In Focus: Jerry Southwell
March 28, 2012 
1. How would you characterize a successful bloom in citrus?
Southwell: A successful bloom results from optimal flower induction weather conditions coupled with a long-term balanced nutritional program to maximize bloom, fruit set, and the fruit-carrying capacity of the tree. Early uniform pollination of flowers yields larger fruit with less variability in size resulting in increased pound solids potential. If the tree is staged for the bloom and early fruit set is accomplished, the potential for premature fruit drop is diminished.
2. How important is proper nutrition in establishing and holding a bloom set in citrus?
Southwell: A healthy tree is the result of proper nutrition derived from the right rate at the right time from the right source. Trees during bloom take up a given amount of nutrients from a potential static supply. It’s static due to the fact that the bloom takes place during the time of the year with the driest and coolest soil conditions, which limit availability and uptake of soil nutrients. Supplemental nutrient addition and irrigation will be needed.
3. In what ways do proper levels of calcium benefit citrus trees and yields?
Southwell: Calcium is often overlooked due to adequate levels reported in most soil test results or leaf tissue. If we examine the calcium content of each flower produced in a normal year (50 to 100,000 flowers), the tree/soil has to provide roughly two to four ounces of calcium per tree just for the blooms. Once the flower has been fertilized and begins the fruit-forming process, it will need nearly 0.2 ounces more calcium per box for the fruit to hold past five weeks. If we assume that 200 pieces of fruit fill a box and if we have five boxes of fruit per tree, that’s another 1 ounce per tree. The total amount of calcium needed in the first five weeks is 24 to 39 pounds. Much of this total will drop back to the ground as aborted flower/fruitlet, but is not available for immediate uptake.
When we have an inadequate supply of available calcium and a bouquet bloom, the sheer number of additional demands upon tree calcium supply drops the fruit calcium content below critical levels and results in a lighter crop than with an average bloom.
Calcium deficiency is partially defined as “death of growing points.” Simply, calcium is needed for cell division or mitosis. In the early spring with bloom and flush representing your photosynthetic capacity and pound solids for your profitability, calcium is greatly needed for development of leaves and fruit.
4. What role does a calcium-based product play in the era of HLB?
Southwell: Calcium and potassium are involved in programmed cell death of pathogens and infected tissue in many plant species. Research is being conducted to determine if this process exists in citrus. We do know that calcium deficient trees are more susceptible to HLB. In some species, calcium can open plugged phloem tubes. These functions have potential in mitigation of diseases such as canker and HLB, but remain unproven in citrus.
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