Answer: It sounds like your plants may be suffering from curly top virus, which is spread by leafhoppers. However, if they survive to bear fruit, that may not be the case. If the plants yellow and die, this is the likely cause. To avoid it in the future, cover your plants with floating row cover to prevent leafhoppers from feeding.
Have you checked the leaves for the presence of aphids? If there's a heavy infestation of aphids, which prefer new growth, they can stunt leaves and stems without killing the plants. You can control aphids with many organic insecticides, from neem oil to insecticidal soap. Or, you can spray them off with a strong blast from your garden hose, and follow up with application of a repellent such as neem or garlic spray. Feed your plants mild fertilizer, since aphids are most attracted to overfed and unhealthy plants. Hope this helps!
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