- The foliar symptoms are initiated as whitish grey superficial spots on the upper surface.
- These spots enlarge forming large patches of powdery growth of the fungus.
- When the attack becomes severe, defoliation followed by death of the plant occurs.
- Considerable yield reduction results due to the infection. Fruits also get covered by powdery mass but this is not common.
- The fruits remain under sized and sometimes deformed.
The disease is favoured by overcast skies, high temperature, reduced light intensity and succulent plant growth. The conidia of the fungus spread by means of wind and insects. The cleistothecia develop on crop debris and this can help in the survival of the fungus. The fungi are influenced by the age of the plant and air, humidity and temperature. Sixteen to 23 day old leaves are highly susceptible while very young leaves are almost immune.
Randomly mark five one square meter area from the plot. From each square meter select 5 leaves at random and record the incidence of the disease.Count the leaves showing symptoms (even if a spot is present that leaf is considered as infected). Work out the average leaves showing infection.