By Davie Kadyampakeni and Megan Dewdney
The University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) conducted a six-year project to determine if plant nutritional fertilizer sources coupled with specific crop protection chemicals help mitigate citrus diseases. This project was conducted on a 5-acre commercial citrus grove block near the Citrus Research and Education Center (CREC) in Lake Alfred.
The study compared two specific fertilizer blends. The first blend was with calcium nitrate, triple superphosphate, potassium sulfate and potassium magnesium (commonly called K Mag) with a grade of 9-1-14 11Ca, 7.6S, 2Mg, 0.08Zn, 0.04Mn, 0.025B applied at 180 pounds nitrogen per acre per year. The other blend had a conventional grower program fertilizer of 16-2-16 composed of ammonium nitrate, diammonium phosphate and potassium chloride. It was also applied at 180 pounds nitrogen per acre per year.
Sulfur, manganese, boron and zinc were supplemented in four splits at equivalent rates supplied by the first program, but calcium and magnesium were omitted. In the conventional grower program, the sources of sulfur and micronutrients were manganese sulfate monohydrate, zinc sulfate monohydrate and granulated boric acid.
The fertilizers were applied in four splits of 20% in February, 20% in April, 30% in June and the remaining 30% in September annually. The treatments (Table 1) were with or without crop protection products, namely Aliette [Aluminum tris (O-ethyl phosphonate), 80% active ingredient] and Velum Prime (fluopyram, 41.5% active ingredient). The two Velum treatments were applied in April and May every year. The Aliette treatments were applied in May, June, July and August yearly.
Table 1. Study treatmentsa
| No. | Nutrient Sources | Crop Protection | Micronutrients (Soil-Applied) |
| 1 | Improved programb | Psyllid control only | Part of blend |
| 2 | Grower programc | Psyllid control only | Grower sources |
| 3 | Improved program | Psyllid control, Aliette soil | Part of blend |
| 4 | Grower program | Psyllid control, Aliette soil | Grower sources |
| 5 | Improved program | Psyllid control, Velum Prime soil | Part of blend |
| 6 | Grower program | Psyllid control, Velum Prime soil | Grower Sources |
| 7 | Improved program | Psyllid control, Aliette and Velum Prime | Part of blend |
| 8 | Grower program | Psyllid control, Aliette and Velum Prime | Grower sources |
a Aliette [Aluminum tris (O-ethyl phosphonate), 80% active ingredient]; Velum Prime (fluopyram, 41.5% active ingredient)
b Improved blend of calcium nitrate, triple superphosphate, potassium sulfate and K Mag with a grade of 9-1-14 11Ca 7.6S 2Mg 0.08Zn, 0.04Mn 0.025B applied at 180 pounds nitrogen per acre per year
c 16-2-16 composed of ammonium nitrate, diammonium phosphate and potassium chloride applied at 180 pounds nitrogen per acre per year. Sulfur, manganese, boron and zinc were supplemented in four splits at equivalent rates supplied by the first program.
Overall, impacts of the treatments were not seen until 2.5 to 3 years into the project. Researchers started observing better root growth at shallow and deep soil layers, dense canopies, good juice quality (Brix greater than 10.5) and greater fruit yields. The fruit yields started at about 290 to 300 boxes per acre in the first two to three years and increased to around 350 to 600 boxes per acre in the last three years of the project. The improved fertilization and timing along with the use of Velum and/or Aliette improved root development, maintained the tree canopy and increased fruit yield and juice quality.
Davie Kadyampakeni and Megan Dewdney are associate professors at the UF/IFAS CREC in Lake Alfred.
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