Smut fungi produce large amounts of black sooty spores which show up as unsightly dark brown or black blotches on leaves, stems and fruit. Corn smut is the common example in Ohio. Resistant cultivars and protective sprays provide control. They produce chemicals that destroy plant tissue or cause abnormal growth. Bacteria enter through wounds, stomata or other natural openings.
Bacteria can cause leaf spotting as on English ivy.
Fireblight on crabapples, pears, mountain ash, hawthorn, cotoneaster and pyracantha is a bacterial disease. Disease-free stock and resistant cultivars plus sanitation help prevent bacterial diseases. Streptomycin and fixed copper sprays may help slow the spread and development of bacterial diseases. However, chemical controls for bacterial diseases are less reliable than for many fungal diseases. Previously many mycoplasma-caused diseases were thought to be caused by viruses.