- This fungal pathogen affects all parts of the plant- roots, stem, leaves and berries.
- During rainy season the tender leaves and succulent shoot tips of freshly emerging runner shoots trailing on the soil turn black when infected.
- The disease spreads to the entire vine, from these infected runner shoots and leaves, during intermittent showers due to rain splash.
- The branches break up at nodes and the entire vine collapses within a month . This is the most destructive stage of the disease and is commonly known as "quick wilt" or "foot rot".
- If the damage is confined to the feeder roots, the expression of symptoms is delayed till the cessation of rain and the vine starts showing declining symptoms such as yellowing, wilting, defoliation and drying up of a part of the vine.
- Foliar infection usually starts on very young leaves with characteristic brown to black colour with fimbriate margin.
- On mature leaves infected area produces concentric zonations with grayish centre.
- Foliar infection leads to varying degrees of defoliation.
- Infections are also observed on spikes as brownish patches resulting in their shedding.
The disease consists of two phases viz. aerial phase and soil phase. 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; root contact between healthy and infected vines, contaminated farm implements, movement of personnel, animals, etc. Termites and slugs also act as passive carriers of the inoculum. Generally disease spreads in a centrifugal pattern.
The foliar infection occurs mainly through splash dispersal. 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. The disease is generally noticed during June to September coinciding with the South -West monsoon. Low temperature of 22.7- 29.80C, short duration sunshine hours, high rainfall (15.8-23.0 mm/day) and RH of 81-99% favours the incidence of the disease.
Foliar infection starts immediately after the first few monsoon showers on runner shoots at the base of the vine or on tender leaves at the lower region of the bush.Randomly select 100 keaves and calculate the % infection mild 1% moderate 5% serve >5%. Also look for the collar and other symptoms