Differentiating Between Drought and Root Rot

  • Feb 12, 2019

Dr. Ben Faber, soils/water/subtropical crops advisor for Ventura and Santa Barbara Counties, recently shared a blog post about the steps California avocado growers can take to determine whether a tree is afflicted by drought or Avocado Root Rot. Following is a summary of his recommendations.

The first step is to assess the tree’s canopy. Step back and take a look at the overall canopy to assess the level of thinning and dieback. Now examine the leaves up close. Are the leaves limp, yellowing, have tip burn and are topped with lots of flowers? Is the fruit sunburned? These are signs that the tree is under stress and doesn’t have the energy to produce and maintain healthy leaves.

Having collected observations of the canopy, now it’s time to look at the ground surrounding the tree. If there’s not natural leaf mulch beneath the tree, this also is indicative that the tree is stressed and is struggling to take up water. The issue could be a lack of water (poor irrigation timing, amounts or distribution) or a lack of roots (Avocado Root Rot).

To determine whether the water uptake issues are due to poor irrigation or Avocado Root Rot, apply water and observe the tree for a couple of days. Does the tree perk up within two days of irrigation? If not, it’s time to dig into the soil around the tree to observe the tree’s roots.

Upon digging, if you observe no roots, only large roots or small roots that are blackened and brittle the tree most likely has Avocado Root Rot. This can be verified with a lab test, but Dr. Faber notes that during certain times of the year and with certain disease conditions, the test results can return a false negative. If you suspect Avocado Root Rot and the lab test comes back negative, it’s best to retest with another sample later in the season.

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