A relatively new invasive pest to the San Joaquin Valley citrus scene is the Asian citrus psyllid (ACP). It was discovered several years ago in Tulare County and has led to large quarantine zones in the county because of the deadly disease the pest vectors. Huanglongbing is a fatal tree disease that can manifest itself in leaf yellowing and the eventual death of the tree. Before the tree dies fruit is rendered bitter and unmarketable. Though no cases of the disease have been discovered in Tulare County some citrus industry officials fear it’s just a matter of time before it is discovered.

Grafton-Cardwell said she had hoped that the ACP would suffer from the freeze experienced in early December but those hopes were dashed when a single adult psyllid was discovered near Richgrove on a trap card put out after the freeze. This suggests that the freeze did little to knock down overwintering psyllid populations in the area.

Agronomic practices during the freeze, such as irrigation and wind machine use tend to create microclimates that the overwintering adult ACP populations can use to survive, she said. It’s generally only the nymph stages of the ACP that are likely harmed by freeze and adverse weather conditions. University research suggests that temperatures cold enough for long enough can have a lethal effect on psyllid populations, but those conditions are extremely rare in the San Joaquin Valley (SJV) of California.

Grafton-Cardwell expects psyllid discoveries in the SJV could be lower in the spring and greater in the fall. The pest is already well-established in southern California, where it was first discovered in 2008. Four years later one HLB-infected tree was discovered in a residential neighborhood in Los Angeles County.

Yet another possible impact of the freeze and drought in citrus groves could be the negative impacts to beneficial insects, Grafton-Cardwell said. These tend to suffer the greatest losses from such events, when compared to their invasive counterparts.

California Red Scale could also be particularly troublesome this year, as well as Citricola Scale, which she says she’s seen in some of her research blocks even after the freeze.

“Stressed trees have more scale,” she said.