Saturday, January 21, 2017

South Pasadena Ailing Avocado

Area underneath Avocado tree. 

South Pasadena Ailing Avocado

Q. I live in South Pasadena and we have an avocado tree that is more than 50 years old that appears to be dying. The canopy has shrunk significantly, the leaves have brown edges and are falling and there are a lot of dead branches. In addition, the tree is producing less and less fruit each year.  

We've tried to increase watering the tree, but it does not appear to be helping. Any recommendations to help save our tree?

A. You actually have a very lucky tree; the conditions I see in the photo are not the best for avocados.

The area underneath an avocado tree should be free and clear of lawn and high amounts of soil compacting human activity. Also, the best thing to have underneath an avocado tree’s canopy is a thick carpet of its own fallen leaves.

The avocado’s leaves decay to from a substrate that is perfect for those organisms and microorganisms, insects, worms, protozoa, bacteria, fungi, nematodes etc. which are beneficial to the avocado. Add to that the fact compacted soil tends to be devoid of these organisms and the amount of water that the lawn underneath the tree needs to keep it green is an ideal breeding ground for a type of fungi-like organism (Phytophthora) that eats avocado roots for dinner, and you have the perfect recipe for the slow but sure demise of your tree.

Also, the drought has probably caused considerable salt buildup underneath the root zone of the tree. Fortunately, these recent rains should take care of that.

So what to do? Remove all lawn from underneath the canopy of the tree (on both sides of the fence if possible). Apply horticultural gypsum to the soil at the rate of about 25 pounds scattered throughout the area underneath the canopy, then lay down a 5-inch-thick layer of shredded (if you don’t have squirrels or rats, they love the shredded stuff) or small sized (this one’s the best) fir bark underneath the entire area underneath the canopy of the tree except for an are 4-5 inches from the trunk (you don’t want the fir bark piled up against the trunk, that can cause a condition where the tree’s bark becomes infested with insects and fungus owing to the humidity raising and fungal spore nurturing nature of the fir bark). Also Then allow the avocado’s soil nurturing leaves to remain where they fall in Perpetua.

Do not feed your avocado much; high nitrogen levels in the leaves and tissues favor pest infestation. Use about ½ strength Avocado/Citrus food just once a year (in November -it’s too late now). If you have a problem with leaves falling off after this, it is most probably Persea mite. This pest is mostly a nuisance but during the drought has become more than that, causing total defoliation in some cases. It can be controlled using horticultural oil and cultural management.

Please let me know how these measures are working or not in about six months’ time. 

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