These problems, diseases and pests are known to affect Lettuce plants:
Snails and slugs
Cucumber Mosaic Virus : Cucumber Mosaic Virus (CMV) was first found in Cucumbers, hence its name - however it is not limited to affecting only that plant. Mainly transmitted by Aphids and spread mechanically by humans. Can also be transmitted by seed. Can overwinter in roots of affected plants. Also known as: banana infectious, chlorosis virus, coleus mosaic virus cowpea banding mosaic virus, cowpea, ringspot virus, cucumber virus 1, lily ringspot virus, pea top necrosis virus, peanut yellow mosaic virus, southern celery mosaic virus, soybean stunt virus, spinach blight virus, tomato fern leaf virus, pea western ringspot virus
Slugs : A snail without a shell. A mollusc with an elongated, soft body with a shiny appearance due to the slime coating.