Septoria lettuce*

Salad septoria

( Septoria leaf spot )

General

• Worldwide widespread fungus, especially in humid production areas. Rather known in the field by its synonym " Cladosporium ". Several races are currently present in the field, circumventing varietal resistance and revealing different virulence profiles.
• Worldwide widespread aerial fungus which does not seem to be a harmful parasite on the various lettuces.
• Parasitism expressing itself seriously only in a limited number of DROM-COM.
• Disease can be observed in the open field, such as under shelter.

• Susceptible botanical family(s)

• Production areas affected :

• Organs attacked

Symptoms

• Symptoms :
  • Rapidly brown, necrotic chlorotic leaf spots developing first on lower leaves (Figure 1). Irregular in shape, more or less delimited by the ribs, they measure 5 to 10 mm in diameter. A yellow halo surrounds them (figures 2 and 3).
  • The center of the necrotic tissue disintegrates and the leaves are thus covered with holes.
  • When they converge, large lesions alter the limbus.

• >>> More symptoms
• Signs : numerous and tiny dark brown to black globular masses (figure 4), pycnidia visible on both sides of the blade. These structures  contain spores that are usually filiform, hyaline, with one to 3 septa (Figure 5)
• Possible confusion :  Sigatoka

Biology

• Storage : on plant debris, seeds and wild lettuce ( Lactuca seriola ). Some weeds harbor it.
• Infection : contamination is ensured by the conidia which germinate and whose mycelium penetrates and invades the leaf tissues. The full cycle of this fungus can occur in 5-10 days.
• Sporulation : formation of pycnidia in altered tissues (figures 4) of pycnidia containing elongated and septate conditions (figure 5).
• Dissemination : the conidia ensure the dissemination of the disease following splashes of water. The seeds also allow the dissemination of S. lactucae over long distances. Workers, work tools and animals also contribute.
• Favorable conditions : periods of humid and relatively warm weather favor the spread of this fungus. Its thermal optimum is between 20 and 24°C. Insufficiently fertilized or etiolated plants would be more susceptible.
  
  

Protection

• No resistant lettuce varieties are currently available.
• If you have any doubts about the sanitary quality of the seeds, disinfect them for 30 minutes in water at around 48°C.
• The floor of the nursery as well as the structure of the shelters will be disinfected.
• Use healthy plants .
• Carry out crop rotations longer than 4 years in the open field.
• Ensure good drainage of cultivated plots.
• Planting new plantations close to infected crops should be avoided.
• Avoid too high planting densities in order to favor the aeration of the foliage.
• 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.
• fairly quickly plant residues (old affected leaves), during cultivation following the various cultivation operations, and at the end of cultivation after uprooting the plants. They should be destroyed and not left on the ground.
• If necessary, spray fungicides taking into account authorized uses ( e-phy ).

* Several other species of Septoria have been described on Lactuca : Septoria ludoviciana Ellis & Everh. 1894 , Septoria fernandezii Unamuno 1921 , Septoria schembelii Melnik 1965 , Septoria unicolor G. Winter 1885 , Septoria sikangensis Petr. 1947 and Septoria lactucina Petr. 1931 . More recently, Septoria intybi Pass. has been reported in Italy on Cichorium endiviae.