Killex is a product that will control over 50 varieties of lawn weeds, while leaving your lawn unharmed. It is effective when applied to the leaves of actively growing weeds. It will not prevent new weeds from producing so apply only when weeds are present..eedEx. Weedex Dandelion Bar is a weed killer that contains 2,4-D for the control of a wide range of turf weeds including plantain, dandelions, legumes.