"HLB made the trees look like they were starving to death," he says, likening his nutritional program to feeding his trees a Mediterranean diet rather than a McDonald's diet.
"If a tree is satisfied with micronutrients, it doesn't express [greening] symptoms" or expresses them to a lesser degree, says Bob Rouse, citrus horticulturist also at the university's Immokalee center.
Keeping trees well fed
Fighting off HLB's effects on leaves and keeping them green helps the tree continue producing enough food to beat back other symptoms, Rouse says.
One recent study suggests addressing phosphorus deficiency can help reduce greening symptoms.
Over the years Boyd has tweaked and tinkered with the cocktail's formula, which includes phosphite, magnesium sulfate, manganese sulfate and zinc sulfate. His latest change adds trace amounts of nickel.
Most growers have followed Boyd's lead and adopted some form of a nutritional program as a greening defense, Rouse says.
Several companies offer their own premixed formulations.
"Some growers are more successful than others" with the nutritional programs, he says.
"The Boyd program is the hardest and most cumbersome for most people" because it requires gathering and mixing all the components, says Joe Davis Jr., president of Davis Citrus Management in Avon Park. "But he's made them work beautifully."
Davis' company uses a Boyd variation in some of its groves and two commercial versions in others, depending on specific problems with the location and citrus variety. A formula that offers added help against canker and greasy spot, for example, is the obvious choice for a grove also battling those diseases.
Foliar micronutrients remain crucial
Rouse has been studying Boyd's original formula since 2008, testing which mix of components works best and which might be dropped with little or no impact.
So far a mix that omits only the systemic acquired resistance, or SAR, products shows the best performance, Rouse says. The micronutrients in the foliar applications appear to be the crucial element in combination with a liquid nitrogen-potassium-phosphorus fertilizer to cover all nutrient bases.
Three to four foliar sprays over the growing season supplement a soil fertility program, he says. Greening inhibits nutrient uptake through the roots.
Refocusing on root health
While Davis plans to continue attention to foliar nutrition, this coming year will see greater efforts to improve root health.