Application of phosphite in the management of cercosporiosis in coffee

The application of phosphite formulations, in a preventive manner and associated with other control measures, can help in the management of cercosporiosis, an important disease capable of causing direct and indirect losses in coffee plants.

Coffee crops are subject to several factors capable of reducing productivity. The diseases stand out, especially cercosporiosis, caused by the fungus Cercospora coffeicola capable of causing losses of up to 30% in productivity when uncontrolled. Its main symptoms are brownish necrotic leaf spots, with a light center, which may or may not be surrounded by a yellowish halo and elliptical, depressed lesions on the fruits. Therefore, losses can be direct, by affecting the fruits, depreciating the quality of the drink, and indirect by reducing the leaf area, defoliation and consequent reduction in photosynthesis. Cultivations with greater spacing favor the disease, because the fungus produces a toxin called cercosporin, which is activated by light and is related to the virulence of the fungus.

The main way to control cercosporiosis is the application of fungicides. For a long time, copper-based products (copper oxychloride, Bordeaux mixture) with protective action and a broad mode of action were the only ones used to control coffee tree diseases. However, in the 1960s these fungicides were replaced by systemic ones that have both protective and curative action and a specific mode of action, among which strobilurins, triazoles and mixtures of both stand out. The constant application of these fungicides has selected populations of C. coffeicola resistant and this made the disease, previously secondary, gain greater importance. Furthermore, the market has increasingly demanded that the foods produced contain minimum or zero amounts of residues from products such as fungicides, insecticides, among others. As a result, companies and research institutions have focused their studies on reducing the application of chemical phytosanitary products or finding low-toxic products that could be an alternative source for controlling cercosporiosis. Highlights include plant extracts, foliar fertilizers, resistance inducers, among others.

Foliar fertilizers are applied to coffee plants to address deficiencies in micronutrients such as Mn, Zn, Cu, Mo and B or macronutrients, mainly Ca and K. The application of these products can indirectly reduce the intensity of blind spot, as they provide macro and micronutrients. These are cofactors (activators) of plant defense enzymes. This increases the activity of the plants and reduces the intensity of the disease when compared to a plant that did not receive the application. Furthermore, nutrients promote greater and better growth/development of plants, leading to the formation of physical barriers such as greater thickness of the wax layer, closure of stomata and increase in the thickness of the plant cell wall.

Phosphites are salts derived from phosphorous acid, registered and marketed as foliar fertilizers with potential for controlling coffee tree diseases, according to several studies by the Laboratory of Parasitism Physiology at the Federal University of Lavras (UFLA). Research focuses mainly on rust management (Hemileia vastatrix), cercosporiosis (Cercospora coffeicola), Phoma spot (Phoma tarda) and haloed spot (Pseudomonas syringae p.v. garcae) with phosphites and characterization of modes of action (biochemical, molecular, among others). These products have a triple mode of action in controlling plant diseases, which are the induction of host resistance and nutrition, in addition to direct toxicity against fungal and bacterial pathogens. However, phosphorus nutrition does not occur, as the phosphite ion is not metabolized by the plant to be converted into phosphate, which is the only form in which the plant absorbs phosphorus. Another characteristic of phosphites is their translocation via xylem and phloem, which facilitates and optimizes application. The price of these products is competitive when compared to commercial fungicides. However, the control provided by these products is generally intermediate, and it is ideal to replace one of the applications of the fungicide cyproconazole+azoxystrobin, for example, with an application of phosphite in field conditions. In the nursery, more applications should be carried out interspersed with those of fungicide, according to the level of incidence of cercosporiosis.

For greater effectiveness of phosphite in controlling cercosporiosis, application must be carried out preventively, activating defense mechanisms so that, when invaded by the fungus, the plant has its defense ready to prevent or delay the colonization of plant tissue. A study was carried out with the objective of evaluating the effect of applying commercial formulations of potassium phosphites on the severity and incidence of blind spot in coffee seedlings.

The test was carried out in a Ufla greenhouse. The commercial phosphites Reforce, Pepfós and Green Fós were used, compared with the commercial fungicide cyproconazole+azoxystrobin, with the resistance inducer acibenzolar-S-methyl with a control without application. These products were applied to coffee seedlings of the Topázio cultivar with 6 pairs of leaves. After application, the fungus was inoculated (Cercospora coffeicola) by spraying a suspension with 3x10⁴ spores per milliliter of water. The plants were then stored for 72 hours in a humid chamber with a humidity of approximately 80±2% and a temperature of 25±2ºC. After the appearance of symptoms (30 days after inoculation), five assessments of severity (injured leaf area) and defoliation were carried out. Based on severity and defoliation, the area under the severity (AACPS) and defoliation (AACPD) progress curve was calculated, in addition to the controls provided individually by the products used. Severity and defoliation progress curves indicate growth over time. AACPS and AACPD represent the “accumulation” of the disease over time.

It is possible to verify that all the phosphites used promoted a reduction in the severity and defoliation of cercosporiosis over time, presenting an effect very close to that of the fungicide and much smaller than those of the control. 

All phosphites used promoted control of AACPS (A) and AACPD (B) of cercosporiosis with the same effect as the fungicide and resistance inducer. Controls of 74 to 87% were obtained in AACPS and 79 to 89% in AACPD. 

Based on the results obtained, it is possible to recommend any of the three potassium phosphite formulations for the control of coffee leaf spot in the nursery at the same doses used in this trial. New trials will be set up in the field to verify the effectiveness of these products in this environment, since it is subject to the action of many other factors that may or may not favor the intensity of blind spot. This way we will be able to know the best application system for phosphites and whether their association with fungicides is even viable.

Manoel Bastista da Silva Júnior, Mário Lúcio Vilela de Resende, Alexandre Ribeiro Maia de Resende, Victor Augusto Maia Vasconcelos, Rossiane Oliveira Vilela, Lucas Gabriel Pimenta Nogueira, Federal University of Lavras; Bruno Henrique Garcia Costa, Agrichem do Brasil

Article published in issue 214 of Cultivar Grandes Culturas.