Downy mildew on maize

The pathogen produces two typical symptoms. 1. On leaves, initial symptoms include chlorotic streaks on the upper surfaces associated with white, cottony growth on the corresponding lower surfaces consisting of sporangiophores and sporangia. The leaves later turn brown, necrotic, and finally totally dry. 2. The tassels are malformed as small, green leaflike structures (called “crazy top”), which makes the plant unproductive. 

The pathogen produces hyaline, upright, short, stout, branched sporangiophores bearing spherical sporangia. The disease is spread mainly via airborne sporangia that require relative humidity >90% for germination.