Subtropical Fruit Crops Research & Education
University of California
Subtropical Fruit Crops Research & Education

Distinguishing Between Drought and Avocado Root Rot

We recently had a series of workshops on Avocado Root Rot and how to manage it.  A common question was how to figure out whether the tree was diseased or just stressed from lack of water or from an accumulation of salts that is also a reflection of how water is being managed.  So there are several steps to follow to figure out a droughted tree from a root rotted tree.  If the tree is stressed from drought, eventually though, it quite likely can lead to root rot. 

So here are the steps:

First, look at the canopy overall and then more closely

Then, look AT the ground

Then, look IN the ground

If you look at the tree from a distance and the canopy is thinning with dieback (staghorning)

And on closer inspection, the leaves are flagging

And when you look more closely, the leaves are small, yellow, have tip burn and there are lots of flowers

And the fruit is sunburned

And you look at the ground and there's no natural leaf mulch.  No energy to produce leaves, no canopy to portect leaves from wind?

Now is the time to think there is something seriously wrong.  There is something wrong with the water uptake in this tree.  Either a lack of water or a lack of roots.  Is it the timing, amount or distribution of the water? These are all issues that can be corrected if there's sufficient water to do so.  Maybe the soil is too wet?  It could be asphyxiation.  Lack of air.  That can be corrected. 

If it's not too wet, when you apply water, does the tree perk up?  Give it a couple of days.

If not, then start digging. This is something that should be done on a regular basis just to see how those roots are doing. 

And when you start digging, there's no roots

Or only big roots

And if you do find any little roots, they are blackened and brittle

And you have applied water and the tree doesn't perk up,

The tree probably has Avocado Root Rot disease caused by Phytophthora cinnamomi.

There can be other reasons, for a tree collapse like this, like a gas pipe leak, gopher activity in young trees, a chemical/fertilizer spill.  Probably other things that kill roots, but a field diagnosis like this process can pretty much identify the problem as root rot.  It can then be verified by a lab test to make sure.  However, there are times of the year and disease conditions when a test will come back negative and it might be necessary to retest with another sample at another time of year. 

avocado root rot black brittle
avocado root rot black brittle

avocdo root rot big roots
avocdo root rot big roots

avocado root rot no roots
avocado root rot no roots

avocado root rot no mulch
avocado root rot no mulch

avocdo root rot leaves flowers
avocdo root rot leaves flowers

avocado flagging leaves
avocado flagging leaves

avocado thinning canopy
avocado thinning canopy

Posted on Monday, February 11, 2019 at 6:00 AM

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