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Author Topic: Pawpaw nutrient deficiency help, please!  (Read 524 times)

Triloba Tracker

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Pawpaw nutrient deficiency help, please!
« on: September 05, 2020, 12:57:55 PM »
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

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Re: Pawpaw nutrient deficiency help, please!
« Reply #1 on: September 05, 2020, 02:06:36 PM »
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.
Har

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Re: Pawpaw nutrient deficiency help, please!
« Reply #2 on: September 05, 2020, 10:19:45 PM »
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

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Re: Pawpaw nutrient deficiency help, please!
« Reply #3 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?
Har

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Re: Pawpaw nutrient deficiency help, please!
« Reply #4 on: September 06, 2020, 04:14:30 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?

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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Re: Pawpaw nutrient deficiency help, please!
« Reply #5 on: September 06, 2020, 04:25:55 PM »
You know, you're right....in a lot of ways the deficiency signs are in line with Magnesium.

And on that topic, Spectrum Analytic states this:
"Cation competition: Soil with high levels of K or Ca will typically provide less Mg to the crop"

Which seems to line up in terms of my Calcium levels.

Ironically it mentions Mg is more available at relative higher pH levels. This point may have something to do with it - a couple of the trees showing the most yellowing are ones where I applied a bit more sulfur than others in the fall.
Also some seedlings i planted this spring, i included a fair amount of sulfur as i backfilled the holes. Those seedlings are showing yellowing of the lowest/oldest leaves.

Gee whiz this stuff seems so complicated! :o

Thank you again Har and everyone for your continued (hopefully) help!

Guanabanus

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Re: Pawpaw nutrient deficiency help, please!
« Reply #6 on: September 06, 2020, 10:00:02 PM »
Is the Iron really just "1"?  It should be in a similar amount as Manganese.

Until a US lab has a database for Pawpaw, I suggest that you study Australian and New Zealander recommendations for growing Atemoyas, which they call "custard-apples."  They have very extensive and professional literature, specific to this important industry there.

Doing both leaf analysis and soil analysis at the same time, is best.
Har

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Re: Pawpaw nutrient deficiency help, please!
« Reply #7 on: September 07, 2020, 03:59:07 PM »
Thanks!
Yes the iron really is listed as 1. On earlier tests itís actually 0.
I have tinkered with iron chelate foliar and soil drench in the past with no change in the foliage.

I do have a PDF about annona nutrient deficiencies but I find the pictures hard to see and not very helpful. But I will keep looking.


I do plan to get a tissue analysis very soon.

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Re: Pawpaw nutrient deficiency help, please!
« Reply #8 on: September 09, 2020, 09:13:23 PM »
I sent some material off today to the Penn State lab. Canít wait to see the results.

In the meantime this morning I tested foliar spray of Epsom salts I bone tree, and potassium sulfate on another. I mixed both at a rate of 2 TB per gallon.

By this evening there was no sign of leaf burn but also no sign of improvement either.

This leads me to wonder a few things:
Is it too late in the season for these to do any good anyway?
How long does it take for foliar feedings to show perceptible efficacy?

Guanabanus

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Re: Pawpaw nutrient deficiency help, please!
« Reply #9 on: September 09, 2020, 11:07:47 PM »
Old leaves, that already show severe deficiency, are unlikely to be corrected by any treatment.
Har

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Re: Pawpaw nutrient deficiency help, please!
« Reply #10 on: September 10, 2020, 08:20:42 AM »
Old leaves, that already show severe deficiency, are unlikely to be corrected by any treatment.

Thanks!! Thatís kind of what I figured.
I suppose the idea would be to start feeding earlier and prior to extreme symptoms.

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Re: Pawpaw nutrient deficiency help, please!
« Reply #11 on: September 16, 2020, 03:11:01 PM »
I got my tissue analysis back today.
Of course they were not able to give me "normal" values for Pawpaw. So at this point the data is somewhat meaningless, but I thought I'd put it here anyway.
I have some pawpaw folks trying to help me interpret it.

Macros (expressed in %....% weight? doesn't say)
Nitrogen 2.19
Phosphorous 0.25
Potassium 0.96
Calcium 1.27
Magnesium 0.11
Sulfur 0.22

Micros (ppm)
Mn 46
Fe 37
Cu 4
B 76
Zn 19

NateTheGreat

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Re: Pawpaw nutrient deficiency help, please!
« Reply #12 on: September 18, 2020, 01:22:45 PM »
With the leaves about to go deciduous and drop, seems like discoloration shouldn't be too concerning. That said my guess is magnesium deficiency. "symptoms consist of interveinal chlorosis (leaf veins stay green while the regions between them turn yellow). Older leaves lose their green color except in the veins. "

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Re: Pawpaw nutrient deficiency help, please!
« Reply #13 on: September 18, 2020, 02:25:51 PM »
Thanks so much for your input!

Almost everyone Iíve talked to suspects magnesium.
The paradox though is that my magnesium in the soil is higher than potassium, leading me to think if it were one of the two, it would be potassium.

However, that assumes the plant needs equal amounts of both, which is almost certainly not true.

I think itís not just a seasonal thing - now that this has come to a head, I realize other symptoms earlier in the season are all probably Mg deficiency.

