The current huanglongbing test for infected trees can show a false positive, but it isn’t because the test is ineffective.
Trees infected with huanglongbing (HLB) can test negative on the current test. University of California Davis professor Carolyn Slupsky says this is not because the test isn’t effective though, and the problem comes down to where you sample the tree.
More About Detection
The California Department of Food and Agriculture (CDFA) says detection of the disease is extremely difficult by symptoms alone. Diagnostic laboratories utilize molecular assays to detect the DNA of the bacterium in plant hosts and in insect vectors to confirm the presence and identity of the pathogen. However, diagnostics are difficult when there are no symptoms because the pathogen population in the tree may be too low to detect. Therefore plant samples are generally collected from symptomatic foliage. Veins and petioles are cut from the leaves and processed in the laboratory to maximize the chance of detecting the bacteria.
HLB has been described as the most devastating disease of citrus in the world. HLB affects almost all citrus cultivars, and causes substantial economic and environmental losses to the citrus industry as well as backyard citrus by shortening the life of trees and making fruit and juice inedible. Read more from CDFA.