Tough and kinda "ugly" lettuce—stress? Disease? Pest?

Question: Two of my lettuce plants are clearly struggling in some way. Their leaves are dull-looking and tough, and one has brown spots on the leaves. They may have different issues, but I figure it's similar enough to group together. The pictures are of the unhealthy plants, and a neighboring healthy plant of each variety for comparison.

responder: The Question Asker Replied June 20, 2023, 12:39 PM EDT
response: And the other pair of plants

responder: Lindsey K. Kerr, MS, MHP (she, her, hers)  Replied June 20, 2023, 3:06 PM EDT
response: Hi Daniel, Do you know the names of these two lettuce varieties? Are the brown spots only on the green variety? They look like insect damage to me, but it's hard for me to tell. Have the plants exhibited these negative characteristics for weeks or they just recently changed? The unhealthy B photo looks like the lettuce is beginning to bolt--grow tall and flower. Lettuces and other greens bolt because of light and/or heat. Lettuces are often triggered by our long summer day length to flower, set seed, and die. When they start to grow taller and put up the flower stalk, their textures can change and they often become bitter. At that point, it's time to pull them out and compost them.  Here is a University of Minnesota bulletin on lettuce and bolting.   Lindsey K. Kerr, MS, MHP (she, her, hers)Consumer Horticulture EducatorMichigan State University Extension

responder: The Question Asker Replied June 20, 2023, 11:38 PM EDT
response: The red ones were labeled "Red Crisphead" at the Farmer's Market. They may be a more specific variety, but I don't know. The green ones I started myself—they're "Little Gem" romaine. The brown spots are only on this one plant, yes—not the red one. It's not just the spots—the leaves have a mottled appearance as well, and a duller surface finish. Insect damage is certainly possible—it seems intuitively strange that it would affect one plant and not a neighboring one, but I know that just happens sometimes. I don't see any visible insects though—what sort would cause this? Is there a disease that might contribute as well? For the red one, I would call attention to the leaf margins, which look...well, "burnt" is a good descriptor, but unlikely to be the problem per se—these are adequately watered and mulched, and did suffer from a little sun damage earlier but recovered fine before these issues started. And, not something you can see, the leaves feel almost twice as thick and tough as on the healthy plant. They've been like this for...I'd say probably a week and a half? I'm not always the best at noticing, and then following up, right away, but we definitely got a harvest or two from them after transplanting about a month ago. I agree the unhealthy B plant is probably starting to bolt in response to whatever is stressing it, but none of our other plants are bolting yet, so I'm thinking it's exactly that—stress from whatever insects, disease, etc.

responder: David Lowenstein  Replied June 22, 2023, 5:04 PM EDT
response: The green lettuce has a virus. The cause could be mechanical, from insects or seed. Regardless, it's safe to eat but should be harvested very soon to avoid accidentally spreading to other plants. Virus symptoms can be patchy and affect plants without a pattern, like a healthy one adjacent to an infected one.   I'm less certain about the issue on the first plant. The white spots could be residue from aphids or leafhoppers.  Heat and dryness may be contributing factors too.

responder: Lindsey K. Kerr, MS, MHP (she, her, hers)  Replied June 23, 2023, 9:34 AM EDT
response: Hi Daniel, I wanted to follow up about the red lettuce. I was harvesting my lettuce this week after seeing your questions. My romaine type lettuce was fine and tasty. The red leaf lettuce I have was terrible! Although still a small plant, it was tough and bitter. I think this related to the weather--our day length and heat are causing lettuce to bold--and variety dependent. Some types of lettuce are better in heat than others.  I suggest that you try growing your lettuce from seed next spring. It's easy to grow and you can choose a variety that suits your taste.  As Dr. Lowenstein said in an earlier email, it is best for you to pull the diseased green lettuce as soon as possible so that insects do not spread the virus to your other lettuces.  Lindsey K. Kerr, MS, MHP (she, her, hers)Consumer Horticulture EducatorMichigan State University Extension

responder: The Question Asker Replied June 23, 2023, 12:55 PM EDT
response: Thank you for the advice. I went ahead and pulled both plants yesterday—I could see that neither of them were really growing any more, they were technically growing new leaves but those leaves were staying extremely tiny and all snarled up in the middle, not anything that would become useful to eat. I'm definitely moving towards growing from seed—in fact I have some transplants almost ready to replace these, that I was planning to put elsewhere but they'll be more productive in this plot.