Citrus Greening (aka HLB) now infects citrus trees in every citrus-growing county in Florida. To date, though the cause (bacterial) and the vector that spreads it (an insect called a psyllid) are well known, no cure is on the horizon. In some groves, 100% of trees are infected.
On that news, Coca-cola has just announced that it will plant 25,000 acres of new citrus in Florida.. Do they know something we don't, or is this just the kind of colossally stupid move that companies that big are good at? If they know of a cure, they're playing it close to the chest. Another possibility is that Coke is relying on the one piece of good, or not-so-bad, news on this subject: enhanced nutrition seems to enable the trees to maintain near-normal production of quality fruit, at least for a while.
After failure of initial efforts to control the disease by removing infected trees, growers realized that they might have to remove everything, while hoping that newly planted resets would reach productivity before the disease caught up with them. Controlling populations of the psyllid vector, though expensive, was of only limited help.
Scientists noticed that the appearance of infected groves resembled that of abandoned groves. Abandoned groves look that way because their nutritional requirements are not being provided - they have to make do with what is naturally contained in Florida's sandy soil, which is just about nothing. HLB-infected groves look just like abandoned groves, even though nutrients are provided, because their root systems are damaged and less able to take up nutrients. Details are too complicated to go into here, but scientists have found that various combinations of chemical fertilizers on the ground, including minor elements, plus conditioning the soil with organic additives, plus keeping irrigation water in a pH range of 5.5 to 6.5 helps to optimize nutrient uptake by what remains of the damaged root system. The other half of the program consists of foliar nutritional sprays
Multi-year studies of infected groves have yielded encouraging results. For example, one grove was 100% infected, producing less than one box per acre. The improvement came over a five year period, but in 2012-13 the grove produced two boxes per TREE! If planted at 100 trees per acre, that would be an improvement of 10,000 percent. Impressive results indeed, but this comes with a considerable cost, merely bringing the grove back to productivity levels that would have been achieved at much lower cost before HLB. And in the longer term, little is known about whether the trees will finally succumb to the disease, and how soon.
When HLB first appeared at my place, my reaction was to remove the infected tree, but, like the commercial growers, I soon concluded that this was costly and did nothing to protect the remaining trees. I couldn't really follow the programs that the commercial guys use, but I try to pay attention to the basic principles. I use moderately increased amounts of our own Fruitilizer, which is time-released and provides needed minor elements. I improve the soil with large amounts of manure and wood chips, for better moisture retention and organic content. This allows me to use less of the well water, which does not have the ideal pH. And I give frequent sprayings with a 20-20-20 soluble fertilizer containing minor elements. At this stage, I would have to say the trees look better without looking really good, but remember, these programs achieve their results over a period of years. I'll stay with it for a while, and hope that the next crop will be at least edible. This year, I was able to glean a little fruit from my badly infected Minneola Tangelo and Temple Orange trees. If fruit is undersized or shows the characteristic green color on the bottom side, it won't be edible. If it is normal size and looks otherwise normal, it may be good.
We will have an excellent citrus vendor at our Silver Anniversary Tree Sale this Sunday. Will you fearlessly follow Coca-Cola's lead? Studies about the resistance, or lack of it, of different varieties are ongoing. My personal, unscientific, observations: Low resistance: Minneola Tangelo, Temple Orange. Better resistance: Navel Orange, Cara Cara Red Navel Orange, Fallglo Tangelo, most limes and lemons.
Pete Ray