Black spots on avocado twig

[johnsonw]

I have a Brogdon avocado in my backyard that has been doing very well until the hurricane. Despite the wind and damage, the tree has recovered well and is showing signs of new growth. One thing I have noticed, however, is that one of the branches on the bottom has some black spots on it. It doesn’t appear to be causing the branch to die back, and i only see it on one branch, but I’m concerned because it looks like it could be a fungus. I was told to treat it with Dithane, but I still have no idea what it is. I’ve attached some pictures to show the whole tree, the affected branch, and what the other branches look like. The black spot is only on the surface of the wood. You can scrape it with your nail, and it will pull up the very top layer of the wood. Underneath it is still green. Does anyone recognize what this black spot is?







Thanks in advance!

Will

[CA Hockey]

Someone with more experi nice may correct me if I’m wrong, but I’m pretty sure It is a harmless fungus. Present on many avocados stems and cuttings. Doesn’t appear to affect growth or function.i see lots of it on scions at the exchanges.

K

[johnsonw]

Great to hear! I couldn’t find any disease matching the description on EDIS or anywhere else so I figured it is benign.

[Mark in Texas]

Have this avocado Black Streak on quite a few.  Wrote a Cali. fruit agent, never got an answer.  Am wondering if it's a virus disease like Sun Blotch or what.  Sent tissue samples to a Florida lab, came back benign, said it was probably a cultural issue - "give it good care, water, fertilizer, etc."

Yours looks like either soot from scale or a fungus disease.  Recommend an OMRI approved fungicide like MagnaBon.  It's a copper systemic.  I just lost my entire collection in the greenhouse because of a failed heater but took steps afterwards to curtail any bacterial disease in case something survived the 18F by spraying all branches with another copper product, Phyton35 and doing a thorough soil drench of the same.

Mark

[johnsonw]

Mark,

That looks similar to mine except I can't find any black on the trunk of the tree. A gentleman was kind enough to give me some dithane-M45 at the local garden center and said it should do the trick. So I sprayed the tree yesterday and will follow up with another application a week from now. I'm curious, can you scrape away the top layer where the black is and still see green underneath? At first glance, I thought I could simply scrape the black stuff off of my branch (like a sooty mold) but it appears to be just above the cambium layer so you have to peel the outer bark off a bit. This has me convinced that my tree has a fungus. As I look closer at the image you posted, it almost looks like a sunburn.

I'll take another photo of my branch in a week before I do the second application and see if there is an improvement. It will be interesting to follow the results.

Regards,

Will

[waxy]

Have this avocado Black Streak on quite a few.  Wrote a Cali. fruit agent, never got an answer.  Am wondering if it's a virus disease like Sun Blotch or what.  Sent tissue samples to a Florida lab, came back benign, said it was probably a cultural issue - "give it good care, water, fertilizer, etc."

Yours looks like either soot from scale or a fungus disease.  Recommend an OMRI approved fungicide like MagnaBon.  It's a copper systemic.  I just lost my entire collection in the greenhouse because of a failed heater but took steps afterwards to curtail any bacterial disease in case something survived the 18F by spraying all branches with another copper product, Phyton35 and doing a thorough soil drench of the same.

Mark

Hi Mark, this may be me going on a tangent but do you keep separate pruners for different trees to avoid contamination?
I'm quite OCD and have a massive collection of trees so I have each labelled for different trees/species, rinse with alcohol each tree is pruned.
Not sure if anyone else does it besides me, pretty expensive but peace of mind at the end of the day.

[Mark in Texas]

Mark,
 I'm curious, can you scrape away the top layer where the black is and still see green underneath?

Yes you can see green.  I think you have a fungus. Dithane is a good product but it is not a systemic.  If the product doesn't have a surfactant make sure to add one.  Try MagnaBon CS2005. There's dozens of fungicides to choose from - Thionate methyl aka Cleary 3336, Captan.

[johnsonw]

Washing pruners in alcohol sounds like a pretty wise thing to do. I will make sure I do this when it comes time to prune. So speaking of fungicides, how safe is it to eat the fruit if I’ve treated my tree with a fungicide this year? If I remember correctly, I read 45 days after spraying with dithane. Does anyone else worry about eating the fruit later on and ingesting some of the fungicide? Regarding the surficant, I have some genysis so I will use that.

[CA Hockey]

It still looks like the black spots I saw at the crfg scion exchange. Was told it is a harmless fungus on avocados and that it’s very common. Julie frink is the one who told me not to worry about them. I forgot what she called it.

Mark, looks like your tree may have dothiorella canker. Can cause dieback per ucr website but otherwise doesn’t kill tree. Labeled as a minor problem.

[Mark in Texas]

It still looks like the black spots I saw at the crfg scion exchange. Was told it is a harmless fungus on avocados and that it’s very common. Julie frink is the one who told me not to worry about them. I forgot what she called it.

Mark, looks like your tree may have dothiorella canker. Can cause dieback per ucr website but otherwise doesn’t kill tree. Labeled as a minor problem.

Thanks for the heads up.  Almost all trees have it.  "Symptoms observed on avocado with Dothiorella canker include shoot blight and dieback, leaf scorch, fruit rot, and cankers on branches and bark."  Kicker is I don't have fruit rot nor cankers.  There is small branch dieback. 

Regarding fungicide uses and time from application to eating, I'll post a JPG from a Aggie recommended fungicide program for vineyards.  The PHI (post harvest interval) is what you're interested in.  For the reason of following the law you should use only those products labeled for avocados.  Doesn't mean they aren't safe, may mean the chemical company didn't want the hassles and expense of having the product reviewed for a specific crop, in this case avocados.

[johnsonw]

Thanks for the fungicide info Mark, that's very helpful! Looks like PHI is 66 for dithane; the longest interval on the sheet. The tree hasn't flowered yet so that should be plenty of time before I pick any fruit (if it flowers this will be the first year it produces). Speaking of Dothiorella canker, I have noticed an avocado tree in my neighborhood that has similar symptoms. It started at the top of the tree. Branches slowly started turning black. The homeowner pruned those branches off but the black kept working its way downward. The tree is about a foot tall now so they've lost most of the tree. It sounds similar to what you are describing, but probably much more severe.

[Mark in Texas]

Yes, the PHI for dithane is very long.  We use it very early in the season mainly for phomopsis control.

It's sad to watch your tree slowly die and you have no clue how to get a handle on it.  The black streaking I have is intermittent throughout the trees. Not an issue for me anymore.  I'll be starting all over as I lost everything due to a heater failure.  Only thing that looks green is 3 citrus trees.  Am busy giving away citrus fruit and tomorrow we'll be making our second batch of blood orange marmalade.  Never made it before.  It is awesome!

Oh well......

[johnsonw]

Happy Monday, so it's been a little over a week since I initially posted on this thread. I've applied 2 treatments of Dithane-M45. The first application used a tablespoon of the solution in .5 gallons of water. I sprayed the leaves and the trunk thoroughly. After a week, I was ready to apply a second application and was told that the solution should be 4 tablespoons / gallon of water and to use a surficant. Since I'm spraying half a gallon, I used 2 tablespoons of Dithane-M45 along with a .5 teaspoon of gynesis (surficant). I'm attaching a new picture to show the status if anyone is interested.

Regards,

Will