The soap doesn't contact the leaf miner as it does business between leaf cuticles. Leafminer control is not usually essential to save a plant. Though the tunneling is unattractive, little damage normally occurs. Also, because you have them this year is no indication they will visit next year.

If you feel it necessary, leafminers are best controlled with insecticides that are translocated systemically through the plant, which disperses the poison throughout all living tissues, thus killing insect larvae, which, as noted, are otherwise are effectively protected within leaves. Applications are best made during the egg hatch period or just after when mines are first noted. Merit and Orthene are two insecticides that would work, if you don't eat the fruit, but I would urge you to forgo their use in favor of waiting for better times. Cut through the petiole of affected leaves as you notice them & the tree will replace them.

Al

And I'll add that since you need to bring your plant inside during freezing temperatures, you should prune your plant at any time you need to. This is one of those instances when the needs of the humans come before the needs of the plant.....just be conservative with your pruning, making your cuts to an outward growing lateral branch.

Most plants appreciate an occasional 'hair cut'; pruning is not something we should fear, especially with plants that overwinter inside.

As mentioned above, leafminer larvae tunnel through leaf tissue, leaving unsightly trails. It is unslightly, but basically non treatening. And since you use the leaf, and not the fruit, do not use any chemical poisons. In fact, it is suggested not to use any chemicals on any citrus. I sometimes get leafminers on my basil plants, and I just discard the unslightly leafs. Leafminers have lots of natural enemies, including hummingbirds and parasitic wasp. It is suggested that regular spraying of fish, seaweed, molasses, and garlic helps to repel these pests.

However, citrus, unlike lots of other herbs, generally do not benefit from pruning. However, you might want to check out Texas Citrus Pruning.

Also since kaffir limes are hardy to zones 10 to 11, and you are in 9, as am I, then I wouldn't bother bringing it in unless the temperatures are going to drop below 45 degrees or so for an extended period of time. Last year, even with 6" of snow, the only things that I lost were my basils and one Mexican Key Lime, which came back this spring.

Here is a little bit of information on the Kaffir Lime:

Kaffir Lime Citrus hystrix, c. papedia: Family: Rutaceae (Citrus) Zones 10 - 11. All citrus trees are native to SE Asia. Small shrubby perennial trees, 10-16 feet with sharp spikes and unusual double leaves. It needs well drained soil and direct sunlight. Scent is a cross between lime, orange and lemon. Fruit has a rough knobby surface and thick skin. The outer rind is generally the only part of the fruit used if used at all. The Kaffir lime is quite hardy and easily grown in full sun in a container or well-drained position in the garden. In fact the hotter the spot the better. Like all citrus, feed with a good all purpose fertilizer in spring and donÂt forget to give your kaffir lime a little bit of a feed in winter to help it put out a fantastic spring flush of growth. When you notice a yellowing of the leaves, it might be chlorosis, but not iron, but rather zinc. IÂve been told by a owner of a citrus farm in the Valley that generally citrus that get chlorosis generally need zinc, then manganese, and then if these two donÂt work, try iron as a last substitute.

Culinary: Their leaves, zest, and juice are used in Thai, Cambodian, and Indonesian cooking. It is used in Thai dishes, from soups and salads to curries and stir-fried dishes. They are the ingredient that blends marvelously with lemon grass and lime juice in soups.

Dear Tapla, Rhizo_1 and ltcollins1949,

Thank you so much for your advise. I was afraid that my plant might die from these leafminers but now that it won't I am not going to use any more insecticide. I use the leaves for cooking and that is why I did not want to use insecticide at the beginning. However, I could not find much information about this on the net and thought I had to use some insecticide to keep it from dying. I am so glad I found this forum and you have all been so very very helpful. I am not so worried now that I know I will not lose my plant.

Thanks again.

We are herb growers in Australia, and chemical free I would try spraying with garlic or molasses. We use a lot of molasses it's great stuff. Good luck

I bought a Kaffir lime tree from a local nursery few weeks ago, and recently found out that there is a branch with some big leaves (some look similar to lemon leaves, light green & giant)grew out, and those leaves don't smell the same as usual Kaffir lime leaves. Wondering what happens to my tree? and any suggestion to correct the problem? Thank you very much!

jenny, i know this is a year old post almost, but in case you still have the problem (or if others do), thought i would post anyway. i had same problem and wrote to the nursery. most kaffir limes sold outside their countries of origin are grafts onto other healthy citrus trees. if you have a branch that isn't kaffir lime, then all you need to do is prune it off. if you look carefully at the trunk you will see that it is probably growing below the graft line.
hope this is helpful.
kgg