Yellowing autoflower after stretch

[thctony 9]

Hi guys,

 

My autoflowers (strain: Auto Ultimate from Dutch Passion) have been stretching and are the largest of them are now starting to take on a yellow colouring.

 

I've been pouring over the deficiency charts that are readily available but can't home in on what the problems are. Especially confused as I'm seeing signs of both deficiency and excess (yellow tips) so unsure what the best course of action is.

 

Here's some details of my grow:

 

* Seeds geminated 1st September, so in week 7 of the grow at the moment.

* Light schedule 18/6

* PH stable at 6.0

* RDWC system

* Plants are drinking well

* 2.4m x 1.2m tent

* Under 3 x Telos 10 LED lights

* RH constant at around 60%

* Temperature 26 degrees (day) and 22 degrees (night)

 

* Background EC of 0.7 (water is hard here)

* Shogun Hydro Bloom A+B 1ml/L

* Shogun Calmag 1ml/L

* EC stable at 1.2

 

I'm way under the feed schedule suggested by Shogun - but I figured that since i'm still seeing nute burn (on new growth) then I shouldn't be adding more nutes. But then I'm seeing signs of what I think are nutrient deficiiencies in the yellowing leaves, so think I could be unwittingly starving them. I'm seeing this happening in leaves about mid-way up the plant and up. Lower growth doesn't seem to be affected.

 

In a word.... stumped!

 

 

Appreciate any thoughts that you can give!

 

 

 

 

Edited October 16, 2021 by thctony

[tokenroll 30,476]

up the food is my first thought, or light burning but im sure the waterboys will be off more help. 

 

Edited October 16, 2021 by tokenroll

[thctony 9]

The other thing that I've been wondering is whether the plants are suffering from light stress (which is the cause of the yellow tips, rather than nute burn) and also a lack of nutes (since I'm under-feeding, thinking that the yellow tips have been caused by overfeeding). 

 

This combination of things would explain most of the symptoms that I've shown in the pics above (I think) but would definitely prefer some other opinions since this is my first grow in about 15 years!

Edited October 16, 2021 by thctony

[thctony 9]

2 minutes ago, tokenroll said:

up the food is my first thought, or light burning but im sure the waterboys will be off more help. 

 

 

Yeah, so I think the plants won't be affected by heat from the lights (they're at least 40cm away from the top of the plants). Though I am wondering whether the lights are too powerful for the plants. I've no real experience with diagnosing that though

[Shumroom 23,563]

How's the res a few days after setting? 

ph EC temp? 

 

@badbillybob @stu914

Any other thoughts. 

 

Atb 

 

 

[thctony 9]

Res pH and EC is pretty much stable at EC 1.2 and pH 6.0 Fluctuations of 0.1 over a few days is what I'm seeing. Temp is maintained between 19 and 20 degrees with a chiller

 

I've just been back into my tent to have a closer inspection of growth at the top of the plants. Leaves that are exposed to direct light appear to be affected far more than leaves that are shaded (even partially shaded). 

 

These leaves that aren't affected look pretty healthy, to be honest. No yellow tips, whole leaf a pretty consistent shade of green. Leaves around it that are exposed to the light have been yellowed significantly, and have tip burn.

 

I'm really beginning to think that it is the intensity of the lights causing my problems. Even so I'm still unsure whether the nutes I'm giving are adequate or not. 

 

Perhaps the best course of action at the moment is to raise the lights to the top of the tent and wait to see how the plants are affected before changing anything nute-wise?

Edited October 16, 2021 by thctony

[badbillybob 32,984]

1.2 ec is plenty for rdwc in my opinion. if the water is coming out of the tap at 0.7, cal mag is the last thing it needs. 

its possibly the lights bleaching them, i dont know how far away they are from the plants. the plants look cold too, what are the leaf surface temps? 

 

im also no fan of the strain..... i grew it out years ago, and it took forever to finish, something ridiculous like 110 days, and after cutting, dryin and smoking it, i realisd that id wasted my money on electric. sorry to be the bearer of bad news like...

Edited October 16, 2021 by badbillybob

[stu914 42,126]

I would hazard a guess at light bleaching as all your other perameters look ok and the upper part of the canopy is affected the most.

I have to agree with Billy and it might be best to cut your losses now, being autos there's little chance of them improving, sorry bud...

[thctony 9]

1 hour ago, badbillybob said:

1.2 ec is plenty for rdwc in my opinion. if the water is coming out of the tap at 0.7, cal mag is the last thing it needs. 

its possibly the lights bleaching them, i dont know how far away they are from the plants. the plants look cold too, what are the leaf surface temps? 