What I really want to know is the why. All I can figure from the soil tests above are that the high calcium is displacing the Mg cations.
Another thing Iíve been coming back to is sulfur treatments Iíve done to lower the pH. I realize now that Mg and K availability actually *decrease as pH gets more acidic.

So one of my theories is that the trees with the most dramatic chlorosis are the ones to which Iíve applied the most sulfur.


NateTheGreat

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Re: Pawpaw nutrient deficiency help, please!
« Reply #14 on: September 18, 2020, 04:38:51 PM »
If you look at the ratios of potassium to magnesium in the soil vs in the leaf, it's 194:393 in the soil vs 0.96:0.11 in the leaf, or about 1 to 2 vs 9 to 1. Sounds to me like there's an issue with magnesium uptake. Since the pH was 6.8, which seems on the high end for pawpaw, I doubt it's too acidic. From the table on this site, 0.11 Mg would be low for basically any crop. It also says if you have over 150 in the soil you don't need to add any for corn, so I doubt your soil is deficient in it. https://extension.umn.edu/micro-and-secondary-macronutrients/magnesium-crop-production

I think the issue is excessive Calcium. "In nutrient solution experiments it has been shown that high availability of the cations Ca, K and Mn can lead to strong decreases in Mg uptake... Slightly increasing the Ca concentration in the nutrient solution then rapidly restores the membrane functionality, so that the uptake of other cations is enhanced and leakage reduced. Further increasing the Ca concentrations in the nutrient solution then turns the positive synergistic effect of the nutrients into an antagonistic cation competition for uptake. This is reflected by a reduction in uptake of Mg (and K) when the Ca concentration in the nutrient solution is further increased"

https://link.springer.com/article/10.1007/s11104-012-1567-y

Edit: I looked and Epsoma Organic Soil Acidifier is only 18% elemental sulfur. 80% is gypsum, which contains calcium.
« Last Edit: September 18, 2020, 04:53:10 PM by NateTheGreat »

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Re: Pawpaw nutrient deficiency help, please!
« Reply #15 on: September 18, 2020, 05:05:39 PM »
Amazing..thanks!!

So I could either:
1) Reduce the Ca in the soil
2) Supplement Mg in the root zone
3) Supplement Mg via foliar feeding

(1) I doubt this is even possible, however, i had someone tell me that adding phosphorous causes a reaction with calcium that essentially permanently sequesters the calcium in the form of rock phosphate. I'm not sure that's true nor do i know how much phosphorous that would require and if that amount would be toxic to the plants. Seems sketchy.

(2) It seems like adding Mg to the soil would be iffy since we already think the Ca in the soil would kinda "block" it from being absorbed by the roots. However, i wonder if a hit of Mg, especially in liquid form, might still have a fighting chance to be absorbed, at least partially, by the roots. Not sure?

(3) seems the most likely to succeed, but doesn't seem like a true long-term solution. But with that much Calcium (again assuming that's my culprit) I don't know if there's any other way to get Mg to the plant.

NateTheGreat

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Re: Pawpaw nutrient deficiency help, please!
« Reply #16 on: September 18, 2020, 05:52:33 PM »
I bet it will go down on its own in time. I'm hardly finding anything about reducing excessive calcium levels, which makes me think calcium probably won't stay high on its own. Maybe adding Epsom salt (MgSO4) would help? Then again doing anything might just make it worse. I saw some stuff about Phosphorous and Sodium removing Calcium, but you could easily do more harm than good. One site said growing leafy root crops with high oxalate levels would help. https://www.researchgate.net/post/How_to_reduce_excessive_calcium_levels_in_soil

"Gypsum is not acid soluble and will not change the soil pH. It helps to shift the Ca and Mg levels in soil and offers a readily available form of sulfate sulfur, a valuable secondary nutrient that benefits the soil and crop. The sulfate in gypsum binds with excess Mg in the soil to form soluble Epsom salt, which moves lower into the soil profile. This Mg is replaced by Ca, improving water holding capacity, root development and soil quality." source: http://www.gypsoil.com/news-and-events/gypsum-and-lime

If the Ca causes the Mg to precipitate as MgSO4, I don't know what adding dissolved MgSO4 would do. Maybe some of the SO4 would combine back with Mg and some with Ca in the soil, but if there's MgSO4 in the soil already that's come out of solution... idk. Maybe "lower in the soil profile" means the MgSO4 is basically out of the picture. People do say MgSO4 makes blossom end rot worse by reducing Ca availability, so maybe that would work.

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Re: Pawpaw nutrient deficiency help, please!
« Reply #17 on: September 18, 2020, 05:55:20 PM »
I really appreciate the time youíve taken to help!!

Will keep pondering this one and spend more time on yours and Harís recommendations.

Guanabanus

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Re: Pawpaw nutrient deficiency help, please!
« Reply #18 on: September 20, 2020, 12:58:00 PM »
TrilobaTracker,

Your Pawpaw Leaf Analysis, compared to Atemoya Optimal Leaf Levels:

Extemely low Mg,
extremely low Cu;

slightly low N, K, Mn, and Zn;

a little high P.

CA is mid optimal, so NOT a problem in the leaf.


See Agrilink:  Custard Apple Information Kit
Queensland Department of Primary Industries
Part 3, page 23;  and Part 4, page72.
Har

 

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