Fungus that causes alternaria brown spot resistant to strobilurins is found in SP

Populations of the fungus that causes alternaria brown spot resistant to strobilurins, one of the most effective chemical groups and the most used in Brazil to control the disease, were identified in tangerine orchards in the state of São Paulo. The discovery, made by researchers from Fundecitrus, Instituto Biológico (IB) and Escola Superior de Agricultura “Luiz de Queiroz” (Esalq/USP), indicates a loss of efficiency of strobilurins and the need for changes in management.

Alternaria brown spot causes defoliation, drying of branches, premature drop and fruit depreciation. The Ponkan tangerine and the Murcott tangor, which occupy 90% of the 12 thousand hectares with tangerines and hybrids in the São Paulo citrus park, are generally very affected by the disease. According to Esalq/USP professor Lilian Amorim, the resistant fungus has already been found in Bariri, Buri, Conchal, Paranapanema, Porto Feliz, Pratânia, São Pedro do Turvo, Socorro and Ubirajara, although the survey is still ongoing.

Fundecitrus researcher Geraldo Silva Jr. highlights that, in addition to strobilurins, copper-based fungicides and triazoles are registered with the Ministry of Agriculture, Livestock and Supply to control the fungus Alternaria in citrus and can be used in areas where there is resistance. “These products must be used at recommended doses and intervals and restricted to critical times for the occurrence of the disease”, he advises.

According to IB researcher Eduardo Feichtenberger, the use of copper-based fungicides should be done preventively and at shorter intervals, since they do not have systemic action and young tissues (shoots and fruits) generally develop very quickly. “In other regions, it is important that citrus growers adopt measures to prevent fungus resistance, such as reducing the number of applications with strobilurins [maximum three per harvest] and rotate, alternate or mix chemical groups of fungicides to control different diseases caused by fungi throughout the harvest”, he points out.

Citrus growers must opt ​​for integrated management of alternaria brown spot, which also includes planting healthy seedlings and resistant varieties and cleaning and aeration pruning, as well as avoiding heavy nitrogen fertilization, very dense plantings and areas with a very favorable climate for the fungus.