Sporangia land on healthy foliage and germinate in the presence of moisture. In low temperatures, if adequate water is available, zoospores are formed and released. These zoospores swim in water and can migrate over the wet leaf surface. Coming in contact with the host tissue, they encyst, and germinate. The germ tube formed by zoospores penetrate the leaf epidermis at multiple sites causing small spots.
Sporangial masses are white on dark colored leaf lesions.
These are blown to healthy plants and continue the disease cycle. In the tropics, chemical spray programs must be implemented before disease is observed, especially during cool winter periods. Once foliar infection develops epidemics can become uncontrollable. Keeping the number of leaf rots low is crucial. Good coverage with fungicides is important.