 

im also no fan of the strain..... i grew it out years ago, and it took forever to finish, something ridiculous like 110 days, and after cutting, dryin and smoking it, i realisd that id wasted my money on electric. sorry to be the bearer of bad news like...

 

Thanks @badbillybob - makes sense on the CalMag / tap water.

 

The plants had grown much closer to the LED lights over the past week or so as they've been stretching (which is also when the problem appeared). I'd say they were around 30cm away this evening before I moved them to the top of my tent which is 220cm tall. They're now around 60cm from the top of the tallest plant.

 

How to take leaf surface temps? Do I need a laser thermometer or something like that?

 

Regards the strain - I think I'll wait and see how they turn out as I have quite a few weeks invested in them already. I'm not in it for the smoke - I'm making extracts for my wife who's pretty ill so my fingers are crossed that it'll yield something that can be used for that at least.

[Shumroom 23,563]

30cm away from a Telos 10 is definitely too close without dimming the light. 

 

You do need to be careful not to allow plants to grow too close to the light. 

 

It's usually not a temperature issue with LEDs but too much light(PPFD),

without all other variables being increased this will lead to problems. 

 

Atb 

 

Good luck with your wifes meds. 

 

[badbillybob 32,984]

10 hours ago, thctony said:

 

Thanks @badbillybob - makes sense on the CalMag / tap water.

 

The plants had grown much closer to the LED lights over the past week or so as they've been stretching (which is also when the problem appeared). I'd say they were around 30cm away this evening before I moved them to the top of my tent which is 220cm tall. They're now around 60cm from the top of the tallest plant.

 

How to take leaf surface temps? Do I need a laser thermometer or something like that?

 

Regards the strain - I think I'll wait and see how they turn out as I have quite a few weeks invested in them already. I'm not in it for the smoke - I'm making extracts for my wife who's pretty ill so my fingers are crossed that it'll yield something that can be used for that at least.

should be fine for extracts to be honest so no worries there, its just that i didnt enjoy smoking it. im sure it will have plenty of goodness for your wifes needs. best wishes to her.

and yeah a laser thermometer is what i use. they arent too expensive and give a good idea of leaf temp surface temp etc. 

 

good luck with it, i hope they do well for you both.

[raffles62 57]

It could be the lights. Less likely if shaded leaves look normal. How many watts are they pulling at the wall?

 

Possibly you've fallen into the same trap I did with my current grow. Dead leaf tips can mean under fed (as opposed to overfed/nute burn) especially if the plant is pale overall.

Edited October 21, 2021 by raffles62

[thctony 9]

Updating this one with some new photos.

 

The yellowing has continued through the plant that I photo'd before - but has changed a little in its characteristic. Lights were moved to the very top of the tent (can't get them any higher) a week ago now, but the problem has progressed - in one plant more than others. Perhaps important to note - this plant was the largest during veg so would have been exposed to more light than the other plants.

 

I'm still not 100% its a lighting issue, but its difficult to reason that its a nute problem since the other plants in the RDWC system (fed off exactly the same nute solution) are not exhibiting the same symptoms - or at least not with the same severity.

 

Today I have switched off the Telos 10 in the centre of the tent to further reduce the amount of light being emitted. (I'll have to rearrange the other lights to cover the centre of the tent a bit better now).

 

Interested to see if these photos give you guys (particularly @badbillybob & @Shumroom) any further insight into whether this is likely a lighting issue or possibly something else.

 

@raffles62 I've doing a little test for a few days - pushing a EC a little higher than it has been to see how the EC/pH fluctuates.

 

 

 

[badbillybob 32,984]

what ph are you putting in there?  it looks like it might be ph related 

 the central one (ole yeller) - the burning on the leaf edges in some of the pics makes me think the ph is too high in the root zone.  the burnt leaf tips indicate the feed is too high, but this might have been an earlier issue. it might just be a fussy feeding fucker  phenotype

i dont think its light bleaching, having seen the pics, because that would just affect the top of the plants and ole yeller is yellow right through.

the only other thing i can think of is something oddball, like  sulphur defficiency, caused by ph issues locking it out. if the leaves have a pinkish red or orangy hue to the undersides this will be it. 

 

thats about all i can think of mate, hope you get it sorted

[thctony 9]

Right now the pH is 6.0. It was between 5.5 and 6.0 during the first few weeks. Very rarely has it been above 6.0. 
 

Interesting that you mention sulphur deficiency. I have “very hard” water here - it’s EC is 0.7 out of the tap. I’m seeing a build up of what appears to be limescale within the my RDWC control unit, so I’d assume that continues through the pots the plants are growing in. 
 

Could high concentrations of calcium / magnesium cause a lock out of sulphur?