The attached photos capture an insect that is attacking our horseradish leaves.   The bugs are about 1/2 inch long.   I've never seen this bug on our property before.  It showed up about 2 weeks ago and is now in such numbers that there can be 50 on a single leaf!!!  I was hoping you could 1) identify the critter and 2) suggest one or more remedies acceptable for an organically certified farm and nursery.   I am awaiting approval from our certifying agent for the use of a mixture of Dawn detergent and vinegar.  I don't know if that will work but it can't hurt.  I've seen that approved for organic operations elsewhere.
Thanks,
Dennis