a gallon of water, every 2 weeks. I've done this for about 5-6 months now.

After a few months, one of the trees looks really healthy now, but the 5th tree, the one the picture, did not improve. It actually looks more yellow in person than it does in the photo.

All of the trees get the same amount of water. We cut back for winter and usually add more when it gets warmer (we're in Palm Springs, CA). I've checked for bugs and there is no infestation or anything. I also tried to give it the stick fertilizer bars for about a year (every 3 months). I just see no improvement. Anyone have any idea what could wrong with it? I really appreciate any advice.