Black sapote leaf drop/disease

[stressbaby]

Hi,

Several years ago @Ethan gave me a small black sapote. I live in Missouri. The tree is potted and spends the winters in the greenhouse, summers outside. The tree is now 5-6' in height. It started flowering 2 years ago and has borne fruit. Per usual, the tree came inside the greenhouse this past fall. It has a sunny spot and is evenly watered.

Generally for me this tree holds the leaves through the winter and drops leaves the next spring or summer. In the past week, this tree has demonstrated dramatic leaf drop. The leaves are perfectly green, not yellow or brown. On closer inspection, there appears to me to be some dieback. Some lower branches are completely black, and some smaller secondary branches have also turned black and died.

The roots look OK.  I spray with Neem every couple of weeks in the winter. I hit it with a fungicide today. This is not normal based on my experience with the tree.  Thoughts? 

[Saltcayman]

I have noticed the same on one of mine.  I just pruned off the small black branches.  The tree seems to be healthy...

[stressbaby]

Thanks Saltcayman, I hope you are right.

[Guanabanus]

Consider spraying or drenching (not both the same week) with Potassium Phosphite (active ingredient of many products): Organocide Plant Doctor, K-Phite, AgPhite, Elemax Foliar Phosphite, Super Foliar Phosphite, etc.

If the tree looks as though you might lose it, consider drenching with Aliette or Flanker, and then not allow any fruit to grow the following season, so as not to harm yourself.

[Saltcayman]

Thanks Har,  I will pick up some Potassium Phosphite to have on hand...  I did not realize this could be a sign of potassium deficiency...

[Guanabanus]

Potassium Phosphite is a fertilizer (Potassium and Phosphorous) that also activates plants' SAR --- systemic acquired resistance.  This is active against bacteria and fungi that get into plants' veins --- phloem and xylem.   In nature plants normally encounter Phosphate;  Phosphite is a slightly different, highly penetrative, unnatural molecule that is perceived as in invasive substance;  therefore, it sets off the plant's "immune response".  Phosphite is eventually metabolized into useable Phosphorous-containing molecules.

Potassium and Calcium and Silicon all increase plant hardiness against weather and pest stresses.

[Saltcayman]

Thanks!  That is really helpful information.  Really appreciate your willingness to share your expertise:)

[EvilFruit]

Thank you Har for sharing your experience with us.

happy new year

[stressbaby]

My thanks as well.