|The foliage is yellow and twisted.|
|Citrus trees are evergreen and their leaves can remain for about 3 years; if the oldest leaves are yellowing during the winter months, it's nothing to worry about as they will drop off in the spring when new growth begins. If the new leaves are yellowing, it could indicate poor fertility, a need for ironite, or an indication that a buildup of salt is affecting the roots. You might also carefully inspect the leaves. Leaf miner insects can cause leaf curl, as can psyllid insects. For positive diagnosis, why not clip a few of the affected leaves off the tree, seal them in a plastic bag, and take them to your local garden center or Master Gardener Clinic? Helpful folks there can identify the problem and suggest suitable remedies.
Best wishes with your citrus tree!