I have two avocado trees outdoor planted in different locations. One is <1yr the other is >20yrs. Both with direct sunlight. Zone 10a. The trunks on both have randomly turned black about 5" up the trunk to the top. The leaves are dead or dying. One is on drip watering (mature one) and the baby is within a self watering area.
Help.
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Avocado trees will develop root rot when over-watered. The soil around the trunk and roots should be allowed to dry out some between waterings. To check if the tree needs watering, you should dig your fingers down into the soil about 5 inches deep. If the soil is still moist, skip the water, and if dry at that depth, water sparingly. From your explaination of your watering system, you may be over-watering. Another problem can be with the water itself....too many salts and minerals in the water. My best advice is to take away the drip irrigation, carefully dig up and replace as much soil as you can without disturbing the trees' roots too much, and watch your watering. With black trunks and dead leaves, it might be too late to save them. Good luck.
This is a long term disease that has been studied for years but they still can't find any cure for this. The trees are suffering from root rot. The main feeder root of the tree is diseased and turning black. The small feeder roots that should be white are also turning black. You will see some of your branches at the tip turning black also. There is a way to try and save your tree if you start right now and start using integrated cultural management practices.
The avocado tree roots will die if they are constantly wet. They need a really good drainage system so the roots can stay healthy and continue to grow. Considering one of your trees is on a drip watering system and the other is in an area that has self-watering the trees are getting way too much water and this is destroying the roots of your trees. An avocado tree roots will not reach out and search for water. The roots are in the first six inches under the soil. Only water the trees when the soil is dried out and do not keep the soil moist and wet all the time. You should also apply gypsum and mulch to the soil on the top and around the tree. Here is a good article that will teach you how to control and stop root rot in your avocado tree. I have highlighted the main issues here and there are a few other things that you should look at and do. www.californiaavocadogrowers.com/
You may be able to save the young tree by transplanting it but I really doubt you can save the older tree.
I would recommend that you contact your county extension agency and ask for help as they will know all about what is happening to avocado trees in your area. It would be best to include several pictures if possible.
www.gardeningknowhow.com/
If you try to save your young tree; when you dig up the small tree, examine the trunk and roots and try to carefully remove any of the soft, diseased looking bark and roots.
I would ask for advice from the experts before applying any DIY solutions.
Some people say to pour a solution of 3% Hydrogen Peroxide mixed with water (one part peroxide -2 parts water) over the entire trunk & root system to kill the fungus but I have not used this solution but I do not think it will hurt the plant.
Another solution sometimes recommended is 2 teaspoons vinegar (white or apple cider are sometimes use) to one quart of water.
Some people say you can pour this solution around the trunk of an older tree and it sometimes helps if the tree is not too far gone.
This could be disease from sun burn, or cankers. They like moist soil with good drainage. Avoid over watering this causes disease.
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