Lettuce help needed

[Steve Robinson]

Can anyone advise me on this issue that's just come up in my DWC bed?  I've searched this forum as well as the internet and can't identify it.  Older leaves begin to wilt at the edges progressing until the entire leave turns white and dies.  New leaves seem to still be coming on and growing well.  System is 150 gallon FT with two 50 gallon grow beds alternately flooding for 15 minutes and draining 45 minutes.  GB's drain into a sump which pumps into two small (5 gallons each) DWC beds and drain back into the FT.  Each DWC bed has aeration.  System is in my garage which is currently about 68 degrees.  Don't see any obvious insects on the plant and it seems to be confined to the more tender varieties of lettuce.  Everything in the GB's look great and growing fast!  Today's readings are Ph 7.0, Ammonia .25 ppm, nitrites 0, nitrates 80+.  I also used a soil test kit and got a reading on the Phosphorus and potassium which showed medium to high on each.  Maxicrop was added a couple of months ago when the system was started. Only water and fish food have been added since.  Thanks for your help!

[Steve Robinson]

Forgot to mention, I initially had a 400w HID about 18 inches above each bed. Thinking this might be contributing to the problem, I replaced one with a GrowPanel 45 LED. No visible change.

[Vlad Jovanovic]

Steve, just out of curiosity...what is the temp like at 18 inches away from that 400Watt HID? Are you using "Cool Tubes"? If not, you may want to back those puppies up a bit...to more like 48 inches away from the tops pf your plants...And get some fresh air moving through there...What's your ventilation set up like?

[Steve Robinson]

Thanks for the input Vlad. Not sure what the temp is but I'll check tomorrow when the lights kick on but I now have LED lights above the questionable bed? Still have HID's above the other. Will take your advise and raise it. As far as ventilation, I have none. I do have a small fan I can set up to move the air some.

[RW]

I have a very similar setup and I'm seeing this problem too.  I'm pretty sure it's light related. i have T5's about 4 inches over the plants. this seems to happen on the leaves that don't get enough light. I suspect that as new leaves stretch toward the light and the old leaves start to wither and die.

 

Good idea Vlad on checking the temp. I had a hard time growing anything this summer. The water temp was about 86, but the plant area was 110. Basil and oak leak lettuce varieties worked best in the high temperature. I have a small fan that turns on when the pump turns on. I'm sure that helps some too.

[Steve Robinson]

Good tip RW. That does seem to be the case? I've raised the light which should lower the temp and give broader light coverage! Will let you know!

[Vlad Jovanovic]

Wow, 110 Degrees sure is pretty warm for lettuce...I'm sure the fan probably helps too...Good air circulation in an indoor set up seems pretty important, and may go a long way in avoiding certain diseases...

I had a test system set up in a garage this summer with a good variety of different lettuces as well as some fruiting plants. The Iceberg and Romaine varieties (and only on 3 or 4 plants total) exhibited what looks like the same problem Steve is having. Only a few of  the outer leaves were affected. I clipped off the affected leaves and added a small fan and the problem just ceased never to return. Might have been a coincidence, but I doubt it.

The 'general rule' for HID's is at 400Watts 48" should give you a safe distance from your plants as well as 4 square feet of coverage. That being said, during cold nights (near or below freezing) I have placed 400Watt HPS light less than 3 feet away from the tops of my hot peppers with no problems whatsoever. Again, the cold night air took care of most of the heat being radiated by the light at that distance. If you place your hand underneath the light at about where your "canopy' is, and you can feel warmth/heat, your light is too close. If its lukewarm sort of and your not sure if you feel it or not, that means you are probably ok...Also, HPS lights seem to give off slightly less heat than MH.

Hope that the problem disappears for you the way it did for me...Small fan/circulation is better than no fan/circulation.

[Steve Robinson]

I have raised the light and added an oscillating fan. I've also added a small amount of Maxicrop and have ordered some cheated iron to add. The problem seems confined to two varieties of lettuce. they were in a mix I bought from Baker Creek Heirloom Seeds so I don't know their names. One looks like a type of butter lettuce and the other looks like endive. Another type called Little Gem is doing great. Guess I'll keep an eye on them and hope what I've done helps! Thanks for all the help guys! I'll keep you posted.

[Vlad Jovanovic]

Oops, I meant to say 16 square feet coverage (400Watt at 4 feet away) not 4 square feet...

Yeah, keep us posted...good luck!

[jason maggs]

do you smoke cigarettes steve? because It also looks like a fungus/mildew that lettuce can catch from tobacco (even dried tobacco rolled up in a cigarette)

[Steve Robinson]

No Jason, I don't smoke. Can't think of any way for them to have been contaminated by tobacco. Wont rule that out though! Thanks for the input!

[Jane]

is there adequate air circulation ?

to high of humidity ?

[Steve Robinson]

Hi Jane. I have an oscillating fan and a small stationary fan blowing on the plants. You may be onto something with the humidity. I just checked and the relative humidity is 74%! My system is in my garage and it's pretty cold outside. My garage door is insulated but there's a lot of condensation on some areas. Any suggestions for lowering the humidity without lowering the temperature too much?