Diseases of cole crops (
Alternaria blights or leaf spots on cole crops are caused by several species of the fungus Alternaria. Disease occurs in wet winters in Arizona when there is sufficient rainfall to enable wind blown spores to germinate on the leaf surface. The leaf spots are dark and circular, varying in size up to 2 inches. Alternaria spp. survive in infested plant tissue, in plant residue and in seed. When sufficient moisture is present, the fungus produces spores that are carried in wind and splashing rain.
Disease is controlled by (1) cultural practices such as rotation to
crops other than cole crops, (2) control of cruciferous weeds, (3) plowing
under plant residues, (4) planting disease free seed, and (5) preventive
applications of azoxystrobin (Amistar), cyprodinil plus fludioxonil (Switch), chlorothalonil (Bravo) and maneb (Maneb).
For photos and more information see:
February 20, 2013