Posts Tagged: huanglongbing
Invasive meltdown
Ants can be a huge nuisance in and outside our homes, particularly if you have food lying around. But now, it turns out, they’re unwelcome, too, on citrus trees.
A year ago, UC Riverside entomologists released Tamarixia, a parasitoid wasp and natural enemy of the Asian citrus psyllid (ACP) imported from Pakistan, into a biocontrol grove in Riverside, Calif. Tamarixia can serve as an excellent biocontrol agent against ACP, a citrus pest first detected in 2008 in Southern California that is capable of spreading citrus greening disease, or Huanglongbing.
Female Tamarixia can kill psyllids also by “host-feeding.” They use their ovipositors as daggers to stab psyllid nymphs numerous times until the nymphs start to bleed. As bodily fluids ooze out of the nymph, Tamarixia sucks up this rich protein needed for developing more eggs.
An excellent way then to control ACP populations! Yes, but only until the ants come marching in. Argentine ants are threatening to disrupt the biocontrol of ACP by battling it out with Tamarixia on citrus branches. While not quite a Vader-Skywalker lightsaber duel on a precarious walkway, an “invasive meltdown” begins when the ants gang up to protect the nymphs.
“ACP nymphs produce a white, sugary waste product called honeydew, a good carbohydrate source for the ants,” explains Mark Hoddle, the director of the Center for Invasive Species Research at UC Riverside, whose research team has released Tamarixia into several Southern California citrus groves. “The ants, therefore, will protect the nymphs from Tamarixia. We have seen ants chase female Tamarixia off the psyllids, and even catch and eat them!”
“If you kill off the ants, Tamarixia can play the role of the biocontrol agent it was cast to do on citrus trees,” Hoddle says. “We’re seeing that the ants are impacting Tamarixia in two ways: they are preventing Tamarixia’s establishment in some areas; and, where Tamarixia is already established, the ants are not allowing these parasitoids to reach their full biocontrol potential.”
Two Asian citrus psyllids found in Tulare County
This week a quarantine goes into effect in some parts of Tulare County to stop the spread of Asian citrus psyllid, according to a 3-minute story on The California Report. The decision comes after officials found ACP in traps near Strathmore and Terra Bella. For an update on the pest and the disease it can carry, The California Report's Rachael Myrow spoke with Mark Hoddle, UC Cooperative Extension specialist in the Department of Entomology at UC Riverside.
Myrow asked why the effort to prevent movement of ACP has not been successful.
"It's very difficult to police the movement of all types of citrus plants in and out of infested areas," Hoddle said. "People may accidentally and unwittingly move plants that have Asian citrus psyllid on them out of infested areas in Southern California to uninfested areas. Another way these psyllids may move is they potentially have the ability to hitchhike on farm machinery or even vehicles."
Listen to the full interview here:
Some citrus orchards in Tulare County will have to comply with quarantine restrictions.
Micronutrient deficiency can look like HLB infection
Neil O’Connell, UC Cooperative Extension advisor in Tulare County, a citrus expert, recommends that field staff also be well versed on these issues since they are in the field daily during the citrus harvest.
Huanglongbing, a disease spread by Asian citrus psyllid, is the worst citrus disease in the world. The disease was detected on one tree in Southern California in March, the first such find in the state. Officials are asking for farmers and home gardeners to be on the look-out for other HLB-infected trees.
O'Connell says deficiencies of zinc, iron and manganese can resemble leaf symptoms found in trees with HLB.
"Some deficiencies have fairly similar symptoms," O'Connell said. "If you are very familiar with deficiency patterns in these elements then it is much easier to separate this out. You can recognize whether the problem is zinc, iron, manganese, or another deficiency while possibly ruling out HLB."
A distinguishing characteristic of HLB infection is a yellow area that crosses from one interveinal area to another, O'Connell explained.
Reaching the public critical when contending with invasive pest threats
"We're really good at providing detailed information to researchers, agricultural commissioners, Cooperative Extension advisors, inspectors and border protection agents about what to look for and how to respond," said Beth Grafton-Cardwell, UC Cooperative Extension specialist in the Department of Entomology at UC Riverside. "We can reach thousands of people that way."
But with Asian citrus psyllid and Huanglongbing, "we're dealing with backyard situations, which is a whole new ballgame."
Campbell attended a conference in Davis last week focused on "Educating the public about new invasive species threatening California's plant ecosystems." Conference topics -- Huanglongbing disease, Asian citrus psyllid, light brown apple moth (LBAM), quagga and zebra mussels, European grapevine moth, sudden oak death, Japanese dodder, gold-spotted oak borer and red palm weevil -- were addressed by scientists, public officials, a public relations professional and a Sacramento Bee reporter.
"The public needs to be a partner in our efforts to respond to an invasive pest threat," said UC Davis post-doctorate researcher Margareta Lelea, who studied public reaction to LBAM treatments in Santa Cruz. "We need to figure out how we get to shared issues that the public cares about. The community has to be heard and feel like a partner in solving pest problems."
HLB still in the news
The greatest immediate threat may be to the homeowners of Los Angeles County, 60 percent of who have a citrus tree in their yard, said Elizabeth Grafton-Cardwell, UC Cooperative Extension specialist and research entomologist in the Department of Entomology at UC Riverside and director of Lindcove Research & Extension Center.
The citrus greening bacteria probably spread from the cutting of budwood illegally brought in from outside the country, the article says Grafton-Cardwell said.