Blight
Blight is a rapid and complete chlorosis, browning, then death of plant tissues such as leaves, branches, twigs, or floral organs. Accordingly, many diseases that primarily exhibit this symptom are called blights. Several notable examples are:
Fungicide use in the United States
Leaf blight occurs in areas with hot and humid weather. The spores land on onion leaves, penetrate the skin, and rapidly kill the leaf. This causes a severe reduction in bulb size, as high as 50%, and can happen in less than a week. Applications of foliar fungicides can be used to control leaf blight. These include azoxystrobin, chlorotholonil copper, mancozeb, maneb, and mefenoxam.