Nute burn? I think not. So what deficiency is it?

Hello all you fellow growers!

Firstly, I would like to thank all who post here. There's more practical knowledge on this (and others) forum than can be found in any book, so thank you for sharing it.

I am currently growing two strains: Chronic and Bullshark. they are flowered on separate NFT trays, but in the same room. The room has 2 x 600W HPS; good ventilation system; heater; UV de-ioniser. All ventilation and heaters are thermostatically controlled. The batches I will be discussing here are currently in week 6 of flowering. My tap water is VERY hard, with a base ppm of 500.

My issue: The chronic plants have developed serious yellowing of the leaves, beginning between the leaf veins, in the middle of the plant then working it's way up to the top cola. Necrosis has begun in the most severe cases. This started at around week 4. Despite there being no environmental difference, and being on the same nutrient regime (Hesi), the Bullshark strain shows no problems at all.

I initially thought it was nute burn, but the most severe cases are occurring on the plants with the largest buds, some being over 2 inches diameter at the top (and the chronic is so far producing much larger buds than the Bullshark, although the Bullshark is frosty as F**K - even the branches). So naturally this lead me to think that it was in fact a deficiency (despite using the full range of Hesi nutes at their recommended strength). The only difference is that the Chronic was vegged for 10 days whereas the BS went straight from rooted clone to flowering.

I'm sorry the pictures aren't great (the lights just went off and I wanted to get in and out as quick as possible), but if anyone has any suggestions as to what the cause of this severe yellowing and eventual necrosis is I would really appreciate any input.

Peace and joy to you all

Maya101

P.S. Just before posting this I added some Cal Mag to the Chronic reservoir, as I have been leaning towards it being a magnesium deficiency, but I'm just not sure.

Looks like a combination of a few things. Nute burn for sure!!! Heat and or light stress as well! Deficiencies won't curl leaves upwards like that.

Thanks for the reply,

But if it's nute burn why would it be most pronounced on the plants with the biggest buds? Could it be that the bigger plants have more root mass, so are taking up too much nutes? Unlikely, as I would have thought it's to do with the concentration of the solution. I use air cooled reflectors, but I suppose it could be heat stress, but again, it's not showing on the other strain. I don't think it's light related, if anything I could up my lights to 1000W, but maybe I'm wrong. My day temps get up to 27C and night temps down to 19C. I know 27C is high, but is it so high that it would cause this?

Its a heat/light burn stress issue.

OK thanks, I've raised the lights as no doubt you're right. They were about 50cm above the plants, but I thought that would be OK given that I use air cooled reflectors. It does make sense though as the symptoms are most pronounced in the tallest plants.

Thank you!

Yes, extra crispy chicken.

I've been feeding Hesi nutes: Hesi hydro bloom 5ml/ltr; Hesi Powerzyme 2ml/ltr; Hesi PK 0.25ml/ltr in week 4, increasing the PK each week.

I think *BUDS is right about the heat/light burn, I don't think it's nute burn.

yea id say heat burn cuz the leaf tips go upward. the necrosis is due to old age, and the bigger the buds = worse the decay, to an extent, thats normal. up the micro nutes, raise the light, drop the temps a bit, and youll be ok