The occurrence of branch rot, also known as peduncular rot, branch gummosis, or bot gummosis, is causing concern among Brazilian citrus growers. This disease is linked to stress in citrus plants due to high temperatures, drought, and other diseases like greening.
Branch rot is caused by fungi from the Botryosphaeriaceae family, including Lasiodiplodia and Dothiorella. These fungi can exist on the plant without causing harm, but turn pathogenic under stress conditions. Symptoms include rot in branches, peduncles, and fruit, bark cracks, and severe cases, drying of the crown. Gum exudation, a defense response to fungal infection, is noticeable in younger tissues.
Fundecitrus postdoctoral researcher Thiago Carraro explained, "The fungus can remain, broadly speaking, in two stages: endophytic, within the tissues without harming the plant, or pathogenic, when it begins to degrade the cells to absorb nutrients and reproduce."
Thermal and water stress have exacerbated the disease in São Paulo orchards. Fundecitrus researcher Geraldo Silva Jr. noted, "We had a period of high temperatures and water deficit in February and March of this year, which left the plants quite affected. In some situations, in addition to the climate issues, the plants also had other diseases, which left them vulnerable to infections by the Bot fungus. When it rained, the environment became more humid. The fungi infected and colonized the plant tissues, and the symptoms were observed."
This pattern has been observed in September and October harvests, with increased disease occurrence during these months.
Correct diagnosis is essential for managing branch rot. Effective management integrates cultural practices, chemical and biological controls, and stress mitigation, such as using sunscreens to lower temperatures. Proper management of other diseases is also necessary.
There is limited research on product efficacy for branch rot in Brazil. In other crops, triazoles, strobilurins, carboxamides, and some multisite fungicides and resistance inducers have been effective. Silva emphasized, "It is important to apply fungicides as a preventive measure against infection by Bot fungi, especially during periods of intense stress followed by rain."
Fundecitrus has initiated studies to identify Bot fungi species in São Paulo orchards and aims to explore the relationship between branch rot, greening, and other stress factors, as well as evaluate chemical and biological product efficacy under Brazilian conditions.
Source: Citrus Industry