Is it a disease? Is it a beetle boring into the tree? It looks scary when your avocado branches have volcanoes or streaks of white powder on them. What is that white stuff?
It is the dried sap. When a branch is injured in some way, the sap runs just like your blood runs when you scrape your knee, and then this sap dries into a white powdery form on the outside.
More specifically, this avocado sap is a seven-carbon sugar called mannoheptulose, or in a slightly different form it’s called perseitol. That name might seem familiar if you remember that the botanical name of the avocado is Persea americana.
I can’t taste the seven carbons, but I can taste the sugar. You can wipe a little powder off with your finger and lick it and taste the sweetness.
Why is it happening?
Why is a tree oozing sap? Is it anything to worry about? Avocado trees exude sap for various reasons, but they are all related to stress or injury.
The injury can be straightforward, such as a kid climbing the tree and scraping its bark, or your pruning of a branch. In such cases, seeing the white exudate is actually a good thing. It means that the tree is healthy and it is merely trying to protect its wound.
Also, avocado trees periodically shed branches, especially small branches on the interior of a large tree’s canopy where there is not a lot of sunlight. Often, I have noticed, some white powder will form at the base of such a branch as it dies and dries. (See an example of this in the photo at the very top.)
Then there are many other less obvious reasons for the white powder to appear on avocado branches or trunks, and they can be harder to diagnose, and they can even be a challenge to correct.
What to do about it?
Recently, Ben Faber gave a webinar presentation on these harder-to-diagnose issues, which he collectively referred to as avocado cankers. Faber is a University of California farm advisor for Ventura and Santa Barbara Counties. He gave an overview of six stresses, or pests or diseases, that will cause some form of white powder to appear on avocado trees.
If you’ve got white powder appearing on your avocado tree’s branches or trunk, and you don’t think it’s related to a pruning wound or some other minor physical damage, or a small branch dying naturally, then watch Faber’s presentation, or see this blog post by Ben Faber, or look at the University of California Integrated Pest Management page for causes of cankers on avocado trees.
Do note, however, that most of these diseases appear in avocado trees that are under water stress, says Faber. And often they can also be corrected by good irrigation. These are diseases with names like Black Streak, Bacterial Canker, and Botryosphaeria Canker.
My experience certainly corroborates this. After the record heat wave in early July 2018 (117 degrees in my area), there were a high number of branches with white exudate on my Hass avocado tree. Many of these branches also died back.
In a sense, it was due to water stress but also it was due to the extreme level of heat. At a point, avocado trees can’t handle heat so high no matter how well you’re watering. But if you’re watering well in general, the symptoms will be short lived in a mature tree, says Faber.
So just after that record heat, my Hass tree had symptoms consistent with Botryosphaeria Canker (sometimes called Limb Blight), but I watered as best I knew how, we got great rains last winter, and I believe I watered very well this past summer too. The tree has recovered well and is carrying a decent crop.
It has long been observed that, for avocados in California, getting the watering right is getting almost everything right.
(See my posts, “How much and how often to water avocado trees in California” and “Protecting avocado trees from heat.”)
So what is that white powder? It’s dried avocado sap. What does it indicate? Usually nothing serious, but possibly a stress or disease that is related to watering. Any other possibilities? There is the remote chance that you’re dealing with a pest/disease complex like Fusarium Dieback (caused by shot hole borers) or a very serious one that has yet to appear in California but has devasted trees in Florida, called Laurel Wilt. If you suspect that beetles are boring into your avocado tree, do check out these links.
Lastly, should you leave the white powder alone or wipe it off? I don’t know if it matters. I’ve always left it alone because I think of it as similar to a scab. Except that sometimes out of curiosity I have to check if it’s still sweet.
(Read more about the workings of mannoheptulose and perseitol in avocado trees in the South African Journal of Botany.)
You might also like to read my posts:
Thanks for this post, Greg! I searched all around the internet trying to figure out what that white powder is and you are the first person to explain it so clearly. Your blog is a fantastic resource for backyard avocado growers and much appreciated.
I agree,
I have a white like fungus on 2 lower branches and haven’t been able to kill it. It seems to spread up the branches slowly.
I’ve tried brushing on Vinegar, fungus treatments like Dr. Earth, hydrogen peroxide, nothings working! I am in Orlando Florida.
I do have Mole issues in the yard and noticed a nearby Mole trail leading right up to my Tree, Maybe it’s the problem.
Its its first year it has produced fruit, as many as 80 avocado’s so far, Has Mexican, I don’t want to lose this tree, any other Help would be Greatly appreciated, I can send photos of the fungus to help others learn as well
Google “ambrosia beetle”. I’m out here in Orlando and was actually able to get them out of my avocado. Email me danmangold@yahoo.com.
