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??

What the heck is going on with this? Is it sun damage, or did I burn it with too much fertilizer by accident? It looks like somebody painted the leaves beige, but it doesn't rub off.

Also, does anyone know why the leaves are curling like maniacs? Is it nutrient deficiency, or leaf curl virus?

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From the deep glossy green patches on the leaf it points to overgenerous fertilizer. A leaf has a top, bottom and middle layer of cells - particularly the top layer is designed for protection, bottom layer is for gas/moisture exchange, and the middle layer, protected from above and below, is the soft biochemical factory. If the colour does not rub off, likely something has killed off the soft cells in the middle. This can happen with fertilizer - there is a carrier in the nutrient to help get it into the leaves through the roots. Too much fertilizer and the salts can accumulate with a double whammy effect: first making it hard for the root hairs to do their job and get the nutrient inside the plant, and second when the rich nutrient hits the soft leaf cells it can destroy them. The deep green sort of points to this; in some places the factory cells have survived, in other areas not.

Unnaturally twisted leaves can also point to chemical poisoning from an attempt to control bugs, maybe with a sprayer that was previously used to carry herbicides. Tiny amounts of modern sprays can have devastating effects when applied outside their normal parameters.

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  • Ah, I see. I've been feeding them fish emulsion every 7-10 days or so. I guess I should cut that down to every 3 weeks and double check the dose. Yeah it was infested with mites under the leaves and every one of my plants got powdery mildew (humid climate, construction site across the road). I tried controlling it with neem oil and peroxide once a week each. Cheers for the help Colin!
    – Rob
    Mar 9 at 7:12
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Most probably it is due to imbalanced fertigation. Brown patches might be due to potassium deficiency which does not necessarily mean that your fertilizer does not have it. It could be due to high concentration of fertilizer of not balance PH.

I would suggest you switch to tap water on some plant and observe the new growth. One of the symptom I'm seeing here is calcium deficiency which is pretty immobile in the plant and if the new growth gets healthy with tap water, you should consider redesigning your fertigation.

I was having similar issue which I managed to mitigate mostly by redesigning my fertilizer. check out my question here. Hydroponic Chilli plant deficiency

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