Early blight control: when to end the protection of fruits of each variety

In the São Paulo citrus belt, black spot infections of fruits usually occur from the time the petals fall, in September/October, and can last until the end of the rainy season, normally in April. This period requires attention to the protection of orchards, as oranges are susceptible to this important citrus disease that affects different species and commercial varieties of citrus, and is responsible for high premature fruit drop.

Black spot, in addition to leaving the fruit with a stained appearance, which harms its sale in the fresh market and also export to disease-free areas, can reduce plant production by up to 85%.

Some studies have shown that the number of fungicide applications to control early blight can be established according to the orange variety. The earliest ones, such as Hamlin, require fewer applications and the later ones, such as Valência and Natal, require the protection of the fruits until the end of the rainy season. The same can be observed for the age of the orchards, with the oldest ones (generally over 12 years old) being those that require protection throughout the rainy season.

In the current harvest, the months of November and December 2022 and January 2023 were marked by a large occurrence of intense rainfall, above the historical average of recent years in the citrus belt. In this very critical period for the occurrence of early blight, all orchards should be protected following the recommendation to use strobilurin in association with mineral oil.

From February onwards, conditions generally become less critical for the occurrence of the disease in early varieties and younger orchards. As a result, the focus now turns to the management of older orchards and late-maturing varieties, in which early blight tends to cause severe fruit drop if control is not carried out correctly.

In these orchards, it is important that the citrus grower continues with control until April, when the rainy season usually ends. 

Find out more about controlling early blight on citrus at Cultivar Hortaliças e Frutas

Strict control of early blight on citrus

Management recommendations

Plants are more susceptible in times of high rainfall and prolonged periods, due to the production and dissemination of the fungus that causes black spot and also because the fruits are green. Therefore, attention must be doubled during this period.

According to Fundecitrus researcher Geraldo Silva Jr, the recommendation for older orchards and orange orchards of Pera, Valencia, Natal and other late varieties is that the petal fall is controlled until April, which will total between 180 and 220 days of protection. On the other hand, younger Hamlin orange orchards and other early oranges that do not have a history of early blight occurrence will not require protection after February, as they are harvested from June to August. Therefore, infections that occur in fruits of these early varieties from March onwards will not result in high rates of symptoms and fruit drop, as the period for the expression of black spot lesions is very long.

“As the orchard ages, the fungus that causes black spot accumulates on the plants and there are no control actions that eliminate this fungus. Therefore, the most important thing is to pay attention to monitoring the disease and correct management in the different varieties of citrus, focusing on older orchards with a history of the disease”, warns Silva Jr.

This adjustment of the number of applications depending on the variety and age of the orchard also helps to reduce the amount of strobilurin used throughout the harvest on farms and to avoid the selection of resistant fungi. Strobilurins are generally associated with mineral or vegetable oil at a dose of 0,25% - however, for early varieties and in young orchards, they have proven to be efficient even without the addition of oil or at lower doses of up to 0,15%. Therefore, it is possible to adjust the number of applications and the oil dose per orchard profile, maintaining control efficiency and reducing costs.  

The producer must pay attention to the interval between strobilurin applications, which must not exceed 35 to 42 days, mainly from November to February, and the strobilurin dose must be at least 2,8 mg of active ingredient/m3 of canopy.

Another important factor is to observe the incidence of citrus canker in orchards and carry out joint management of early blight and canker with the use of fixed copper, at a dose of at least 30 mg/m3 of canopy, every 21 days, until the fruits reach 5 cm.

For good results, it is essential that the application technology used is recommended. Sprayers must be maintained, regulated and calibrated with a volume above 75 mL of spray/m3 of canopy to efficiently control early blight. Orchards must be pruned so that equipment can travel along the planting streets without the spray tips touching the plant branches.