My tomato seedlings were doing fine then suddenly new growth is stunted and deformed. This has happened on four different varieties. Is this a fatal condition or is there a cure? Will I need to discard them and can I then put new plants in the same location? Photos included below.
Hi- the symptoms- curling, twisting, smallish leaves- is consistent with herbicide injury. Some herbicides, such as 2,4-D and clopyralid, mimic natural growth regulators in plants causing hormonal imbalances leading to plant death.
Your plants will most likely not grow out of the injury to produce a decent crop (tomato is especially susceptible to this type of herbicide injury). You may want to look for new plants.
An herbicide may have drifted in to your garden area. It can also travel with stormwater or irrigation run-off from lawn areas treated with herbicides, including "weed & feed" products. A less likely source would be a soil amendment- grass clippings, straw, manure, compost- that may have been contaminated with one of the long-residual herbicides such as clopyralid or aminopyralid. If you suspect the later you can test the soil that the tomato plants are growing in by mixing some soil with potting soil and planting bean or pea seeds in the mix. If the soil is contaminated you will see poor germination and distortion symptoms.
These two web pages have detailed information on herbicide contamination and how to perform a bio-assay to test for it: