Non-parasitic diseases of flue-cured leaves

As was the case for "air-cured" tobacco, the non-parasitic lesions observed in the cured product of Virginia tobacco can be linked to different causes during the successive stages of development and transformation of leaves.
 

• During growth  :

- Excess nitrogen generates very thin, dark brown to black leaf  tissues  ;
- In contrast, the lack of nitrogen will generate, as do a low soil pH or soil-borne diseases, thick leaves, smooth  texture and dull leaden colour  ("grey tobacco", figure 1);
- The reddening spots of leaf tissues ("cherry red") shows a tobacco too rich in nornicotine;
- An iron and/or manganese intoxication will induce a greyish brown metallic colour of  tobacco leaves (figure 2).
 

• At harvest :

- tissue areas  remaining green ("green fixed"), are a sign of harvesting immature leaves.
 

• During curing :

- Yellowing
 Plant tissue areas  remaining green ("green fixed") show either premature fixing of colour, too low relative humidity or too cold temperature;
 Browning of the leaves ("scalding") is related to a too rapid temperature increase without well monitored ventilation;
Grey to brown colouration of the leaf lamina which is also thicker and elastic ("sponge") is related to a too long yellowing phase.
-  Colour fixing
 Irregular browning and reddening of the lamina (scorching) are caused by maintaining the temperature above 71 ° C for too long.
- Rib reducing phase (Stem drying)
 Browning or blackening of leaf  tissues adjacent to veins and midribs ("run-back"), figure 3) is caused by the drop in temperature during curing.