Importance of integrated management measures to combat citrus canker

An unprecedented and large-scale survey carried out by Fundecitrus to measure the importance of integrated citrus canker management measures and their impact on production has come to an end. The study proved that the installation of windbreaks, copper applications and citrus leaf miner control promote different levels of disease reduction. The effect of these control measures, tested in eight different combinations, was evaluated during three harvests in relation to the incidence of symptoms on leaves and fruits, productivity and production losses.

“All measures contributed to the reduction in citrus canker rates”, says Fundecitrus researcher Franklin Behlau, responsible for the study. “The work showed that the potential loss due to the disease can exceed a third of production and that the adoption of control measures can reduce these losses to insignificant levels”, he says.

The study also demonstrated that windbreaks and covers are the most important actions. “When these two measures are combined, the incidence of leaves and fruits with citrus canker and the reduction in production due to the disease are minimal. When they are used in isolation, however, they have intermediate performances”, says the researcher.

The combination of windbreak and copper was more efficient than the other treatments for all variables evaluated. Plants that received these measures simultaneously showed a reduction close to or greater than 90% in the incidence of citrus canker on leaves, harvested fruits and loss of production, as well as productivity – accumulated in the three harvests – 113% and 120% higher when compared to those in areas without management.

The experiment was installed in 2010 and evaluated from 2015 to 2017 at the experimental station of the Instituto Agronomico do Paraná (Iapar), in Xambrê, western region of the state. Before starting the evaluations, in 2013, the plants were pruned to standardize the size of the orchard due to replanting carried out in previous years. The orchard was made up of 5,2 Valencia orange trees grafted onto Cravo lemon, distributed over an area of ​​10 hectares. Trees of Casuarina cunninghamiana were used as windbreaks and applications of copper (40 mg of metallic copper per cubic meter of canopy; 0,6 to 0,8 kg of metallic copper/ha) and citrus leaf miner control (Abamectin 300 mL/2.000 L) were used. carried out every 21 days.

Fundecitrus and the Citrus Research and Development Foundation (CRDF), an institute that promotes science in Florida (USA), financed the project, carried out in partnership with Iapar, Cocamar Cooperativa Agroindustrial, Escola Superior de Agricultura “Luiz de Queiroz” (Esalq/ USP), University of Florida (UF) and United States Department of Agriculture (USDA).

Fruits for table and industry

 Behlau highlights that when all measures are adopted uniformly and on a large scale on the property, it is possible to reduce citrus canker to the level required by legislation, of up to 1%, to enable harvesting in table fruit orchards. “It is important to highlight that in this experiment there was a need to keep untreated plants, which may have contributed to the relative increase in the disease in the other plots”, he explains.

When control measures are analyzed in isolation, copper stands out. Plants subjected only to copper applications showed lower productivity (-16,2%, -13,9% and -9,4%), but progressively closer, over the three harvests, to the average of treatments that combined windbreaks and copper. On the other hand, when copper was used alone, the incidence of citrus canker in harvested fruits remained well above (between 15% and 30%) that required by legislation for table fruits. “Thus, in orchards destined for industry, with priority for productivity, the windbreak makes a smaller contribution in the medium and long term than in orchards destined for the production of table fruits”, concludes Behlau.

Control of the leaf miner, despite having less impact, continues to be an important control measure, as the injuries caused by the insect harm the sprouts and development of plants.

According to Behlau, the study points out that citrus growers should evaluate the characteristics of their orchards to define which citrus canker management strategies should be adopted. “The producer must mainly consider the destination of the production to identify the best control actions”, she points out. “Other important factors are the susceptibility of the planted variety, the climate favorability to the occurrence of the disease and the topography of the land, which implies greater or lesser exposure to the wind”, he recommends.

The researcher says that citrus canker responds very well to control measures. "In this short time since the management was implemented in São Paulo, it has already been possible to notice that citrus growers who make use of the information generated by research are efficiently reducing the impact of the disease in orchards. On the other hand, neglecting its occurrence can bring serious consequences for production”, says Behlau.

HOW DO CONTROL MEASURES ACT?

WINDBREAK: reduces the spread of bacteria and the creation of wind wounds, which leads to a reduction in infection.

COPPER: forms a protective layer on the surface of leaves and fruits and prevents bacteria from entering the tissues and the appearance of new lesions.

CONTROL OF CITRUS MINNER: it acts on the young form of the insect (larva), which causes a large area of ​​injury on the leaves, an important entry point for the bacteria.