Believe it or not, avocado bark is like our skin and gets sunburned. If left unprotected, a branch that is exposed, especially to the south or west sun, will burn.
The branch in the photo above is on a young Pinkerton avocado tree that grew out a long limb which drooped enough to expose some of its young skin to the overhead afternoon (west) sun. It got scorched during a recent heat wave.
What to do? Put on sunscreen. For avocados, Coppertone will not do. But white latex paint will. It doesn’t need to be full strength: diluting the paint 50/50 with water will make a sufficiently opaque coating.
And then paint it on.
With the white latex sunscreen, the branch is protected and usually won’t get burned further. If left unprotected, the branch would get burned so badly that the bark would turn completely black and begin cracking and eventually die.
The best case scenario is that new leaves and branches grow over this exposed branch and shade it. However, if this doesn’t happen and the branch remains exposed to the hot sun for many months (no leaves grow over it to shade it), then it will eventually still be damaged somewhat even though it is covered with paint.
Here is such a damaged branch on a Reed avocado tree that has been exposed yet painted for a few years now:
Notice that the bark is slightly damaged and cracked on the top but the branch remains alive. More than that, what you can’t see in the photo is that it is also fruitful. In fact, it was the weight of the fruit a couple years ago that bent down the branch and exposed it to sun in the first place.
It always pays to paint any section of a branch on your avocado tree that doesn’t have leaf cover to protect it since this gives it temporary relief until leaves can eventually shade it naturally.
Incidentally, avocado fruit can get sunburned as well. As with branches and leaves, fruit that get sunburned are usually on the south or southwest side of the tree. Sunburned fruit develop yellow spots that turn black if they’re more extremely burned. Don’t cull these fruit though. They’ll usually mature and ripen just fine.
Sunburned leaves on new trees
If you plant an avocado tree in the summer, there’s even the potential that the leaves will be sunburned during the first few weeks in your yard. This can happen if a couple of conditions coincide. One, you live away from the beach where the temperatures get to 90 and up. And two, the tree had been kept in some shade at the garden center or had just come out of a greenhouse at the nursery before being delivered to the garden center. The relatively intense sun of your yard can be too much too fast. I’ve experienced this many times.
To prevent it, I’ve taken to shading any such trees, especially on their south and west sides.
I have some 60% shade cloth that I use for this, and sometimes I wrap it around a tomato cage, as here:
I remove the shade after a couple weeks and during a mild spell of summer weather. This helps the new trees acclimate and avoid sunburn. Always remember that keeping an avocado tree well-watered is important in helping it stand up to heat. (See my post, “How much and how often to water avocado trees in California.”)
Extreme heat waves
And then there are record-setting heat waves like Southern California experienced on July 6 and 7, 2018. The thermometer in the shade on my porch reached 113! Avocados are said to shut down the photosynthesis in their leaves when the temperature reaches the 90s (read more about that here), but then if it gets over 100 leaves may start to burn. Any new (red) leaves at the tips usually burn first, and then if it gets around 110 even old leaves and small branches wilt and burn.
This is if the tree is healthy and well watered going into the extreme heat. If not, then damage will occur at lower temperatures and more extensive damage will occur overall.
There’s nothing you can do to entirely stop heat damage to an avocado tree once the temperature reaches around 110 unless your tree is very small. For a small tree, shade it. Simple as that. Use shade cloth as I described above, use a beach umbrella, a chair, a table, whatever fits over the tree. (Beware of entirely enclosing the tree’s sides and creating an oven, however.)
For a big tree, the only practical thing to do is mitigate the damage by making sure that the tree is well watered just before the heat hits. Also, maintain high soil moisture throughout the hot spell. This might require watering every day for a few days. For more on this, see my post, “How to water plants through a heat wave,” and “Caring for your garden during a heat wave.”
After the heat wave has passed, don’t be in a rush to prune out burned leaves and twigs. Just as with frost-damaged leaves and twigs, they’re ugly but they may provide important shelter to surrounding leaves and branches. The best thing to do is leave them alone until you see new growth sprouting up behind them. At that point, it’s OK to prune out the dead stuff; it’s definitely not necessary though. If you do want to clean out the burned material, you can often just crunch it and break it off with your bare hands at that later time.
(Read about dealing with sunburned avocado trees from a farmer’s perspective in this blog post from University of California Farm Advisor Ben Faber.)
Here are a few of my sunburned avocado trees on July 8, 2018:
Will your avocado tree recover if it has been severely burned? That depends both on how healthy it was before the burning as well as on how carefully you care for the tree afterward.
Look at these toasted young avocado trees:
It so happens that these trees were “toasted” by extreme cold rather than extreme heat. But the principles are all the same.
These young avocado trees were very healthy before the cold damage, and they recovered even though almost every leaf of every tree was lost. Here’s how: all exposed branches were painted, and water was given judiciously. If a tree has no leaves, it uses very little water. If you continue to give it a lot of water, as you had before, then its roots will rot. Therefore, until the tree has grown back a full canopy, you must be cautious about only watering it once the soil has dried somewhat.
On the other hand, if a young tree went into severe heat already in marginal health and got toasted, it’s probably better to save the effort and buy a new, healthy tree to replace it. I’ve tried to coddle sickly young avocado trees many times and found it rarely worth the work.
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