What could the problem be? These seedlings were fine until a couple of days ago although one seedling shrivelled up and died. Now, all my plants seem to be affected as well as the peppers. Some of the leaves are curled under. I’m wondering if the hot humid weather was a factor. Will this affect the plants once they are planted? Any remedies to treat leaves?
Thank-you for contacting Toronto Master Gardeners with your question. It is so disappointing when you see your plants faltering, especially when you have grown them from seed.
You have not mentioned how much light your plants are receiving, nor whether they have been given any fertilizer. It does look, however, as though your seedlings have been hit with a bit of sunstroke. Young leaves are very fragile and can burn easily. With so few leaves on the plants, you should leave them in place as long as they can contribute energy to the plant through photosynthesis. If (when) they shrivel or dry up completely, remove them so that they do not attract fungus or disease. As long as the newer leaves are remaining green and healthy, your plants should be able to be transplanted successfully.
Here is some advice on a similar problem given a few weeks ago on the TMG website:
While fertilizer can certainly cause the kind of whitening of leaves you have noticed on your tomato plants, the fact that you are in the process of hardening them off and they have just had their first major exposure to sunlight makes sunburn on the leaves a more likely cause of the problem. When you first bring your plants into the sunlight, they should be put in a shady spot for a few days. They should also be protected from any strong winds as this can also cause the leaves to scorch. Ensure that your plants are well watered. Avoid any fertilizer for the first week or two outside.
You can proceed with this approach with your plants. Hopefully, they will have enough unharmed leaves or leaf area to continue to photosynthesize and produce food for your plants. It is better to leave the scorched leaves on the plant unless they wither and become crisp. In this instance you should remove the dead leaf material so that it does not become a magnet for disease. But as long as there is any green on the leaves they are essential to the growth of the plants.
Best of luck with growing your seedlings!