Inconclusive Results Hint at More HLB

Taylor Hillman Citrus, Pest Update

inconclusive results
The current huanglongbing disease test can produce inconclusive results and California citrus leaders say the industry should assume there are more infections in the state.

The current test for huanglongbing (HLB) disease is to run an Asian citrus psyllid or tree sample through a polymerase chain reaction (PCR) machine. The machine cycles 40 times, and if it can’t find the bacteria associated with HLB, it comes out negative. There is a gray area, however, that can produce inconclusive results. “There are some non-regulatory cycle levels between 33 and 39 with an insect that if the machine fluoresces during those cycles, the regulatory agencies say that isn’t necessarily a positive,” Citrus Integrated Pest Management Specialist Beth Grafton-Cardwell said. “What might be going on is the machine is detecting something that is like the bacteria, or the bacteria amount is so small, it can’t really find it.”

Grafton-Cardwell said these inconclusive samples worry researchers and should be looked at as positive finds when it comes to managing the pest and removing trees in the future. “If you survey psyllids around the state, you find quite a few that are found together that have those inconclusive results,” Grafton-Cardwell said. “That kind of suggests that maybe something is brewing in other regions of California.”

The disease has only been found in two residential areas of Los Angeles County. The California Department of Food and Agriculture has found two PCR-positive trees in Hacienda Heights and 28 in San Gabriel. Grafton-Cardwell said some let out a sigh of relief as the industry may have dodged a bullet. However, she and many others believe it would be wise for the California citrus industry to assume the worst. “It would be better to assume we have problems elsewhere and pay a lot of attention to them rather than to stick our heads in the sand and pretend nothing’s wrong,” Grafton-Cardwell said.