This fungus remains dormant in the soil during dry season and gets activated during rainy season as the soil moisture builds up. The disease spreads through infected planting materials, zoospores in soil water; rain splashes; contaminated farm implements, movement of personnel, animals etc. The disease consists of two phases viz. aerial phase and soil phase.

Aerial phase

Aerial phase consists of infection of leaves, stems and spikes. During rainy season the disease appears on tender leaves at the lower region of the bush starting as dark brown spots which enlarge rapidly covering the major area of leaf. These leaf spots are characteristic with 'fimbriate margins'. The infected leaves drop off prematurely. In addition, the fungus infects green stems causing rotting. Whenever branch infection/stem infection occurs, the foliage beyond the point of rotting turns yellowish and sometimes exhibits wilting symptoms. Foliar infection starts from runner shoots at the base of the vine or on tender leaves at the lower region of the bush. With the soil splashes during monsoon, the leaves get infected and rot. In the infected leaf spots, zoosporangia (fungal sacs) are produced and from the tiny spores stream into droplets of water. During the rainy season the disease gradually spreads from the base of the vine and reaches upper regions of the bush in a ladder like fashion through rain splashes. Also the disease spreads across to nearby vines through rain splashes. Foliar infection leads to different degrees of leaf and branch shedding depending on the severity of the disease. However, foliar infection will not lead to death of the vines but it debilitates the vine.

Disease cycle

With the onset of rains the soil moisture builds up. The soil moisture induces the dormant propagules of P. capsici to germinate. This leads to the formation of mycelium and zoosporangia (pear shaped fungal sac), an asexual phase of life cycle. This is termed as an 'explosive phase' since disease spreads very fast during this phase of fungal growth. With the available free moisture, spores (called zoospores) later come out from sporangia and travel in the droplets of water and spread. These tiny spores settle down on roots and cause infection. With the onset of rainy season soil moisture builds up and extensive root production takes place. These tender fibrous roots are highly prone to disease and the fungal spores in the soil causes root rot. Infection that starts on the fibrous root system, reaches the main root and ultimately the collar region or foot region of the bush. Depending on the severity of infection, the vines exhibit various symptoms like foliar yellowing, breaking off the stems at the nodal region, defoliation and wilting symptoms. When the infection occurs at the foot region, the vines collapse leading to death and hence it is called 'quick wilt' by the farmers. The disease gradually spreads to adjacent vines and causes death leading to severe crop losses. Root infection and stem infection are fatal and cause death of the vines.

Season

It is prevalent during wet period of the year (south west monsoon period (June-July to August-September) in India and during January-March in Indonesia and Malaysia).