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Pawpaw nutrient deficiency help, please!

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Triloba Tracker:
I recently posted this on another fruit forum but I hope some of you guys can help me out.

Today i noticed a few of my pawpaw trees are showing some very clear issues.
This it the third year of my orchard but first time i'm seeing this.
Also, the symptoms only began appearing a few weeks ago.

These pictures are showing older leaves - younger leaves look totally fine.








I consulted the frequently used document for diagnosing pawpaw nutrient issues, and none of the pictures really look like this; however, the verbal description of potassium deficiency is pretty close (older leaves, yellow margins)

Also, the very well-respected Spectrum Analytic website says this about K deficiency:

"The classic and almost universal leaf deficiency symptom is marginal chlorosis of the older plant leaves."

Spectrum goes on to say:

"It might also show as a fruit crop that doesn't quite develop the proper quality or flavor."

While this is a really small sample size, my one pawpaw fruit this year tasted terrible.

Also I have seen mention of K deficiency causing persimmon fruit drop. My pawpaw dropped i believe prematurely, which also fits.

**Thoughts?**

Now then, to save time let's assume this is potassium deficiency.
**How should it be corrected?**

I had the orchard tested this spring with these main results:
pH 6.8
Phosphorous 519 pounds/acre
Potassium 194 (considered in "high"range)
Calcium 9806 (yes, 98060
Magnesium 393
(these are Mehlich-1 values)

I have known for a while that i need to get my pH down. It actually started 3 years ago at about 7.5 and thru elemental sulfur and compost, it's come down. I want to get it down even more, to 6 would be wonderful.

I'm not sure getting it to 6 will make this issue go away because...... I have 50x higher Calcium content than K. Spectrum Analytics mentions Calcium competes with K. That's an awful lot of Calcium. Mg is also high compared to K.

So I guess I don't know if adding K to the soil will really do anything. I could try foliar feeding i guess but don't relish that thought.

Part of me is freaking out thinking that I am doomed with so much Ca and high pH.

Help!

Guanabanus:
When I looked at your pictures, before I read your comments, I had 3 suspects for the cause of deficiency symptoms:  Manganese, Potassium, and Magnesium.
As I don't have any good experience with Pawpaw plants, I am extrapolating from other species.

With Magnesium deficiency, the half or third of the leaf nearest the stem is still very green between the veins, and there may be a green extension along the midrib.
This is the pattern in the third picture.

In Annonaceae species, Potassium deficiency can show as marginal yellowing, or even firing;  but it often shows as yellowing bands between the secondary ribs, followed by black spots, which falsely seem to be Anthracnose.  Or both marginal and interveinal chlorosis (yellowing).  I imagine that it is some co-deficiency that determines which pattern shows.

In Manganese deficiency, all the ribs / veins are pale, with the primary and secondary ones bordered on each side by narrow strips of green.  In your pictures, the strips of green are wide, so I am unsure.

The relative amounts of elements considered desireable in leaves and in soil is different.  In soil, one wants to see way more Magnesium than Potassium.  In leaves, one wants to see way more Potassium than Magnesium.  The plant can usually provide that distinction, when plenty of both are available.

The amount of Calcium in your soil is just fine, and you don't have to add more. And pH of 6.8 is also good.

I suggest that you add Sulphate of Potash-Magnesia (Sul-Po-Mag, a.k.a. K-Mag) to the soil around some of your trees, and Manganese chelate or sulfate around some others.  When not sure, experiment;  keep written records, or tag or flag.

Triloba Tracker:
Thanks so much, Har!

What I donít understand is if the soil test values show sufficient K and Mg (which they do) then what is causing the deficiency?
Is it just some transient condition like excess moisture or is it some quirk of these specific trees that is completely out of my control and needs correcting just by adding the deficient nutrients?

The only thing Iíve added to the soil was conservative amounts of ammonium sulfate in April and elemental sulfur last fall.

Guanabanus:
Was your soil tested for Boron and metalic micro-nutrients?  Zinc, Iron, Manganese, Copper.

Was sufficiency of soil nutrients judged for a crop of pawpaws, or apples, or corn?

Triloba Tracker:

--- Quote from: Guanabanus on September 06, 2020, 03:29:59 PM ---Was your soil tested for Boron and metalic micro-nutrients?  Zinc, Iron, Manganese, Copper.

Was sufficiency of soil nutrients judged for a crop of pawpaws, or apples, or corn?

--- End quote ---

Good question - I honestly forgot that the micros are listed on my test. Here they are:

Mn  = 14
Fe = 1
Zn = 2.2
B = 3.8
Na = 28

Unfortunately I do not have data on Sulfur, CEC, organic content, soluble salts, or buffer pH.
 
Also, I'm not aware of any lab in the USA that will give recommendations for pawpaw. No one that I know has any kind of baseline yet for it.
I had the lab give me Peach and Apple crop recommendations. The only recommendations are to add N in the spring.

My comment on sufficiency was based on the following information from the test. (University of TN)


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