Mike Roberts

Research Sheds Light on Water Needs of HLB-Infected Trees

Citrus greening, also called Huanglongbing (HLB), is known to affect the fibrous root growth of citrus trees, among other things. The disease has turned the Florida citrus industry into one that measures its inputs very carefully against bottom lines, so every dollar that can be saved is important. One UF/IFAS greenhouse study suggests that citrus growers can safely irrigate their HLB-infected citrus trees a little bit less than healthy citrus trees.

Details of the Study

UF/IFAS researchers conducted a greenhouse study from October 2019 to July 2021 using 20 potted Valencia orange trees on Kuharske citrange rootstock. The trees were grouped into either HLB-positive or non-HLB-affected groups. Half of the trees were irrigated at 100% using an evapotranspiration-based irrigation schedule, and the other half were irrigated at 80%, or at a deficit irrigation.

Researchers wanted to assess the effects of deficit irrigation on citrus tree growth, water availability, stem water potential, sap flow, and root growth. The hypothesis researchers were working with was that HLB-positive trees used less water to “complete their biological functions” due to the severe loss of fibrous roots caused by the disease.

Study Results

The researchers found that there was no difference in tree height and in stem water potential between the HLB-positive trees given 80% irrigation and those given 100% irrigation. Additionally, the sap flow of non-HLB-affected trees was greater at both levels of irrigation than the HLB-positive trees, but that HLB-positive trees had sap flow levels comparable to each other at both levels of irrigation from March–April and June–July 2021. The researchers also found that sap flow was at its maximum in HLB-positive trees between 11 a.m. and 4:00 p.m. 

Those trees that were labeled as HLB-positive had an average water use of 1.6 millimeter per day, and those that were labeled as non-HLB-affected had an average water use of 2.1 millimeters per day. Researchers concluded that non-HLB-affected citrus trees use approximately 20% more water a day than HLB-positive trees, thus proving their hypothesis in a controlled setting.

The takeaway from the research was that citrus growers could potentially water HLB-positive trees less than healthy trees as a water-saving measure without causing water stress to the citrus trees.

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