A study carried out by Brazil’s Fundecitrus in partnership with the Agronomic Institute (IAC) showed that additional fertilization of orchards had no effect on increasing the production of trees with citrus greening. The research was conducted in well-nourished adult orchards with a low incidence of greening. Results were published in January in the journal PhytoFrontiers of the American Society of Plant Pathology.
LONG-TERM LARGE STUDY
“We carried out an experiment that lasted six years, with eight treatments and four replications,” Fundecitrus researcher Renato Bassanezi said. “Each plot consisted of 1,200 plants.”
The idea for the giant study came when the research group noticed that producers in Florida were adjusting orchard nutrition. “They had adult plants already affected by greening, and with the additional application of nutrients they did not show a major reduction in production,” Bassanezi said. “Our objective was to replicate what they were doing and combine it with other treatments defined by the IAC team.”
Foliar application of additional products occurred each time the plants vegetated — five or six times a year.
“There was a treatment that consisted only of fertilization with macronutrients, nitrogen, phosphorus and potassium (NPK),” Bassanezi said. “Another one was NPK plus micronutrients (zinc, manganese and boron). Another was NPK plus micronutrients that were recommended in Florida, where the proportion of manganese and zinc was higher. There was another one that was NPK along with potassium nitrate and micronutrients, another one in which we added potassium salicylate and micronutrients, another one that was complete with all the products, and yet another one that was the commercial product sold at the time.”
The research also sought to show what impact each treatment had on reducing the symptoms of greening and nutritional deficiencies.
RESEARCH RESULTS
“We evaluated the percentage of plants that were deficient in zinc, deficient in manganese, deficient in magnesium; (that had) yellowed branches, mottled leaves, deformed fruits and fruit drop,” Bassanezi said. Nutritional deficiencies were suppressed, but symptoms related to greening remained in 100% of the plants.
The study also showed that none of the treatments made a diseased plant produce like a healthy plant. “In all treatments, the severity of the disease increased over time, and production was reduced,” said Bassanezi.
PSYLLID CONTROL
The research also evaluated the efficiency of psyllid control on the incidence of greening.
“We left a plot with all treatments without spraying for the psyllid. In those we sprayed, we had an incidence of the disease after six years of age of around 26%,” Bassanezi said. “In what we didn’t spray, it was 52%. This shows the importance of controlling the insect so that greening does not spread throughout the orchard.”
CONCLUSION
The research made it clear that if there is already good nutrition in the orchard, there is no advantage in doing more than what was already recommended in order to increase production in diseased plants.
“Nutrition does not have the ability to cure the plant with greening,” Bassanezi concluded.
Source: Fundecitrus
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