2017 ASHS Annual Conference

As most citrus growers are well aware that Huanglongbing (HLB) or Citrus Greening is one of the most devastating citrus diseases in many parts of the world. The disease is widespread in Florida, Texas, Brazil, Mexico and other major producing areas causing significant concerns about the economic viability of these citrus industries. Leaf chlorosis develops as a result of infection with Candidatus liberibacter asiaticus (Clas) including interveinal chlorosis of young leaves, similar in symptomology to manganese (Mn) and zinc (Zn) deficiencies that develop early in the growing season, followed by amorphous mottling of older leaves which develop later in the growing season. Nutrient deficiency-like symptoms develop in HLB-affected trees, including potassium (K), phosphorus (P), magnesium (Mg), calcium (Ca), Mn, Zn, and iron (Fe). HLB causes fibrous roots to decline within a few months after infection and before foliar symptoms develop. Fibrous roots are responsible for the bulk of nutrient uptake and their decline likely explains the deficiency symptoms that develop in the canopy. Research has demonstrated that HLB symptoms can be reduced by ground and/or foliar applications of micronutrients, especially Mg, Mn, Zn, and boron (B). Water management is also a critical factor in maintaining vigor and productivity of citrus affected by HLB. These responses have promoted development and use of enhanced foliar nutritional programs in Florida and other areas of the world. Efficacy of these programs have been a topic of considerable discussion and debate. Fertilization programs have varied considerably among growers, and have consisted of various rates and application schedules of essential macro- and micronutrients and irrigation management.