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Please Help Identify What's Plaguing Seedlings

Posted by squirrellypete z7b GA (My Page) on
Mon, Dec 31, 12 at 4:48

Okee doke, I set up my first lighted shelving rig some weeks ago and started my first seedlings. I am a total noob at growing veggies from seed, let alone growing indoors under lights. I did not use sterile potting mix (yes, I know it's a no-no but my options are a bit limited by price and limited local selection). I used my own mixture of cheap potting soil, sphagnum peat moss and perlite until it was a consistency I felt comfortable with....wouldn't stay soggy but wouldn't dry out overnight.

First major ooops.....I did let them get too dry once and they suffered for it. Many things wilted, especially the broccoli. Tomatoes seemed relatively unphased.

Watering on a much better schedule now, letting top of soil dry out some between waterings but not throughout. Most of the plants seemed to be recovering nicely and once they did I fertilized with diluted fish emulsion to which they seemed to respond to overall. you can see in the pics there is some kind of pest or disease infecting the leaves. Sorry some are a little my camera can do.

Sick Seedlings 1

Sick Seedlings 5

Sick Seedlings 3
See the tiny black specs on the left infected leaf??

Sick Seedlings 4

I've shown you the tomatoes but other plant varieties are showing the same thing, notably the lettuce. The least affected seem to be the herbs, basil and cilantro. Initially I was leaning toward a pest but I'm hoping you guys can help me identify it, be it pest or disease or both and suggest a course of action. It begins on the leaf edges until the leaf becomes paper-like. There are also very tiny black shiny specks in this browning area. Again, I can't figure out if these belong to a critter or the result of a disease. Other leaves seem healthy enough and unaffected at this point. I don't want this to get out of control if I can stop it. We always have a lady bug invasion in our house every year and A few survivors have set up shop in my growing area and will fly around the seedlings. Lady Bugs shouldn't have any downside, right? I've also noticed one or two tiny flying gnat-like critters. I've heard ya'll talk about fungus gnats but as this is my first time indoor growing I wouldn't know one if it jumped up and bit me.

Advice is appreciated. I'm going out of town in a week and will be setting my lights up on a timer and having someone water for me if needed while I'm away. I don't want to come home to a vegetable leper colony! I was concerned about trying something like a Bayer 3-1 product on such young plants, didn't know if it would harm them. These are a long way off from being harvested or producing fruit so I'm not opposed to chemicals if it's called for.

Thanks for any tips.

Follow-Up Postings:

RE: Please Help Identify What's Plaguing Seedlings

Hi Danielle,

Well, it's hard to tell. It could be some kind of disease like blight or gray mold. Mold could be caused by over-watering, damp conditions, and/or lack of good air circulation. If it is some kind of disease, it's going to be hard to stop it. Prevention, rather than cure, is usually suggested.

I'm wondering if it could be as simple as a lack of potassium. You said you fed the plants with a diluted fish emulsion. Is that the only fertilizer you used? Fish emulsions are relatively mild fertilizers and usually quite low on potassium (5-1-1 or maybe 5-2-2). You might want to try fertilizing with something like diluted Miracle-Gro Tomato Plant Food (18-18-21). It also contains many micro elements like Magnesium, Copper, Iron, and Zinc.

Sorry I can't be of more help,


RE: Please Help Identify What's Plaguing Seedlings

Yes, that's the only fertilizer I've used at this point. Similar to what I would typically do with outdoor cucumbers, melons and moonflower always went bananas when I did this, although I usually did full strength since they were older baby plants.

I really do not think that overwatering is the problem in my case, however circulation might be. I have yet to add a circulation fan which I said I was going to do from the get go and did not. I'll pick one up next time I'm in town.

Should I be plucking the diseased leaves to prevent spread to other leaves, assuming this is not a systemic problem? Again, I didn't know what impact plucking any leaves, even infected ones would have on plants this young. They all have true leaves at this point but some only 2 or 3 depending on the crop.

I can try the diluted miracle grow next time I fertilize and see if there is improvement. They are planted in a mixture containing potting soil (as well as sphagnum peat moss and some perlite added for aeration). I assumed there were some nutrients present in the potting soil but perhaps not enough, it was not a high quality one.

How often should I be fertilizing? Weekly? Every couple of weeks?

Thanks for any input.

RE: Please Help Identify What's Plaguing Seedlings


Regarding the question of whether or not to remove the affected leaves, I don't know. The problem is that we don't really know what's wrong with the leaves :-) Personally, I'd probably remove them, but that's just me.

How often to fertilize? The problem there is that we don't know whether or not your potting soil already contains fertilizer (or how much). At least for awhile (and while the plants are that small), I'd probably mix the liquid fertilizer at about one forth (1/4) strength and use it every time I watered the plants. If things improve and as the plants grow larger, you could gradually work up to what the manufacturer recommends (every 7 to 14 days full strength during the growing season).


RE: Please Help Identify What's Plaguing Seedlings

I know it may be too late by now, but that looks a lot like fertilizer burn from too much of it, too strong.

RE: Please Help Identify What's Plaguing Seedlings

Hey all,

I'm still not sure what the diagnosis is/was. I did remove the affected leaves before our trip and watered well. The lights were on a timer for 16 hours a day while we were gone and the plants look healthier now that we're back. Maybe I should go on vacation more often lol.

Susan, thanks for the reply. You could be correct, I just don't know. But I wouldn't think fish emulsion at half strength would burn them.

I did not have a chance to try the miracle grow before I left in case it was that they weren't getting enough nutrients. Now that we're back I've repotted most of them today and will try miracle grow or something of that nature next to see how they respond. Again this is my first attempt at this so maybe I am wrong, but they do seem small to me for 8 week old plants. Of course letting them dry out too much set them back I'm sure.

They also were moved out into the greenhouse a couple of days ago and they also seem "perkier" in the cooler temps since doing so. Again as a first timer I'm not sure if this was a smart thing to do or not but I need to make room on the indoor light rack for some ornamental seeds. I've observed daytime winter temps in there up to 85 and nighttime usually stays 40-50 with the wood stove on below freezing nights. The sunlight does concern me though so I'll have to monitor them.....I have not yet set up any supplemental lighting out there and this time of year the daylight may not be sufficient to keep them growing well.

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