What is it and does it work on my Mexican key lime that has what appears to be various issues going on from yellowing leaves, to yellowing leaves turn brown and getting holes in them and worst of all, leaf curling.

Answer #3 · Maple Tree's Answer · Hi Rafael-The small amount of yellowing may be too little or too much water. Both will cause yellowing and curling of the leaves including the older leaves. Check soil moisture and make sure it is moist but not too wet or dry. Leave that curl upward and inward can be a sign of too much water. A few of the yellow leaves look as though they may be older leaves. Some of the older leaves will naturally yellow and drop in time. Most of the leaf curl appears to be on the newer young leaves. Several common pests such as aphids, spider mites, and citrus leaf miners will attack the soft new leaves. The older thicker are hard for these insects to penetrate and are normally leaf along. Like I mentioned before check closely for any tunneling or furrows runing through the leaves. I can't see any at this time on your pictures. These would be an indication that the leaf minor eggs have hatched and the larvae are tunneling as they feed. Open the curled leaves and look closely for any signs of insects. Aphids and spider mites are very small so you have to look closely. Sometimes it is easier to see them with a magnifing glass. With only a few of the leaves having brown spots it looks as though this was caused by some type of insect that has entered the leaf to feed on the sap. The leaf tissue will die and turn brown around the damage possibly leaving some holes also. You mentioned seeing some spider like webbing.
I uploaded a picture of some webbing caused by spider mites for you to look at. With the heavy curling of the newer leaves I'm assuming it is being caused by either leaf minors or aphids. I would spray the tree with horticultual oil or Neem oil making sure both the top and bottom of the leaves are well soaked. Having have had both of these insects on my dwarf citrus trees that had curled the new leaves. This damage makes the leaves look lousy for awhile but new growth has always continued without much harm to the trees. Let me know what you find withing the curled leaves.

John)

Answer #1 · Maple Tree's Answer · Hi Rafael-Bacillus thuringiensis (or Bt) is a soil-dwelling bacterium that is used as a biological pesticide. There are several types of Bt that can be used for killing a specific insect. Bt applied to the soil can can kill insect larvae that feed on the plants roots and enter the plant from beneath the soils surface but can also kill insects that feed on the foliage. You would need to know the specific insect you want to kill in order to acquire the proper strain of Bt. In your case other insecticides can normally be used to kill the insects that may be causing the damage.

The yellowing, browning, holes in the leaves, and leaf curling can be caused by serveral things. I would first check the foliage closely for insects. Holes in the leaves may be caused by sap sucking insects such as aphids, mites, and others. Holes can be made by these insects in the foliage causing yellowing and browning of the leaves. Other insects such as leaf miners which bore into the leaves and lay their eggs can cause the yellowing and curling of the leaves. Look closely for any tunneling on the surface of the leaves. These insects are normally found on the new tender leaves and not the older leaves. The tunnels appear as undulating white or yellow lines on the leaf surfaces. Other insects may be seen in grouping on the underside of the leaves only so make sure you inspect both sides of the foliage carefully as many of these insects are very small. Most insects that may have damaged your lime can be taken care of with treatments of a horticultural oil or Neem oil.

Environmental factors can also cause the yellowing, browning, and curling of the leaves. Too much water can cause yellowing and browning. Fungal diseases can cause spotting throughout the leaves and their margins eventually causing yellowing then browning with small holes in the center of some spots.

With the leaves curling and holes showing I'm thinking it may be a pest problem possibly with a nutrient deficiency also. Are the leaves yellowing with possibly the veins staying green? Check the leaves especially the new young tender leaves for signs of pests. Also check the soil and make sure it is not too wet. Eight inches or so below the surface should feel cool and moist but never too wet. If possible upload a picture of the tree and an upclose picture of the infected or damaged leaves. This may help to identify the problem. Above this answer and to the right of your name below your question you will see where you can upload a picture. Let me know what you find after inspecting the tree.

I noted a few links below that will give you some facts about Bacillus thuringiensis and its usefullness and how it works.

http://www.bt.ucsd.edu/index.html

http://npic.orst.edu/factsheets/BTgen.pdf

John)

Answer #2 · Rafael Flores's Answer · Here are some pics. Like I said, it seems like almost 2, 3, 4, or more issues going on, right? I thought I saw what looked some kind of spider web between some leaves. Just a small strand. No bugs or caterpillars spotted.)