Possible phosphorus deficiency? Pls help diagnosing!

Hey folks,

Here's the situation:
I have 4 plants growing outdoors here in South Africa. 3-4 weeks into flower. All the plants are generally in good health but lower fan leaves are progressively yellowing and falling off as expected some faster some slower. One plant though is showing signs of a possible Phosphorus deficiency but I'm not confident and don't want to assume that when it might be an excess of something. Please help me diagnose the problem.

SYMPTOMS:
(Refer to the attached pictures for examples)
Symptoms are displayed on fan leaves increasingly towards to bottom.
The affected leaves show crispy bronze coloured tip mostly on the middle finger. This can be found up on the mid level fan leaves to a lesser extent.
The lowest fan leaves most affected also have bronze patches on the margin and middle region of the leaf blade.
Symptoms also seem to be consistent with leaves exposed to the least sunshine which I interpret either as unproductive leaf targeted as nutrient source for flower or that the leaf is unable to use up excess nutrients and show burnt patches. I really don't know.




GROW OVERVIEW:
I have been growing organically in 50L fabric pots, starting out with a well prepared super soil.
Throughout the 2 month veg I was just watering with the addition of microbes and some fermented plant tea once a week and plants were in optimal health.
As the stretch began at the onset of flower some yellowing appeared in the lower leaves so I started introducing some products extra inputs for food and boosting microbial activity. Inputs are at follows:

LIQUIDS:
Biogrow and Biobloom (Biobizz) at conservative recommended levels to give them a little extra. I also introduced some store bought high potassium FFJ (probably banana peel/molasses tea) but concerned that this might be overdoing it.

DRY AMENDMENTS:
top dressed with a good organic soil amendment (Elemental Blend) at the start of flower and then with some high phos bat guano about 2-3 weeks in.

PH:
For a week or so I have been adjusting my water-feed PH to 6.3-6.5. For the first two weeks of flower I had to no PH up and with the biobizz my watering PH was a bit low around 5.6-5.8 which was a little low but not too much of a concern as the is some dolomite in the soil.


Any feedback and advice will be much appreciated!!!!

Looks like leaf septora.

Signs of leaf septoria
Yellow leaf spot initially shows up on the lower leaves of your plant. These spots may vary in shade from white to a grayish brown to yellow, initially
displaying little circular lesions. Once it starts to grow it starts looking like a bump and its size continues to increase.

Plants low in Nitrogen can be susceptible to septora.

jimihendrix1 said:

Looks like leaf septora.

Signs of leaf septoria
Yellow leaf spot initially shows up on the lower leaves of your plant. These spots may vary in shade from white to a grayish brown to yellow, initially
displaying little circular lesions. Once it starts to grow it starts looking like a bump and its size continues to increase.

Plants low in Nitrogen can be susceptible to septora.

Click to expand...

Thanks for your reply jimihendrix1!

I looked into Leaf Septoria and it seems that in general that condition appears a bit more spotty with more circular spots. It also seems to be usually a result of high moisture/humidity.

The conditions here are very dry and often windy.

Most of the examples on my plant look like it affects the tips first and then sometimes emerges as a gradual patch in on other parts of the leaf.

This photo though looks alot like septora.

Whats the PH of your soil?? Dolomite can take forever to break down. Calcitic also called Agricultural Lime is better for faster PH change. The medium I use has a balance of both Calcitic Lime, and Domonitic Lime at a rate of 2/3 parts Calcitic to 1/3 parts Dolomite. I use Promix BX as my medium, its Sphagnum Peat based with perlite, and vermiculite. It comes with both of those types of lime, at those ratios. Supplying both calcitic, and dolomite also assures they are getting enough of both calcium, and magnesium. Promix BX has a 6.2-6.3 ph.

You may have nutrient lockout from low ph. Just a thought anyway.

jimihendrix1 said:

This photo though looks alot like septora.

View attachment 5090697

Click to expand...

I agree that it is more similar, but that is only one of the leaves which is also a little drained of nitrogen. Septoria spots typically show up with more pronounced yellowing immeditately around the edges each spot. On mine, that is not the case and possibly even the opposite.
On most of the affected leaves it is the tip that has been affected like burn from an excess or deficiency. I'm not saying that it's not Septoria, but I'm not convinced.
I appreciate the input in any case. If not Septoria then is there a similarity to a particular nute deficiency or excess?

jimihendrix1 said:

Whats the PH of your soil?? Dolomite can take forever to break down. Calcitic also called Agricultural Lime is better for faster PH change. The medium I use has a balance of both Calcitic Lime, and Domonitic Lime at a rate of 2/3 parts Calcitic to 1/3 parts Dolomite. I use Promix BX as my medium, its Sphagnum Peat based with perlite, and vermiculite. It comes with both of those types of lime, at those ratios. Supplying both calcitic, and dolomite also assures they are getting enough of both calcium, and magnesium. Promix BX has a 6.2-6.3 ph.

