How to control septoria in industrial tomato production

The occurrence of septoria or septoria spot in recent years has increased in tomato production fields for industrial processing in Brazil. The disease is caused by the fungus Septoria lycopersici Spegazzini and occurs in practically all tomato-producing regions in the world, being more common in hot and rainy seasons. It is favored by prolonged periods of high humidity and moderate temperatures. In the case of low cultivation, aimed at the tomato segment for industrial processing, it becomes even more problematic due to the density of plants and shrub growth, which encourage the formation of a microclimate favorable to the disease.

The pathogen causes plant defoliation, significantly reducing fruit productivity and quality. In some regions or growing seasons, losses caused by the disease can reach 100% of production, due to the death of plants (Pereira et al, Technical Communication 96: CNPH, 2013).

Septoria can occur at any stage of tomato development, but symptoms usually appear on lower leaves shortly after fruiting begins. They can appear on the petioles, stem and flowers of the plant, rarely on the fruits. Initially, they appear on the underside of the leaves in the form of small water-soaked spots with a more or less circular to elliptical shape, measuring 2mm to 3mm in diameter. As the disease develops, the lesions acquire a grayish-brown color in the center, with darkened edges and a narrow yellowish halo around them, reaching up to 5 mm in diameter. In severe attacks, the lesions coalesce, the leaves turn yellow, dry and fall. New lesions caused by Septoria lycopersici can be confused with others caused by black spot (Alternaria spp.), which makes identification difficult. The main characteristic that helps in identifying the pathogen is the appearance of small black dots in the center of the lesions. These points are fruiting bodies of the fungus, called pycnidia, from which the fungus spores are released. Fruits produced on severely defoliated plants are reduced in size and burn due to direct exposure to sunlight. In tomatoes for industrial processing, scalded fruits end up generating poorer quality pulp, due to changes in color.

Currently, there are no commercially available tomato cultivars or hybrids with satisfactory levels of resistance to septoria. This is attributed to the difficulty in transferring resistance factors, generally quantitative, from wild species to advanced tomato lines (Kurozawa & Pavan, Manual of Phytopathology V. 2, 2005).

Control of septoria in tomato plants is commonly carried out with the foliar application of contact and systemic fungicides, often used to control early blight (Alternaria sp.) and late blight (Phytophthora infestans). Contact fungicides may be less effective than systemic fungicides because they are easily removed by rainwater or sprinkler irrigation. Currently, there are many fungicides registered with the Ministry of Agriculture, Livestock and Supply (Mapa) to control the disease, such as cuprics, triazoles, isophthalonitrile, dithiocarbamates and strobilurins. However, many of the active ingredients have not shown satisfactory efficacy when environmental conditions are very favorable to the occurrence of the disease.

In order to evaluate the efficiency of these products in managing the disease, the Instituto Federal Goiano Campus Morrinhos, in partnership with Embrapa Hortaliças, began a study with the aim of testing the main fungicides registered for this disease in tomato plants under controlled home conditions. of vegetation and in the field, in low tomato cultivation, simulating a crop intended for industrial processing. The first experiment was carried out in a greenhouse located at Embrapa Hortaliças (Brasília-DF), from February to March 2013. 901-day-old seedlings (cultivar N25) were transplanted into one-liter pots containing fertilized and sterilized soil. . Two days later, the first application of fungicides was carried out, using a manual sprayer, until the point of runoff. A second application was carried out seven days later. A control only inoculated with S. lycopersici and the following active ingredients were evaluated: propineb, metiram + pyraclostrobin, azoxystrobin + difenoconazole and difenoconazole. The plants were inoculated with a manual sprayer one day after the second application, using an inoculum suspension at a concentration of 3×104 conidia/ml, and subjected to a humid chamber for 18 hours. A randomized block design was used, with four treatments, four replications and plots consisting of four pots with one plant. The severity of the disease was assessed 12 days after inoculation, using the scale adapted from Mello et al (Fitopatologia Brasileira, 1997). The first three true leaves of each plant were evaluated.

The field trial was conducted in the experimental area of ​​the Instituto Federal Goiano, Campus Morrinhos (17°49'28,85"S, 49°12'6,48"W and 892m altitude), with planting on May 14, 2013. To transplant the seedlings (cultivar N901, 25 days) into the field, they were arranged in single rows, with a spacing of 1,20m between rows and 0,25m between plants. Irrigation was carried out by sprinkler via a central pivot. The regime used was similar to that used in commercial crops, applying weekly irrigation depths of 20mm in the first month of cultivation, and 30mm until approximately 14 weeks of cultivation, when irrigation was cut to concentrate fruit maturation. The experimental plot consisted of three lines, each with 24 plants. The plots were arranged following the experimental design in randomized blocks, with four replications for each treatment. The treatments consisted of applying the same products already described, with the same concentration, but in a spray volume of 500L/ha. Applications of the products began ten days after transplantation, and were carried out at intervals of 14 days, totaling five applications. For application, a manual sprayer pressurized with CO2 was used, with a constant pressure of 2bar. For inoculation, leaves with symptoms of septoria were collected from crops with an epidemic of the disease. These leaves were taken to the laboratory to confirm the etiological agent. Confirming that it was S. lycopersici, the leaves were kept in a humid chamber for 48 hours to encourage sporulation of the pathogen. They were then crushed in an industrial blender, the solid part was separated into sieves and the liquid obtained was diluted in water and sprayed on the plants 53 days after planting. To assess the severity of the disease, the percentage of injured leaf area was evaluated, based on the central line of each plot. Assessments were carried out at 23 and 33 days after inoculation. Due to the advanced state of fruit maturation, most likely due to the intense defoliation caused by the disease, the harvest, which was scheduled for 120 days after transplanting, was brought forward to August 6, 2013 (112 days). The central lines of each plot were harvested, the total number of fruits were weighed and the values ​​were transformed into tons per hectare.

In the greenhouse test, all products managed to reduce the severity of the disease to significant levels in relation to the untreated control. with a control percentage greater than 85%. However, under field conditions, the reduction in disease control was less significant, reaching maximum control rates of 39% with propineb in the first evaluation and 32,25% with difenoconazole. With these results, it is clear that there is still potential to increase the level of septoria control in the field, investing in application technology studies that enable control levels close to that observed in a greenhouse. Chemical control presents the possibility of reducing losses caused by the disease, resulting in increased productivity and improved quality of raw materials in the tomato segment for industrial processing.

This article was published in issue 88 of Cultivar Hortaliças e Frutas magazine. Click here to read the edition.