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I'm growing some butter lettuce in a grow bag full of Happy Frog potting soil. It's been particularly rainy the last few days. Today I inspected the plants and a few of them popped right off of their stems. They had rotted all the way through at close to soil level.

It looks like a fungus got them. Does this mean I watered them too much? What should I do now?

Here's some photos.

Click on pictures to see larger close-up view.

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I havent seen this exactly before, but it does look like that soil is very wet... not sure if it is some sort of moisture retaining soil, but if it is, I would mix it with some sort of normal garden soil mixture... or peat or something that doesn't have polymer gelling agents... make sure you have good drainage, and replant.

it also looks like there could be some maggots there, you could reduce that problem with some diatomaceous earth on the surface; actually if you sprinkled 1/4 inch worth of quartz sand and DE on the bed it wouldnt stay wet on the surface.

of course if it isn't usually this wet, you could just replant and hope for the best.

I personally wouldn't have any concerns about eating the lettuce, after you trimmed off the yucky stuff; but use some heightened discretion, throw it away if it tastes bad, dont feed to a baby, dont feed it to someone who is immunocompromised, etc...

EDIT:

no maggots, I mistook some of the perlite... enter image description here

  • It's 100% Happy Frog potting soil. Since it's container gardening, you kinda need extra water retention, right? Though it has been uncharacteristically rainy recently. The Grow Bags should have plenty of drainage. What makes you think there are maggots? And will DE even do anything in an outdoor setting? Exterminators have told me otherwise. Though I guess if you're using a whole 1/4 inch of it... Anyway, the spores in the photo have disappeared in the morning. Should I leave the roots to rot in place or should I cut out more of this plant to prevent the growth of fungus? – Nick Retallack Jan 11 '17 at 22:05
  • I would probably pull the roots. – Grady Player Jan 12 '17 at 2:02
  • The next day I noticed a slug nearby. Could a slug have plowed through the stalks and killed these off? – Nick Retallack Jan 12 '17 at 21:12
  • @NickRetallack I don't think so, that doesn't seem like their style... but anything is possible I guess.... they make an iron based organic slug and snail bait that works really well... – Grady Player Jan 13 '17 at 19:53
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That you can't see a problem except when you tried to harvest the lettuce suggests it's a very acute problem that hasn't affected its growth. I'd blame a fungus rotting the bottoms, and since you're using a potting mix with sudden high rain fall, it probably got too wet letting the fungus attack and overwhelm the stems.

The spores are now in your potting mix so I'd be inclined to toss it into the compost heap, and start again in a more sheltered position.

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Lettuces need steady growth in moist but not wet soil, in warm but not hot or cold conditions, and in full sun when you can keep the water right. For fungus to get started, there needs to be a wound or constantly saturated tissue. The wound can come from careless hoeing, bending the stem to reveal the base, critters nibbling (slugs, cutworms and so on), sharp stones, many possibilities. Including early harvesting of basal leaves for salads if the tear leaves a jagged wound. Speed tearing of basal leaves is fine if you can control the water and plan on removing the plant fairly quickly before fungus can get a foothold. Leaves are not designed to separate from the stem easily until they are way past edible.

The images seem to suggest a number of adjacent plants affected. I'd go for a nibbler.

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