brown spots

[scorch]

Any ideas? I'm growing autos under a 250w HPS light. Air comes through a passive inlet, then vented through the light hood to an inline extractor. They are in 20cm/8inch pots filled with B and Q potting compost. I suspect the potsize will be frowned upon, but its always worked in the past
I have been growing autoa for a couple of years, but recently they have been starting to develop dead leaves as shown. In the past I have been using a half strength mix of old timer bloom after 4/5 weeks, but suspecting that to be the culprit I have stopped, and gone back to my cheap and cheerful npk generic tomato food. That doesn't seem to have had any impact either. I water them twice a week, supplying enough water til it runs out of the bottom.
I can't think of anything I'm doing differently!

 

[namvet]

Hoe old are the plant with those? It almost looks like nute burn,but you say you were going half strenth so thats a hard one to figure out .Maybe low calcium or mag.Whats your intake and runnoff ph?Are they pretty dry in between watering, and how often are you applying nutes?

 

[scorch]

Hoe old are the plant with those? It almost looks like nute burn,but you say you were going half strenth so thats a hard one to figure out .Maybe low calcium or mag.Whats your intake and runnoff ph?Are they pretty dry in between watering, and how often are you applying nutes?

They are almost 7 weeks old, I started feeding them with half strength old timer at week 5. I water them twice a week and feed them at the same time. I would have to measure the ph, I have got so used to my system working that I haven't had to worry about it!
I have tended to water too often in the past, but I try to make sure that I can stick my finger into the top of the pot and feel it dry for 3 inches or so.

 

[Muddy]

It looks like a cal/mag deficiency but it could be caused by a lockout from your pH being off. Need to check it first before you do anything else.

 

[scorch]

using good old litmus papers, the water I use for watering is 6.x and the run off is about the same.

 

[Cave Dirt Cody]

How big are the plants? I have had to water everyday to keep big plants in small containers happy. A good sized auto can drink a half gallon a day. Easy.

 

[70sdiver]

Looks like a lock out I'd do a slurry test on your soil its self . When in doubt just flush it out.

 

[scorch]

Ok, I flushed them three days ago. Should I reintroduce nutrients?

 

[JM]

they look pretty far along to me... i think id just finish them at this point... giv em another 3-7 days and chop.... :smoke:

 

[AndyBotwin]

they look pretty far along to me... i think id just finish them at this point... giv em another 3-7 days and chop.... :smoke:

Agreed. If my math is right you're around 9 weeks old, so I'd just water them and wait for the last of the leaves to die off. I've had plants with a late bloom mag deficiency like that and there's not much you can do about it. The damaged leaves won't recover so just let the plant suck the nutrients out of them and give her the ax..