338 G. McCOLLUM AND E. BALDWIN
regulations for commercial citrus nurseries were imposed soon after
CLas was detected in Florida. Citrus nursery stock production must be
under screen, inspected on a regular basis, and treated with insecticides
during production and prior to shipment (Florida State Statutes DPI reg-
ulations).
D. Therapeutic Approaches to Maintain Productivity
When a citrus orchard becomes infected with CLas and subsequently
exhibits HLB symptoms, growers are faced with the difficult decision
of whether to remove trees or to simply continue orchard management
until economic returns fall below an acceptable limit. Removal of a
mature citrus tree represents an immediate 100% loss of profitability
for a tree that will take many years to replace and produce a return on
investment. For this reason, many growers have attempted to maintain
the productivity and profitability of orchards with HLB-affected trees.
- Enhanced Nutrition and Systemic Acquired Resistance.The simi-
larity of CLas-induced chlorosis that mimics nutritional deficiencies,
and an early belief that HLB was actually a manifestation of nutrient
deficiency rather than due to a pathogenic agent, prompted workers in
China to investigate the effects of fertilizer treatment on HLB. Xia et al.
(2011) conducted an extensive review of the Chinese literature dating
back to the 1930s describing effects of fertilizer treatments on HLB-
affected trees. They reported finding no consistent evidence to support
the nutritional approach as an effective means of maintaining tree pro-
ductivity or slowing disease progress. However, they did state that field
surveys and interviews with Chinese scientists and growers indicated
that HLB-symptomatic trees can remain productive for years when man-
aged appropriately. Appropriate management includes not only plant
nutrition, but also irrigation and pest control, or in other words, any
treatment that contributes to productivity in a healthy tree. Still, HLB
cannot be overcome with good nutrition. Although greater inputs may
prolong the life of an HLB-affected grove in the short term; in the long
term, continuing to maintain declining trees leads to reduced produc-
tion and fruit of declining quality.
Soon after HLB was confirmed in Florida, an anecdotal report by
Maury Boyd, a South Florida citrus grower, suggested that foliar
applications of various nutritional products, including micronutri-
ents, enhanced the vigor and productivity of HLB-affected trees (Giles
2009). Mr. Boyd had developed a “cocktail” composed of two Bacillus-
based biofungicides (Serenade and Sonata), hydrogen peroxide, a