For many years, tomato growers, in the open field and in shelters, have occasionally observed the appearance of leaf spots on their plants, which are quite similar to those caused by A. tomatophila : initially dark spots, which do not take long. not to turn brown and necrosis. They also have concentric patterns and a more or less marked chlorotic halo (Figures 1 to 3). However, unlike early blight and other comparable leaf diseases, the stems and fruits do not show symptoms. Another surprising element, these spots always appear at the same time in several crops located in the same production area, crops sometimes several kilometers away and with different agronomic contexts. In an affected plot, a large number of plants and leaflets are affected. It should be noted that laboratory investigations have not made it possible to associate the presence of a pathogenic microorganism with it.
 

This pathological context is quite characteristic of a non-parasitic problem having a limited time sequence and a distribution in space on the contrary much more extensive. Various investigations have taken place in order to respond to several hypotheses envisaged (climatic problem, damage linked to pollution ); they did not make it possible to find the cause of this physiological affection.
 

Let us note all the same that these spots and their appearance modalities somewhat recall an affection occurring on tobacco and called “drought spots” ( drought or drought spot ). On this nightshade, we sometimes see the presence of brownish interveinal necrosis on the lower leaves of many plants. They often appear at the same time in several plots located in the same production area. Their origin, still poorly understood, is thought to be due to a very temporary break in the water supply to the plants, which would immediately have repercussions on the leaves through their partial drying out.
 

This information, if it does not provide a solution (there is none at present), is intended to spare you unnecessary fungicide treatments, especially anti-alternaria.

Last change : 07/08/21