
Agriculture
Agribusiness
September 13, 2024
New strategies in the fight against greening
Debate analyzes soil improvement measures to increase plant health and tolerance in Brazilian citrus farming
The largest producer of orange juice in the world and a leader in juice exports, Brazil is in full war against an enemy that has already defeated other countries: greening. This is the disease considered the most destructive in global citriculture, according to Fundecitrus (Citrus Defense Fund), and its causal agent is a bacterium. Transmission occurs through an insect called psyllid.
The disease reduces the plant’s productive capacity, causing a major impact on the harvest. A survey conducted in 2021 by Fundecitrus showed a critical incidence of greening in the interior of the State of São Paulo, the country’s main citrus-producing hub. The highest numbers were recorded in the cities of Limeira (61.75%), Brotas (50.40%), Porto Ferreira (37.84%), Avaré (29.41%), and Duartina (26.15%).

The elimination of symptomatic plants is mandatory up to the eighth year after planting, according to state legislation. The problem is that the incidence has been growing and already reaches 79.38% in Limeira and 77.06% in Brotas, according to data released by the entity in September 2024. In the case of Porto Ferreira, there was a jump from 37.84% to 71.77%. “I have no doubt that we need to seek alternatives,” states agronomist engineer and citrus cultivation specialist consultant Gilberto Tozatti.
In this month’s interview, Revista Estratégias e Soluções, from Editora Pecege, hosted a debate on this subject based on the experience of agronomist engineer Kunio Nagai, who has been working as a consultant in sustainable agriculture for 30 years and helped small farmers in Pilar do Sul, São Paulo, to control the disease in their orchards, which have already passed their cutting age. Also participating in the conversation were researcher Diogo Manzano Galdeano, doctor in molecular biology from Unicamp, PhD in Plant Pathology from the University of California (USA), and Tozatti, who is also a member of the Citrus Consultants Group (Gconci).
Watch the following conversation (click on the video).
Although the evolution of greening in 2024 has slowed down compared to previous numbers – 6.29 percentage points of growth from 2023 to 2024, versus 13.66 percentage points from 2022 to 2023, on average –, Fundecitrus data are concerning and demand joint alternative strategies for Brazil to try to avoid the same fate as the United States – where productivity has already fallen 74% since 2005.
Bokashi
The focus of Kunio Nagai, who provides free guidance on small farms spread across the State of São Paulo, is soil improvement. The technique he teaches calculates fertilization based on soil chemical analysis and the export of elements according to the crop. The basis of the treatment recommended by him is an organic fertilizer of oriental origin known as bokashi.
Nagai reports that in 2021, in Pilar do Sul (SP), he found producers facing difficulties with their dekopon orchards (a species of tangerine), which had declining productivity due to greening. Currently in the third year of the treatment recommended by Nagai, the orchards have returned to normal production and practically have no more symptoms of the disease.
Graduated from the Luiz de Queiroz College of Agriculture, USP, in 1961, Nagai is the author of the book “Soil Management and Fertilization (IPTDA Jatak, 2008)”. For him, improving the soil is synonymous with increasing plant health and making it more tolerant to pathogens, which contributes to a more profitable and sustainable agricultural system.
Bokashi is an anaerobic compost of bran to which effective microorganisms are added, responsible for restructuring the soil and inducing the plant to emit rootlets, important structures for nutrient absorption.
“The area of microbiology is little studied,” states Tozatti. “These field observations are facts, there is no doubt, we also observe in other situations the use of microorganisms, with greater plant tolerance [to diseases],” he says. “I think we need to delve deeper into this subject.”
In Diogo Galdeano’s opinion, the discussion about soil microbiology makes sense, but the subject needs more studies to verify if there is indeed a reduction of bacteria in the plant. “We need to test this in research, with various treatments and controls,” he says. Galdeano is working on research, which began during his post-doctorate in the USA, to synthesize RNA molecules from viruses normally found in psyllids, which would be capable of switching off insect genes involved in the transmission of the bacteria that causes greening.
The hope is that joint debates and efforts can lead to strategies to curb the advance of greening and leverage the competitiveness of Brazilian citrus farming. “We must not stop controlling the psyllid, we must not stop eradicating symptomatic plants. However, in a system like this, we already have to think about coexistence,” defines Tozatti.
About the interviewees
Kunio Nagai – Agronomist graduated from USP/Esalq, has been a consultant in sustainable agriculture for 30 years and author of the book “Soil Management and Fertilization (IPTDA Jatak, 2008)”;
Gilberto Tozatti – Agronomist engineer graduated from Unesp, he is a consultant specialized in citrus fruits and is part of the Citrus Consultants Group, which operates throughout the country;
Diogo Galdeano – PhD in Molecular Biology from Unicamp and PhD in Plant Pathology from the University of California (USA). He is an associate professor in the Department of Phytopathology at the Federal University of Viçosa (MG).
Who published this videocast
Renata de Gaspari Valdejão Almeida