Found 2 spots on the trunk of a 2yr tree. Appears to be the shot boring, can’t cut out 5 and 12 inch from ground. Read the report, . Washed trunk with hydrogen peroxide. Next day found white rings showing the tiny hole. Inserted a fine drill bit lightly twisting,pulling out removed some goop, rinse same with peroxide couple more times . The frass is diminishing
Question. The avo tree already planted on the property we just moved into was planted over or near the septic tank leach field.
Are the avocadoes safe to eat or should I just take out the tree and plant a new one .
The tree is about 10 years old.
Eddie Munoz
Hi Eddie,
I hope those avocados are safe to eat: Some of mine are planted over my leach lines, and I’ve eaten fruit from friends’ trees that are growing over theirs too.
As far as I’ve experienced, there isn’t any danger in eating fruit from such a tree. Yet I can’t say that I know this for sure.
I called a County agency & they said trees don’t carry bacteria & viruses from soil into the fruit. But, if you eat fruit from the ground, it’s possible that it was contaminated.
Hi Greg,
Love the blog. Just tried some tree sap (white powder). I planted my 5 foot tall Avocado 2 months ago. I live in west Irvine near Laguna Hills. My first one got brown tips and died. I worry this one is heading down same path. Soil felt a bit moist so added some gypsum a week ago. Thoughts? Can I send you some photos of the tree including some close-ups of the leaves to get your thoughts?
Hi Richard,
Link to some photos posted to https://imgbb.com/ or Google Drive or some other platform.
Have you tested your soil drainage? See: https://gregalder.com/yardposts/how-to-plant-and-stake-an-avocado-tree/
Have you watered your new tree approximately like this? https://gregalder.com/yardposts/how-to-water-a-newly-planted-avocado-tree/
Thank you for all the info on avocado trees. I’m in FL and just planted my second tree I grew from seed (accidentally in my compost lol) . The first is doing great and I just saw this white powder on the 2nd. It’s my first born so to speak. I’d never forgive myself if I did anything to harm it.
Definitely have soul that drains quickly. I’ll take care to make sure it gets plenty of water since it’s just been transplanted from a planter.
Wacked back my avocado tree. It was getting too tall. Sent it in to shock lost all blooms except 1. So I have one avocado on the entire tree. Also have the dried white powered sap now. I put a cone of silence (like they use on dog or cats) on the trunk to keep the rats from climbing. Works really well. I had lost 45% of harvest to rats in 2018. In 2019 loss less with cone of silence and Irish spring soap. I hang little pouches of cheese cloth with shredded Irish spring soap in them on branches. RATS HATE Irish spring soap. Thanks for your expertise.
Thanks for this. What’s Irish spring soap??
Hello Greg,
Several members of our avocado group for home growers on Facebook have recently noticed that some of the younger branches of their avocado trees have black/brown spots. I looked through UCANR’s “IPM for Avocados” book, and I couldn’t find info about what might be causing the spots. One member reported that he can wipe the spots off the branches. He also noted that he cut one of the branches and found a “canker” inside the branch.
What is causing the spots? How should the members manage this issue?
The link connects to a photo of one of the trees on Facebook.
Thank you for your assistance,
Olivia
Hi Olivia,
Sorry for the late reply! I consulted with a veteran farm advisor on avocados and he said that’s a reaction to mild sun scald.
If you look at your trees, you notice that it’s more present on tops of branches and branches that are on the south side of the canopy or other sunnier sections. (Not that it’s not found elsewhere though.)
Thanks for your reply, Greg. I think I may have contacted the same farm advisor as you (BF) while I was awaiting your response. I didn’t know that some sunburn damage can be wiped off. BF stated, “The black stuff that you can rub off is a response on the part of the tree to sunburn. It’s not enough to cause dead tissue, but a slight wounding that the tree responds to by releasing a bit of sap and there is a sooty mold fungus that grows on it. It’s only topical.”
Thank you for sharing your expertise. I’ve learned a lot about growing avocados from reading your Yard Posts. I frequently share your articles and videos with members of our avocado group. I attended the Avocado Production Course last year, and I remember one of the instructors stating that you could be teaching the class. In my view, you ARE teaching, via the Yard Posts and videos.
Hello, I read Ben Faber’s info on canker. My 4 year old haas avocado tree has canker but it doesn’t fit any of his descriptions. Also, it has a black sooty film on some of the branches that I can rub off with my finger. The black marks are often in the shape of spots but not always. They are not on the trunk but are on many branches. The canker is in random places, not where I have trimmed. I tried google images. I can’t find a photo that looks like what my tree has so I’m not sure how to help it. The tree lives in Camarillo, CA and it isn’t that hot here. Any idea where I should look next? Thank you!
Hi Lauren,
Have a look at this page showing various kinds of cankers on avocado trees and see if any match yours: http://ipm.ucanr.edu/PMG/C008/m008bpcanker.html
Also know that many causes of cankers on avocados are opportunistic. They are always present, but they only take hold in the tree and develop symptoms when the tree is stressed, most often by improper watering or high heat (not for you in Camarillo though). Once the tree is not stressed, it can recover 100% and the symptoms disappear.
there is any chemical to control that