Avo's are very suseptable to root rot. I'd guess that 90% or more of tree loss, especially new trees, is from that. Too much water. once you have lost one tree to it in a planting area, the next tree will have a very high chance of dying from it to (it's prevalent in the soil now), so be sure to try a spot several feet away if you try again. good luck

I would agree with the previous assessment. Young avocados cannot tolerate anything under 30 (or over 100)... but it sounds a lot like root rot which unfortunately is common in avocados, at least here in CA. Overwatering, or trying to grow them in clay or boggy soil, makes the plant susceptable to rot root (they need well-drained moist soil but never wet feet), which often shows up as branch dieback and general lack of vigor due to the damaged roots' inability to uptake nutrients and moisture. The symptoms are often misdiagnosed as lack of water, so most people make it worse by watering more. I would keep cutting it back and adjust the water. Avo trees are sensitive to salts, so water deeply in well-drained soil and let dry before watering again. We usually deep water twice a week on average. I've seen young trees come back after being cut off just a couple inches above the graft... so don't give up unless you can confirm root rot.

@socks: Yes, the trees looked healthy when we bought them. They are planted in our backyard. The backyard soil has a lot of stones/rocks since we purchased the property, and it looks like a construction site. I was told by the nursery that native soil is sufficient for planting avocado, as they have sensitive root system and don't like compost and manure. I told the nursery the soil in my backyard has a lot of stone and the quality is poor, but they told me it's fine, and not to water the trees often. When we were planting the trees, we filtered away the rocks/stones, so the soil was like thin powder form. Since I haven't been watering the young trees much, the leaves started to fall off. The nursery told me that it's lacking of water, so I started to irrigate more often. Then, the new leaves, buds, and branches are starting to die back. I contacted them again today, and they said the tree has root rot now, and the most I can do at this point is to reduce the irrigation amount and keep my finger crossed. I did research online, and i'm not sure if it's really root rot or not. If it is, I doubt the trees can survive without taking any treatment.

Sorry to tell you, but your tree is definitely dead - or at least in the process of dying. I see you have a bag of fertilizer there. Did you recently fertilize it? Avocados are very sensitive to salt build up and will experience salt burn when you fertilize them. Too much of it will cause necrosis to travel from the roots, up the stem and out toward the tips of the branches. From the looks of it, your tree is experiencing this as the trunk is dead and the extent of dead tissue is progressing toward the branch tips. This is even an issue here where we grow avocados in the ground. A friend of mine sprinkled fertilizer on the surface of the soil near his 10-foot avocado last summer. With all the rain we've had, the fertilizer dissolved and soaked into the ground, causing the avocado to burn and die - a whole 6 months later. It is best to not fertilize young avocado trees at all.