Sit, don't know if this will help or not, but in the future, once you see rootstock, remove ASAP..it takes nutrients from main tree. That rootstock takes over fast, and all we find are large thorny stems.

Has your tree ever produced full size, mature fruit in the past? Toni

Toni - it produced one, count 'em one, fabulous ruby red grapefruit last January that was perfect! Many of the specimens on the tree now are yellowing at a small size, or looking a bit bruised. They are not even close to the full size of the grapefruit that came off in January, so I'm concerned I'll lose the whole crop. My garden center told me thin the crop by 50% per branch - if there are 3 on a branch take of at least one fruit, maybe two. I haven't done this yet. Still searching for the right remedy. He also said that not all citrus ripens exclusively in winter. I;'m in southern california, in the san fernando valley, and we have had some very hot temps lately. I'm giving the tree less water, but I don't know why the fruit is accelerating its yellowing so fast!