HELP! Grow problem - stem weak

[bswanson58]

The problem:
As you can see in the pictures, the plant is generally healthy, but the stem just above the surface appears to be dying. This is the second plant I've grown from this seed and the second time this has happened. The stem above the surface becomes constricted/weak and then darkens in color. From here, the plant will weaken and eventually fall over. The plant never appears too stressed from leaf appearance until this problem starts. I do not notice any pest or mold problems, and have not had any in the past. The roots are white and clean, reasonably abundant, without any signs of rot.

I have been growing for a couple of years with other strains and gained some experience, but this problem I can't solve and haven't found any answers yet. The setup and nutrient levels are consistent with several grows in the recent past, without problems. I have been very diligent keeping ph levels within range, as well as everything else that I understand, especially on this grow.

What is the problem here, and how can it be prevented?
This plant, I'm sure is doomed...

The Specifics:

strain is Dr. Seedsman CBD
seed started in RapidRooter
plant is currently in it's fourth week
problem noticed in third week
hydroponics setup
General Hydroponics nutrients (FloraMicro/Gro/Bloom) + HydroGuard
nutrient strength is currently 10ml (Micro), 13ml (Gro), 3ml (Bloom), 6ml (HydroGuard) in 10 liters water
ph maintained between 5.8 and 6.2
ambient temperature is generally upper 60s (F), water resevoir around 66 F, humidity around 40%
150W full spectrum LED grow light, approx 1 foot above plant
there is gentle air flow (fan) on the plant, as well as ventilation out of the grow chamber

Thank you for any help,
Bill

[SirSmksAlot]

I'm wondering if the stem is getting wet? I had this happen to a seedling of mine before and it was caused from being kept too wet and it developed a fungus.

[gbauto]

The only time I've encountered this using rapid rooters is when they stay saturated with solution-that creates an environment for damping-off of the stem.

[BaccaRacca]

It's damping off.

Cool and damp does it. That particular strain may be particularly vulnerable to one of many funguses that cause the problem. If you keep your seedlings covered at this point, uncover them and give them more air. A small fan could help. Otherwise change your potting medium. I use a perlite/peat moss mix 75%/25%, and preventing damping off is one reason I use it.

The following article provides more details, and other ways to prevent the condition: https://www.planetnatural.com/pest-p...e/damping-off/

I may not know much about modern cannabis growing, but general gardening and plant propagation, I know.

[bswanson58]

Thanks for all the help, it seems my problem is conclusively a case of damping-off. I'm trying one application of Organocide Plant Doctor (10ml in 10L) in my hydro reservoir as well as a foliage spray of the solution to see if the plant can be revived.

Bill.