Question

It sounds like you have cabbage loopers which are known to have a voracious appetite for all members of brassica genus of plants of which turnips are one. Treating your leaves with oil, vinegar and spices will not deter them. If anything, they make think you are applying salad dressing in order to make the leaves more palatable for them! What you need to apply is some form of Bacillus thuringiensis otherwise known as BT. BT is available under trade names such as Dipel and Thuricide. Because of their specificity, these pesticides are regarded as environmentally friendly, with little or no effect on humans, wildlife, pollinators, and most other beneficial insects.