Research Nets Going Over Citrus Trees To Prevent Huanglongbing Disease

Blocking Psyllids Carrying Disease is Key

By Jessica Theisman, Associate Editor

Beth Grafton-Cardwell is the director of the Lindcove Research Extension Center in Tulare County and research entomologist based out of the University of California, Riverside. She recently told California Ag Today that there is work being done on installing a net structure to protect trees from Asian Citrus Psyllids, which spread the deadly Huanglongbing disease. Texas A&M researchers are installing net structures on the edge of groves to block psyllids from coming into an orchard.

Psyllids have a preference for borders. These nets could have yellow sticky strips of material with an insecticide on it, so there would be an attract and kill process.

Beth Grafton-Cardwell

Other research is looking at netted structures that will completely enclose the citrus trees.

“Researchers are going to construct a completely enclosed net structure to grow the citrus trees in a block at Lindcove,” Grafton-Cardwell said. “We will study how well one can grow citrus under the screen so there could be the ultimate protection against pests and diseases.”

“The mother trees and increased trees have to be grown under the screen, but the field trees do not necessarily have to be,” she said.

Cold temperatures in the winter to protect the citrus from the psyllid.

“The cold temperatures hardened off the tissue, which makes it hard for the psyllid to find any place to lay eggs, and they probably cost some mortality to the psyllid,” Grafton-Cardwell explained.

Most outbreaks are in Southern California. Los Angeles, Orange County, and a few trees in Riverside.

“Prevention is working and there are fewer outbreaks in the Central Valley,” Grafton-Cardwell said.

Dr. Mark Hoddle and Dr. Kelsey Schall (both from UC Riverside) have been monitoring backyard situations. They are researching the release of beneficials such Tamarixia and other generalist predators like Syrphid flies.

“They have been reducing psyllids by about 70 percent in the backyards, and that’s really good news,” Grafton-Cardwell said.

BREAKING NEWS: ACP QUARANTINES IN MERCED AND MONTEREY COUNTIES

ASIAN CITRUS PSYLLID (ACP) QUARANTINES IN MERCED AND MONTEREY COUNTIES

Quarantines are now in place in both Merced and Monterey Counties due to recent Asian citrus psyllid (ACP) detections.  One ACP was detected near the City of Merced in Merced County and two ACP in one trap within the City of Salinas in Monterey County.

The quarantine zone in Merced County measures 123 square miles, bordered on the north by Kenney Avenue; on the south by W Dickenson Ferry Road; on the west by Shaffer Road; and on the east by

SaveOurCitrus
SAVE OUR CITRUS app is a free USDA iPhone to report and identify the four leading citrus diseases: citrus greening, citrus canker, citrus black spot and sweet orange scab. Report your symptoms, upload a photo and citrus experts will respond. ACP

E Yosemite Avenue. Monterey County’s quarantine measures 111 square miles and is bordered on the north by Pesante Road; on the south by the Salinas River; on the west by Castroville Road; and on the east by Gabilan Creek. The quarantine maps for both Merced and Monterey Counties are available online at: www.cdfa.ca.gov/go/acp-maps. Please check this link for future quarantine expansions in these counties, should they occur. Quarantines in new counties will be announced separately.

The quarantine prohibits the movement of citrus and curry leaf tree nursery stock, including all plant parts except fruit, out of the quarantine area and requires that all citrus fruit be cleaned of leaves and stems prior to moving out of the quarantine area.  An exception may be made for nursery stock and budwood grown in USDA-approved structures which are designed to keep ACP and other insects out.  Residents with backyard citrus trees in the quarantine area are asked not to transport or send citrus fruit or leaves, potted citrus trees, or curry leaves from the quarantine area.

ACP county-wide quarantines are now in place in Imperial, Los Angeles, Orange, Riverside, San Bernardino, San Diego, Santa Barbara, Tulare and Ventura Counties, with portions of Alameda, Fresno, Kern, Kings, Madera, Merced, Monterey, San Benito, San Francisco, San Joaquin, San Luis Obispo, San Mateo, Santa Clara, and Stanislaus counties also under quarantine.

The ACP is an invasive species of grave concern because it can carry the disease huanglongbing (HLB), also known as citrus greening.  All citrus and closely related species, such as curry leaf trees, are susceptible hosts for both the insect and disease.  There is no cure for HLB and once a tree becomes infected, the diseased tree will decline in health and produce bitter, misshaped fruit until it dies.  In California, HLB has only been detected on residential properties in Los Angeles County.  This plant disease does not affect human health.
Residents in the area who think they may have seen ACP or symptoms of HLB on their trees are urged to call CDFA’s Pest Hotline at 1-800-491-1899 or your local agricultural commissioner’s office (Merced County (209) 385-7431; Monterey County (831) 759-7325).  For more information on the ACP and HLB, please visit: www.cdfa.ca.gov/go/acp.

Patience: How Homeowners Can Help ACP Detection

Authorities Need to Monitor ACP Detection, Confronted With Impatient Homeowners

by Patrick Cavanaugh, Farm Director

44111-CCM-Web_Headshot_Joel-Nelsen
Joel Nelsen, President of California Citrus Mutual

Joel Nelsen, the president of the Exeter-based California Citrus Mutual noted that most homeowners do not realize how intensive it is for authorities to monitor traps for the Asian Citrus psyllid (ACP) at their homes.

“Most people don’t realize how intrusive this process is,” said Nelsen. “You’ve got a member of the County Ag Commissioner’s office driving down a street. He sees a citrus tree in a front yard, or he can see it’s tall enough in the back. He knocks on the door. The homeowner’s not home, so he has to come back.”

“Later, he comes back to the home and again, knocks on the door and finds that the homeowner is home. He says, ‘Can I put a trap out here to find out if you’ve got the Asian citrus psyllid?’ The homeowner hopefully says, ‘Yes.’ He comes back in two weeks. He looks at the trap. There’s no ACP. He comes back two weeks later, and if the homeowner is home, he looks at the trap,” Nelsen explained.

“It’s a constant bother to that homeowner,” Nelsen said. “Eventually, they find more than one ACP. Then the inspector says: ‘Can I spray a crop protection material on your tree and kill the Asian citrus psyllid?’”

“Hopefully the homeowner says, ‘Yes,’” said Nelsen.

CCMLogoNelsen noted that the inspector visited five times already within a two month period, and now he needs to do inspect elsewhere, so having that homeowner be amenable to that much intrusiveness is a significant goal.

Nelsen noted, “The consumer education program that forms the partnership between us and them, from our perspective, is vitally important so the consumers understand what Huanglongbing (HLB)—the fatal citrus disease carried by ACP—is”.

“Then when you find Huanglongbing (HLB),” said Nelsen, “and hopefully it’s very minimal, that homeowner is more likely to agree that the tree must be removed. Fortunately, everybody has said: ‘Yes.’”