Management of Asian rust in grapevines

Asian grapevine rust is an aggressive disease that requires rapid and accurate diagnosis to prevent damage to productivity and fruit quality. Adequate chemical control and pruning, in tropical regions, during the dry season, are strategies to manage the fungus. 

Asian vine rust is caused by the fungus Phakopsora euvitis and was first reported in 1988 across eastern Asia. In Brazil, it was identified in the state of Paraná, followed by Mato Grosso, Mato Grosso do Sul, São Paulo, Santa Catarina, Bahia and Pernambuco.

To detect the disease in the field, it is necessary to observe the lower surface of the leaves, examining them carefully to check for yellowish pustules that spread under the leaves. Thousands of urediniospores are formed in these pustules. Chlorosis is observed on the affected leaf, followed by tissue necrosis.  

Diagnosis

Confirmation and diagnosis of this fungus are carried out in the laboratory, observing the pustules and preparing slides to observe the urediniospores and teliospores under an optical microscope.

Symptoms

Dissemination and epidemiology

Infected vine leaves are sources of spore dispersion, mainly by wind. This ease in spreading results in repeated cycles of infection in the grapevine. Research has revealed that the optimum temperature for spore germination is 24°C with a minimum of 8°C and a maximum of 32°C, which combined with high humidity can trigger epidemics. In tropical and subtropical climates, the fungus persists only in the uredinial state without the need for an alternative host and can survive unfavorable conditions in dormant buds. In colder regions, the fungus preferentially occurs at the end of the crop cycle. The complete cycle of this rust occurs only in Asia, where there is an alternative host plant for the fungus, called Meliosma myriantha, which does not occur in Brazil.

disease control

Cultivars like Italy (V.vinifera), Isabel (Vitis labrusca x V. vinifera) and Niagara are susceptible to rust. However, they are the most consumed, therefore requiring the use of fungicides to control the disease. In tropical regions, during the dry season, the vine must be pruned, avoiding the period of greatest rainfall during the grape maturation phase.

Regarding chemical control, to date only four fungicidal products are registered to control grapevine rust:

Josiane Takassaki Ferrari, Ricardo José Domingues, Jesus G. Töfoli, Instituto Biológico/APTA/SAA

Article published in issue 79 of Cultivar Hortaliças e Frutas