Jerry, hard to tell with the dead branches, since we can't see the stems. Prune it back to live wood, and cleanse your pruners with 1:10 bleach with each cut. The first and largest problem I see is all the grass under your tree. Your citrus is going to be in competition continually for both macro and micronutrients with the grass, which is a big nitrogen hog. Get rid of the grass from under your tree, out to the drip line or beyond (edge of canopy). Also, make sure your citrus is not getting sprinkled by your lawn sprinklers. Citrus really do not like their trunks hit with lawn sprinklers, it can eventually kill a young citrus tree. Create a nice well under your tree, and water deeply once a week (twice if it is really hot and dry). The chlorosis you see I suspect is due to the competition from the grass. You should be fertilizing with prescribed amounts of a citrus fertilizer every 2 to 3 months. I've included a link to your local U of Florida Extension program for citrus pests, and I would definitely do a little searching through this site. This is your resource for where you live for citrus, and you should find a lot of great info on their site. Another link on their site, Dooryard Citrus Culture & Care will help you understand how to grow citrus at home, and the best conditions for your home citrus:

U of Florida IFAS Extension: Cultural Practices for Dooryard Citrus

Patty S.

Here is a link that might be useful: U of Florida IFAS Extension: Citrus Problems in the Home Landscape

Thanks, Patty! I didn't realize the sprinkler was a problem -- I'll turn it off. I cut the dead branch off right after I took the photo, and there are no more dead branches now. If another branch dies, I'll prune it back as you suggested. Would close up photos of the stems help you? I can get close up photos of anything you need if you'll tell me exactly what to photograph -- I'm a photographer. As for grass under the trees, there actually isn't any -- the photo is cropped to only show the canopy excluding the spot directly under the tree. There is no grass anywhere near the tree trunk and I've keep it cleaned out beyond the drip line from the day it was planted. I have fertilized according to the prescribed schedule with organic citrus fertilizer. It's possible that I have over watered -- I've watered the Robinson and Satsuma almost every day since I planted them. Thanks for the link -- I'll check it out. Jerry

Well, that's helpful, Jerry! Yes, do include close up photos of the branches. Look for small bored holes. Not as familiar with pests in your neck of the woods, but sudden branch die back usually means the cambium layer was interrupted, and the branch is not getting any nutrients. Good to know about the grass, definitely an issue with citrus. And yes, this faint chlorotic appearance could just be from too much water washing away the micronutrients. Otherwise, your tree actually looks pretty darned good.

Patty S.

Since this tree is specifically 'Robinson', and since you are in Florida, I suspect you're seeing Robinson Dieback Diseases, which is unique to that variety, caused by the fungus Diplodia natalensis. Not much to be done about it. Your second photo shows some manganese deficiency, but that's easily corrected with a nutritional spray containing Mn (note that it is not the same as magnesium, Mg).

Malcolm, thanks for your reply! I think you've hit the nail on the head. As I read more about citrus and Robinson specifically on the University of Florida IFAS links I think I made a poor decision when I chose a Robinson. Looks like even if it does live I'll have to plant a pollenizer for it. If I might ask, which pollenizer cultivar would you recommend? My next door neighbor keeps bees and his bees are regular visitors to my back yard so I should not have a problem in that regard. Jerry

Jerry, As long as there are other citrus trees in the neighborhood, you're probably just fine. But if you want to plant a pollenizer, nearly any other variety that makes good pollen would be fine (any grapefruit, tangerine, or tangelo; any orange other than a navel; any lemon; not 'Tahiti' lime)

Malcolm - My neighbors on all three sides have citrus so I'll wait and see what happens. I realize it won't be producing for a while until it gets established. I'll just keep a close eye on it, back off on the water, and give it some nutritional spray containing Mn. If another limb dies I'll take some close up photos and upload them to this thread for examination. Thanks again, Jerry