You may have nutrient lockout from low ph. Just a thought anyway.

Click to expand...

Yeah, I wonder if there's something to that. I have been adjusting my watering PH to 6.3-6.5, but perhaps there is something in the soil bring the PH down. I was using this high potassium ffj (banana peel/molasses tea) which had a low PH and perhaps I overdid it a touch and has built up in the soil. I used a fairly mild dose of it though (1ml/L ).

Fertilizer in general will drive your ph down.

Have you also been giving your plants nitrogen?? Its a myth to cut out nitrogen in flowering. Plants need an ever increasing amount of everything from seedling- flowering. The last 2 weeks they can do with less nutrients, but if you use dry nutrients in the soil, they will just take what they need if they have the proper ratios.

All nitrogen to a plant is, is protein. Humans eat protein and convert it into nitrogen. Plants skip that process, and just need nitrogen. Its not logicl to cut protein when they flower. They will grow the most theyve ever grown when flowering, along with the creation of hormones, stigmas, trichomes.

Do you also have a Calcium Source?? Magnesium?? Lack of calcium, can also cause yellowing, and spots.

Id still check the PH. Lockout can cause all kinds of symptoms..
Also not saying youve done this, but if youve limited nitrogen, and added potassium, and other nutrients, your soil could also be out of balance, and causing lockout. Along with ph imbalance.

It looks like phosphorus to me. 3-4 weeks flower the plants are needing that higher P for the growth spurt. If N was your issue you'd have 100%yellow leaves on the bottom, and they don't just die and fall off. P will turn bottom most leaves completely necrotic. It starts out blotchy and these blotches can vary in formation plant to plant, but blotches still none the less.

I'd also suspect your substrates pH is high as the plants tend to prefer a more neutral pH in flower. A good fluctuation between 6.5 and 7 is normal.
Any way to test a sample? Soil testing kit mabey? pH meter or strips?

jimihendrix1 said:

Fertilizer in general will drive your ph down.

Have you also been giving your plants nitrogen?? Its a myth to cut out nitrogen in flowering. Plants need an ever increasing amount of everything from seedling- flowering. The last 2 weeks they can do with less nutrients, but if you use dry nutrients in the soil, they will just take what they need if they have the proper ratios.

All nitrogen to a plant is, is protein. Humans eat protein and convert it into nitrogen. Plants skip that process, and just need nitrogen. Its not logicl to cut protein when they flower. They will grow the most theyve ever grown when flowering, along with the creation of hormones, stigmas, trichomes.

Do you also have a Calcium Source?? Magnesium?? Lack of calcium, can also cause yellowing, and spots.

Id still check the PH. Lockout can cause all kinds of symptoms..
Also not saying youve done this, but if youve limited nitrogen, and added potassium, and other nutrients, your soil could also be out of balance, and causing lockout. Along with ph imbalance.

Click to expand...

Thanks for all of this input.
I have been giving the plant nitrogen via Biogrow (1m/L every watering) and the top dress 3 weeks back that had seabird guano in it.
Top dress also contained Gypsum, dolomite lime and calcitic lime RE Calcium and Magnesium.
Additional Magnesium boost via epsom salts last week and 4 weeks previously.
The Bat Guano (3-13-4) top dress I did just over a week ago is also another good calcium source on top of everything else.

On the phosphorus front, I have been using 1.8ml/L Biobloom which is slightly under the recommended level as I was concerned with overdoing the phosphorus on top of the bat guano. Perhaps I should increase the biobloom because now in week 4 the recommended dose is actually up to 3ml/L.

Meanwhile I have a small soil sample mixed up with distilled water and will test PH shortly.

McShnutz said:

It looks like phosphorus to me. 3-4 weeks flower the plants are needing that higher P for the growth spurt. If N was your issue you'd have 100%yellow leaves on the bottom, and they don't just die and fall off. P will turn bottom most leaves completely necrotic. It starts out blotchy and these blotches can vary in formation plant to plant, but blotches still none the less.

