Etienne Rabe left vice president for horticulture with Wonderful Citrus and Nick Hill chairman of the Citrus Pest and Disease and Prevention Program during a break at the 2016 California Citrus Conference

Etienne Rabe, left, vice president for horticulture with Wonderful Citrus, and Nick Hill, chairman of the Citrus Pest and Disease and Prevention Program, during a break at the 2016 California Citrus Conference.

Arsenal of weapons target ‘black plague' (HLB) in citrus

The “four pillars of HLB control” are psyllid control, nursery sanitation, HLB positive tree removal, and early detection, says Tom Gottwald, USDA-ARS at Fort Pierce, Fla. He says scientific models can predict where a HLB infection outbreak may occur based on citrus transport corridors, the distance to Mexico, the presence of psyllids, proximity to citrus groves, and packinghouses.

Tail wagging at warp speed, a springer spaniel named Bello is on the hunt for a deadly disease in a Florida citrus grove.

The tail only ceases to wag when the dog finds what it’s sniffing for – the presence of the deadly disease Huanglongbing (HLB) in a tree. The dog sits. That’s its way of pointing to the diseased tree.

The short video of Bello at work was just one of an arsenal of weapons outlined at an Exeter conference for California citrus growers seeking to save their industry in the fight against the disease that has ravaged groves in Florida and elsewhere.

The 2016 California Citrus Conference was a day-long information-packed program that included a warning that winter freezes could mean some long nights for growers, the announcement of plans to build an $8 million HLB containment facility dedicated to industry research, and calls for stepped up enforcement of tarping citrus as it moves through the state.

The notion of using dogs to detect the deadly HLB disease is not new.

Examples of successes include a dog named Chelsea sniffing out psyllids, some of them carrying HLB, in a package at a Fresno cargo facility in August 2009. Two weeks later, a dog named Tassie found psyllids in a package in Sacramento.

But there are drawbacks for the use of the canines in groves in California, said Neil McRoberts, professor of plant pathology at the University of California, Davis.

“Dogs are not able to screen massive acreage of citrus,” he said. “And they are most useful where you already know you have a problem.”

There is clearly not the extent of known infestation in California that there is Florida, where the proponent of using canines and other techniques – including risk modeling – comes from.

Tom Gottwald, plant pathology research leader at the USDA’s Agricultural Research Service in Fort Pierce, Fla., touted canine use in Florida to sniff out citrus canker, HLB, and Plum Pox.

He showed videos of Bello and others on the job, pointing out that the tremendous sense of smell the animals possess which has enabled them to find everything from termites to truffles, drugs to explosives, and arson accelerants to melanoma.

For canker alone, the animals achieved a detection level of 99.7 percent, Gottwald said. In field trials, 10 dogs achieved an overall HLB accuracy of 99.17 percent.

Gottwald discussed the “four pillars of HLB control” – psyllid control, nursery sanitation, HLB positive tree removal, and early detection.

He also talked about models that can predict where an outbreak of infection from HLB is likely to occur based on risk factors, including citrus transport corridors, the distance to Mexico, the presence of psyllids, proximity to citrus groves, and packinghouses.

Similar models have been used, he said, to help the Centers for Disease Control to pinpoint risk for the presence of Zika or Ebola.

Gottwald opened his talk by referring to human beings “who move HLB” as part of an invasive species, and referred to the “high connectivity” to global populations that is shared by California and Florida.

He discussed the need for regional responses to the psyllid-HLB threat. In Florida, citrus health management areas formed whereby neighbors joined forces in area wide efforts to keep the threats at bay.

In California, much the same is happening, except the operative term is “psyllid management areas,” in which 25 to 35 growers band together in each area to coordinate simultaneous pesticide spraying. The need for these growers to be diligent in doing that was mentioned by several speakers at the Exeter conference.

Among them was Beth Grafton-Cardwell, IPM specialist with the Department of Entomology at UC Riverside, and director of the Lindcove Research and Extension Center. She said about 225 such pest control areas are in the San Joaquin Valley alone.

Grafton-Cardwell said the disease can spread quickly, but it takes nine months to two years for the bacteria to spread throughout the tree so the bacteria can be detected in the leaves. She said insecticide treatments don’t kill all the psyllids, but Actara is an effective insecticide, in part because of its longer residual toxicity.

Grafton-Cardwell pointed to parasite releases of Tamarixia and Diaphorencyrtis that are also helping but warned that controlling ants is critical because they protect the ACP.

The Exeter program opened with Joel Nelsen, president and chief executive office of California Citrus Mutual, who discussed the need to sustain funding from the industry and federal government to combat HLB and the psyllid. 

Nelsen said some $17 million a year is raised for the battle from assessments on growers. Another $4 to $6 million comes from the Citrus Research Board. The federal government adds between $3 million and $5 million for efforts in California alone.

Nelsen expects the new containment facility at UC Riverside, which will be owned by the California Citrus Research Foundation, will open in June, and will be dedicated to working on California issues. UC researchers will be enlisted in the effort.

It will be a safe place to house the psyllid and root stocks that are infected and for the California industry to work on finding a cure that could be shared with others, Nelsen said.

While UCR has its own containment facility, Nelson said relying on that would mean navigation through more bureaucracy and higher expenses. Plus, he said, “We want to control the research.”

Nick Hill, chairman of the Citrus Pest and Disease Prevention program, referred to the threat from HLB as “the black plague” and suggested commonsense steps that need to be taken by farm labor contractors and crew bosses to stop the psyllid spread.

Training sessions are underway to warn those in groves to keep bins and picking bags clear of leaves, and to keep vehicle windows and trunks closed.

Both Hill and Grafton-Cardwell talked of the need to cover loads of citrus with tarps as they move through the state, and Hill said some $1.5 million will go to stepped-enforcement on tarping.

As for the weather outlook, Tom Dunklee, president and chief atmospheric scientist with the Global Forecast Center, said the chance of a “hard freeze” in the coming winter will be “better than average” as cold air from the north is sent southward.

“We could have severely cold weather as in 1990,” Dunklee said, pointing to an anomaly in which warmth over the Bering Strait between Alaska and Russia is expected to send cold air south.

He predicted it will be “moderately wetter than average over much of the Valley,” and average snowfall in the Sierra will be near 130 percent.

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Other speakers at the Exeter conference included Steve Petrie, director of agronomic services with Yara North America, discussing the role of nutrition in HLB management. He emphasized that improved nutrition is not a cure, but it can buy some time “until genetic resistance can be incorporated into citrus.”

Petrie explained that improved nutrition - especially from nitrogen, phosphorous, and calcium - helps form one or more robust physical barriers that reduce infection and stimulate natural defense compounds.

Calcium, he said, binds cells together “like a glue.” He said a combination of nutrient and insecticide treatment performed best in mitigation of HLB.

Fred Gmitter Jr., University of Florida Research Foundation professor of citrus genetics, looked at scion and rootstock cultivars that defy HLB disease.

“We look at what remains standing after the wave passes,” Gmitter said, showing slides of trees that, though 100 percent infected by HLB, appear healthy and continue to bear marketable fruit.

“Florida is a grand experiment in natural selection,” he said, adding that keeping the infested tree producing means taking care of nutrition and canopy management.

One of his success stories appears to be a variety he nicknamed ‘Bingo’ and bearing a seedless tasty piece of fruit that he said rivals that of the Clementine. Gmitter did not know how the variety will perform in an orchard setting.

He said some 17 rootstocks have been released that have the potential to be more HLB tolerant.

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