The greatest threat to cotton and wheat is

SO₂ is poisonous, and irritates the respiratory system of animals and humans. A continuous exposure to concentration of 0.2 ppm lasting for 3-4 days or even 0.5ppm for full day has been reported to damage the lungs and increase the rate of mortality. In plants and grasses, SO₂ also produces leaf injuries (called necrotic blotching). Sulphur dioxide damages, barley, alfalfa, cotton and wheat.