Integrated agricultural production systems (SIPA), also known as crop-livestock-forest integration (ILPF), contribute to the reduction of plant diseases in grain crops, both in the roots and in the aerial part of the plants. Research developed by Embrapa, in partnership with the Federal University of Paraná (UFPR) and conducted in a long-term experiment by the Agronomic Institute of Paraná (Iapar), concluded that it is possible, in areas managed with ILPF, to reduce the amount of pesticides needed for disease control, as the forestry component is an important factor in reducing the survival of pathogens in the soil, as well as reducing the intensity of foliar diseases.
The results of this unprecedented study were published in the November 2020 issue of the international journal Agricultural Systems. Entitled Plant diseases in afforested crop-livestock systems in Brazil, the article is written by agricultural engineer Alexandre Dinnys Roese, from Embrapa Agropecuária Oeste, in partnership with Erica Camila Zielinski and Louise Larissa May De Mio, both from the Department of Phytotechnics and Phytosanitary at Federal University of Paraná (UFPR).
Roese explains that the study was aimed both at diseases caused by fungi that survive in the soil and foliar diseases, whose pathogens survive in cultural remains and volunteer plants, and can be dispersed through the air, as is the case with rusts. Fieldwork was conducted in long-term experiments in the municipality of Ponta Grossa (PR), from 2013 to 2016.
Among the advances provided by this research, contributions related to the behavior of soil diseases in soybean and corn crops and foliar diseases in soybean, corn and oat crops stand out.
The research methodology analyzed three different production systems: agroforestry (ASP), with soybean and corn rotation in the summer, cattle grazing on oats with ryegrass in the winter, all located between rows of eucalyptus with grevillea; agropastoral system (AP), with soybean and corn rotation in the summer and cattle grazing on oats plus ryegrass in the winter; and control area (CO), with only soybean and corn rotation in the summer and oats plus ryegrass in the winter, but without animal grazing. The total area of the experiment occupied 12 hectares.
According to Roese, there is little study on the relationship between the forestry component and diseases in crops, and scientists wanted to know whether the presence of trees in the production system influences the occurrence or severity of diseases in crops, and how this would happen. “This was a suspicion based on empirical observations in the field, that in places using the agroforestry system, also known as ILPF, there was a reduction in diseases. Through this study, we are confident that this decrease is true for most diseases. This aspect has been scientifically proven and we now understand how this occurs”, comments the scientist.
He celebrates the results, which reduce both soil and foliar diseases, highlighting that in the study the diseases were used as biological models.
According to Roese, trees provide a change in the microclimate, modifying numerous aspects of crops, such as: duration of leaf wetness, temperature, air humidity, wind speed and incidence of light.
The agronomist emphasizes that diseases are very dependent on microclimate, and as trees alter the microclimate, they end up drastically influencing plant diseases in crops, which justifies the relevance of this research.
“Data related to microclimate were monitored inside the plant canopy, in soybeans and corn. We observed that, with the presence of trees, there is a shorter duration of daily leaf wetness, lower light intensity, lower daytime temperature, higher nighttime temperature, greater air humidity during the day and lower wind speed”, reports Roese. According to him, the shorter duration of leaf wetness occurs due to less dew formation, which, in turn, is influenced by the smaller reduction in temperature at night, as the tree tops form a barrier that reduces energy loss ( temperature) during the night.
Roese explains that soil diseases are caused by microorganisms (fungi, bacteria and others), natural inhabitants of the soil, but in imbalance in this environment. The microbiota present in the soil is responsible for balancing the presence of these disease-causing agents.
Soil suppressiveness to pathogens is the name given to the soil's ability to suppress, totally or partially, one or more diseases, even when the disease-causing agent (pathogen) is present in the soil and all environmental conditions are favorable to the disease.
The soil diseases evaluated were the damping-off of soybean plants, caused by the Rhizoctonia fungus, and white mold, caused by the Sclerotinia fungus. In both cases, the agroforestry system reduced disease incidence or pathogen survival. These results were also related to greater microbial activity and greater presence of beneficial fungi in the soil in the production system that includes trees.
“The soil microbiota is favored by the intensification of the production system, that is, the increase in the number of cultivated species and the presence of animals. Thus, the forest component benefits the microbiota, which directly contributes to the reduction of diseases,” details the agronomist.
The study also sought to identify the benefits of the agroforestry system in reducing foliar diseases of soybeans and corn and its relationship with the presence of trees in the crop. Leaf diseases are those that occur in the aerial part of crops and that can be caused by fungi, bacteria and other microorganisms that remain in the straw or that survive on alternative host plants. They are typically spread by wind and rain splash.
In general, all of these diseases are controlled through the spraying of specific pesticides. Therefore, research like this contributes to the reduction of this type of input, which is beneficial for the environment, worker health and reducing crop production costs.
For soybeans, the work analyzed rust, mildew and powdery mildew, as well as the dispersion of rust and powdery mildew spores in the air. The results demonstrate that the adoption of the agroforestry production system provided lower rust and mildew severity, despite increasing the severity of powdery mildew.
White spot, rust, helminthosporiosis and cercosporiosis in corn crops were also evaluated. The agroforestry production system showed lower severity of white spot, rust and cercosporiosis. As for helminthosporiosis, there was no difference in the severity and number of lesions between production systems.
For Roese, the results prove that afforestation reduces most diseases in crops. “However, agricultural crops subject to powdery mildew must take extra care in wooded production systems. This disease has increased in severity, including in oat cultivation during the winter,” he states.
The expert emphasizes that, despite the relevance of these results, most of them were already expected. “Those who defend agroforestry systems always mention the reduction of plant diseases as one of their benefits. However, this statement was based on the concepts of the system, its greater proximity to natural environments and the expectation of greater resilience to stress. However, there were still no experimental results to prove this. And that’s what we did,” he concludes.
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