Diseases of onion and garlic (
Botrytis leaf spot
Botrytis leaf spot occurs on onion but has not been reported on garlic. It is caused by the fungus Botrytis cinerea. The leaf spot lesion initially has a small white, necrotic center surrounded by a light green halo. The fungus survives on old bulbs or onion leaf debris as sclerotia or mycelia and in soil as sclerotia; (photo 1) spores produced from infested soil or plant debris are carried to onion leaves by wind or splashing water.
Cultural practices that promote air movement and rapid drying of leaves can help reduce infections and disease severity. Rotation with non-susceptible crops such as alfalfa or small grains suppresses the buildup of sclerotia in soil. Preventative application of fungicides when environmental conditions favor disease development can be an effective disease management tool. Fungicides with activity against Botrytis include benomyl, chlorothalonil, dicloran, iprodione, mancozeb and maneb. Resistance to some fungicides has been reported, and any of these chemicals should be alternated with others.
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February 10, 2003