- 10-dog unit is early-warning system for tree-killing disease
- Detecting before symptoms emerge, more accurate than lab test
Mira’s nose is so sensitive that she can smell sick citrus trees, and U.S. orange growers are hoping her super sniffer will help combat one of the biggest threats ever to their crop.
The government has trained 10 dogs including Mira -- a 32-month-old German Shepherd-Belgian Malinois mix -- to identify a bacteria that has been killing citrus trees for a decade in Florida, the biggest domestic producer. Similar to canine teams that sniff out bombs, drugs and even bed bugs, this one is on the hunt for a disease known as citrus greening. There’s no cure, but growers hope the animals will give them more time to find one by slowing the contagion.
Florida’s orange harvest is forecast to reach a 52-year low this season, down 71 percent since 2004 as tiny bugs called Asian citrus psyllids spread the bacteria. It cost the citrus industry $7.8 billion and 7,500 jobs since 2006. Dogs, with 50 times more scent receptors in their noses than humans, sense chemicals that trees emit when infected. They’re accurate 99.7 percent of the time -- better than laboratory tests -- and identify diseased trees before symptoms appear.
“They’re pretty much the forefront of early detection for us right now,” said Yindra Dixon, a public affairs specialist for the Animal and Plant Health Inspection Service, a unit of the U.S. Department of Agriculture.
While researchers have failed to find a cure for the disease, also known by the scientific name Huanglongbing, they devised ways to slow its spread. One technique requires farmers to encase trees in steam to overheat the bacteria without killing the plant. Some apply nutrients directly on the leaves to keep trees productive even as they’re dying. Others use more pesticides to kill the psyllids, but the downside is the bugs developed resistance to some chemicals and too much can burn the fruit. Penicillin has been shown to suppress the bacteria, but concerns over antibiotic resistance have limited wider use.
Citrus greening blocks the passage of nutrients through the tree’s vascular system, causing the plant to thin and yellow. Trees can take years to die, but their fruit production declines and eventually is too small to justify the expense of treating the symptoms.
Florida is expected to harvest 69 million boxes of oranges this season, or 56 percent of domestic production, and the state is the top grower of grapefruit, USDA data show. Each box weighs 90 pounds. California will supply 52.5 million boxes of oranges, and is the dominant supplier of tangerines and lemons. Texas ranks second in grapefruit.
Since 2005, when the disease was first found in the U.S. in Miami-Dade County, 15 states or territories have been placed under full or partial quarantine for the presence of the Asian citrus psyllid.
The bugs, which transmit the bacteria, reproduce rapidly and can fly a mile without pause, making them especially difficult to contain or kill. Researchers are still trying to understand how psyllid populations reduced by pesticides still manage to recover and spread the disease, said Robert Shatters, research molecular biologist for the USDA Horticultural Research Laboratory in Fort Pierce, Florida. While the disease exists in other countries like Brazil, the world’s biggest orange grower, the flat landscape and close proximity of farms in Florida make it particularly susceptible to contamination.
“This is a disease where your neighbor is your worst enemy,” said Thomas Spreen, professor emeritus of food and resource economics at University of Florida in Gainesville.
Already, about 75 percent of Florida’s groves are infected. The USDA is planning to dispatch most of the new canine unit to California, Arizona and Texas, where the disease is less widespread and early detection could be used more broadly, Dixon said.
“There is such a grave concern in areas where this disease does not exist that people want to know if it is there,” said Tim Gottwald, research leader and plant pathologist at the USDA.
Training dogs to detect citrus greening was funded by the Huanglongbing Multi-Agency Coordination Group, an emergency response team created by the USDA in 2013 to figure out how to eradicate the disease. The MAC invested $1.8 million of its $20 million research budget for 2014 and 2015.
Tests show the wet noses of the dogs are more accurate than DNA sampling techniques, which can require several hours or days to complete and are subject to lab-related and sampling errors, Gottwald said. The animals also have detected the disease in trees that didn’t show symptoms until days or weeks later, he said.
Once trained, Mira and the other dogs have shown they are both eager and accurate, said Jerry Bishop, the training director at Coast to Coast K9 Teams, the company working with the USDA to coordinate grove inspections by the animals.
"As soon as she comes out of the kennel, she likes to chest bump you," Bishop said of Mira. “She’s like, ‘Let’s go to work. I’m ready.’"
Spreen, the emeritus professor, says the dogs offer a potential cheap and efficient bit of hope for growers faced with devastating losses.
Even if the dogs aren’t 100 percent accurate, “you could probably suppress the infection enough in your grove to really make a big difference,” said Spreen, who owns 19 acres of citrus groves. “The dogs could potentially be a godsend.”