Florida citrus growers use antimicrobials to fight greening

WASHINGTON, March 16, 2016 - Florida orange and grapefruit growers who have been battling the Asian citrus psyllid are getting some help, but it may be years before the state’s citrus industry recovers from the damage wrought by the tiny pest.

On March 4, the state’s agriculture commissioner, Adam Putnam declared an emergency that allows growers to use three antimicrobials, or bactericides, not currently registered for use on citrus to fight the disease – streptomycin sulfate (FireWall 50 WP), oxytetracycline hydrochloride (FireLine 17 WP), and oxytetracycline calcium complex (Mycoshield).

The department asked EPA in December for an exemption to use the products. EPA concurred with Putnam’s declaration, allowing Florida to go ahead, but without making a formal decision on the application submitted under the Federal Insecticide, Fungicide, and Rodenticide Act’s Section 18.

“The time for growers to make these applications is now, as our citrus is currently flushing (creating new leaf growth) and will commence blooming soon,” Putnam said in his declaration. Meanwhile, on March 9, USDA’s National Agricultural Statistics Service increased its estimates for Florida’s orange and grapefruit harvests. NASS’s new estimate for boxes of oranges for this year is 71 million, up 2 million from February’s estimate. NASS estimated grapefruit production this year at 10.7 million boxes, up 200,000 boxes from the Feb. estimate.

Both projections are well below production from just a few years ago. The 2012-13 orange crop in Florida was 133.6 million boxes, and the grapefruit crop was 18.3 million boxes.

The psyllid feeds on new leaf growth, spreading Huanglongbing (HLB) disease, also known as citrus greening for the color it turns the fruit. The pest, about the size of an aphid, was first discovered in Florida in 1998, and the disease surfaced seven years later.

Since then, millions of trees have been lost and production in the state’s $10.7 billion citrus industry has dropped precipitously. Between 2004 and 2014, the amount of Florida land planted with citrus shrunk by nearly a third, from about 750,000 to 515,000 acres. Overall citrus production dropped by 58 percent, from nearly 300 million boxes of fruit to 124 million boxes, and average orange yields sunk from 428 boxes an acre to 250 boxes.

Brian Rund, communications manager for Nufarm, the registrant for Mycoshield, said that growers have been spraying the bactericides “pretty heavily” in order to keep the disease in check, prolong the productive life of the trees and reduce fruit drop. Even though the situation represents “the most severe agricultural crisis I’ve ever seen,” Rund said that researchers with USDA and universities have launched an “unprecedented effort” to come up with solutions

There is, however, no cure for the disease, said Pete Spyke, who owns The Orange Shop in Citra, Florida. “They decline to the point that they become unproductive and become a source of infestation,” he said.

However, researchers have developed genetically modified fruit trees that are resistant to the disease. On April 30, 2015, the EPA granted an Experimental Use Permit to Southern Gardens Citrus (SGC) in Florida, authorizing tests of citrus plants containing the protein derived from spinach, which SGC developed through a research program with Texas A&M University.

In February, USDA awarded $20.1 million in grants to universities for research on the disease.

Kevin Shea, administrator of USDA’s Animal and Plant Health Inspection Service, told a subcommittee of the House Agriculture Committee Tuesday that the agency has been working on developing resistant tree varieties and antimicrobial treatments to “knock the disease down.” In California, where greening has been detected in backyards but not in commercial groves, he said research is taking place on biocontrol – finding other insects to prey on the psyllid.

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