ACP Quarantine in San Joaquin County, Guidelines and Scholarship

Expanded ACP Quarantine

Two portions of San Joaquin County have been placed under Asian citrus psyllid (ACP) quarantine following detections of one ACP within the City of Manteca and one within the City of Lodi. The quarantine zone in Manteca measures 105 square miles and in Lodi it measures 95 square miles.

The quarantine prohibits the movement of citrus and curry tree nursery stock 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 that are designed to keep ACP and other insects out. Residents with backyard citrus trees in the quarantine area are asked not to transport citrus fruit or leaves, potted citrus trees, or curry leaves from the quarantine area.

Asian citrus psyllid (Source: UC ANR)
Asian citrus psyllid (Source: UC ANR)

The ACP, a tiny (0.125 in. length) mottled brown insect that is about the size of an aphid, 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 trees are susceptible, and there is no cure. Once infected, a diseased tree will decline in health with yellowing shoots, asymmetrical leaf mottling and abnormally shaped bitter fruit until it dies—typically within three years.  HLB was detected once in California, in 2012, on a residential property in Hacienda Heights, 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 citrus trees are urged to call CDFA’s Pest Hotline at 1-800-491-1899.  For more information on the ACP and HLB, please visit: www.cdfa.ca.gov/go/acp

ACP Effective Treatments

The University of California Agriculture and Natural Resources’ Integrated Pest Management (IPM) Program  has developed treatment guidelines for citrus growers within the quarantine zones. A general principle when applying insecticides to control ACPs in commercial citrus is that no one insecticide fully controls ACP across all life stages because:

  • All stages are difficult to contact with insecticides; eggs and nymphs are tucked inside new foliage and adults can fly.
  • Some insecticides show better efficacy against one stage over another.
  • Because systemic neonicotinoid insecticides require root activity for uptake, they are best applied during June through September.

The UC IPM Guidelines for Citrus provides a ranked list of insecticides that are effective against the Asian citrus psyllid with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honeybees, and the environment are at the top of the table.

According to Mark Hoddle, UC Riverside (UCR) Director, Center for Invasive Species Research, “The science of biological control, the use of a pest’s natural enemies to suppress its populations to less damaging densities,” shows promise against the ACP with releases over the last three years of Tamarixia radiata–a parasitic wasp from Pakistan–in urban areas of southern California Thus far, this natural ACP enemy helps to control ACP growth in residential areas, but is inadequate for commercial application.

Biological Control Scholarship Fund

Harry Scott Smith (Source: Citrus Research Board, "Citrograph")
Harry Scott Smith (Source: Citrus Research Board, “Citrograph”)

Harry Scott Smith was the first to use the phrase “biological control” in 1919 at the meeting of Pacific Slope Branch of the American Association of Economic Entomologists at the Mission Inn in Riverside. Smith worked on the biological control of gypsy moth with USDA, then moved to the University of California Riverside where he eventually created and chaired the Department of Biological Control, which offered the only graduate degree in biological control in the world.

The Harry Scott Smith Biological Control Scholarship Fund at UCR aims to attract the brightest students to study biological control by providing assistance to its students to attend conferences to present their research or to participate in training workshops. More information on the Scholarship, past awardees, and a list of donors can be reviewed on the website.

Sources: CDFA; UC IPM; UC Riverside (UCR); UCR Center for Invasive Species Research; USDA Animal and Plant Health Inspection Service (APHIS)

UPDATED MITE SAMPLING FOR AVOCADO ORCHARDS

Center for Invasive Species Researches the Mighty Mite

Every 60 days, California gains a new and potentially damaging invasive species. (UC Riverside)

This rate of invasion, on average, results in six new species establishing in California each year. Economic loses to California from invasive species are estimated at $3 billion per year.
The unique climate and geography of California provides diverse ecosytems that are perfect for the establishment of a diverse variety of new pests. UC Riverside’s Center for Invasive Species Research (CISR) researchers lead the way to determine how pests enter California, where invading populations came from and why these pests are successful in establishing California as their home.
Ricky Lara
Ricky Lara, a UC Riverside graduate student researcher with Mark Hoddle, Ph.D., Biological Control Specialist and Principal Investigator, is focusing on updating and reinforcing the integrated pest control program against the non-native persea mite that infests Southern California avocado orchards.
“High persea mite populations cause premature leaf drop and defoliation. Defoliation leads to sunburned bark and fruit, aborted or dropped fruit, and severely stressed trees, which ultimately reduces yields,” said Lara.
My first objective,” began Lara, “is to further develop a presence/absence sampling plan for growers so they can make keep track of pest densities throughout the growing season to guide spray application decisions. This sampling method will prevent misuse of pesticides and for PCAs to be able to provide growers with better information.”
“Because counting mites on avocado leaves is so difficult, we use a presence/absence method, or binomial sampling, by choosing 30 random leaves per tree, on orchard trees located where the mites prefer.” The sampling simply requires the numbers of avocado leaves infested with the persea mite and the numbers of clean leaves with no persea mites. This ratio of infested leaves to clean leaves is used to estimate the average number of persea mites per avocado leaf. Thus, binomial (presence vs. absence) sampling is fast and simple, and allows large areas of orchards to be surveyed quickly.

Persea Mite (UC Riverside)
“Next, I will figure out where the persea mite comes from and find and examine its natural enemies,” explained Lara. “The logic is that if a pest is not native to the area, its natural predators aren’t here either.”
Lara remarked, “Furthermore, I plan on assessing the risk that novel pesticides being developed for persea mite control pose to beneficial predatory mite populations that attack persea mite. By reducing pesticide use and conserving the presence of predators, we expect to enhance the avocado orchard ecosystem’s capacity for self-regulation of persea mite by making better use of natural enemies for pest control.”
The persea mite infests 99% of avocado acreage in California (There are no records of this pest in the San Joaquin Valley but it has been reported from avocados growing in San Francisco.) This mite is sensitive to high temperatures (>95oF) and low humidity when experienced over several consecutive days, and abrupt population crashes in the field have been observed under these conditions. The persea mite most likely originated from Mexico and arrived in California on smuggled plants.
Scientists at UCR have investigated the efficacy of releases of predatory mites for persea mite control. A highly effective natural enemy, Neoseiulus californicus,is commercially available and has been shown to be very effective, but is cost prohibitive. Seven commercial cultivars of avocado have been screened for resistance to persea mite feeding, and a new cultivar, Lamb Hass, is quite resistant to this pest.
Several species of predators occur naturally in California avocado orchards, and they have been observed to feed on persea mites. Yet, none of these natural enemies provides effective control of the mite. Nonetheless, their presence in orchards is desirable because they probably lessen the severity of persea mite infestations and will feed on other pest species.
Work is currently in progress monitoring persea mite populations, assessing predator quality after an imported shipment arrives, and refining release methodology, rates and timings of these predators.