Some plants repel insects naturally. Grow them in between your crop to deter insects. By knowing the wild plants that grow in your area, you can prepare your own herbal insect repellent at no cost. Add cow urine to help extract the repelling compounds from milky latex leaves, bitter-tasting leaves and aromatic leaves. It is best to alternate two types of herbal repellent. Prepare a second type of insect repellent with the paste from, ginger, garlic and chillies.