Different non-parasitic diseases 

One should be particularly vigilant when dealing with tobacco leaf spots. Always keep in mind that chemical injuries (figure 1) and nutriotional disorders (figure 2) sometimes create symptoms that are much similar in appearance to spots that have been described in several other sections. If you have the slightest doubt, we recommend that you complete your diagnosis by a specialist laboratory.

For furhter information on the various chemical injuries and nutritional disorders, see the corresponding links.
 
Note that at the approach of harvest, the midrib and secondary veins of tobacco leaves occasionally turn brown on varying lengths (vein browning ) (figure 3). These symptoms are often wrongly attributed to Erwinia spp. or PVY. In most cases it is likely that the saprophytic micro-organisms, namely bacteria, benefit from the leaf maturity to invade the veins. In rainy or foggy periods, after a sprinkler irrigation, water commonly tends to be retained and accumulate on the veins, which facilitates the development of saprohytic bacteria.