Cirtrus plants are suffering from Leaf curl and yellowing leaves

I have four citrus trees, three that came with the house and were nice a healthy, lemon, mandarine and ornamental grapefruit, and one that my parents planted when they were here a few years ago, a lime.

Recently I have had problems with my Citrus Trees, some of the problem was exposure to a weed killer and my lemon tree which has flowered and fruited each year decided to drop all its leaves and start dying back. A couple of months ago after I watched a program on the telly where they chopped back a tree back to a few sticks to prevent a disease, I took drastic action on my own lemon tree and chopped it back to a couple of feet off the ground. it is now starting the grow back, the growth is about 6 inches. I figured that it had a year from when I cut it to grow branches, flower and fruit.















Lemon Tree after drastic action















Leaves on Lemon Tree growing back

My mandarine tree has also started to die, on one side only, so this also needs attention. This tree fruits every other year with loads of fruit. In 2003 it fruited so it was not due to fruit this year anyhow. I can remember that I read somewhere that to stop the fruit occuring every other year that you should thin the tree out so it doesn't 'wear' itself out. Looking at this bush I noticed the other day that it's leaves have started to curl, and when inspecting one particually curly leaf, I must have interupted a snail party within the leaf as they all came toppling out.















Snail Party















Yellow leaf on Mandarin


Four Wind blowers are citrus growers so should know a thing or two and this is what they say;

Citrus Leaf Curl

If the leaves on your dwarf citrus are curling, there are three common
possibilities:

1. Some insect pests will cause some leaf curl. In spring, aphids might do this
   on soft new leaves. Look inside the curl for presence of insects. If none are
   present, consider 2 or 3 below.



2. Overwatering can cause leaves to curl or cup INWARD. Also, stress from very
   hot weather will do it.



3. Sometimes leaves will cup DOWNWARD in the late fall or early winter. This is
   not a problem to worry about, as the new growth will come out with normal shaped
   leaves in the spring and the trees seem to produce flowers and fruit in
   proliferation once established.

This forum post also has loads of info on looking and treating for bugs on lemon trees, which can also be a problem.

This guy here has posted pictures and life cycle of leaf miners which also cause leaf curl.

Another problem is the knobs on my grapefruit, if I remember correctly this tree is supposed to be ornamental and it has always fruited well, but as time has gone by the fruit s more knobbly each year. I will update when I have found the problem.

Knobbly, stunted grapefruits