Researchers develop a system to prevent citrus disease

Climate monitoring technology is used to reduce the incidence of postbloom fruit drop in citrus groves and to enhance fungicide efficiency.

By Fabio Reynol

Agência FAPESP – A tool for use by citrus growers will enhance fungicide efficiency and reduce the number of fungicide applications while reducing the incidence of postbloom fruit drop (PFD), a disease that causes damage to citrus groves, especially in southeastern São Paulo State.

The technology is being developed as part of the project entitled “Development and establishment of an on-line forecast system for citrus postbloom fruit drop epidemics”. This project is supported by FAPESP and is one of the outputs of the thematic project “Molecular epidemiology and management of postbloom fruit drop of citrus in new planting areas in São Paulo State”, executed between 2008 and 2013.

PFD, which is caused by the fungus Colletotrichum spp., occurs only during bloom and only when bloom coincides with a period of heavy rain. Most citrus species in Brazil bloom between June and October, when rainfall is not usually abundant. For this reason, the disease does not occur every year.

The strategy currently used to combat PFD consists of spraying groves with fungicide after the first rain event. This reduces the product’s effectiveness and can be wasteful if the next rain washes the fungicide away.

Spraying after precipitation may be too late to be effective because the pathogen may already have infected the flowers. Periodic preventive application can waste fungicide and money because if it does not rain, or if it rains only a long time after spraying, the effort will not be useful.

The most effective method entails application of fungicide shortly before precipitation, but this requires a weather forecasting service. “We’re developing a system that couples weather forecasting with the monitoring of conditions for infestation by the disease to provide reliable information with which citrus growers can combat the disease effectively,” said principal investigator Lilian Amorim, an agronomist and professor at the University of São Paulo’s Luiz de Queiroz College of Agriculture (ESALQ-USP).

Fungicide application up to four hours before a rainfall event proved effective in combating PFD, Amorim explained.

“The method in current use involves spraying after rain or before it’s known whether or not there will be rain. We want growers to economize and apply the product before it rains but with the knowledge that it will rain,” she said.

The project calls for the use of a network of weather stations near citrus groves that can send information in real time to growers. The weather stations will feed data to a central system, which will analyze the data, correlate it with favorable conditions for infestation by the disease, and present recommendations for growers. The service will focus on growers in southeastern São Paulo State.

From strawberries to citrus

The technology is inspired by a system used in the United States for early warning of threats to strawberry plantations in Florida, where six weather stations collect climate data.

That system is designed to determine the probability of occurrence of the two main diseases that infest strawberry plantations: gray mold, caused by the fungus Botrytis cinerea, and anthracnose, caused by Colletotrichum acutatum, which belongs to the same family as the fungus that causes PFD in citrus.

“If a threat is detected, growers receive smartphone or email messages indicating the need to spray crops with fungicide,” said Natália Peres, associate professor at the University of Florida (UF). Peres developed the system in use there and is helping to develop the Brazilian version.

Peres and her research group in Florida are adapting the system developed for strawberries to Brazilian conditions. “We’ll use the same platform,” she said. “The system has interesting advantages, such as automatic data collection from weather stations and a user-friendly interface. These features will be part of the Brazilian system as well.”

Aside from the groups affiliated with ESALQ-USP and UF, Geraldo José da Silva Júnior from the Research & Development Department of the Citrus Defense Fund (Fundecitrus) and Angélica Giarola from the National Space Research Institute (INPE) are also participating in the project.

Silva Júnior believes that the system that is currently being developed will be an important tool for combatting PFD and will also represent savings for growers. The partnership with Fundecitrus will ensure that the system is available to end-users. “One of the goals of our participation in the project is to help develop an online platform that’s accessible to citrus growers,” he said.

Giarola’s role is to enable real-time delivery of detailed meteorological data, which she will integrate with data collected from weather stations in citrus-growing areas.

To test the effectiveness of the technique, the researchers involved in the project will maintain three experimental citrus groves for comparison. The first will have no monitoring, the second will be treated with conventional PFD controls, especially spraying after rain, and the third will be monitored by the proposed early warning system, with the use of fungicide according to the system’s recommendations. Tests will be performed during the 2015 and 2016 harvests, after which the project is scheduled to end.