Cercospora leaf spot is one of the oldest and best-known fungal diseases on sugar beet crops. Caused by the fungus Cercospora beticola , this disease manifests itself through symptoms on the foliage of the plants and causes significant yield losses every year. The fight against this disease is based on knowledge of its development cycle and the implementation of appropriate prevention and control methods that we invite you to discover in this article.
Description of Cercopora leaf spot of sugar beet
Cercospora leaf spot is caused by Cercospora beticola , an ascomycete fungus of the Mycosphaerellaceae family . It occurs mainly on the foliage of beet plants.Â
This disease, first reported in France in 1887, has been affecting beet crops for a long time. Its resurgence in recent years, particularly in irrigated regions, highlights the importance of rigorous management of this disease.
The fungus Cercospora beticola is particularly aggressive and can cause significant damage when infection occurs early in the season . Warm and humid climatic conditions are conducive to its development, allowing the rapid spread of the fungus in cultivated plots.
Biology and development cycle
Cercospora beticola infection begins with the germination of a spore on the surface of a leaf. This germination occurs ideally when temperatures are between 25°C and 30°C, combined with high humidity , encouraged by rainfall or irrigation. The fungus then enters the leaf via a stomata and then develops inside the leaf parenchyma.
Once established, Cercospora beticola produces conidia, which are multiplication spores. These conidia are spread by rain or splashing water, allowing the fungus to spread to surrounding plants.
Early attacks, especially in irrigated areas, aggravate the damage and lead to a significant reduction in yield.
The development cycle of Cercospora leaf spot depends largely on climatic conditions. Heat and humidity are the main factors in the spread of the fungus. In the absence of favourable conditions, the disease cycle is slowed down, but it can nevertheless persist in the soil or on crop residues, waiting for more favourable conditions.
What are the symptoms of Cercospora leaf spot?
The first symptoms of Cercosporiosis usually appear as early as mid-June , although this timing can vary depending on weather conditions.
Infected leaves have small, round, grayish spots , surrounded by a red or brown border , visible on their upper surface. These spots enlarge and eventually merge, forming large necrotic areas.
On the underside of the leaves, small black dots appear in the center of the spots: these are the fruiting bodies of the fungus.
Over time, the multiplication of spots causes the leaves to dry out completely, giving the field a burnt appearance. The plant reacts to the loss of its foliage by producing new shoots and lengthening the collar. This reaction weakens the plant and has direct consequences on the yield, in particular a reduction in sugar content.
The damage caused by Cercosporiosis is all the more significant when the infection occurs early in the season. Late attacks , in September or October, have a lesser impact on yield. However, in plots where the disease is present recurrently, yield losses can be very significant and also affect the quality of the harvests.
How to combat Cercospora leaf spot?
The fight against Cercosporiosis is based first of all on preventive measures and appropriate crop management. Among the recommended practices, the choice of less susceptible sugar beet varieties, especially in plots where the disease is regularly observed. In addition, the lengthening of crop rotations is an effective method to reduce the risk of infestation, because it limits the presence of the fungus in the soil.
The triggering of fungicide treatments must be reasoned and carried out at the appropriate intervention thresholds. The reasoned use of fungicides helps to limit the spread of the fungus while preserving the ecological balance of the plot.
Agrobiotop biological solutions:
Our solutions apply to organic and conventional agriculture. They are positioned on two strategic axes:
- Action on the ground
- Action on culture (Sugar beet)
For action on the ground:
Pour l’action sur les cultures :
