Answer: That is a tough one to answer. Pesticides (even organic ones) are labeled for a specific plant and a specific pest. Without knowing what is eating them, it is all but impossible to recommend a control.
The culprit is most likely a caterpillar or some type of beetle. Some pests are nocturnal and may be found feeding at night. Do some Sherlock Holmes work by going out with a flashlight at night to see if you can catch them at it.
Here is a "generic" approach to controlling the unknown pest. Check around the base of the plant in the top inch of soil for any caterpillars hiding during the day. Destroy any you find. Then cover the plant with a small piece of floating row cover draped over the plant. Allow extra slack in the cover to give the plant room to grow. Cover the edges of the rowcover with a little soil to "seal it off". That should do the trick.
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