You will need to dig down into the soil around the plants to feel the soil. The key is to keep it moist and with the many factors of soil type, sun or shade, slope, etc. it is difficult to say how often you need to water. The fact that the plants are crispy is not a good sign and their recover is in doubt. That said all that is in your power at this point is to try and avoid too dry or soggy wet while you see whether or not they are going to pullout of this. I don't think the problem is related to any insects.
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