Help protect California's citrus from ACP

May 4, 2015

[From the April 2015 issue of the UC IPM Retail Newsletter]

In June 2013, we wrote about the Asian citrus psyllid (ACP) in UC IPM's Retail Nursery and Garden Center News. At that time, ACP was mostly found in parts of Southern California. It has since been detected in multiple locations in the Central Valley and has been detected in the San Francisco Bay Area. Thus, the psyllid is established near, or threatening much of, California's commercial, nursery, and residential citrus (Figure 1).

Because ACP can transmit the bacterium causing the most devastating disease of citrus in the world, huanglongbing (HLB) or citrus greening, it is imperative that this insect pest be managed as effectively as possible (Figure 2). To keep the psyllid from spreading further by riding on plants, ACP host plants (citrus and close relatives such as orange jessamine and Indian curry leaf) in affected counties are under quarantine; they cannot be moved out of these quarantine areas.

We cannot stress strongly enough that retail nurseries and garden centers, residents, and maintenance gardeners can all play major roles in minimizing the spread of this pest and HLB. Please read the following guidelines to learn more about what you can do in your backyard, your retail store, and what to tell customers.

Best Management Practices for Nursery and Garden Centers:

  • Citrus trees are treated with insecticides when they leave wholesale nurseries. However, these treatments remain effective for only about three months. Ensure fast movement and turnaround of your citrus stock before trees become unprotected.
  • Excessive watering can leach out soil-applied insecticides, so only water enough to wet the soil in pots. 
  • If possible, place trees inside a screened-in structure to protect them against psyllids. If not an option, take advantage of ACP's preference for sunny, warm conditions by keeping citrus and other hosts under shade structures or even inside the store.
  • As you are caring for and handling your citrus stock, carefully check the leaves and stems for psyllids. If you see the psyllid, contact your County Agricultural Commissioner as soon as possible.
  • Be sure your garden center or nursery sells or buys certified disease-free trees from a reputable source. Uncertified trees may provide the insects with a source of disease they can pass on to other trees.
  • Learn more about ACP by taking the free online course designed for retail nurseries and garden centers. Locate the section called "Nursery Courses" and click on "ACP and HLB for retail nurseries".

For Homeowners and Landscapers:

  • Citrus trees sold within an ACP quarantine area will have a blue or yellow tag on them indicating they must stay within the quarantine area. Everyone needs to comply with quarantines in order to protect uninfested areas.
  • Learn how to carefully check the leaves and stems for psyllids and disease symptoms whenever caring for citrus.
  • If you suspect you have seen the psyllid pest, immediately call the CDFA Hotline 1-800-491-1899. CDFA personnel will tell the caller if they will be treating the reported trees or if the homeowner should manage the ACP population.
  • Don't try to “prune out” a psyllid infestation on a tree. Citrus responds to pruning by production of new shoots that are highly attractive to the psyllid.
  • If you or your clients are in an ACP-infested area, it's important to handle green waste carefully. Double bag pruning material before moving them offsite to prevent transporting ACP to new areas.
  • Information about insecticides effective against psyllids and tips for application are available in the UC IPM Asian Citrus Psyllid Pest Note.
  • If you or your clientele think they have seen the disease, immediately call the CDFA hotline. CDFA personnel will take leaf samples to confirm infection of the tree by a biochemical test.
  • We encourage everyone to learn more by taking the free online course about ACP and HLB in residential citrus. For homeowners and landscapers, click on the “ACP & HLB” link under “Master Gardener Courses”.

         Be vigilant and help to protect California's citrus trees!

See these websites for more information:

By Elizabeth E Grafton-Cardwell
Author - Emeritus Entomology Cooperative Extension Specialist
By Cheryl A. Wilen
Author - Area Integrated Pest Management Advisor - Emeritus
By Matthew Daugherty
Author - CE Specialist and Entomologist