I'd also suspect your substrates pH is high as the plants tend to prefer a more neutral pH in flower. A good fluctuation between 6.5 and 7 is normal.
Any way to test a sample? Soil testing kit mabey? pH meter or strips?

Click to expand...

Thanks for your feedback too!
Like I said to jimihendrix1 I'll be double checking soil PH shortly.
I'm always a bit unsure with the feed levels at this stage in the grow. One of the plants for instance is getting some clawing on new leaf growth lower down around the bud sites which to me is indicating too much N while another plant is loosing fan leaves pretty rapidly to apparent N deficiency. The other two are looking pretty much ideal aside from the one with these bronze tips and blotches.
I will take some photos of the plants from further back now they are in afternoon shade.
I just want to make sure that if I have a defiency for example that it is not due to some lockout situation instead of not feeding enough. I also want to rule out the possibility of some kind of nutrient excess.

Okay so my soil PH is reading between 5.8-5.9.
I suppose that is problematic for Phosphorus and Calcium.
(For soil PH test I took about a table spoon of soil from around the edge to about an inch depth and stirred into some distilled water. let it sit for half an hour and just took a reading with my PH meter. Hopefully the result is reliable.)

I have been adjusting my water-feed PH to 6.4-6.5 with PH up (KOH) but if the soil PH is 5.8 then I'm guessing that's not enough to keep the Phosphorus and calcium available. Should I counter this low soil PH by adjusting my watering PH up to 7 for a few waterings?

I have also some micronised dolomite lime at hand. I could top dress with it or perhaps mix it into the water with my next watering. I don't want to swing the PH abruptly but then again not sure with the micronised dolomite what's possible.

Any recommendations?

P.S. I just tested the PH of the Bat guano I top dressed with recently using the same method at it is reading PH 4. Perhaps that is the main culprit. That's a bit of a surprise because the company from which I sourced the Bat Guano claimed they tested it's PH at 6.65.

shrine420 said:

Okay so my soil PH is reading between 5.8-5.9.
I suppose that is problematic for Phosphorus and Calcium.
(For soil PH test I took about a table spoon of soil from around the edge to about an inch depth and stirred into some distilled water. let it sit for half an hour and just took a reading with my PH meter. Hopefully the result is reliable.)

I have been adjusting my water-feed PH to 6.4-6.5 with PH up (KOH) but if the soil PH is 5.8 then I'm guessing that's not enough to keep the Phosphorus and calcium available. Should I counter this low soil PH by adjusting my watering PH up to 7 for a few waterings?

I have also some micronised dolomite lime at hand. I could top dress with it or perhaps mix it into the water with my next watering. I don't want to swing the PH abruptly but then again not sure with the micronised dolomite what's possible.

Any recommendations?

P.S. I just tested the PH of the Bat guano I top dressed with recently using the same method at it is reading PH 4. Perhaps that is the main culprit. That's a bit of a surprise because the company from which I sourced the Bat Guano claimed they tested it's PH at 6.65.

Click to expand...

Is your soil peat based? That could be your cause...

You could sprinkle a little bit of dolomite on the surface soil and scratchit a bit in, then water. It would take a few watering to get results that are visible but raising the pH now will only get her back on track quicker. Keep your ingoing waters pH at 6.5

If I top dressed it with lime Id use 2/3 Calcitic, and 1/3 part Dolomite

McShnutz said:

Is your soil peat based? That could be your cause...

Click to expand...

The soil in not Peat based. It may have been the bat guano I added. Funny that perhaps in trying to provide abundant phosphorus I ended up locking it out.

jimihendrix1 said:

If I top dressed it with lime Id use 2/3 Calcitic, and 1/3 part Dolomite

Click to expand...

That's a good ratio, if it were granular dolomite. Micronized acts quicker than the granules. Calcitic for immediate action

McShnutz said:

You could sprinkle a little bit of dolomite on the surface soil and scratchit a bit in, then water. It would take a few watering to get results that are visible but raising the pH now will only get her back on track quicker. Keep your ingoing waters pH at 6.5

Click to expand...

Okay thanks for the advice. What do you reckon constitutes a little bit? I have A very fine powdered (micronised) dolomite. Plant pot is 50L. I was thinking perhaps 100ml?

jimihendrix1 said:

If I top dressed it with lime Id use 2/3 Calcitic, and 1/3 part Dolomite

Click to expand...

Thanks for the recommendation. Perhaps I can pick up some calcitic lime in a few days but for now I have to work with the micronised dolomite I have.

Leave your ph sample for 24-48 hrs,re test again see if any difference.