In biological control living organisms or viruses are used against pathogen in order to eliminate the disease.
By using such controls the adverse effects on plants and environment are minimised. Part or fertilizers added to crop fields are passed down to water bodies during rains through surface run-off.
Presence of extra nutrients brings about dense growth of plant and animal life.
The phenomenon is called eutrophication. Growing disease resistant varieties is the best method of disease control.
However late blight fungus has number of races and resistance to all the races is difficult to achieve.