Rainy periods are favorable for early blight and require adequate protection of orchards

The beginning of 2022 was marked by the occurrence of frequent and intense rains in the São Paulo citrus park. This condition of prolonged humidity requires attention to protecting orchards against early blight, a disease that affects citrus and is responsible for a high rate of premature fruit drop. In addition to favoring fruit infections by the fungus that causes the disease, these more intense rainy periods can also compromise control efficiency, as well as the protection program adopted on citrus farms.

Fundecitrus researcher Geraldo Silva Jr highlights that “in the state of São Paulo, fruit infections due to black spot usually occur from the time the petals fall, in September/October, and can last until the end of the rainy season, generally in April . It is during this period that disease management has been carried out in São Paulo’s orchards.”

Impacts of the disease

In addition to causing fruit to fall, which can reduce plant production by up to 85%, black spot leaves the fruit with a stained appearance, damaging its sale on the fresh market and also export to other regions, such as Europe.

In the 2020/21 harvest, early blight was responsible for the decline of approximately 3% of fruits, around 10,21 million boxes. The greatest damage from the disease has occurred in older orchards and late-maturing varieties, mainly in plants that are poorly nourished or affected by other diseases.

Management recommendations

The management of black spot begins with the adoption of measures that prevent the causative fungus from entering the area. Once black spot is established in an orchard, there are no control measures that eliminate the disease. Thus, with the disease established, management must be carried out with different associated strategies, generally with chemical and cultural controls.

The different studies conducted by Fundecitrus in partnership with Esalq-USP have demonstrated that the fungus that causes early blight can be produced in orchards in São Paulo from October to March, which is the season with greater volumes and frequencies of rain and longer periods of wetness. of plants. Furthermore, the fruits at this time are green and in the phase of greatest susceptibility to fungal infections, especially between November and January. “Therefore, attention to disease management must be redoubled during the rainy season and fruit protection must be carried out in all orange varieties with the use of more efficient products, such as strobilurins”, emphasizes Silva Jr.

From March onwards, rainfall tends to reduce and management becomes a priority in older orchards of mid-season and late maturing varieties. As early varieties are generally harvested in June and July, there is not enough time for significant expression of early blight symptoms in fruit infections from March onwards. Some studies have shown that, although infection can occur at different stages of fruit development, whether green or ripe, symptoms related to premature fruit drop are expressed in greater quantities from 100 to 360 days after infection.

The use of mineral or vegetable oil also helps control the disease. For early varieties and in young orchards, little or no use of oil is recommended, while for late varieties and in older orchards, the recommendation is that oil be used in a dose of 0,25% (5 L/2000 L) .

“It is important to highlight that successful management is strongly related to the application technology used”, concludes Silva Jr. Sprayers need to be regulated and calibrated, product doses, application speed and spray volume must be adequate, as well as orchards must be pruned so that the plant branches do not touch the nozzles, which could compromise the application.