Stemphylium spp.

Stemphyliosis of Solanaceae

General

• Fungi distributed differently around the world; particularly serious disease in the tropical and humid subtropical production zones, very present in the DROM-COM.
• Fungi very specific to the aerial organs of Solanaceae, mainly foliar.
• Several species responsible for identical symptoms in Solanaceae: S. solani GF Weber, (1930) (figures 1 and 2), S. lycopersici (Enjoji) W. Yamam., (1960) (syn. S floridanum CI Hannon & GF Weber , (1955) (figures 3 to 5); S. botryosum f. sp. lycopersici Rotem, Y. Cohen & I. Wahl, (1966) (anamorph Pleospora herbarum (Pers.) Rabenh., (1854); S. vesicarium (Wallr.) EG Simmons, (1969) (syn. Pleospora allii (Rabenh.) (figures 6 to 8). Ces. & De Not., (1863); S. botryosum Sacc., (1886). S. solani and S. floridanum would rather be restricted to tropical regions, while S. botryosum f. sp. lycopersici and S. vesicarium would be found preferentially in more northern areas.
• Disease rather observed in the open field, sometimes under shelter.

• Susceptible botanical family(s):

Biology

• Preservation : easy from one season to another on and in the soil, on various plant debris (leaflets, stems, senescent floral parts, etc.) of Solanaceae  and many alternative hosts, cultivated or not. S. solani and, to a lesser degree, S. floridanum are capable of attacking several cultivated (eggplant, pepper, etc.) or wild ( Solanum carolinense, S. lycocarpum, etc.) solanaceae. Note that the strains of S. solani affecting cotton are aggressive on tomato, potato and blue lupine in Brazil. S. floridanum is described on Allium, safflower, gladiolus and chrysanthemum. S. vesicarium and S. botryosum f. sp. lycopersici can also count on their perithecia (resulting from their sexual reproduction) to be preserved from one season to another, their ascospores being able to ensure the primary contaminations.
• Infection : Penetrate their hosts directly through the cuticle or through various wounds. Rapid invasion of tissues thanks to their mycelium, spots being already visible 5 days after the first contaminations.
• Sporulation : form conidiophores and conidia visible on the underside of the lamina.
• Dissemination : by conidia especially by wind, air currents, but also by splashing water following rain or sprinkler irrigation. Remember that plants can transmit the disease if infections occur in the nursery.
• Favorable conditions : favored by humid climatic conditions, in particular the presence of water on the plants (rain, dew, sprinkling, condensation in greenhouses) and by high temperatures. Their thermal optima are between 23 and 27°C, depending on the species.

Protection

• Use resistant varieties if possible.
• Set up healthy plants: check their quality.
• Avoid planting crops close to other sensitive crops (tomato or pepper or eggplant).
• Eliminate weeds that can serve as intermediate hosts.
• Ensure good drainage of cultivated plots.
• Avoid too high planting densities in order to favor the aeration of the foliage.
• Strip the lower parts of the plants in order to eliminate the first affected leaves and improve the ventilation of the plant cover.
• Avoid irrigation , prefer drip irrigation. If they are essential, carry them out in the morning so that the vegetation drains quickly during the day.
• Under cover, ventilate as much as possible.
• Do not allow workers to work while vegetation is wet.
• Eliminate plant residues fairly quickly, during cultivation following the various cultivation operations, and at the end of cultivation after uprooting the plants. They will have to be destroyed.
• If necessary, spray fungicides taking into account authorized uses.