A superfood, traditionally kale is known as a hardier vegetable that rarely suffers from pests and disease, but it was found to have high amounts of pesticide residue when tested in each of the past several years. Luckily kale is a staple of the organic farm marke scene--to the point that it's a cliche. If you want kale, you can find it organic.
Can't find organic kale? Safer alternatives include cabbage, asparagus and broccoli. Dandelion greens also make a nutritious alternative.