When conventional citrus farmers spray pesticides–many of them systemic pesticides like neonicitinoids–all the Asian citrus psyllids die, but so do the good insect populations that keep those numbers in check. “Over time,” says Shade, “the Asian citrus psyllid numbers will rebound because all of their enemies are dead. We want to make sure that the methods we work with maintain health populations of those native predators.”
University of Florida scientists are also looking at trees that are naturally resistant to the disease. “There are two groves that appear to be resistant,” says Shade. “We don’t know if the tree is resistant to the bacteria, or if it’s not attractive to the Asian Citrus psyllids, but for a long-term solution we’re looking at naturally-occurring resistant genes that can be bred using traditional breeding techniques (no GMOs).”
Will California Oranges Be Spared?
Meanwhile, in southern California, where citrus greening has only been found in one tree but psyllids have spread wide and far, scientists are doing what they can to minimize the damage that is very likely ahead.
The USDA has pledged $1.5 million to help the state–which grows 80 percent of the nation’s citrus sold as whole fruit–to produce and unleash around a million of the psyllid-killing wasps a year.
According to David Morgan, who heads the effort for the California Department of Food and Agriculture (CDFA), about 80 percent of the wasps the state has released have been in a 7, 000 square mile urban area spanning from Ventura County down to Imperial County. “We release them about every three miles,” he says.
The idea is to pre-empt the disease in backyard citrus trees, which could easily become a vector spreading Citrus Greening to farm orchards. They’re also breeding and releasing the wasps on farms, with an increased concentration on abandoned orchards and organic orchards.
“That’s a way of assisting them with their protection of their crop against this pest,” says Morgan. “[The psyllid] is very small and it reproduces very quickly. It has now covered such a huge area that we don’t have enough man power or money to be able to carry out an eradication program, but we’re trying to find a way to reduce the population.”
It’s an ominous wait. “It’s kind of like Ebola,” says Morgan. “Only Ebola takes 21 days. Citrus Greening takes two years.”
When it comes to longer-term solutions, Morgan says that while genetically engineered orange trees might in fact be part of the equation, he sees a great deal of possibility for organic growers as well.
“Somewhere along the lines there’s a possibility that these plants lost their ability to be resistant against this disease. People are actually going back and they’re looking at wild types of citrus and seeing whether any of these are resistant to the disease. They could use classical breeding to do that, but it will also take time,” Morgan says.
The transgenic citrus from university of Texas would be on the market now if it really worked.
In Florida there are breeding the flying dragon rootstock into varties for HLB resistance.
We have found out this technology works on other tree diseases and other trees like apple, peach, pomagrante, and avacoda to produce organic fruit.