Golovinomyces cichoracearum var. cichoracearum

(powdery mildew of tobacco)

The plants affected by Golovinomyces cichoracearum var. cichoracearum anc. Erysiphe cichoracearum, "powdery mildew" or "white mould” show highly characteristic symptoms. The powdery, white felting covering the leaves (figures 1 to 3 and 4a) is such a characteristic symptom that there should not be any confusion in diagnosis. The white felting is formed of mycelium network superficially colonising the lamina, topped by numerous short conidiophores bearing several conidia chains (figures 4b, 5 and 6). Despite the specificity of these symptoms there are confusions sometimes, especially when the leaves get white spots following sirrigation with very salty water or treatment of the plants that leaves  sediments on the leaves.
 

Figure 1	Figure 2	Figure 3	Figure 4	Figure 5	Figure 6

Generally one can observe this obligate fungus in France in July. It first colonises the lower leaves. It seems obvious that its location within the canopy is favourable to its development. This disease was rare in the past, but it currently prevails in almost all tobacco production areas and often requires the use of preventive fungicide treatments.
 
For further information see the fact sheet of Golovinomyces cichoracearum var. cichoracearum.