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On guard against rot

System makes it possible to control citrus disease with less fungicides spraying

FUNDECITRUSCitriculture has gained a new tool for combating postbloom fruit drop [PFD], a disease that cause the fruit to drop and the loss of up to 80% of the production, when it hits the orange groves. Farmers can now use a control system that calculates the conditions that favor the occurrence of the disease, such as rain and the stage of development of the blossom, and indicates the right time for spraying with fungicides. The software was developed at the School of Agronomic Sciences of the São Paulo State University (Unesp), in Botucatu, under the coordination of Professor Nilton Luiz de Souza, by engineer agronomist Natália Aparecida Rodrigues Peres, the author of the doctoral thesis about the new system.

The project won funding from FAPESP and enjoyed partnerships with the University of Florida, in the United States, and Citrovita, a company from the Votorantim group that owns 3 million orange trees in the region of Itapetininga (SP). The results show that, by adopting the hew system, the farmers save about R$ 200.00 per hectare on applications of fungicides. Brazilian producers can, free of charge, use the system on the Internet, at the address.

“The work began in 1997”, says Professor Souza, who has been researching into funguses that cause plant diseases for 30 years. “It was when company representatives called on our Phytosanitary Defense Department to ask for collaboration in solving this disease, which was threatening the production of oranges in Itapetininga.” PFD is a problem that affects several regions in Brazil, the largest producer in the world, with over 1 million hectares of trees planted and a crop that added up to 371.3 million boxes of oranges in the 2002/2003 harvest. The fungus (Colletotrichum acutatum) acts in all the orange producing regions, including Santa Catarina, Rio Grande do Sul, Goiás, Rio de Janeiro, Bahia and São Paulo, a state that accounts for 70% of the Brazilian citrus production.

At the beginning of the studies, Natália was finishing her studies for a master’s degree in horticulture on post-harvest diseases, also caused by funguses of the Colletotrichum genus, in fruits like avocados, bananas, guavas, mangoes, papayas, passionflower and strawberries. With the conclusion of her master’s degree studies, she went back to PFD disease caused by the same fungus. Accordingly, between 1997 and 1998, Souza and Natália started to test fungicides and to study the cycle of the disease, to find out the best strategy for control. To carry out this research, a meteorological station was then set up, to collect the climatic data on rainfall, temperature and leaf moisture, which sends the signals via radio to a computerized center.

In the period from June 1999 to July 2002, Natália dedicated herself to the research that resulted in the System for Foreseeing and Controlling Postbloom Fruit Drop in Citruses. In 1999, she traveled to the United States, where she was attached for one month to the University of Florida, in the city of Lake Alfred, with Professor Lavern Wayne “Pete” Timmer, one of the greatest specialists in PFD in citruses in the world. Back in Brazil, Natália did the field experiments on the plantations in Itapetininga and in the groves in Florida. In this work, she discovered that fundamental in combating the disease was to do the spraying at the right moment. The presence of PFD varies from year to year, according to rainfall coinciding with the blossoming of the trees or otherwise. The fungus needs humidity and nutrients from the flowers to reproduce.

The cycle of the disease is rapid. The first symptoms are observed between four and five days after infection. “The sources of inoculation are the reproductive cells produced in the sick petals, disseminated to the healthy flowers by means of the rain. In the periods between blossomings, the fungus survives in the leaves and in the calyxes (the part of the flower that is going to bear the fruit), making it difficult to eliminate it by spraying with fungicides or other treatments”, the researcher says. “PFD causes pinky-orange coloring on the petals and induces the young fruit to fall, although it leaves the calyxes stuck to the branches, a symptom known as little star, characteristic of the disease.”

Evolution in the analysis
One of the difficulties in combating PFD is determining the ideal moment to apply the fungicide, because, for the control to be efficient, spraying is necessary when the climatic conditions are favorable to the disease. The producers traditionally carry out sprayings in accordance with the stage of development of the blossoms. But this condition does not always coincide with the most humid period. “Moreover, in some years, when the rainfall is not favorable to the dissemination of the fungus, the sprayings can be avoided.”

Natália’s control system is based on a model for forecasting the disease, developed previously in Florida, which indicates the need and the ideal moment for applying fungicides. This American model takes into consideration the number of flowers infected in 20 trees, the total quantity of rain in the last five days, and the number of days of leaf moisture after the rains. “The model is used by many producers in Florida, and following the gathering of the data, they decide for the need or otherwise of spraying”, the researcher says.

The new system developed by Natália, in partnership with Timmer, Howard Beck and Soonho Kim, from the University of Florida, is called the Postbloom Fruit Drop-Fungicide Application Decision (PFD-FAD). It takes into consideration the same variables as the American model, but it also considers the stage and the intensity of the blossomings, the history of the disease in the grove, and the variety of citrus, as well as factors that induce the occurrence of flowers out of season and favor an increase in the presence of the fungus. After selecting all the parameters, using multiple choice menus, the system calculates the value for the risk of the disease occurring and generates a recommendation to spray or otherwise.

Controlled humidity
The system has now been tested in the last two years in Citrovita’s groves, in the region of Itapetininga, and compared with the Florida model and other more simple kinds adopted by the producers. In this period, according to the researcher, only one spraying was indicated by her method, which represents a significant control of the disease and savings of funds for the producers. To have an effective control of the disease, it is necessary to monitor the climatic conditions that are decisive in the disease’s epidemiology. “Data has to be collected on rainfall and leaf moisture, which can be dome by means of automated meteorological stations, manual collectors, or even, depending on the region, on climatic stations at research institutes.” Natália Peres says that a simple pluviometer makes it possible for the producer to collect data on the rainfall, and leaf moisture can be estimated visually.

Natália worked until December on a postdoctoral project at the São Paulo Biological Institute, where she studied fungal citrus diseases that are not yet occurring in the United States, with finance from the University of Florida. This year, the agronomist engineer is starting to work at that university, where she took an entrance exam at the beginning of 2003, and was selected, amongst 30 candidates, to research diseases in strawberry growing and to lecture in the chair of Plant Pathology.

The Project
Epidemiology and Control of Colletotrichum acutatum, the Causal Agent of the Premature Fall of Young Fruit in Citruses (nº 99/04604-9); Modality 
Regular Line of Research Grants; Coordinator Nilton Luiz de Souza – Unesp; Investment R$ 21,538.25 and US$ 8,710.00