Coffee rust monitoring

Since the arrival of coffee rust in Brazil, ways have been sought to harmonize living with the disease and maintaining production. However, the search to reduce its incidence in the field to zero has prevailed, a way of thinking that is not always more economical and sustainable. Therefore, monitoring is a highly valuable technical tool, which can be used both in creating a management area and in evaluating the control strategies used.

Coffee rust, caused by the fungus Hemileia vastatrix, arrived in Brazil in the 70s. Its main symptom is the occurrence of pustules with orange spores on the underside of the leaves. The main damage caused is premature leaf fall, which causes damage to the plant and reduces production.

Since the arrival of rust in Brazil, efforts have been made to establish techniques for dealing with the disease and ensuring the maintenance of national production. Rust control typically involves a series of tools such as the use of resistant varieties, protective fungicides, especially copper-based, and systemic products applied to the aerial part and soil. The use of these tools, associated with fertilizer management, spacing between plants and irrigation, among other agronomic techniques, has resulted in Brazil not only living with rust, but also increasing its production.

The fact is that coffee rust is present in practically all Brazilian plantations, increasing in importance according to cultural practices, climate, productivity, spacing and even failures to deal with it. It is not uncommon to see it having a strong impact in specific situations throughout Brazil. In other words, dealing with this topic is always important and there is something more to be learned.

Without a doubt, chemical control is essential when conditions are favorable to rust. There are several ways to combine products available on the market. This is what is called chemical management of the disease. Each industry has its technological package and consultant agronomists also develop their strategies. The measures used will also depend on the way the producer conducts his farming, of course. Logically, it is the producer who has the final decision. It is up to the producer to choose which control methods and how to adopt the available tools.

Some principles must be followed to ensure the best efficiency of fungicides in coffee crops, such as the use of copper-based products, which are copper oxides or hydroxides. These products alone are less efficient than systemic fungicides, such as triazoles, however, they are important in improving control and reducing disease resistance to a given product. Systemic fungicides are more efficient in controlling rust, however, the continuous use of the same active ingredient can favor the selection of resistant populations, leading to the loss of their effectiveness. This is not the desire of either the industry that invested in the development of the product, or the producer, who ends up losing an additional tool to control the disease. There are some mixtures on the market containing micronutrients and copper, recommended for rust control. The advantage of these mixtures is that they combine disease control with the correction of small nutritional deficiencies in the crop.

Each chemical product has its advantage and disadvantage, so they must be used judiciously, taking advantage of what each one has to offer. Copper-based products cannot eliminate the disease already established in the leaf, therefore, their use is recommended preventively, in combination with systemic treatments or at the beginning of the epidemic, when the disease affects at least 5% of the leaves of the third or fourth pair. in the productive sectors. As they act as a chemical barrier, protecting the leaves from fungal attack, protective products should not be applied on rainy days. During application, the syrup must reach the underside of the leaves.

Systemic fungicides have a lesser or greater ability to penetrate the leaves and eliminate rust after the disease has established itself. It is the well-known curative effect. These types of products allow the farmer to wait for the right time to spray, if he wants to obtain efficient control of the disease with fewer sprays. To do this, the producer needs technical monitoring and criteria for chemically intervening in his crop.

Producers know better than anyone that the importance of rust varies each year, according to crop productivity, plant nutrition and the climate, which especially in recent times has been a predominant factor. Therefore, it is important to define which products will be used, how and when they will be applied.

The producer can decide when to apply a systemic product based on a phytosanitary warning system, application at predetermined times (application calendar) and application according to sampling of the disease in the crop.

In an experiment conducted in the north of Espírito Santo, on a Conilon coffee farm, an attempt was made to comparatively identify the best time to apply systemic fungicides (with curative effect) based on the quantity of diseased leaves.

To sample rust in the Conilon crop, 60 leaves were collected monthly, three leaves on each side of the plant, on ten plants per plot. The collection was made on the third or fourth pair of leaves of the productive branches. Subsequently, the percentage of leaves with at least one rust pustule was counted. The experiment was carried out from January to July 2012.

Systemic fungicide spraying was carried out when the number of diseased leaves reached 2,5% (T1), 5% (T2), 10% (T3), 15% (T4), 20% (T5) of the total leaves collected . The application was carried out according to a recommended calendar for the region (T6). Control was also carried out through the application of a systemic fungicide via soil (T7). One plot did not receive chemical control for rust, being considered the control, to find out whether there were conditions favorable to the disease.

Graph A in Figure 1 shows that the application of systemic fungicide, when the number of diseased leaves varied from 2,5% to 10%, provided the best level of rust control. A similar result was obtained with the application of the product via soil in March of that year.

In the year in which the experiment was conducted, rainfall was irregular, which caused the low efficiency of the control based on predefined dates (Figure 1, B). The same occurred in the case of applying fungicides with 15% and 20% of diseased leaves.

The advantage of waiting for the onset of rust to begin chemical control with systemic fungicides is to apply at the correct time and avoid unnecessary applications. This system demands a greater presence in the field on the part of the producer and equipment and labor conditions for the rapid application of the products. On very large properties, monitoring can be adopted together with other methods, such as preventive or soil application. The disadvantage is that, in the field, a zero level of disease is often desired. This way of thinking is not the most economical and sustainable, however, it continues to prevail. Another factor that hinders the adoption of this system is the lack of training for the producer.

Coffee certification in Brazil has grown and one of the requirements is the adoption of good agricultural practices in certified areas. Monitoring the disease in the field is a highly valuable technical tool and can also be used to create a management area and evaluate the control strategies used.

The graph presented is part of the master's thesis in Tropical Agriculture at Ufes, São Mateus campus, defended by Olivério Poltronieri Neves. The experiment is part of a project financed with resources from the Brazilian Coffee Consortium, the National Council for Scientific and Technological Development and the Espírito Santo Research Support Foundation.

Marcelo Barreto da Silva, Federal University of Espírito Santo 

Article published in issue 189 of Cultivar Grandes Culturas.