The disease branch rot is worrying Brazilian citrus growers because of its recent increased occurrence in orchards. Branch rot is also called peduncular rot, branch gummosis or bot gummosis.
The main reason for the disease’s occurrence is stress caused to citrus plants by high temperatures, severe periods of drought and attacks from other diseases, such as greening.
Fungi of the Botryosphaeriaceae family (known as Bot fungi), which include Lasiodiplodia and Dothiorella, cause branch rot. Fungi can remain on the plant without causing damage but become pathogenic when the tree is under stress.
Bot fungi cause rot in branches, peduncles and fruit, cracks in the bark of branches and, in severe cases, drying of part or all of the crown. Gum exudation can be observed, especially in younger tissues. This gum, which has a sticky and viscous appearance, is a sugary substance released by the plant as a defense response to the stress caused by the fungal infection.
“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,” said Fundecitrus postdoctoral researcher Thiago Carraro.
Thermal stress and water stress have favored the disease occurrence in São Paulo orchards.
“We had a period of high temperatures and water deficit in February and March of this year, which left the plants quite affected,” said Fundecitrus researcher Geraldo Silva Jr. “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.”
Silva said this dynamic has also occurred in some harvests in the months of September and October, periods in which the occurrence of the disease can increase.
A correct diagnosis is very important for control of branch rot. To reduce disease impacts, management requires the integration of cultural practices, chemical and biological controls and stress mitigation, which can be done with sunscreens to reduce temperature. Citrus growers must also manage other diseases appropriately.
There are not many studies evaluating the efficacy of products for branch rot under Brazilian conditions. In other crops, the most effective fungicides have been triazoles, strobilurins, carboxamides and some multisite fungicides and resistance inducers.
“It is important to apply fungicides as a preventive measure against infection by Bot fungi, especially during periods of intense stress followed by rain,” Silva said.
Fundecitrus has begun studies to identify the species of Bot fungi present in São Paulo orchards. It intends to investigate the relationship between branch rot, greening and other stress factors, as well as evaluate the efficiency of chemical and biological products under Brazilian conditions.
Source: Fundecitrus
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