Besides HLB, Red Scale Challenges Citrus

By Charmayne Hefley, Associate Editor

While much of the talk in the citrus industry is about how to fend off Huanglongbing (HLB) disease, one of the most devastating citrus diseases, Dr. Beth Grafton-Cardwell, director of the University of California Agriculture and Natural Resources Lindcove Research and Extension Center, reinforced that HLB isn’t the only pest that can overtake California’s citrus orchards.

Grafton-Cardwell explained how last year’s warm winter led to an increase in the California red scale, Aonidiella aurantii, population. “Normally we have cold conditions that kill off the younger instars of the scales and [basically] restarts the system. But we didn’t really have any low temperatures last year, so the scales didn’t go into their usual hibernating phase. They just kept cranking out crawlers and adding in an extra generation or two of production. So the higher number of scales on the trees made it much more difficult for the growers to control.”

Grafton-Cardwell explained while it is difficult to speculate whether this coming year will yield another large population of the California red scale, “We have already received more moisture as a result of seasonal rainfall, which should help hinder the pest. Hopefully we’ll get some cooler weather conditions too–not freezing because citrus groves don’t like freezing temperatures–but cold enough to knock out some of the scales and get the population back under a manageable level,” she said.

Nevertheless, despite the challenges that California red scale can cause, Grafton-Cardwell said, overall, citrus growers need to keep their focus on the fight against the Asian Citrus Pysllid (ACP), Diaphorina citri, and its ability to spread HLB. “Growers need to start thinking in terms of: California has the [HLB] disease and it’s going to start spreading in southern California soon,” Grafton-Cardwell said. “What do we do to prevent it from spreading up here into the San Joaquin Valley?”

Photo source: “Life Stages of California Red Scale and Its Parasitoids,” UC ANR Publication #21529, by Forster, Lisa D.; Robert F. Luck; and Elizabeth E. Grafton-Cardwell; with photos by L. Forster and M. Badgley)