Fertilization frequency, micronutrient management and rootstocks can all impact the yield of HLB-affected sweet oranges, Tripti Vashisth recently told a Citrus Nutrition Day audience in Lake Alfred, Florida. The educational event was held at the Citrus Research and Education Center, where Vashisth is a University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) horticulturist.
HLB-affected trees should be supplied with a constant supply of nutrients at higher rates than are recommended for healthy trees, Vashisth said. She added that nutrient availability allows HLB-affected trees to respond to abiotic and biotic stresses.
Vashisth said application of micronutrients at a 20% higher than recommended rate can improve productivity of HLB-affected trees. Soil-applied nutrients are better than foliar micronutrients, she added. She suggested the following rates for soil-applied micronutrients on sweet oranges:
- Manganese: 12 to 15 pounds per acre
- Zinc: 12 to 15 pounds per acre
- Iron: 6 to 10 pounds per acre
- Boron: 0.75 to 1.5 pounds per acre
ROOTSTOCKS AND NUTRIENT UPTAKE
Vashisth reported on the nutrient uptake in potentially HLB-tolerant rootstocks. She found that rootstocks were different in their nutrient uptake efficiency for only three nutrients, and not for the rest of the nutrients studied. The rootstock A+Volk x Orange 19-11-8 has the highest nutrient uptake efficiency for phosphorus, potassium and sulfur among several rootstocks tested, Vashisth said.
The rootstock UFR-4 has the poorest nutrient uptake efficiency for potassium and sulfur, while the US-896 rootstock has the poorest efficiency for phosphorus uptake. Swingle rootstock has zinc uptake issues, potentially resulting in HLB susceptibility, Vashisth said.
Vashisth and fellow Nutrition Day presenter Brandon White, a UF/IFAS Extension agent, both discussed the role of soil pH in nutrient uptake efficiency. White said after ensuring crops have sufficient water, soil pH is the most important thing to ensure crop health. He recommended citrus growers keep soil pH between 5.8 and 6.5. See more from White’s Nutrition Day presentation.
According to Vashisth, there is interaction between HLB and soil pH. HLB-affected plants showed better growth at low pH. On the other hand, healthy plants are not significantly benefited at low pH, she said.
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