What is eating my winter lettuce roots?

[BarbaraMember]

I have (or should it be had) a reasonable stock of overwintering lettuce in my polytunnel, which survived the cold quite well. Recently the outer leaves of one variety of green lettuce starting wilting then the inner ones. The worst affected plants were no longer connected to their roots! I suspected cut worm but saw none, so so pulled up a few plants that were just a little bit affected, to investigate. On the main root just below the surface there were little white worms. They were very small and difficult to spot. Most were about 5mm long and less than a 1mm thick. I couldn’t see any legs, even with magnifying glass, so assumed they are worms or larvae. After trawling the internet I could only come up with a pot worm and various nematodes in the identity parade, but with no certainty!
The red lettuce which were planted next to the affected green ones are now showing the same signs, so I pulled some up and again found these tiny worms.
I’m not sure what they are. They could be pot worms but these are supposed to be harmless, be moving in to “clean up” after another pest. But the scale of the damage makes me suspect they are something else, such as a harmful nematode.
Has anyone seen any similar damage or does anyone know what these “worms” are?

[charlesModerator]

 Hello Barbara

These pests sound horrible and I do not know them. But it has been a tricky winter for lettuce and mine in the tunnel have suffered some losses, from a rotting of the stem, to do I think with a combination of freezing and then fungal rot. The worst affected are an earlier sowing of 1st September, (compared to 8th September) and I have lost more in the less ventilated, damper bottom tunnel, although both tunnels have had some doors open night and day.

Apart from that, and a few plants of Red Frills suffereing the same fate, the survival rate is impressive.

[greenfingerMember]

Did you ever find out what these worms were?

I’ve just discovered the same things eating my lettuces.

[charlesModerator]

 I never was sure what ate Barbara’s lettuce roots. Recently I had one plant keel over and found a fat, white maggot which I think was cutworm, only one and its effect was totally terminal, the other hundred and fifty lettuce plants are fine so it is not a problem. I hope that yours are mostly healthy.

[urbansmallholderMember]

Just had a quick look through pests, diseases and disorders and the only thing that seems to fit the description is lettuce root aphid. Might be worth ‘googling’ it to see if this is right??

[charlesModerator]

 These aphids have a similar effect on the lettuce, causing it to suddenly wilt, but are so small that you can barely see them, myriads of white fluffy insects nibbling lettuce roots, and often some whitish powder around the roots as well.

I think they are often present in summer but unnoticed, until a shortage of moisture causes the lettuce’s lack of roots to be exposed, and then there is a domino effect as they spread to neighbouring plants. Also they can bring viruses which cause lettuce leaves to become more coloured and smaller.

Most common habitat for the aphids in winter is poplar trees and I am fortunate to have none nearby, managing most summers to escape with only minor damage. But if they are a serious problem, you can grow endive and chicory as alternative salads.

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