Single Branches turning Yellow on seemingly healthy plants, help!

A couple weeks ago one of my Magic Melons completely gave up on transporting nutrients to 2 of its branches. The plant looks like it’s diverting any resources it would send to these branches to the rest of this plant. The branches themselves are still alive, but forming significantly dwarfed flowers.

They are connected to the main-stem without breakage. There is no bug damage visible on the stunted branches themselves. The rest of the plant has no signs of anything unhealthy. I’m in a 200 gal smart pot, with a coco-heavy soil mix, and have been feeding tea brews, cal mag, and sea blast grow/bloom as well as spraying fish hydroslate.
This issue appeared after 2 weeks of wildfire smoke that nearly blocked out the sun.

So my main thoughts are that either I had a fusarium or pyth problem that only effected the roots that power the 2 branches that are no longer getting nutrients. That maybe I corrected the developing root rot by altering my watering to compensate for the wildfire smoke after I saw that far less water was evaporating from the run-off around each pot. Or, that some sort of bug chewed through the roots associated with the stunted branches. Or, that the roots for those branches broke through the floor of the smart pot and found themselves growing in oxygen deprived clay and decomposing granite and are dying.

If anyone has seen this before, and isolated the cause, I would love to know so I can prevent this from occurring ever again.

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Most Interesting post I’ve seen in awhile and have nothing. @Oldguy what are your thoughts?

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Damn brother. :man_facepalming: You’re making me think and I’m not nearly high enough yet. :joy:
Seriously tho , I’m no further ahead than you are on this one.
It’s def an odd situation with those few branches yellowing on an otherwise healthy plant.
I know the op has checked for fusarium and Pythium but something is affecting those branches. Just not certain what.
:v:

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Usually a pest boring into the stem

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I wasn’t sure, so I started tagging. Insect boring seems plausible. Thanks spineynorman.

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The only other thing I have seen do that is stem rot.
If there is a fungal problem that has attacked that particular stem it will do that.
Problems in the root zone will present all over the plant, not just one particular stem.
I avoid using straw and other mulches for that exact reason. They are always fungal carriers.
Looks like this…
image

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I can finally post again! Ok so as an update, I finally found an indicator of something more specific. I see what appears to be something like Septoria spotting developing on the yellowing leaves. There are no bore holes, and these yellow branches amazingly have smaller sub-branches closer to the main stalk that look healthy with only minor signs of yellowing, which I think gives me the answer.

Is it possible that those sick branches are connected to roots that pushed through the smart pot into a clay/granite layer, which firstly suffocated them, then maybe dried enough to leave them injured, which allowed the resident fungal pathogens to rot out the root up to the point of where it passed through the smart pot. The remaining root is healthy in the pot, making the older growth closer to the base of the branch healthy and able to take in nutrients. It also is just enough root to keep the branch hanging onto life. Because the smart pot itself isn’t over saturated the fusarium has a difficult time breaching the pot and hitting the rest of the plant, leaving the plant looking perfectly healthy, minus the branches that were supported by the now rotted/dead roots that passed into the ground. I’m going to see an inevitable contamination which I believe I can keep at bay till harvest as I have been doing with several other plants (my property is literally riddled with fungal pathogens from the dying oak trees all around me).
It is also possible that the clay layer under the pot merely suffocated and locked out the roots that broke through, and the Septoria spotting/fungal pathogen has recently started traveling up the injured roots which is why the branch didn’t just wilt?. Plz lemme know if this theory sounds reasonable. Here is a pic of a plant that wasn’t sitting on top of a bad ground layer (200 gal smart pot, about 9 ft tall by 7 ft wide I think -