A difficult-to-identify citrus pest has lime importers calling for an S.O.S.

Inspectors started turning back shipments of Mexican limes because of possible contamination of sweet orange scab the week of Dec. 6, a move surprising to importers, said John McClung, president of the Texas Produce Association, Mission.

It’s on their list of actionable pests, McClung said, but is difficult to distinguish from common discolorations and markings, and until now has not been a target for quarantine.

“It is nearly impossible to identify on fruit with visual observation because the symptoms are so similar to common, or sour orange scab, or even wind scarring,” McClung said.

Importers aren’t sure why the U.S. Department of Agriculture’s Animal Health Inspection Service suddenly decided to start rejecting shipments.

“The probability is that both Texas and Mexico have had sweet orange scab for generations,” McClung said. “Loads started being routinely rejected as of Dec. 6.”

A representative from APHIS could not be reached for comment immediately.

Jesus Munoz of Pharr, Texas-based United Brokers, said every load he’s had inspected has been rejected this week, with the exception of one load of lemons.

“In Pharr they’re checking pretty close to 100% of the loads,” Munoz said. “Every load they check, they reject.”

Inspectors are doing the best job they can, Munoz said, but the sudden change has been hard on the importers and Mexican exporters.

“Limes are the backbone of many of these businesses,” he said. “This is a major concern.”

In November, Texas citrus shippers voluntarily halted shipments to other citrus producing states to investigate whether sweet orange scab poses a threat to other citrus producing states.