unhappy lettuces

[bigpepperplant]

Hi, I sowed some winter density lettuces a month ago in a plug tray in my polytunnel; they came up fine but yesterday I noticed some of the bottom leaves had a sort of white fur on them and have wilted. Is this frost or some sinister mould...?

[bigpepperplant]

[sandersj89]

It could be a fungal problem due to poor ventilation. If it is only the lower leaves remove them and try and open the tunnel doors during the day to allo some air to move around them.

Jerry

[john_miller]

The white fur is probably grey mould, Botrytis cinera, which is a secondary pathogen. The wilting is of more concern and may indicate the presence of one of the damping off fungi. Ventilation will help but also try not to get the soil surface wet, especially overnight into the early morning.

[jennym]

When sowing them in trays, there are a couple of things that help prevent this I've found.
First, use sterile compost, and if, like me, you are short on cash, microwave garden soil (7 mins full power for one large pot)to sterilise it.
Second, I water the compost before sowing, and after, only ever plunge the trays into a larger tray of water so they soak it up from the base instead of wetting the leaves.
Third, you can spray the surface of the compost with a solution containing bordeaux mixture as a preventative, before sowing the seeds.
Fourth, as discussed, keep them in an airy, well ventilated place. Pick out infected leaves or plants.

[bigpepperplant]

hi, thanks for all your advice. It's difficult to keep it ventilated cos the tunnel's 40 minutes drive from home! I did water them from above the other day and that's probably what encouraged the mould. I put them under fleece a couple of days ago thinking it might be frost damage so when I get down there again, I'm sure they'll be a mass of mould! Oh well, I'll bear all your points in mind next time...

[john_miller]

Third, you can spray the surface of the compost with a solution containing bordeaux mixture as a preventative, before sowing the seeds.

Wouldn't Bordeaux be neutralised upon contact with the soil by the copper being adsorbed onto soil particles? If it isn't, could bigpeppers (or anyones) month old lettuces be protected by a (careful, given that it may not be cleared for leafy crops) re-application?

I put them under fleece a couple of days ago thinking it might be frost damage so when I get down there again, I'm sure they'll be a mass of mould!

Putting them under fleece might be enough to kill the fungi without damaging the lettuce. It is the heat and moisture in your poly tunnel that will have encouraged the damping off.

[jennym]

The Bordeaux mixture does seem to work when applied onto the compost surface - last year I did several batches in diferent ways, and this seemed 100% effective.
However, yes, it could be sprayed onto the leaves in the early stages - copper based products are currently permitted in Uk for use in organic situations, some certification bodies allow it on a case by case basis. It is used in as a preventative where a threat exists, but its use may be reviewed under EU legislation. I have also used it as a preventative for late tomato blight.

[john_miller]

I have only ever used it as a preventative for blight on tomatoes. I do wonder if it is cleared for direct use on crops where the leaf itself is eaten as residues may be more difficult to remove from these tissues than from a tomato fruit? Is it specifically able to be used on lettuce without burning tissue?

[jennym]

Interesting. I'm sure its been used on seedling lettuce without burning tissue BUT, upon checking, I find that operators are now required to check with the Pesticides Safety Directorate for advice on field of use. So, there may indeed be a problem with leafy crops.