Septoria lactucae Pass. (1879)  

Septoria leaf spot

- Distribution and damage

This fungus is widespread worldwide . It is not considered to be a serious parasite of various lettuces. Occasionally observed in France in the 1960s, it seemed to have disappeared from intensive lettuce crops. It reappeared recently in the Paris region during summer crops.


- Symptoms

leaf spots Irregular , chlorotic, delimited by veins, brown, sometimes very wide when they are confluent (figure 1). A yellow halo surrounds them (figure 2). They are dotted with numerous pycnidia containing generally filiform, hyaline spores with one to 3 partitions (figure 3). The center of the necrotic tissue breaks up, leaving the leaves covered with holes. These spots develop mainly on old leaves (Figure 4).


- Elements of biology

Septoria lactucae survives on plant debris , seeds and wild lettuce ( Lactuca serriola ). Some weeds would harbor it. Its conidia, formed inside pycnidia (figures 5 and 6) ensure contamination and dissemination of the disease following splashing. The seeds also allow the fungus to spread over long distances. Work tools and animals also contribute. The full cycle of this fungus can occur in 5-10 days.

Periods of humid and relatively hot weather favor the spread of this fungus. Its thermal optimum is situated between 20 and 24 ° C . Insufficiently fertilized or etiolated plants would be more sensitive


- Protection

In the countries where it is authorized, fungicide treatments are carried out when the attacks are important. In France, no fungicide is registered for this use on salad .

The old diseased leaves will be removed at the time of harvest, they should not be left on the ground. In the open field, crop rotations greater than 4 years should be considered. The soil will be well drained . If you have any doubts about the sanitary quality of the seeds, they can be disinfected for 30 minutes in water at around 48 ° C. New plantings near infected crops should be avoided. The nursery floor as well as the structure of the shelters will be disinfected . Seeds can be produced in relatively dry areas free from the fungus. No resistant salad variety is currently available.


NB (1) : 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.

NB (2): The legislation on pesticides evolving very quickly, we advise you to consult the e-phy site of the Ministry of Agriculture and Fisheries which is an online catalog of plant protection products and their uses, materials fertilizers and growing media approved in France. This also applies to all biological products based on microorganisms or natural substances.